The nexus between prenatal greenspace exposure and low birth weight (LBW) remains largely unstudied in low- and middle-income countries (LMICs). We investigated a nationwide retrospective cohort of 4,021,741 live births  across 31 provinces in Iran during 2013–2018. Greenness exposure during pregnancy was assessed using satellite-based normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI). We estimated greenness-LBW associations using multiple logistic models, and quantified avoidable LBW cases under scenarios of improved greenspace through counterfactual analyses. Association analyses provide consistent evidence for approximately L-shaped exposure-response functions, linking 7.0–11.5% declines in the odds of LBW to each 0.1-unit rise in NDVI/EVI with multiple buffers. Assuming causality, 3931–5099 LBW births can be avoided by achieving greenness targets of mean NDVI/EVI, amounting to 4.4–5.6% of total LBW births in 2015. Our findings suggest potential health benefits of improved greenspace in lowering LBW risk and burden in LMICs. Quantifying well-being effects of greenness is of great importance for achieving the Global Nutrition Targets 2025 for low birth weight. Here, the authors show underlying health benefits of improved green space in lowering low birth weight risk and burden in Iran. Pregnancy is a susceptible time period for environmental exposures, and adverse birth outcomes are known to be associated with neonatal morbidity and mortality, as well as life-long consequences such as stunted growth and mental retardation2. Given the well-defined exposure period during pregnancy, birth outcomes may be particularly helpful in identifying potential health effects of greenness3.Accumulating studies have linked greenness with an array of health improvements, including decreased mortality, enhanced cognitive functions, and positive birth outcomes1, while the overall evidence on low birth weight (LBW) remains less consistent4. Notably, there still existed considerable research gaps in prior greenness-LBW investigations. First, one in seven live births globally suffered from LBW in 20155, of which ~90% occurred in low- and middle-income countries (LMICs). Despite this fact, the majority of existing greenness-LBW studies have been conducted in high-income countries (HICs), leaving an extensive scarcity of evidence in LMICs6. Second, only sporadic studies have provided national evidence using millions of live birth records spanning the entire country8, thus making it inadequate and not convictive for valuing greening efforts as health-promoting measures in public policy making. Third, no prior analysis has quantified the potential benefit of reducing LBW in LMICs by achieving the well-defined target of green space coverage. To achieve the Global Nutrition Targets 2025 for LBW—a 30% reduction in the number of LBW babies by 20259, it is greatly essential to clarify to what extent the enhancement of vegetation density can contribute to alleviating the LBW burden in LMICs.To date, a number of population-based studies have examined the associations between greenness and birth outcomesIn this study, we conceived a nationwide observational study of ~4 million mother–infant pairs, utilizing birth records from 2013 to 2018 spanning 31 provinces in Iran. Our primary purpose was to derive the nationally representative exposure–response (E–R) relationship between greenness exposure during pregnancy and the risk of LBW in Iran; a secondary aim was to quantify the avoidable burden of LBW attributable to improved greenness under counterfactual exposure scenarios.We investigated birth outcomes of LBW  and term low birth weight . By excluding 47,102 ineligible birth records  and enhanced vegetation index (EVI) with multiple buffers . Compared with mothers with normal birthweight infants, mothers with LBW/TLBW infants experienced consistently lower greenness during pregnancy within 500-m to 3000-m buffers. For instance, mothers with LBW infants were exposed to mean NDVI 0.287–0.292 and EVI 0.207–0.210, while mothers with normal birthweight infants were exposed to mean NDVI 0.315–0.319 and EVI 0.227–0.230, respectively.−3000m and EVI−3000m were associated with odds ratios (ORs) of 0.911  and 0.885 (0.881–0.889) for LBW, 0.899 (0.895–0.902) and 0.871 (0.866–0.875) for TLBW, respectively. The associations between greenness and LBW/TLBW remained greatly robust to sensitivity analyses based on various exclusion criteria and additional adjustments for socioeconomic status (SES) variables  for LBW and 0.956 (0.955–0.958) for TLBW, respectively. Comparable risk estimates were seen in analyses using different greenness indices and buffers  between greenness exposures and LBW/TLBW, suggesting consistent evidence for L-shaped curves under different greenness indices and buffers , less educated , and village-dwelling  mothers. Similar results were also observed for TLBW and EVI−3000m  and avoidable numbers (ANs) of LBW/TLBW by linking the E–R functions to spatially resolved estimates of live births, and maternal greenness exposures Fig. . Higher This national study investigated the association between greenness exposure during pregnancy and LBW in LMICs. By involving ~4 million Iranian live births, our study provided robust evidence that elevated greenness was associated with decreased risks of LBW and TLBW. Stratified analyses revealed potential heterogeneities in greenness-LBW associations between subpopulations, suggesting significantly greater greenness-associated benefits among younger, less educated, and village-dwelling mothers. These findings from association analyses suggested the potential health benefits of improved greenness in lowering LBW risk and burden in LMICs.