In torsional testing, the DTN proved more resistant to torsion in the worst-case surgical setup (p < 0.05) for both ± 4 Nm and ± 8 Nm. The equivalent stiffness of the DTN against the MDTP supports the use of this implant for SMOT fixation and should be considered as a treatment option particularly in patients presenting vascularisation problems where the MDTP is an inappropriate choice.The Distal Tibia Nail  has demonstrated higher biomechanical stiffness to locking plates in previous research for A3 distal tibia fractures. It is here investigated as a fixation option for supramalleolar corrective osteotomies (SMOT). Sixteen Sawbones tibiae were implanted with either a DTN (n = 8) or Medial Distal Tibia Plate  and a SMOT simulated. Two surgical outcome scenarios were envisaged: “best-case” representing an intact lateral cortex, and “worst-case” representing a fractured lateral cortex. All samples were subjected to compressive  and torsional  testing. Samples were evaluated using calculated construct stiffness from force–displacement data, interfragmentary movement and Von Mises’ strain distribution. The DTN demonstrated a greater compressive stiffness for the best-case surgical scenario, whereas the MDTP showed higher stiffness ( Joint malalignment leads to an imbalance in load transmission across the joint surface resulting in increased impact and compressive loads on a part of the joint3. Individuals with a joint malalignment are at greater risk of osteoarthritis (OA)6. Corrective osteotomies are carried out to straighten the axis of a long bone in order to improve load transfer across the joint surface2. In the case of the distal tibia, a SupraMalleolar OsteoTomy (SMOT) is carried out to realign the ankle joint where the tibial pilon meets the superior surface of the talus bone8. Following this procedure, an implant is used to stabilise the osteotomy; to date the only available implants for this procedure are locking or dynamic compression plates9. The most important disadvantage of plate osteosynthesis at the distal tibia is the need for a large medial incision, which may be the origin of wound healing disturbances and infection. Especially in patients with compromised soft tissue coverage, the risk of complications is enhanced10.Lower limb malalignment is a frequent post-operative condition due to the operative procedure or malunion; however, this problem can also be related to genetic disposition, as is the case in people with bowed legs as a birth deformity11 and changes in plantar pressure zones following osteotomy12. Ettinger et al.9 is the only study to have carried out biomechanical assessments of the different compression plates available for SMOT, finding a difference of up to 632 N mm−1 in axial stiffness (range 1985–2617 N mm−1) and 0.66 Nm deg−1 in torsion stiffness (range 3.48–4.14 Nm deg−1) between models.Previous research for SMOT has focused on the evaluation of the osteotomy zone14. Plating has been a solid option until now but patients with already compromised soft tissue in the distal tibia are put at risk when using this method16. The aim of this study was to assess the biomechanical stiffness of the DTN compared to the current standard fixation method of plating for SMOT fixation. The assumption is made that if the DTN is not significantly lower in stiffness than the Medial Distal Tibia Plate, then it can be considered as an intramedullary fixation option for SMOT. Based on results from previous studies14, we hypothesise that the DTN will demonstrate a greater biomechanical stiffness compared to the plate.The Distal Tibia Nail  is a new treatment option for far distal fractures, covering the zone in which a SMOT would be performed14 and AO Foundation surgery reference17, respectively. Screw insertion for both implants is conducted through small incisions in the skin using a scalpel. The wedge was 10 mm in height and left 5 mm of lateral cortex intact  were implanted with a Medial Distal Tibial Plate  or a DTN (n = 8) and a Medial Wedge Opening (MWO) osteotomy simulated at 45 mm proximal from the distal articular tibial surface. A brief description of the DTN and MDTP implantation procedures can be found in Kuhn et al.19. A review of this method can be found in Rankin et al.20.All samples were proximally embedded in polymethyl methacrylate  using a template leaving a thickness of < 2 mm of PMMA at the loading site. For digital image correlation (DIC) analysis, two cameras  were placed facing the sample at a divergence of 16°. All samples were covered with white paint and a black speckle pattern . DIC allows for a non-invasive, contactless technique for the measurement of displacement and strain fields across a surface14 of 350 N at 0.1 Hz followed by 700 N at 0.05 Hz with an 18 N compressive pre-load applied. For compression testing, the samples were placed in a double ball-joint setup , and for torsional testing at 2.5 ± 0.5 Nm for the ± 4 Nm tests and 6.5 ± 1 Nm for the ± 8 Nm tests. Mean construct stiffness ± two standard deviations are cited as well as the range (minimum to maximum stiffness).Sample construct stiffness were calculated using an in-house code written in Scilab (version 6.0.2). During preliminary testing, lower construct stiffness detected in the first 5 cycles due to the bedding in of the test setup . The facet and step sizes used for the correlation were 25 and 7 mm, respectively displacement uncertainty (considered as 1/100 of pixel size) was 0.003 mm.The image corresponding to the maximum force application of the last complete compression cycle was identified, and then used to calculate average interfragmentary movement (IFM) in two zones, the lateral cortex and the osteotomy gap, using the Vic3D extensometer tool Fig. c.Von MisStatistical tests were undertaken in Statgraphics Centurion 18 . Tests for normality and heteroscedasticity were carried out using the Shapiro–Wilk and Levene’s tests, respectively. The DTN (n = 8) and MDTP (n = 8) samples were treated as independent sample groups. Biomechanical stiffness constructs were compared between sample groups and within a specific testing phase  using the Student’s t-test for data presenting a normal distribution and the Mann Whitney-U test for non-normal data.All results are presented in graphic form displaying the mean stiffness ± two standard deviations for comparison of the DTN and MDTP implanted samples for all applied loads. A summary table of all main results is given at the end of the stiffness section Table .Table 1A−1 for the DTN group, and 1287 ± 11 N mm−1 for the MDTP implanted group. At 700 N, there was a greater difference between the groups . A significant difference between implant groups was also observed for 700 N compression test  = -3.87, p = 0.002).For the worst-case surgical scenario, at 350 N, there was a significant difference between implanted groups with the MDTP demonstrating higher levels of compressive stiffness  = − 4.51, p < 0.01; Fig. −1 and the MDTP group 2.06 ± 0.06 Nm deg−1.For best-case scenario testing Fig. , mean to−1 against 0.71 ± 0.12 Nm deg−1, for the DTN and MDTP, respectively; U = 11, p = 0.03). At ± 8 Nm, the disparity between the construct stiffness of the two implants was greater with values of 1.42 ± 0.04 Nm deg−1 against 0.65 ± 0.07 Nm deg−1, for the DTN and MDTP, respectively .In worst-case scenario testing, a Mann Whitney-U test found the DTN to have a greater torsional stiffness at ± 4 Nm  and IFM are reported in Table vm and IFMmid (p = 0.06), however IFMlat yielded significant differences (p < 0.05) between the DTN and MDTP implanted samples (Table p = 0.01), both across the fracture gap and the lateral cortex area; no statistically significant difference was observed for the average maximal Von Mises’ strain (p = 0.06).Average maximal Von Mises’s strain around the osteotomy , the DTN proved to be significantly lower in stiffness, leading us to reject our hypothesis. However, IFM levels do not exceed 1 mm for either of the implants; maximum difference in IFM was 0.33 mm across the osteotomy gap in the worst-case scenario for a compressive loading of 700 N. Hence, despite hypothesis rejection, low IFM levels support the use of the DTN for SMOT fixation. Where similar DTN and MDTP sample construct stiffness are observed, Von Mises’s strain levels are of equal magnitude in both the best- and worst –case surgical scenarios.9 are the only authors to have conducted biomechanical tests on implants used for MWO in-situ. The MDTP was one of the implants (fixed to Sawbones samples) used in their study and the authors reported axial construct stiffness of 2182 N mm−1 (2182 kN mm−1 is reported in their article but this is an error of units used), compared to 1641 N mm−1—the maximum calculated stiffness value in the present study. The differing boundary conditions between the two test setups of the present study and that conducted by Ettinger et al. may explain the disparity in results. The present study employed ball joints allowing for axial rotation at the extremity of the sample. Ettinger et al. employed cardan joints which ensure degrees of freedom in rotation as us, but the centre of rotation is not identical regarding the tibial medial axis, leading to different moments. Further, during the present study, vertical displacement measured by the testing machine was quantified to be an overestimation of around 10% of the displacement measured by marker tracking. However, even after correction of this figure, our results are still not in line with those cited by Ettinger et al.Ettinger et al.24. In the current study, we ensured that no greater than 2 mm of PMMA was present between the tibial plateau and the universal joint through which compressive forces were applied. The distal potting could partially cover the distal implants as figured by Ettinger et al., and so influence the mechanical behaviour especially for the DTN. Furthermore, Ettinger et al. controlled for the amount of lateral cortex remaining post-osteotomy and set this to be 5 mm. In our study, the lateral cortex area was not regulated but it is estimated to be less than 5 mm for best-case scenario SMOT outcomes. Nonetheless, the figure reported by Ettinger et al. falls into a similar order of magnitude as in the current study.Images from Ettinger et al. give rise to the idea that substantial extremal potting of the samples was carried out, leading to principal testing of the tibial shaft, which is shorter than the tibia itself and the strongest part of the long bone 5. The significantly higher torsional stiffness presented by the MDTP sample group in the best-case surgical scenario at ± 4 Nm may be attributed to the low moment applied and the symmetry around the osteotomy gap. The in-tact lateral cortex and the medially positioned MDTP create a very stable structure allowing for little movement.Torsional stiffness is greater in the DTN samples for most test configurations—being more valuable in preventing shear strain. Shear movements are known to be harmful to bone remodelling if they exceed axial strain levels−1 for loading at 0.25 Hz to 5 Nm; present study: 3.64 Nm deg−1 for loading at 0.1 Hz to 4 Nm). In this scenario, the difference in loading frequency  did not appear to affect recorded stiffness values, as expected. These results are also in agreement with a previous study comparing the DTN to the MDTP, but for 43-A3 fractures7. The current article found to be 1.42 and 0.65 Nm deg−1 for the DTN and MDTP, respectively, during worst-case scenario testing (closely representing an A3 fracture). Kuhn et al. found 1.83 and 0.55 Nm deg−1, respectively10.Measured torsional stiffness by Ettinger et al. agrees with data presented in the current study . A screw placed against the medial or lateral border of the screw hole will result in (for example) high positive torsional stiffness. Use of medical imaging technique would allow for the quantification of screw position with the designated hole. Such techniques were not employed during this study but should be taken into consideration in future analyses.27. The difference in the average maximal Von Mises’ strains around the osteotomy site between the DTN and the MDTP implant groups for the worst-case scenario surgical outcome is high, but comparison with this level of strain in the literature suggests that this would not have a negative impact on the bone; however, this also depends on load frequency28. Quantification of Von Mises’ strain presented here must, however, be treated with caution as the edge effects will have influenced the mean strain quantified.Recorded Von Mises’ strains fall into the category where new bone generation would be expectedLower stiffness is generally associated with higher Von Mises’ strain for best-case scenario sample groups, this may be also directly related to IFM. However, in some cases a sample with low construct stiffness also yielded low average strain; this discrepancy may be linked to the area over which these parameters are calculated. Stiffness calculations take into account the entire sample, whereas Von Mises’ strain calculations are only taken around the osteotomy site. External factors, such as machine setup and PMMA stiffness will influence total calculated stiffness but not strain distribution.The greater and more concentrated strain around the osteotomy site in the worst-case scenario samples is likely due to the completion of the osteotomy cut through the lateral cortex. This detachment of the proximal and distal fragments allows for greater movement between the two. In the case of the DTN, this may increase bending motion during the compression testing, explaining the high strain zone at the osteotomy opening on the medial side. During compression, lateral bending may occur due to the extra-axial loading point and the proximal and distal fragments will push against the nail in the medial opening. High variability in the Von Mises’ strain of the DTN samples may owe to implant position inside the medullar cavity with or without contact with the cortex.21. For the DTN samples, there is little to no pre-strain across the osteotomy, meaning that osteotomy completion will have left a gap of 0.5 mm (saw blade thickness) over which the proximal and distal fragments can move.Maintaining an osteotomy gap can be associated to an A3 fracture for which the MDTP stiffness in consistently lower than that of nailingIn all samples, the high strain zone in the lateral diaphysis is observed. It is not possible to know the location of the implants’ screws without CT data, but this area may correspond to strain from the screw exiting sites. Further analyses would need to be carried out to confirm this.16. On the other hand, nailing also presents its limitations and has previously been associated with post-operative problems such as fragment malunion30. Concerning the DTN in particular, extensive reaming of the medial malleolus and distal epiphysis of the tibia for nail insertion may lead to necrosis and fracture of the distal tibia. We therefore recommend performing the opening of the entry portal and medullary canal with utmost caution. However, as this implant is still in early stages of use, no longitudinal studies has thus far been carried out and hence no post-operative complication highlighted.Nailing may be preferred over plating for vascular preservation reasons, and compression plating is often associated with soft tissue damage32. The DTN may offer a solution to these problems: The implant is inserted in a minimally invasive way, only requiring small incisions at the tip of the medial malleolus and more proximally. In this way, the danger of as the potential skin irritation and necrosis zone is limited to the nail and screw insertion sites. The DTN is an implant designed specifically for the distal tibia and can cover a range of fracture and osteotomy zones13. Critical factors in using the DTN in retrograde tibial nailing are the selection of the correct entry point, placement of the guiding K-wire, low-pressure creation of the cavern through the medial malleolus with the crown reamer and subsequent low-pressure nail insertion33. In cases of posttraumatic malunions with completely obstructed intramedullary canal the use of a distal tibial nail might be limited or impossible. The potential risk of fracturing the medial malleolus must be taken into account14.The choice of implant is primarily based on the condition of the patient’s soft tissue envelope. In cases where vascularisation and soft tissues are already compromised, due to disease, age or previous injury, the use of a plate can lead to complications requiring a secondary surgery. In the distal tibia, problems such as skin irritation necrosis and infection have been reported35, resembling long bones of young adults. A medium sized Sawbones sample is based on the geometry of a 90-kg male of 1.83 m in height, less than 80 years of age35 and ensure that solely the bone-implant construct is evaluated and results are not influenced by bone quality, which can be a problem when using cadaver bones. However, this type of sample does not reflect reality and may conceal other problems related to both implants, such as with respect to vascularisation in plating and the possible fracture of the medial malleolus while developing the entry portal and the DTN insertion.Sawbones® are composite bones that have been validated to imitate the mechanical properties of human boneThe inclusion of the fibula in the experimental setup is difficult to put in place; while 4th generation Sawbones composite fibula exist, there are currently no methods for considering the inter-osseous membrane that allows for tibio-fibular force transmission. We would expect that both axial and torsional stiffness levels would be higher in all samples with the addition of a fibula, with stiffness construct increasing by a similar level in all samples. This implies that a systematic error occurs in the omission of the fibula and should not be detrimental to the results.10, the DTN has shown superior biomechanical properties in load-to-failure tests for an A3 fracture configuration. In the given study, plastic deformation occurred in the plated samples between 350 and 500 N; complete fracture gap closure occurred at compressive loads between 500 and 700 N. In both cases, the DTN showed no signs of mechanical weakness.No load-to-failure study was carried out for the samples; however, in a previous study by Kuhn et al.Digital image correlation is a useful tool for the quantification of surface strain; however, it presents certain limitations. The facet size used for DIC was relatively high and may have resulted in the loss of information especially in the lateral cortex region. To improve this, it would have been necessary to create a finer speckle pattern on the samples. Extensometer and Von Mises’ measurements were taken at approximately the same area, but as the osteotomy and lateral cortex size were not controlled for and there are no anatomical landmarks in this zone, the placing of the extensometer and centre of the nodal disc in the Vic3D software is not entirely reproducible. In order to obtain DIC data for torsional testing, future studies may seek to concentrate on the lateral side of the tibia where the bone-bridge of the osteotomy is left. This would avoid any correlation problems due to an uneven surface caused by the presence of a plate. The use of an artificial landmark may provide a solution for DIC analysis and the positioning of inspection tools during the data processing procedure.In light of the results presented from construct stiffness and IFM in both best-case and worst-case scenarii, the DTN can be considered for SMOT fixation.VM levels, which are greater and more concentrated in DTN samples than those observed in the MDTP samples. Despite this, fracture gap movement (IFMmid) of the DTN samples constantly remains inferior to 1 mm. Literature reports that fracture gaps of up to 1 mm are ideal for callous formation and bone healing38 and < 2 mm still promotes bone healing, but on a much slower scale than < 1 mm gaps, favouring fracture stability and fragment reunion39. In torsional testing, the DTN samples demonstrated greater resistance to the applied moments in most testing configurations; this is a favourable result as shear movements are known to be most harmful to fracture reconsolidation24.In the worst-case scenario, a significant difference is observed between the DTN and MDTP samples for the calculated compressive construct stiffness and the average ε


Visually guided behavior relies on the integration of sensory input and information held in working memory (WM). Yet it remains unclear how this is accomplished at the level of neural circuits. We studied the direct visual cortical inputs to neurons within a visuomotor area of prefrontal cortex in behaving monkeys. We show that the efficacy of visual input to prefrontal cortex is gated by information held in WM. Surprisingly, visual input to prefrontal neurons was found to target those with both visual and motor properties, rather than preferentially targeting other visual neurons. Furthermore, activity evoked from visual cortex was larger in magnitude, more synchronous, and more rapid, when monkeys remembered locations that matched the location of visual input. These results indicate that WM directly influences the circuitry that transforms visual input into visually guided behavior. Behavior is guided not only by sensory input, but also by information held in working memory (WM). In primates, visually guided eye movements are among the most frequently occurring sensorimotor transformations. Saccadic eye movements occur approximately four to five times each second and require the integration of myriad visual features  into discrete movements that position visual targets onto the fovea. Furthermore, each movement decision reflects not only visual input, but also information held in WM, such as the behavioral relevance of particular objects and features . How senWithin primate neocortex, the output of feature-selective neurons in visual cortical areas converges retinotopically onto neurons in the frontal eye field (FEF) , the preWe examined the influence of WM on the efficacy of visual cortical input to the FEF in behaving monkeys. First, we identified FEF neurons with direct input from visual cortex using orthodromic stimulation from extrastriate area V4. Despite the common assumption of visual inputs synapsing onto purely visual FEF neurons, our results revealed that visual cortical input to the FEF instead preferentially targets neurons with both visual and motor properties. Next, we measured the effect of spatial WM on orthodromic activation of FEF neurons and found that the efficacy of visual inputs was enhanced by the memory of spatially corresponding locations. Specifically, the activity evoked in the FEF from visual cortex was larger in magnitude, more synchronous, and more rapid when V4 input matched the location held in WM. These results demonstrate how the content of WM can influence visuomotor transformations in the primate brain.In and Out conditions, respectively). The neuron responded strongly to a visual cue appearing in the RF and exhibited elevated activity in the delay period when the remembered location coincided with the RF. Prior to saccades to the RF, the neuron also exhibited a burst of motor activity. In primates, direct visual cortical input to prefrontal cortex arrives primarily in the FEF (−40), with most neurons having latencies <10 ms , consistent with monosynaptic transmission . Visual-recipient neurons exhibited a tri-phasic pattern of evoked activity following orthodromic stimulation  (n = 196). We measured the activity of FEF neurons while monkeys performed a spatial WM task that temporally dissociates visual, memory, and motor components of neuronal responses . 