−500m. This estimate was slightly lesser than the pooled risk reduction of 10.0% (1.0–17.0) in a recent meta-analysis of 10 observational studies4, despite substantial heterogeneity among included studies (OR range: 0.55–1.03). Such a discrepancy in effect magnitude could be largely predictable, given that included studies in the pooled analysis were mostly conducted in HICs (9/10). In several studies focused on populations in LMICs, considerable uncertainties also remained with regard to greenness-LBW associations. Most recently, two regional studies in southern China involving 11,258 and 16,184 live births reported reduced risks of 0.69 (0.56–0.85)10 and 0.91 (0.83–0.99)11 per 0.1-unit increase in NDVI−500m, respectively, whereas a null association of NDVI−500m with LBW was found among 18,655 live births in northern China (0.96 [0.78–1.19])12. Great diversity in study demographics and vegetation cover may partially interpret these mixed findings on the direction of associations and the magnitude of effect sizes. Our findings provided national evidence on greenness-LBW association in LMICs, suggesting a possibly effective intervention measure for reaching the Global Nutrition Targets 2025 for LBW in these regions9. More nationally representative or multi-country investigations are urgently needed in LMICs as reference bases for how much increase in vegetation density would be practically appropriate in areas with high LBW prevalence.The current study associated a decreased LBW risk of 7.0% (95% CI: 6.7–7.3) with a per 0.1-unit increase in NDVI14. For instance, inverse U-shaped curves were identified for relationships between NDVI within a 500-m buffer and birth weight, birth height, and GA based on China Maoming Birth Cohort10, indicating that a moderate greenness level may support more favorable fetal parameters. According to the analysis from the Massachusetts Birth Registry data15, NDVI-birthweight association showed an S pattern and significantly larger increments in birth weight were found in low NDVI ranges of 0.25–0.50 than NDVI 0.50–0.75, with an estimate of 6.7 grams (95% CI: 5.2–8.2) versus 2.1 grams (95% CI: 0.1–4.1) per 0.1-unit rise in NDVI−250m. By involving 3 million births, the Texas Vital Statistics program found participants residing in NDVI−250m between 0.37 and 0.45 had the most increase in birth weight (2.7 grams) compared to those residing in NDVI−250m above 0.4514. This evidence from both developed and less developed countries highlighted the potential for substantial health benefits from improvements in vegetation density at low-level greenness areas, which may help reduce socioeconomic health inequalities.In this study, we observed approximately L-shaped E–R curves between greenness and LBW, suggesting a greater reduction in LBW risk at the lower greenness range. This interesting finding was partially echoed by prior investigations on several fetal parameters, despite that heterogeneous E–R functions were still identified3. Less years of education are widely believed to relate to lower SES16. Though several studies found benefits irrespective of SES or more benefits in participants belonging to the highest SES groups15, the present study and more existing studies reported stronger associations between greenness and birth outcomes among mothers with low education level or low SES18, who may be highly deprived of green environment19. Emerging evidence suggested inconsistent findings for urban–rural disparity in associations of vegetation with birth outcomes4. In contrast to prior investigations20, our study found stronger associations among village residents rather than urban dwellers. This inconsistency may be explained by the variation in the criteria used to classify urban and rural areas between studies, and urban residents in some regions may have easier access to higher quality of green spaces as NDVI or EVI cannot tell the type of green spaces16. Compared to residential and educational disparities, age differences in vegetation-birth associations are less discussed in existing studies. In line with a population-based Chinese birth cohort analysis on preterm delivery, we identified significantly greater benefits of greenness in lowering the LBW risks for younger mothers (≤25 years old)16. Younger mothers may face unstable financial income and greater survival stress, usually implying a lower SES. To fill this health gap due to SES inequalities, increasing density of vegetation could be an effective intervention and should be prioritized in the most socioeconomically deprived communities22.As the “equigenic environments” theory suggested, greenness might disrupt the conventional transition of socioeconomic adversity to greater health risk and may be important in filling the pervasive health gap between more and less advantaged persons23, and in