2 = 9.42, p = 0.002) and motor activity  than non-activated neurons. However, the proportion of neurons with memory activity did not differ between the two populations  , with a higher prevalence of visuomotor neurons among the visual-recipient population , and a lower proportion of purely visual  and purely motor neurons   , left. N= 0.039) , right. We considered that the larger motor signals among visual-recipient neurons could have resulted from differences in the alignment of the cue stimulus with the centers of FEF visual and movement fields, as they can be significantly misaligned . Thus, wIn contrast to the disproportionate prevalence of motor signals among neurons receiving input from visual cortex, reciprocal projections of the FEF to visual cortex originate disproportionately from neurons with memory-related activity . This imIn = 0.22 ± 0.005, Spike countOut = 0.18 ± 0.004; p<10−6)     . For eacp<10−10) . The incp<10−10) . Figure p<10−10)  ('Materip<10−63) . Thus, aWe found that visual inputs to the FEF disproportionately drove neurons with both visual and motor properties. Rather than exhibiting purely visual properties, as might be expected , visual-More importantly, we found that the engagement of WM at RF locations increased the efficacy of visual input to FEF neurons. When monkeys remembered RF locations, activity evoked in the FEF from visual cortex was larger in magnitude, more synchronous, and more rapid. The increased efficacy of visual input to the FEF was independent of delay period activity, and it was observed whether or not neurons exhibited WM-related activity. Given that visual cortical inputs appear to drive neurons across functional classes, this result suggests that those inputs interact constructively with WM-related signals within the FEF. Similarly, previous work has shown that the deployment of attention increases the input efficacy of thalamocortical  and cortEvidence from multiple species suggests that top-down attention arises from biases in the selection of sensory input based on the content of WM . A recenMacaca mulatta) were used in this study. All experimental procedures were in accordance with National Institutes of Health Guide for the Care and Use of Laboratory Animals, the Society for Neuroscience Guidelines and Policies, and Stanford University Animal Care and Use Committee.Two adult male rhesus monkeys . Eye monitoring, stimulus presentation, data acquisition, and behavioral monitoring were controlled by the CORTEX system. Visual stimuli presented to estimate V4 RFs were 1.2–1.9°×0.2–0.4° bar stimuli appearing at four possible orientations . All stimuli were presented on a 29°×39° (22″) colorimetrically calibrated CRT monitor (Mitsubishi Diamond Pro 2070SB-BK) with medium short-persistence phosphors (refresh rate 77 Hz).Neurophysiological recordings of single neurons in awake monkeys were made through two surgically implanted cylindrical titanium chambers (20 mm diameter) overlaying the prelunate gyrus (V4) and the pre-arcuate gyrus (FEF). Electrodes were lowered into the cortex using a hydraulic microdrive (Narishige). Neural activity was recorded extracellularly with varnish-coated tungsten microelectrodes (FHC) of 0.2–1.0 MΩ impedance (measured at 1 kHz) in V4, and via linear electrode array  in FEF. Extracellular waveforms were digitized and classified as single neurons using both template-matching and window discrimination techniques . Area V4 was identified based on stereotaxic location, position relative to nearby sulci, patterns of gray and white matter, and response properties of units encountered; the FEF was identified based on these factors and the ability to evoke fixed-vector eye movements with low-current electrical stimulation. Prior to beginning data collection, the location of FEF and V4 within the recording chambers was established via single-electrode exploration.Each day began by calibrating the eye position; once the electrode was positioned in the FEF, the same task was used with stimulation to verify that the electrode was in FEF and estimate the RF center. The fixation point, an ∼1 degree of visual angle (d.v.a.) white circle, appeared in the center of the screen, and the monkey maintained fixation within a ±1.5 d.v.a. window for 1.5 s. For eye calibration, no stimulation was delivered, and the fixation point could appear either centrally or offset by 10 d.v.a. in the vertical or horizontal axis.In each recording session, we first localized sites within the FEF and V4 where neurons exhibited retinotopically corresponding representations, meaning that V4 RFs overlapped with the end point of saccade vectors evoked by FEF microstimulation . PrelimiThe FEF visual, motor, and delay activity were characterized in an MGS task. Monkeys fixated within a ±1.5 d.v.a. window around the central fixation point. After 1 s of fixation, a 1.35 d.v.a. square cue was presented and remained onscreen for 1 s and was then extinguished. The animal then remembered the cue location while maintaining fixation for an additional 1 s (delay period) before the central fixation point was removed. The animal then had 500 ms to shift its gaze to a ±4 d.v.a. window around the previous cue location and remain fixating there for 200 ms to receive a reward. This task was performed with two potential cue locations, located at 0° and 180° relative to the estimated RF center.During the MGS task described above, electrical stimulation was delivered to V4 during the fixation, visual, delay, or saccade period on 50% of trials . For identifying antidromically and orthodromically activated FEF neurons (see below), and evaluating stimulation efficacy, electrical stimulation used consisted of a single biphasic current pulse . Stimulation times were 500 ms after initiating fixation (fixation), 500 ms after visual cue onset , 500 ms after cue offset (delay), or 150 ms after the go cue (saccade). Data from the visual, delay, and saccade stimulation periods were used to identify orthodromically activated FEF neurons; data from stimulation during the delay period were used to measure the impact of WM on visual input efficacy.The probability of firing in each 1 ms bin following V4 stimulation was measured for stimulation trials and compared to the probability of firing in a time-matched window from non-stimulation trials. The first bin in which the probability of firing was significantly greater for stimulation trials was designated the latency of stimulation-evoked spikes. Hartigan’s dip test was used to test the bimodality of the latency distribution .Electrical stimulation of V4 evoked spikes in FEF via both orthodromic and antidromic stimulation. Antidromically evoked spikes (in V4-projecting FEF neurons) were of short latency and were confirmed via the collision test (using stimulation data collected during the MGS task described above). This test identifies antidromically activated neurons: when V4 stimulation was delivered within a few milliseconds of a spontaneously generated spike from a recorded FEF neuron, spikes artificially evoked from that neuron by V4 microstimulation were eliminated. Orthodromically activated neurons will still have an evoked spike in this period following a spontaneously generated spike. The characteristics of FEF neurons antidromically activated by V4 stimulation have been reported elsewhere .10(resp after/resp before)STIM -log10(resp after/resp before)NONSTIM. The proportion of joint spiking  analysis to measure selectivity, as described below. When determining whether a neuron exhibited significant visual or delay activity, activity in the visual and delay periods of the In condition was compared to the activity of the same neuron during fixation (300 ms before stimulus onset), using the Wilcoxon sign-rank test (p<0.05). When determining whether a neuron had significant motor activity, saccade-aligned activity in the In condition was compared to saccade-aligned activity earlier in the trial (450–250 ms before saccade onset), using the sign-rank test (p<0.05).The strength of visual, memory, and motor activity was measured as the selectivity of neurons to the In and Out conditions during the visual, delay, and motor epochs, respectively, and was quantified using an ROC analysis. This method compared the distributions of firing rates for trials in which the memory cue appeared inside versus outside the neuron's RF . The are In the interests of transparency, eLife publishes the most substantive revision requests and the accompanying author responses.Acceptance summary:This study documented the properties of neurons in the frontal eye field (FEF), a cortical brain area traditionally thought to receive visual input and transform that input into motor commands. The authors used extracellular recordings and electrical microstimulation in behaving non-human primates (NHPs) to add to this view by showing that visual input to FEF from visual area V4 appears to be gated by working -memory activity in FEF. This kind of circuit-breaking is rare and valuable in NHPs and provides new insights into mechanisms that subserve the flexible, context-dependent flow of information in the primate brain.Decision letter after peer review:eLife. Your article has been reviewed by 2 peer reviewers, and the evaluation has been overseen by Joshua Gold as the Reviewing and Senior Editor. The following individual involved in review of your submission has agreed to reveal their identity: Shengtao Yang (Reviewer #1).Thank you for submitting your article "Working Memory Gates Visual Input to Primate Prefrontal Neurons" for consideration by The reviewers have discussed their reviews with one another, and the Reviewing Editor has drafted this to help you prepare a revised submission.Essential revisions:1. Orthodromic activation of FEF neurons via V4 stimulation increases the percentage of FEF events that lead to spikes and decreases their latency during working memory. Such an effect appears expectable if FEF neurons are at a higher level of when a stimulus in their receptive field is held in memory compared to a stimulus out of their receptive field. Are the authors suggesting something special about working memory? Would the same outcome not be expected during fixation or smooth pursuit for FEF neurons that are activated by these states? It was not clear that efficacy of transmission itself improves by working memory, just the likelihood that the spiking threshold would be reached. This was considered a major concern.2. It would strengthen the authors thesis to discuss the existing functional evidence  that motor FEF neurons receive visual input and can plan movements accordingly. See for example Costello et al. J. Neurosci 2013, 33(41):16394-408.3. The authors match the receptive location of FEF and V4 neurons to maximize the chances of identifying monosynaptically connected neurons between the two areas. However, a negative finding of no effects of orthodromic activation does not entirely rule out that the FEF neuron under study receive V4 input, from another site. Some discussion is warranted on this point.4. In classical working memory tasks, the task periods usually consist of fixation, cue, delay and then response period. The neural activity during delay period is considered as working memory related signal. However, in current study, the authors didn't point out whether only delay period activity was included in analysis when they compared synaptic efficacy between stimulation and non-stimulation trials, in Figure 4a. Because the differences of neuronal response during fixation period cannot be viewed as relevant to information held in working memory, it may be better if only neuronal activity in delay period was included in their analysis.Relatedly, did all of the 96 visual-recipient FEF neurons show working memory-related activity in the memory-guided saccade task? The example neuron in Figure 3a didn't show a significant difference between In and Out trials during delay period. If the visual-recipient neuron didn't show working memory-related activity, what is the basis for the claim that enhanced synaptic efficacy from V4 to FEF was caused by working memory?5. Did the two example neurons in Figure 4c show adjusted values ? The authors mentioned in Method that Figure 4 showed adjusted values, but it may not be applicable for raster plot in Figure 4c. It may be helpful that using adjusted values show stimulation effects on evoked spike counts during memory In and Out trials.6. Did the authors find some FEF cells showing elevated firing during delay period in outside-RF trials compared with baseline firing? These elevated firings would not be caused by the RF cue and thus could more readily be interpreted as a working memory signal.7. The sample size should be indicated in