Barcelona, Spain, increasing percentage of green area from 6.5% to 19.6% was estimated to avoid 60 (0–119) deaths in 201024. A larger-scale study encompassing 31 European cities found that meeting the WHO recommendation of at least 0.5 hectares of green spaces within a 300-m distance could prevent 42,968  deaths in 201525. These analyses emphasized the great importance of green space in reducing premature deaths and prolonging life expectancy in developed countries1. Quantitative contribution of greenness improvement to reducing adverse birth outcomes remains unstudied across the globe, whereas a number of existing studies in LMICs have investigated the potential health benefits of weakening exposure to adverse environmental factors, such as ambient fine particular matter (PM2.5) pollution. For instance, a modeling analysis of Demographic and Health Surveys (DHS) data estimated a total of 0.83 (0.54–1.08) million stillbirths attributable to PM2.5 exposure exceeding the counterfactual exposure of 10 μg/m3, amounting to 39.7% (26.1–50.8) of total stillbirths across 137 countries in 201526. Using 2.4 μg/m3 as a reference, 1018 (718–1289) thousand and 280 (196–358) thousand PM2.5-associated preterm births were estimated to be avoided annually during 1990–2019 in India and China, respectively27. Compared with ambient PM2.5 exposure, huge research gaps still exist in greenness-attributable assessment, primarily owing to the lack of nationwide evidence regionally and globally. Assuming causality for greenness-LBW associations, our study estimated that, in Iran, 3931–5099 LBWs could be avoided by achieving targets of mean NDVI/EVI with various buffers, representing 4.4–5.6% of total LBWs in 2015. Considering that greenness may alleviate PM2.5-related risks of adverse outcomes28, co-improvements of increased vegetation and clean air could helpfully accelerate the progress of Global Nutrition Targets for LBW in 2025.Through counterfactual analyses, prior studies have reported the alleviated burden of death related to greenspace improvement. Small-scale studies have been pioneered in individual cities; in Philadelphia, USA, 403 (95% CI: 298–618) deaths would be prevented annually for reaching the goal of 30% tree canopy cover in each of the city’s neighborhoods29. Second, NDVI and EVI may exhibit limitations in fully characterizing the maternal experience of being exposed to trees and plants because these indicators do not reflect the type and quality of vegetation30. However, NDVI and EVI can still provide guidance in less developed areas as some of the few widely validated and globally covered vegetation indicators. Third, unmeasured confounding  was likely from the lack of control for potential individual-level risk factors of LBW. However, sensitive analyses via additionally adjusting for provincial-level SES variables provided comparable risk estimates with our primary results. Also, prior cohort studies from Asia11 and Europe31 reported similar greenness-LBW associations between unadjusted and multivariable-adjusted analyses adjusted for various covariates including lifestyle factors such as maternal smoking status. Such evidence suggested a limited influence of residual confounding on our findings. Fourth, our attributable assessments were on the basis of E–R functions derived from association analysis instead of the causal framework, estimates of avoidable LBW should thus be interpreted with caution.Some limitations of our study need to be noted. First, individual maternal greenness exposures were evaluated according to locations of delivery hospitals rather than residential communities, yet robust findings from buffering analyses (500–3000 m) may reduce the influence of such exposure bias to some extent because pregnant women mostly give birth to a hospital not too far from homeIn summary, our study added nationally robust evidence for decreased risks of LBW in association with greenness exposures in different buffers among 4 million Iranian newborns. Approximately L-shaped E–R functions with slopes being steeper at low greenness levels were identified between greenness and LBW. Babies of younger, less educated, and village-dwelling mothers had a greater reduction in the risk of LBW associated with an increase in surrounding greenspace. Our quantitative estimation for avoidable LBW and TLBW in Iran, based on association analyses and counterfactual framework, suggested underlying implications for national and global assessments of the disease burden of adverse birth outcomes associated with lowgreenness exposures and may provide valuable information to address inequalities in LBW risk and to promote environmental justice in LMICs. Future assessments from multiple countries, utilizing sophisticated designs and causal analysis, are greatly warranted to validate findings from this study.32, n = 30,307), neonatal deaths , and cases with undetermined sex  and unmatched exposure (n = 8747), 4,021,741 live births were finally included in our analyses  as a secondary endpoint outcome.16, allows easy and rapid identification of vegetation areas but is sensitive to aerosols and clouds. EVI is then developed as an optimized vegetation index, correcting for canopy background noise, aerosol conditions and soil effects. Thus, we used both NDVI and EVI as exposure indicators to perform the association analysis.We utilized NDVI and EVI, two indicators representing the density of vegetation, to estimate maternal exposure to greenness. NDVI, the best-known and most commonly used vegetation indicator36. We applied the maximum value composite method to rebuild the maximum vegetation index for each pregnant woman throughout her pregnancy. This method could well eliminate the influence of cloud cover and seasons, and better reflect the spatial distribution of green space37. Negative values representing water bodies were not removed and were treated as zero prior to the assessment of greenness exposures38.We extracted these two vegetation indices from imagery generated by NASA’s Terra Satellite, the Moderate Resolution Imaging Spectroradiometer (MODIS) with a spatiotemporal resolution of 16 days and 250 × 250 m. Both indices range from −1 to 1, with values close to zero generally representing bare areas, and higher positive values indicating a higher density of vegetation39. Analyses based on multiple buffers were performed to validate the robustness of our findings.To capture both local and larger-scale green spaces, NDVI and EVI within 500-m, 1000-m, 2000-m and 3000-m buffers around the maternal delivery hospitals were chosen to estimate greenness exposures during the entire pregnancy. These buffer sizes represented 10-, 15-, 20-, and 30-min walking distances from the delivery hospital, respectively4, we considered several sets of covariates in our analysis: (1) maternal demographic characteristics: age, education attainment , residence (city or village), nationality (Iranian or non-Iranian), delivery type , parity , number of fetuses (singleton or multiple gestations) and delivery hospital; (2) fetal variables: infant sex , the season of birth , and GA; (3) environmental factors: average temperature, relative humidity, and PM2.5 concentrations.In light of previous studies on greenness and birth outcomes40. Relative humidity was then calculated using the method recommended by the National Weather Service41. We extracted monthly ground-level PM2.5 concentration at a 0.1° × 0.1° resolution from the global surface PM2.5 datasets released by the Atmospheric Composition Analysis Group43. Exposure levels of ambient temperature, relative humidity, and PM2.5 for each pregnant woman throughout her pregnancy were consistently evaluated by mean values during months from the last menstrual period to the date of birth. Due to the minimal proportions of missing values for some socioeconomic variables, we elected to impute these sparse missing values to the mode of corresponding categorical variables in order to ensure modeling convergence28.Average temperatures and dew point temperatures during the pregnancy period were aggregated from daily gridded estimates (0.1° × 0.1°) derived from a reanalysis dataset of the global climate , which has been developed by the European Centre for Medium-Range Weather Forecast44.We conducted logistic regression models to quantify the association of greenness exposures with LBW/TLBW, adjusting for the confounders mentioned above. A sequential adjustment approach was adopted to determine the models with different adjustment levels. To be specific, Model 1 was a crude model without covariate adjustment; Model 2 was adjusted for maternal age, infant sex and GA; Model 3 was adjusted for covariates in maternal demographic characteristics and other fetal variables; Model 4 (fully adjusted model) was adjusted for covariates in maternal demographic characteristics, fetal variables, and environmental factors. Subsequent analyses were all performed based on a fully adjusted model. Considering the possible nonlinear relationships between birth outcomes and climate conditions, we incorporated temperature and relative humidity in our fully adjusted model using natural spline functions with three degrees of freedom45. Since the linear assumptions between greenness exposure and birth outcomes may not hold, we replaced the linear term of NDVI or EVI with a restricted cubic spline (RCS) term with three knots placed at the 10th, 50th, and 90th percentiles of greenness exposure distribution to examine potential nonlinear relationships according to prior studies46. Likelihood-ratio test was used to compare the goodness of fit between linear and RCS models, where P value < 0.05 indicates a significant violation of the assumption of a linear relationship47. Subgroup analyses were done to evaluate potential effect modifiers, stratified by maternal age , education attainment , and residence . Effect heterogeneity between subgroups was examined through a fixed effect meta-regression method48.We assessed ORs of LBW/TLBW with corresponding 95% CIs for each 0.1-unit increase in NDVI or EVI and for the second through fourth quartile exposure  using the first quartile (Q1) as a reference. Tests for linear trends across quartiles were performed by introducing the median value of each quartile of NDVI or EVI as a continuous variable in the logistic regression model49. Second, records of live births involving multiple gestations were removed considering the influence of insufficient intrauterine growth induced by multiple births. Third, we excluded pregnant women under 