the Figure 3b Venn diagram.8. It would be useful to indicate the electrical stimulus protocol in Figure 1.Reviewer #1:The authors of Working Memory Gates Visual Input to Primate Prefrontal Neurons studied how working memory influence information transmitting from V4 to frontal eye field via extracellular recording and electrical stimulation on behaving primate. They found that V4 neurons target FEF neurons with both visual and motor property, and its synaptic efficacy of V4 to FEF was enhanced by working memory. These findings are interesting and important to our understanding about how our brain acts during daily WM-related activity.Reviewer #2:This is a very interesting study, examining the properties of different types of neurons in the primate Frontal Eye Fields. It is commonly assumed that a serial processing of information takes place in the frontal lobe, from visual representation, to working memory maintenance, to motor output. However, some evidence to the contrary has also been reported, creating a debate in the field. The authors have characterized meticulously FEF neurons receiving V4 projections, by means of orthodromic stimulation. They report two main findings: that visual-input recipient neurons in FEF exhibit substantial motor activity and that working memory alters the efficacy of V4 input to FEF. The paper provides an important addition to our understanding of FEF processing. Although the first result is unambiguous, and goes against the traditional view of the FEF, the interpretation of the second is less straightforward and would need to be qualified further.1. Orthodromic activation of FEF neurons via V4 stimulation increases the percentage of FEF events that lead to spikes and decreases their latency during working memory. Such an effect appears expectable if FEF neurons are at a higher level of when a stimulus in their receptive field is held in memory compared to a stimulus out of their receptive field. Are the authors suggesting something special about working memory? Would the same outcome not be expected during fixation or smooth pursuit for FEF neurons that are activated by these states? It was not clear that efficacy of transmission itself improves by working memory, just the likelihood that the spiking threshold would be reached.2. It would strengthen the authors thesis to discuss the existing functional evidence  that motor FEF neurons receive visual input and can plan movements accordingly. See for example Costello et al. J. Neurosci 2013, 33(41):16394-408.3. The authors match the receptive location of FEF and V4 neurons to maximize the chances of identifying monosynaptically connected neurons between the two areas. However, a negative finding of no effects of orthodromic activation does not entirely rule out that the FEF neuron under study receive V4 input, from another site. Some discussion is warranted on this point. Essential revisions:1. Orthodromic activation of FEF neurons via V4 stimulation increases the percentage of FEF events that lead to spikes and decreases their latency during working memory. Such an effect appears expectable if FEF neurons are at a higher level of when a stimulus in their receptive field is held in memory compared to a stimulus out of their receptive field. Are the authors suggesting something special about working memory? Would the same outcome not be expected during fixation or smooth pursuit for FEF neurons that are activated by these states? It was not clear that efficacy of transmission itself improves by working memory, just the likelihood that the spiking threshold would be reached. This was considered a major concern.We agree that this is an important point worth addressing more clearly. Thus, we clarify in the revised paper in several ways that the observation of enhanced efficacy of orthodromic activation of FEF neurons is not necessarily expected. First, as described in the methods, and clarified further in the revision, evoked spiking responses are always measured as the change from the non-stimulation condition during the same time period. So response magnitude is normalized to this non-stimulation baseline, and thus one could have reasonably expected there to be no change in the evoked activity between the IN and OUT conditions if the combined (stimulation and endogenous) inputs are added linearly. Second, as we clarify in the revised paper, the enhancement effect is observed in neurons whether or not they exhibit delay activity. Indeed, neurons with equal spike rates in the IN and OUT conditions exhibit equally large enhancement effects. To make this point clearer, we have added a supplemental analysis and figure  that is similar to that used previously in studies demonstrating similar increased efficacy with attention . This analysis shows no relationship between the change in efficacy and delay selectivity (i.e. difference in firing rate between IN and OUT conditions). So, whether or not changes in efficacy are also present during changes in ‘states’ other than WM , it is clear that the observed change is not merely due to ‘a higher level’ of activity in the FEF neurons. Note also that, on the contrary, we do not argue that WM is special (in the discussion). Instead, we draw parallels with the effects seen during attention and note other evidence of similar underlying mechanisms.2. It would strengthen the authors thesis to discuss the existing functional evidence  that motor FEF neurons receive visual input and can plan movements accordingly. See for example Costello et al. J. Neurosci 2013, 33(41):16394-408.We thank the reviewers for the suggestion, and have added the following text to the Discussion section:“Moreover, this result is consistent with the observation of equal visual latencies between visuomotor and visual FEF neurons , and the finding that visuomotor neurons exhibit greater visual discrimination than visual neurons during certain saccade tasks .”3. The authors match the receptive location of FEF and V4 neurons to maximize the chances of identifying monosynaptically connected neurons between the two areas. However, a negative finding of no effects of orthodromic activation does not entirely rule out that the FEF neuron under study receive V4 input, from another site. Some discussion is warranted on this point.We have revised the wording in the results (pages 5 and 8) to clarify that we targeted overlapping FEF-V4 receptive fields based on the fact that projections from V4 to FEF appear to be retinotopic and discrete . We now also note that to the extent that there are non-retinotopic projections they could indeed be distributed differently onto the functional subtypes of FEF neurons than the retinotopic projections (page 8).4. In classical working memory tasks, the task periods usually consist of fixation, cue, delay and then response period. The neural activity during delay period is considered as working memory related signal. However, in current study, the authors didn't point out whether only delay period activity was included in analysis when they compared synaptic efficacy between stimulation and non-stimulation trials, in Figure 4a. Because the differences of neuronal response during fixation period cannot be viewed as relevant to information held in working memory, it may be better if only neuronal activity in delay period was included in their analysis.This analysis of efficacy was indeed limited to the delay period. We regret that this important aspect of the results was not clear, and we have added language to the results (page 9), methods (page 17), and the figure 3 caption to clarify this point.Relatedly, did all of the 96 visual-recipient FEF neurons show working memory-related activity in the memory-guided saccade task? The example neuron in Figure 3a didn't show a significant difference between In and Out trials during delay period. If the visual-recipient neuron didn't show working memory-related activity, what is the basis for the claim that enhanced synaptic efficacy from V4 to FEF was caused by working memory?This is an important point of clarification and we thank the reviewer for bringing it up. Indeed, a majority of the visual-recipient neurons did not exhibit elevated delay period activity. As shown in the bar plots in Figure 2b, ~30% of visual-recipient FEF neurons have significant delay activity . In addition, as mentioned above, we have added an analysis of the relationship between delay-period selectivity and the change in efficacy with WM . This figure and analysis demonstrates that differences in firing rates between the IN and OUT conditions do not correlate with the change in efficacy.As for the basis for the claim that enhanced efficacy is a result of WM, that is due to the fact that the location of WM is the only thing that varies between the two behavioral  conditions between which efficacy is being compared. That is a conclusion that quite reasonably follows from the observed differences in orthodromic efficacy between the two behavioral conditions; the magnitude, latency and synchrony of evoked activity all depend on the location the monkey must remember. Note that we do not claim that efficacy increased specifically in WM-related neurons. On the contrary, in the discussion, we suggest that the increased input to what are preferentially visuomotor neurons  might “facilitate the transformation of visual inputs into motor commands.” This is an important point, but it hardly detracts from the fact that WM deployment  clearly alters the efficacy of visual inputs.5. Did the two example neurons in Figure 4c show adjusted values ? The authors mentioned in Method that Figure 4 showed adjusted values, but it may not be applicable for raster plot in Figure 4c. It may be helpful that using adjusted values show stimulation effects on evoked spike counts during memory In and Out trials.Note that the raster plots in 3c (formerly 4c) are necessarily unaltered data, as the adjustment procedure does not operate on individual spikes, and the calculation of joint spiking takes into account the relative timing of those individual spikes. We now clarify this in the methods (page 18).6. Did the authors find some FEF cells showing elevated firing during delay period in outside-RF trials compared with baseline firing? These elevated firings would not be caused by the RF cue and thus could more readily be interpreted as a working memory signal.-4, n=26); overall there was no correlation between FEF neurons’ delay selectivity and their change in input efficacy .This is a good question. Indeed, it has previously been shown that some FEF neurons exhibit visual, motor and delay properties that are not aligned in space . Consistent with this, we found that some neurons exhibited more delay activity when the cue was presented outside of their visual receptive field —although the magnitude of their delay selectivity is lower on average than those with elevated firing rates for the IN condition. Importantly, the enhanced efficacy of orthodromic activation occurs in these neurons as well , and of course the visual responses of FEF neurons do not persist for the 1 second duration of the delay period . Importantly, as stated above, the interpretation that the increased efficacy during the delay period results from differences in WM is based solely on the fact that we are comparing efficacy between memory locations during the delay period , not because individual FEF neurons display delay activity (or not). Again, the difference in efficacy is independent of the amount of delay activity . Indeed, the interpretation doesn’t even depend on any presumed role of FEF delay activity in the control of WM.7. The sample size should be indicated in the Figure 3b Venn diagram.We have added the sample sizes for non-activated and visual-recipient FEF populations to the Venn diagrams in this figure.8. It would be useful to indicate the electrical stimulus protocol in Figure 1.We have moved the stimulation technique, previously shown in Figure 2, into Figure 1, and further details of stimulation timing are now illustrated in Figure 1 supplement 1.Reviewer #2:This is a very interesting study, examining the properties of different types of neurons in the primate Frontal Eye Fields. It is commonly assumed that a serial processing of information takes place in the frontal lobe, from visual representation, to working memory maintenance, to motor output. However, some evidence to the contrary has also been reported, creating a debate in the field. The authors have characterized meticulously FEF neurons receiving V4 projections, by means of orthodromic stimulation. They report two main findings: that visual-input recipient neurons in FEF exhibit substantial motor activity and that working memory alters the efficacy of V4 input to FEF. The paper provides an important addition to our understanding of FEF processing. Although the first result is unambiguous, and goes against the traditional view of the FEF, the interpretation of the second is less straightforward and would need to be qualified further.We hope that the revised manuscript provides a clearer picture regarding the significance and interpretation of the second part of the paper. Clarifications and qualifying statements have been added based on reviewer feedback (see responses to points 1-3 below).1. Orthodromic activation of FEF neurons via V4 stimulation increases the percentage of FEF events that lead to spikes and decreases their latency during working memory. Such an effect appears expectable if FEF neurons are at a higher level of when a stimulus in their receptive field is held in memory compared to a stimulus out of their receptive field. Are the authors suggesting something special about working memory? Would the same outcome not be expected during fixation or smooth pursuit for FEF neurons that are activated by these states? It was not clear that efficacy of transmission itself improves by working memory, just the likelihood that the spiking threshold would be reached.See response to essential revision #1 above.2. It would strengthen the authors thesis to discuss the existing functional evidence  that motor FEF neurons receive visual input and can plan movements accordingly. See for example Costello et al. J. Neurosci 2013, 33(41):16394-408.See response to essential revision #2 above.3. The authors match the receptive location of FEF and V4 neurons to maximize the chances of identifying monosynaptically connected neurons between the two areas. However, a negative finding of no effects of orthodromic activation does not entirely rule out that the FEF neuron under study receive V4 input, from another site. Some discussion is warranted on this point.See response to essential revision #3 above.References:Armstrong, K. M., Chang, M. H., and Moore, T. (2009). Selection and maintenance of spatial information by frontal eye field neurons. The Journal of Neuroscience, 29(50), 15621–15629. https://doi.org/10.1523/JNEUROSCI.4465-09.2009Briggs, F., Mangun, G. R., and Usrey, W. M. (2013). Attention enhances synaptic efficacy and the signal-to-noise ratio in neural circuits. Nature, 499(7459), 476–480. https://doi.org/10.1038/nature12276Bruce, C. J., and Goldberg, M. E. (1985). Primate frontal eye fields. I. Single neurons discharging before saccades. Journal of Neurophysiology, 53(3), 603–635.Costello, M. G., Zhu, D., Salinas, E., and Stanford, T. R. (2013). Perceptual modulation of motor – But not visual – Responses in the frontal eye field during an urgent-decision task. The Journal of Neuroscience: The Official Journal of the Society for Neuroscience, 33(41), 16394–16408. https://doi.org/10.1523/JNEUROSCI.1899-13.2013Lawrence, B. M., White, R. L., and Snyder, L. H. (2005). Delay-period activity in visual, visuomovement, and movement neurons in the frontal eye field. Journal of Neurophysiology, 94(2), 1498–1508. https://doi.org/10.1152/jn.00214.2005Schall, J. D. (1991). Neuronal activity related to visually guided saccades in the frontal eye fields of rhesus monkeys: Comparison with supplementary eye fields. Journal of Neurophysiology, 66(2), 559–579. https://doi.org/10.1152/jn.1991.66.2.559Schall, J., Morel, A., King, D. J., and Bullier, J. (1995). Topography of visual cortex connections with frontal eye field in macaque: Convergence and segregation of processing streams. The Journal of Neuroscience, 15(6), 4464–4487.Sommer, M. A., and Wurtz, R. H. (2001). Frontal eye field sends delay activity related to movement, memory, and vision to the superior colliculus. Journal of Neurophysiology, 85(4), 1673–1685.Ungerleider, L. G., Galkin, T. W., Desimone, R., and Gattass, R. (2008). Cortical connections of area V4 in the macaque. Cerebral Cortex , 18(3), 477–499. https://doi.org/10.1093/cercor/bhm061


Global health partnerships (GHPs) have encountered many challenges during the coronavirus disease 2019 (COVID-19) pandemic. New perspectives and insights are needed to guide GHPs when navigating current and future collaborations. This study aimed to understand perspectives and insights of international partners regarding how the COVID-19 pandemic impacted their GHPs with institutions in the United States. We performed a cross-sectional qualitative study conducted through virtual semi-structured interviews performed between June 12, 2020 and July 22, 2020. We queried academic institutions based in the United States to refer individuals from their corresponding international GHP organizations. We invited these individuals to participate in virtual interviews that were audio-recorded and transcribed. We analyzed data qualitatively to identify themes. Eighty-four United States partners provided e-mail addresses for international partners. Ten individuals from these GHPs completed the interview. Participants reported overall positive experiences with their United States-based partners during the pandemic. The following themes emerged: imbalanced decision-making; worry about partnership continuity; opportunity to optimize communication within partnerships; interest in incorporating technology to facilitate engagement; and a desire for increased bilateral exchanges. Several challenges appeared to exist before COVID-19 and were highlighted by the pandemic. Most respondents were optimistic regarding the future of their GHPs. However, concerns were expressed regarding the implications of fewer in-person international experiences with United States trainees and the desire for stronger communication. Although our results do not represent the perspectives and insights of all GHPs, they provide considerations for the future. We urge institutions in the United States to re-examine and strive for equitable relationships with their international partners. Within these international collaborations, there is increasing movement toward ensuring equity and bi-directionality between institutions.14Global health partnerships (GHPs) between academic institutions based in the United States and international institutions have rapidly expanded in recent decades because of globalization, increased awareness of the economic connections to health, and the desire of medical professionals to be prepared to provide quality care for all.5 many United States-based institutions missed opportunities to strengthen ties with their international partners during this time. Leaders in global health (GH) education based in the United States have discussed the considerations for returning to international travel,6 but little has been documented regarding international partner perspectives and their insights during the COVID-19 pandemic.The coronavirus disease 2019 (COVID-19) pandemic has disrupted GHPs. The need to prioritize local pandemic measures and travel restrictions have forced nearly all United States-based academic institutions to halt international efforts. Although a few institutions have used knowledge gained from their international partners to combat COVID-19 locally,7 These perspectives and insights are critical for navigating this current challenging time. The objective of this study was to understand how the COVID-19 pandemic impacted GHPs between international and United States institutions. Through semi-structured interviews with international partners, we aimed to gain perspectives and insights regarding how GHPs can continue successful elements of their collaborations, how the pandemic highlighted any existing issues, and how to approach new challenges with respect and equity throughout the COVID-19 pandemic and beyond. By doing so, we believe that GHPs can create more meaningful collaborations for the future.Before the pandemic, international partners provided valuable opinions about how to improve experiences for GH and local learners at their institutions.8 E-mail addresses for international partners were requested. Prospective participants were contacted via e-mail or telephone to determine whether they fulfilled the following inclusion criteria: ability to speak English and represented an international institution partnered with a United States-based institution for GH training and international rotations. We excluded participants who were United States citizens representing international institutions because we wanted to prioritize perspectives directly from international partners. Individuals who fulfilled the criteria for the study were enrolled and a virtual interview was scheduled.We performed a cross-sectional qualitative study from June 2, 2020 to July 22, 2020. We queried GHPs from United States-based academic institutions via e-mail to refer individuals from their corresponding international partners. This e-mail described the study objectives and was sent through various GH listservs, including the American Academy of Pediatrics Section on Global Health, the Consortium of Universities for Global Health, and contact lists from the Academic Pediatric Program Directors Global Health Learning Community. These methods have been described elsewhere.Two authors  trained in qualitative interviewing (by M. S. M.) performed the virtual interviews, which consisted of a study overview, verbal demographic survey, and semi-structured interview using an interview guide. The interviewers had no connection to the United States-based institutions or international partners recruited for the study to minimize desirability bias in responses. The author team comprising United States-based pediatric GH educators and members of the Academic Pediatric Program Directors Global Health Learning Community Steering Committee developed the interview guide using an iterative process. Interviewers conducted interviews in English; these interviews were audio-recorded and transcribed for analysis. Transcripts were de-identified, and audio and transcription files were stored in a secure, encrypted Cloud storage file.Descriptive statistics were used to describe respondents’ basic demographic characteristics. The existence of a bilateral partnership was recorded as “yes,” “limited,” or “no” responses. A “yes” answer indicated that within the study participant’s GHP, trainees and faculty from both the international and United States-based institutions traveled to the other site for GH experiences. A “limited” partnership had one or two faculty from the international site who would occasionally visit the United States-based institution for training, whereas the international partner regularly hosted trainees and faculty from the United States-based institution. A “no” answer indicated that the international partner hosted United States trainees and faculty, but none of their own faculty, staff, or trainees traveled to the United States site.a priori codes were created from the interview guide as a starting point for analysis. Two authors  independently performed line-by-line coding using the qualitative analysis software Dedoose.9 Three authors trained to perform qualitative analysis  independently coded open-ended responses and, using constant comparison, identified emerging themes9 that were triangulated to identify central concepts.11We analyzed interview transcripts for themes regarding participants’ perspectives and insights regarding how the COVID-19 pandemic impacted their GHPs with United States-based institutions. The The Indiana University Institutional Review Board approved this project as an exempt study.Eighty-four United States partners completed the initial query collecting e-mail addresses for their corresponding international partners. Forty-five international partners fulfilled the inclusion criteria and were contacted to enroll in the study. Of these, 14 potential participants expressed willingness to perform an interview and 10 participants completed an interview . Of the 31 who did not respond to the study team, one was affiliated with a ministry of health and the remaining 30 were affiliated with academic health centers or universities. Interviews lasted an average of 30 to 45 minutes. Half of the partnerships were less than 5 years in duration and most (7/10) had some degree of bilateral exchange . All parWe identified four emerging themes from the data: imbalanced decision-making regarding activities within partnerships during COVID-19; limited communication during COVID-19; use of technology within partnerships during COVID-19; and future outlooks regarding partnerships after COVID-19.