13 years old and over 50 years old to reduce the likelihood of confounding by abnormal age of conception51. Fourth, analyses were repeated by excluding pregnant women with pre-existing chronic diseases  or maternal delivery complications. Fifth, we additionally adjusted several provincial-level SES variables  in our fully-adjusted model, to partially account for potential unmeasured confounding. These SES variables were collected from the Iran Statistical Yearbook.Several sensitivity analyses were performed to test the robustness of our findings. First, the models were rerun after excluding records with birth weights <500 and >5000 grams to eliminate the confounding effect of extreme observations27, avoidable LBW numbers due to greenness improvement were estimated by linking the E–R relationships to spatially resolved estimates of live births and maternal greenness exposures. Briefly, we predicted the risk of LBW/TLBW associated with greenness exposure with an interval of 0.01 unit, using a counterfactual exposure of mean value in given vegetation indices (NDVI/EVI) and buffer sizes  as the reference.Following the framework of counterfactual analysis widely adopted in prior modeling studies52. We then calculated the ANs of LBW/TLBW births for each 1 × 1-km spatial unit using the Eqs. . mean are defined as 1, suggesting no excess risks associated with poor greenspace. To avoid an overestimation53, Considering the spatial variations in greenness and birth population, we initially resampled the annual maximum vegetation data of a 0.25-km resolution into a 1-km resolution using the nearest neighbor sampling method, to match the gridded estimates of live births in Iran for the year 2015 generated by the WorldPopBy summing up the ANs from each spatial cell, we yielded the national estimate of AN (rms (version 6.2-0), mvmeta (version 1.0.3), and raster (version 3.5–15) packages were applied to perform analyses for E-R association, meta-regression approach, and grid resampling, respectively. Figures were generated using the ggplot2 (version 3.3.6) package. A two-sided P-value of <0.05 was considered statistically significant.All the analyses were performed in R software version 4.0.2 . The Further information on research design is available in the Supplementary InformationPeer Review FileDescription of Additional Supplementary FilesSupplementary CodeReporting SummarySource Data


The timing-related deficits in individuals with attention deficit hyperactivity disorder (ADHD) contribute to the symptom-related difficulties and cognitive impairments. Current assessment and training measurement only target specific aspects of the timing ability, highlighting the need for more advanced tools to address timing deficits in ADHD. The aim of this study is to develop and validate a rhythm-based assessment and training (RAT) program, which intends to provide a comprehensive understanding of and enhancement to the time-related abilities of children with ADHD, thereby demonstrating its clinical efficacy.We will use randomized crossover trials in this study, with participants being randomly assigned to either start with the RAT and then proceed to cognitive training or start with cognitive training and then proceed to the RAT. Both groups will undergo pre- and post- evaluations. The evaluation will be administered immediately before and after the 4-week training period using diagnostic questionnaires, cognitive evaluation tools, and resting electroencephalography (EEG) measurements. Notably, EEG measurements will be conducted concurrently with the RAT evaluations.This study develops and evaluates the feasibility and effectiveness of a RAT while using EEG measurements to elucidate the underlying therapeutic mechanism of auditory rhythm at varying levels of complexity. The study will investigate the potential of RAT as a supplementary or alternative approach for managing ADHD. The multifaceted data collected will yield valuable insights to customize training agendas based on individual developmental stages and prognoses. Attention-deficit hyperactivity disorder (ADHD) is a behavioral disorder commonly observed in children and characterized by symptoms such as attention deficit, hyperactivity, and impulsivity . ADHD caRecent research has highlighted the timing deficits observed in children with ADHD. Individuals with ADHD exhibit deficits in various temporal domain behaviors, such as the ability to perceive and estimate time intervals , to prepTiming ability of ADHD have been measured by interval-based and beat-based tasks. Interval-based tasks measure the ability to discriminate, estimate, and reproduce the duration of time intervals, mostly given with two auditory events . ParticiTiming ability of ADHD observed in interval- and beat-based tasks have been identified as a crucial feature of cognitive deficits. In the interval-based timing ability task, Rhythm, one of the essential components of music, has been vigorously used to evaluate and train the beat-based timing ability. However, its relationship with cognitive abilities of children with ADHD has been sparsely reported. In beat-based assessment, In beat-based training, Research using beat-based training has uncovered a potential relationship between changes in rhythmic performance and