“When the pandemic began, the U.S. closed [their] airports and said students had to be back [in the U.S.], and we [arranged for them to return.]. That is the way the U.S. works in the world.”- Participant, bilateral partnership of more than 10 yearsWhen the COVID-19 pandemic began, most international partners in our study had United States trainees from their partnership onsite or their own trainees were abroad at United States partner sites. Regarding decision-making, United States and international partners had differing approaches to their off-site trainees as the pandemic progressed. For United States trainees onsite at international partner sites, the United States partner decided when they should to return to the United States and relayed their decision to their international partners. For international trainees onsite at United States partner sites, the international partner asked their trainees to contact their country embassy, not the United States institution, for decisions related to evacuation. For the majority (4/6) of the participants interviewed with trainees at their sites at the start of the pandemic, the United States-based institution made decisions regarding the level of ongoing engagement. For example, one participant stated:Although this decision-making was unbalanced, it was understood and well-accepted by participants, especially because their partners based in the United States were liable and responsible for the safety of their own trainees.Locally, international partner sites also had to make decisions regarding United States trainees and faculty traveling within their country during their rotation. A few sites allowed United States trainees and faculty to travel to rural sites. However, representatives from these rural sites asked the United States visitors to not travel to their sites because they feared their presence may lead to increased COVID-19 spread and limited the capacity to contain an outbreak. The international sites reported that they respected the rural sites’ requests, and that this did not incite conflicts with the United States visitors or partners.Minimal conflicts between United States-based institutions and international partners were reported by interviewees regarding decision-making during the COVID-19 pandemic, and those that were identified occurred when international sites were still hosting United States trainees at the start of the pandemic. One example of such a conflict involved the necessity to quarantine. When this incident occurred, United States trainees refused an international site’s request to quarantine for 2 weeks upon arrival, thus prompting the international partner to request the United States-based partner to intervene. Ultimately, the trainees were asked by their home institution to return to the United States soon after the incident.Some (5/10) participants noted that communication between partners decreased during the pandemic, and all expressed understanding regarding why this occurred. Some of participants from smaller partnerships with fewer staff reported feeling grateful for this temporarily decreased engagement because they were struggling to manage local COVID-19 cases and did not have time to engage with partners.Of those who noted decreased communication, a few also noted that communication had shifted to address pandemic-related priorities, such as receiving COVID-19 treatment guidelines from their United States-based partner institution. None of the international institutions reported sharing resources with their partner based in the United States. Several participants noted that although formal partnership communication frequency had decreased, personal communications had increased, with partners checking on each other’s wellbeing. Some described that they wanted more formal communication, but respondents clarified that this desire had preceded the pandemic.“[After the pandemic] most of the conversations might be continued online and then, once in a while, they may visit… because it is more convenient and then it is less expensive.” – Participant, unilateral partnership of less than 5 yearsFew participants reported transitioning to virtual engagement with their United States-based partner institution after travel restrictions were placed; however, most were interested in this possibility. A few participants representing unidirectional partnerships that primarily host United States trainees noted that their institutions were developing content for United States trainees to benefit from local expertise using a virtual platform, and that they hoped to be able to generate revenue by doing this to help support their organization during the pandemic. One participant noted that technology could facilitate more virtual engagement and decrease the need for in-person travel.“I can listen to a lecture from a U.S. professor through the phone and okay that’s great. He’s the great neurologist, and that’s good. [However] I think the most valuable experience from international rotations is actually going abroad, living in a different area, getting away from home.” Participant, bilateral partnership of less than 5 yearsSome participants expressed hesitation toward fully converting to virtual collaborations because they would not adequately replace the immersive in-person experience.Only one participant noted that unreliable Internet would prohibit meaningful virtual collaborations; however, another participant had connectivity issues during the interview that required the responses to be sent via e-mail to the interviewer.“We are a small organization. We got to even smaller [during the pandemic]. We are taking very basic roles and trying to just keep the channels of communication open. But we are not actually doing any teaching, research, or community engagement, which were our 3 pillars. So that is how it has affected us. Obviously, that has huge budget, need, and goal implications for us.” – Participant, unilateral partnership of less than 5 years“We know [partner] is a very wealthy organization. They are very generous and helping us in every way they can, but we know the emergency changed the world and we have an economic crisis worldwide, so we know we are not the priority, the priority is to help locally first. So, my concern maybe is to stop receiving some help from them.” Participant, bilateral partnership of 5–10 years“But for example, we have a relationship with [partner] for about 25 years but [partner] use to sign an agreement with us. The agreement [at present] is only verbal agreement. I don’t know what is the next step with the end of this pandemic.” Participant, bilateral partnership of more than 10 yearsAlthough many participants were hopeful that their relationships with their United States partners would be restored after the COVID-19 pandemic, this hope was often mixed with worry about the relationship continuing at the same level of engagement. Participants from institutions with multiple international collaborations differentiated in that longer-standing partnerships were more likely to continue after COVID-19 than more recently formed partnerships. Fewer visits from United States trainees and faculty were anticipated, and this was a prominent worry for organizations with unilateral partnerships that depend on program fees from visiting United States trainees.“There is no way they can be called an international organization if they don’t relate with other international countries”- Participant, unilateral partnership of 5–10 yearsA few participants recognized the benefits that their institutions provide to their United States-based partner institution and believed these benefits would endure and result in continued engagement after the pandemic. One participant understood how the partnership benefited the United States-based partner institution; therefore, that participant was confident in the future partnership:“I’d love to do something more meaningful for partnerships. It’s good to go for clinical rotations for 1–2 months … but I don’t like the idea of just signing a [Memorandum of Understanding], sending 2 students that way and sending 2 students this way. Yeah, we can do that, but it would be interesting to have professors, faculty members engaging with each other … it can be research or education … we need to deepen and strengthen our relationships”- Participant, bilateral partnership of less than 5 yearsSome participants expressed future desires for their partnerships that stemmed primarily from pre-existing interests and not from the pandemic. The most prominent of these interests was to have their United States-based partner institution host more of their trainees and faculty. One participant described the desire for more meaningful and structured relationships with the partner:Although these common core themes were identified within the dataset, we did not achieve thematic saturation because of the limited sample size.Within this qualitative study, we drew from perspectives and insights regarding international partners to understand how the COVID-19 pandemic impacted and continues to impact GHPs. Despite the limited number of participants, the interviews provided critical considerations for United States-based partner institutions. Overall, international partners were positive about their experiences since the pandemic began. However, it appears that much of the decision-making during the pandemic was unilaterally led by the United States partner, and several participants expressed worry about the state of these partnerships after COVID-19. Many were open to using technology to help continue education and training, although some limitations may arise, such as unstable Internet and the lack of immersive interactions. A few participants expressed the desire for stronger communication and robust bilateral exchanges that would grow more meaningful relationships, but these challenges existed before COVID-19 and were highlighted because of the pandemic.13 Organizations such as Child Family Health International have created repositories of virtual opportunities for GH learning,14 with the primary target of these resources being United States-based individuals interested in GH and unable to engage internationally. Furthermore, some partnerships have embraced bilateral virtual engagements, such as telemedicine consults, practicums, or virtual rounds.15 Future studies are needed to understand the current status, preference, and capacity of virtual learning for both the United States and international partners, and one such study is currently being conducted by Umphrey et al.16Undoubtedly, GHPs will look different during the era after the COVID-19 pandemic. One promising avenue for this change would be increased virtual GH engagements. Most participants reported adequate access to Internet, and many expressed an interest in pursuing virtual options for GH in the future. This does suggest possibilities for the future bilateral exchange of information between institutions. During the COVID-19 pandemic, many organizations launched virtual webinar series to continue dialogue about important GH topics during the pandemic, such as John Hopkins Global COVID Webinars and the American Academy of Pediatrics Global Webinar series.2 is to avoid adverse effects of trainee involvement within the partnership. This principle should have been particularly emphasized at the start of this wide disruption. Similarly, early during the pandemic, participants described instances when their organization stopped sending United States trainees and faculty to rural sites within their country because of concerns that COVID-19 might be transmitted within settings without appropriate healthcare capacity. Although most international travel halted during the peak of the pandemic, United States-based institutions now have an opportunity to learn from and work alongside their international partners to modify predeparture curricula to include appropriate health precautions, define mutual institutional risk management processes, and develop quality cultural humility resources. Furthermore, GH education now has the opportunity to restructure its relationship and address supremacy at a systemic level.17 A foundation of mutual respect and open communication must be further cultivated during the postpandemic era, and the tendency for unilateral decision-making that was experienced within GHPs during COVID-19 must be avoided. Future research and discussions should focus on how to optimize communication and establish mutual, equitable exchanges within GHPs.Most communication between partnering institutions appeared to be positive, with some participants describing that communication during the height of the pandemic focused primarily on the health and welfare of their partners. However, a few experiences may warrant further consideration. One such experience was the refusal by United States trainees to self-quarantine after arriving to the international host country. During the early days of the pandemic, limited understanding about and formal guidance regarding COVID-19 brought great uncertainty and contributed to challenges in communication and decision-making. A guiding principle for ethical and sustainable GHPThe results of this study are limited by the small sample size, resulting in a lack of saturation of themes and a lack of comprehensive representation from international partner institutions. We recognize that we could not capture broad perspectives and insights during this global pandemic and that several limitations resulted in a small sample size. For example, the recruitment for this study occurred during the COVID-19 pandemic; to reach international partners, we relied on United States-based partners to share corresponding e-mail addresses. Prospective participants who were healthcare providers could have been overwhelmed with clinical or administrative responsibilities and, understandably, unable to participate. This is supported by the fact that the majority of eligible participants who were nonrespondents were affiliated with academic health centers or universities. Furthermore, it is possible that only international partners with strong ongoing relationships with their United States-based partner completed the demographic survey and felt encouraged to participate. We also speculated that prospective participants available for an interview represent communities or institutions less impacted by the pandemic at that moment or had adequate resources to engage . It is also possible that social desirability bias may have been inadvertently introduced within this study because the preservation of supportive relationships is a likely priority for many institutions at this time. We attempted to minimize this bias by utilizing interviewers unrelated to the study participant’s United States-based institution and by using neutral, open-ended questioning. We also allowed participants to choose not to name their United States-based partner institution to further preserve anonymity. Although all participants felt comfortable with English, it may have not been the primary language for many. The results of this study were also influenced by the specific time period of data collection during the pandemic. If data collection had occurred later during the pandemic, when more was known about the virus and immunizations were available, then it is possible that experiences of the GHP may have differed. Despite these limitations, our intention was to acknowledge the experiences and not diminish those of others. We feel that participants of this study contributed meaningful perspectives and insights regarding how GHPs can strengthen collaborations in the future.From the GHPs represented in this qualitative study, we found that most international partners are hopeful but also worried for the future of their international collaborations because of the COVID-19 pandemic. Although not representative of all GHPs, the participants’ valuable information provided the United States and international partners with key considerations for discussion and strategic development. As we begin to transition past the acute phase of the COVID-19 pandemic, United States-based institutions have an opportunity to engage in more equitable decision-making, strengthen communication, and collaborate innovatively with their international partners. We will continue to encounter global uncertainties and challenges in the future. Both the United States and international partner institutions should be pushed now more than ever to recognize their dependency on each other, create clear policies for trainee and faculty exchange and safety, and create meaningful deeper relationships while working toward shared health-related goals. This is our way forward, together.


Increasing interest in bio-based polymers and fibers has led to the development of several alternatives to conventional plastics and fibers made of these materials. Biopolymer fibers can be made from renewable, environmentally friendly resources and can be fully biodegradable. Biogenic resources with a high content of carbohydrates such as starch-containing plants have huge potentials to substitute conventional synthetic plastics in a number of applications. Much literature is available on the production and modification of starch-based fibers and blends of starch with other polymers. Chemistry and structure–property relationships of starch show that it can be used as an attractive source of raw material which can be exploited for conversion into a number of high-value bio-based products. In this review, possible spinning techniques for the development of virgin starch or starch/polymer blend fibers and their products are discussed. Beneficiation of starch for the development of bio-based fibers can result in the sustainable replacement of oil-based high-value materials with cost-effective, environmentally friendly, and abundant products. The effects of oil-based plastics and additives on climate, water and soil quality are omnipresent. In the last few decades, many scientific studies and developments have been undertaken in order to manufacture products sustainably from renewable raw materials and thus reduce the dependence on fossil raw materials and the global amount of microplastics. Textiles based on synthetic fibers are supposed to be one of the biggest sources for microplastic due to washing abrasion and the contamination of wastewater. The world fiber market accounted for the largest percentage of synthetic fibers by the early 2000s, which has increased rapidly in comparison to 5% in 1960 [Biopolymers or bio-based polymers are renewable, environmentally friendly and biodegradable materials, which can be used as an ideal substitute for oil-based polymers that are synthetic in nature . The incStarch is the predominant carbohydrate reserve in many plants such as potato, tapioca, and cornstarch . Starch The linear nature of amylose can facilitate the orientation and parallel alignments of hydroxyl groups. The occurrence depends on the conditions for macromolecular chain mobility, particularly by dilution with suitable solvents in most cases. Alternatively, dilution under high temperatures can be applied. By aligning neighboring amylose molecules, the intermolecular interactions can be influenced by the formation of hydrogen bonds. The average polymerization degree of the macromolecular branches in amylopectin molecules is about 25 monomer units. Amylopectin molecules have limited chain mobility and do not align and associate spontaneously due to the highly branched structure of these molecules . Figure Starch without additives is a biodegradable, non-toxic polymer with excellent biocompatibility, but hardly processable without plasticizers due to its complex macromolecular structure and thus limited ability to react to external deformations . Starch Many biopolymers have been used to form fibers using different spinning techniques . Fiber-rStarch was identified as an appropriate substitute for the polyester fiber production. Advantages of starch-based fibers are the global availability and low cost of starch, its biodegradability, and potential for a sustainable production . BesidesVery few reports have been written about starch-based fiber spinning, focusing only on electrospinning. Further literature is available only on patents, describing the applications of different fiber spinning technologies. In this report, we review the possibilities of various spinning techniques that could be used in the production of bio-based fiber from virgin starch and starch/polymer blends and fibers produced thereof. Bio-based fibers can result in the sustainable replacement of oil-based high-value materials with cost-effective, environmentally friendly, and abundant products. Therefore, this paper is expected to be good source of information for those working with the fabrication of fibers from starches and starch/polymer blends.Starch is one of the most important renewable resources and is considered as the second largest source of biomass on earth after cellulose . The majHiemstra and Muetgeert  establisSpinning amylose suffered from different disadvantages such as insufficient fiber tensile strength and cost-intensive adjusted amylose from starch composition, because starches have a higher content of amylopectin . StudiesmT and become hard when they are cooled below mT with a complete chain immobility if cooled under the glass transition temperature gT. Thermoplastics can undergo plastic deformation due to their large molar mass, entanglements, intra- and intermolecular interactions, and chain branches. The morphology of thermoplastics can be fully amorphous (only gT) or semicrystalline with gT and mT [Thermoplastics are uncrosslinked polymers and have a low-viscous flow once heated above a specific melting temperature g and Tm . AmorphoThermoplastic starch can have both an amorphous or semi-crystalline morphology, containing gelatinized or destructured starch in the presence of plasticizers. Fed into an extruder with external heat and applied shear forces of screw–barrel interactions, thermoplastic starch can be molded into plastic products. It can be repeatedly melted and hardened, allowing its processing in common techniques used in the plastic industry. Starches are not truly thermoplastic in nature, which means they have no thermoplastic character in their native form . In the Thermoplastic starch (TPS) composition is a translucent amorphous polymer with comparable properties to conventional polymers. It is obtained by compounding native starch with suitable plasticizers at starch gelatinization temperature. Hydrogen bonds present in native starch will be weakened by this operation which leads to fully amorphous material. The resulting material is known as plasticized starch, destructured starch or thermoplastic starch (TPS) ,23,24. IAttempts to spin thermoplastic starch compositions dates back to 1951. At this time, wet spinning technology was used to extrude the composition of aqueous starch dispersion and glycerol in a methanol/glycerol coagulation bath to obtain starch fibers . The worUsually, it is difficult to obtain sufficient properties from semi-crystalline TPSC alone for fiber spinning processes or fiber applications because of weak mechanical properties, retrogradation, and the high hygroscopic nature of thermoplastic starches TPS. Thus, fibers of TPS blends were investigated in much of the literature and patents on spinning TPSC fibers. A lot of research on the application of starch focused on blending thermoplastic starch and other synthetic polymers ,28,29,30Biodegradable fibers from starch composites have been developed by different researchers. Nakajima and Taniguchi used polybutylene succinate (PBS) as the core material and a starch/polymer composite as the sheath, and successfully spun fibers . DiffereMost of the early attempts made in fiber spinning from thermoplastic starch composition are in the form of patents. Some of thermoplastically processable starch compositions are disclosed in U.S. patent Nos. 4900361, 5095054, 5736586 and PCT publication WO 98/40434 filed by Hanna et al. These abovementioned starch compositions do not contain the high molecular weight polymers which are essential to achieve the required melt viscosity and melt extensibility. The melt viscosity and melt extensibility are essential material characteristics used for production of fine fibers, thin films, or thin-walled foams to avoid fracture and failures .A TPSC composition consisting of dextrin, a kind of destructured starch from tapioca or corn starch, and polyacrylamide (PAM) was developed by Bailey et al. . These rNon-thermoplastic starch composition (NTPSC) consists of starch and water softening to a degree that the material can be brought into a flow. This combination can be processed, e.g., by spinning, to form a plurality of non-thermoplastic starch fiber suitable for forming a flexible fibrous structure . Non-theIn early attempts to produce starch fibers, a wet spinning process was used principally. For example, a starch/solvent colloidal suspension can be extruded from a spinneret into a coagulating bath. Previous studies for wet spinning starch fibers include U.S. Pat. Nos. 4139699, 4853168 and U.S. Pat. No. 4234480 . While sPrevious work conducted by Eden and Trksak  describeIn a patent claimed by James et al. , an NTPSThe conventional fiber spinning methods are melt spinning, wet spinning, and dry spinning. These methods have been widely used in synthetic fiber manufacturing. Melt spinning is used for thermoplastic polymers that can be melted. In melt spinning, the polymer melt can be extruded through a spinneret containing a number of holes. The elongational laminar melt flow causes molecular orientation in the machine (drawing) direction that can be even enhanced by drawing and crystallization upon cooling. The schematic drawing for melt spinning is shown in In dry spinning, a solvent is used to dissolve the raw material to form a solution and the fiber is formed from the polymer solution. In this process, the polymer can be dissolved in a volatile solvent, the solution is pumped through the spinneret to form filaments, and air is used to dry the filaments. Usually, the used solvents in dry spinning are expected to have low boiling point and low latent heat or appropriate volatility, respectively. The schematic for dry spinning is given in These conventional methods have also been widely used in fiber spinning from virgin starch or starch and other polymer blends . Bond etOther researchers have used the wet spinning method for fiber spinning. Nevertheless, the wet-spun fibers are characterized by a coarse diameter, typically greater than 50 µm, and the large amount of solvent used in this process needs an additional drying step and recovery . Some ofBesides the conventional spinning methods, different kinds of new spinning techniques have been developed and used for fiber spinning from starch and starch/polymer blends. Some of the novel developments in starch fiber production include electrospinning ,38,39,40Electrospinning is a fiber spinning technique that uses a high voltage electrostatic field for the production of fibers with diameters in the range of micrometer to nanometer scale. It has become a widely used fiber formation technique in the last decade ,38. The The differences between electrospinning and the conventional methods (wet/dry spinning) are in the fundamentally different processes, where electrostatic attractions enable the process and also the aerodynamic drag at the end of the process . The linApproaches for the electrospinning of nanofibers from natural starches will be economically feasible on a commercial scale even if starches with a high amylopectin content are utilized, because amylopectin is the major component in any natural starches. On the other hand, amylopectin as the major constituent of the starch and a highly branched polymer affects the fiber’s formation during the electrospinning . TherefoA patent designated by Jennifer et al.  describeAccording to Fonseca et al. , solubleHowever, in another study, glutinous rice starch and tapioca starch were used for fiber spinning using an electrospinning technique. In this research, water was used as the only solvent and polymeric dispersions were stirred at 80 °C for 15 min before electrospinning. From the result, it was revealed that unlike tapioca starch, the glutinous rice starch failed to generate nanofibers during the electrospinning ,51.The fabrication of high purity natural tapioca starch (NTS) fibers was reported by Sutjarittangtham et al.  using a More recently, research conducted by Fonseca et al.  revealedThe schematic electrospinning process is given in In order to overcome problems associated with natural starches, starches can be blended with other polymers, chemically crosslinked, or plasticized to improve their properties ,48. In tŠukytė et al.  preparedBicomponent nanofibers from PVA/cationic starch solution were produced by using electrospinning . In thisKong and Zeigler  developeCardenas et al.  also proCentrifugal spinning is also known as rotary jet spinning, rotor spinning, and force spinning . AlthougHowever, other researchers, Li et al.  attempteSolution blow spinning (SBS) has been used industrially since the end of the 19th century, and it is one of the oldest methods of synthetic fiber production. Solution blow spinning is obtained by the combination of elements of both electrospinning and traditional melt blowing technologies . CompareThis process combines wet spinning and dry spinning. In both methods, the polymer solution is extruded through the spinnerets into fibers. Solvent used in this process is removed and drawing of the fibers will be performed to reduce the fiber diameter with a consequent improvement of the mechanical strength. In the case of dry spun solution blowing, the polymer solution is pushed through a spinneret into a heated column, called the spinning tower. Within the tower, the polymer solidifies through evaporation of the solvent. In the case of wet spun solution blowing, the spinneret is placed in a chemical bath. Inside the bath, the polymer is precipitated by dilution or a chemical reaction to form fibers .Solution blowing is quite an innovative technique and is less researched for the production of biopolymer fibers. In solution blowing, a polymer solution is extruded and non-polymer melts. Solution blowing is associated to melt blowing. The only difference lies in the solvent evaporation in the former, rather than melt cooling jet solidification in the latter. Solution blowing is basically an isothermal method. Unlike melt blowing , which pAll spinning techniques above have advantages and disadvantages and should be chosen depending on the application and the associated property requirements. −1–1 years) bio-based resources. For the production of bio-based polymers, different renewable biogenic raw materials such as sugars and polysaccharides , proteins and vegetable oils, as well as biogenic by-products from forest and food industries such as lignin and pine resin derivatives have been used so far [Synthetic polymers are mainly obtained from fossil raw materials (crude oil and fracking gas) as by-products from cracking processes . Fossil resources were created from plant biomass over millions of years. They are therefore not a renewable, but finite resource and need to be substitute by renewable  other biopolymers, (ii) organic or inorganic functional stabilizers, (iii) fillers or (iv) fibers. The resulting biopolymer blends are called biopolymer composites. These composites have a diverse range of applications in the medicine, electronics, construction, packaging, and automotive sectors . The incMany bio-based materials have been utilized in the packaging industry. Among the total plastics usage, “packaging” occupies the top position with 41% of all plastic applications ,78. PlasAmong the natural bio-based polymeric materials, starch has been identified as one of least expensive polysaccharides, which is easily processable with conventional plastic processing equipment. Native starch resources are available all over the world and has a huge potential for solid plastics and other functional polymer applications ,88. It iStarch is commonly used in food and agriculture industries. It can also be used for other applications such as in adhesives and paper binders, textiles, chemical production, or as a feedstock for fermentation . Starch-Some of the advanced application areas of starches are: porous foam structures ,96,97,98The properties of natural polymers such as desirable biocompatibility, biodegradability, chemical stability, non-toxicity, balanced mechanical properties, and high porosity have provided unique advantages compared to synthetic polymers. Starch biopolymer, being the second most abundant biopolymer on earth, should be regarded as a valuable resource for fiber manufacturing. Many research attempts have been made to fabricate fibers from starch and starch/polymer blends. Moreover, the inefficient mechanical strength, hydrophilicity, decreased thermal stability, and difficulty in processability still limit the application of starches for industrial uses, and particularly their application for fiber fabrication. To overcome these limitations, various processes including plasticization and physical, chemical, enzymatic, and genetic modifications have been studied. Blending starch with other biopolymers is outlined as a viable alternative to overcome these limitations and can particularly enhance the mechanical and thermal properties of native starch. Besides the blending and modification of starches, new techniques for spinning starch to micro- and nanofibers have also been developed for their application in different fields.Spinning starch has been performed with additives such as processing aids and without additives. The spinning of native starch has been proved successful for the first time by using electro-spinning. Extensive works are being conducted to fabricate starch fibers from native, modified, and thermoplastic starches using different spinning methods. A number of reviews reported on starch fiber spinning, although most of them cover only a few spinning methods comparatively. This review discussed the recent progress in spinning starch fibers and summarized technologies used in fiber spinning along with their comparison. The review also discussed the progress in applications of starch biopolymers and fibers in areas of different technological applications.Even though there are attempts made in the fabrication of starch fibers from native starches, extensive research and development works are required to develop appropriate and more efficient spinning technologies for starch biopolymers in order to fully utilize them as a source for a bio-based high-value product. Melt spinning has the potential for continuous fiber extrusion with high outputs. In order to minimize shear fracture and the associated degradation of the starch and breaks of the fibers, future work should focus on starch compounds with alternative, eco-friendly plasticizers. Natural plasticizers are supposed to influence the physical structure of starch-based polymers and the rheological properties. The investigation of several processing parameters such as the drawing ratio and cooling conditions might have a decisive influence on the microstructure, and thus the final fiber properties. The characterization of the processing–structure–property relationships of starch-based fibers is part of the future investigations, and will contribute to life cycle assessments and global bioeconomic strategies.