cognitive ability. Collectively from the previous research findings, some concerns arise when evaluating the current state of research. First, previous studies have not fully grasped the timing ability in ADHD due to the restricted use of stimulus lengths and patterns . PreviouIn the present study, we will develop a rhythm-based assessment and training (RAT) that was designed to reflect the complexity of real-world rhythm processing. Four types of rhythmic sequences were generated based on a series of investigations that employed different levels of complexity in rhythmic stimuli . The typRandomized crossover trials, clinical experiments in which participants are assigned randomly to a sequence of treatments and each participant serves as one’s own control in estimating treatment effect , will beBefore the start of the experiment, the participants and their parents will be provided both oral and written information regarding the purpose of the study and will provide written informed consent. Each participant will be randomly assigned to one of two groups and will undergo pre- and post-training evaluations immediately before and after the 4-week training period. In the evaluation session, the participants will proceed in the order of diagnosis questionnaires, cognitive evaluation tools, and EEG recordings. In the training session, participants will undergo a 4-week RAT or a cognitive training program. The program will be conducted five times a week, with each session lasting 30 min per day. After a 1-month washout period, the training session schedule will be switched between the two groups.Diagnostic and Statistical Manual of Mental Disorders 4th edition (DSM- IV) and diagnosed with ADHD based on the Korean version of Kiddie-Schedule for Affective Disorders and Schizophrenia-Present and Lifetime (K-SADS-PL) in a semi-structured clinical interview conducted by a single board-certified psychiatrist; (3) intelligence quotient (IQ) score above 70; (4) have not received medication for ADHD treatment in the past or have received medication in the past but for less than 1 year and not within 4 weeks of the study. The exclusion criteria are as follows: participants with (a) congenital hereditary problems; (b) acquired brain injury such as cerebral palsy; (c) spasmodic disorder, other neurological disorders, or untreated dysesthesia (sensory disturbance); (d) diagnostic history or current state of schizophrenia and childhood psychosis; (e) intellectual disability; and (f) comorbid condition with obsessive-compulsive disorder, depressive disorder, or bipolar disorder. Comorbid conditions, such as anxiety or enuresis, will be allowed except for the symptoms in exclusion criteria. In addition, participants could apply the medication targeting other types of coexist pathologies, not with the symptoms which meet the exclusion criteria.Participants who have met the eligibility criteria will be enrolled in the study after they provide informed consent. Participants and their parents will receive oral and written information detailing the purpose of the study. All experimental protocols will be approved by the Institutional Review Board of Hanyang University Medical Center. Approximately 40 children with ADHD will be recruited through Hanyang Medical Center outpatient clinics or online recruitment posts. The criteria to be included in the examination are as follows: (1) 8 ≤ age ≤ 15; (2) satisfied the criteria of ADHD based on The rhythm-based assessment training (RAT) is a tool using rhythmic sequences for measuring the timing ability in children with ADHD. The four types of auditory rhythmic sequence, named isochronous (ISO), syncopated (SYN), metric (M), and non-metric (NM) , were seThe RAT will include assessment and training sessions. The assessment session will include two types of tasks: (1) a maintenance task in which participants will be asked to listen to the four types of rhythm sequences and then to mentally rehearse the sequences, and (2) a reproduction task in which participants will be asked to listen to the four types of rhythm sequences and then to tap the sequence . A total of 40 trials of rhythmic sequences, 10 trials for each of the four rhythmic sequences, will be randomly presented in each task. In the assessment session, a trial will consist of (1) baseline, (2) rhythm presentation, (3) baseline, (4) cue, and (5) task performance . In the rhythm presentation, each rhythmic sequence will be presented three times with a 2.5-s interval to provide participants with more opportunities to encode temporal information accurately .The training session will consist of practice and main session. In the practice session, the participants will undergo eight practice trials, two trials for each of the four rhythmic sequences to be familiarized with the stimuli and task. In the main training session, participants will be asked to listen to, mentally rehearse the sequences, and tap the rhythmic sequences. A total of 60 trials of rhythmic sequences will be presented; however, the number of rhythmic sequences given to each of the four types of rhythmic sequence will vary upon the individual baseline ability. In the training session, a trial will consist of (1) rhythm presentation, (2) cue, (3) rhythm maintenance, (4) cue, and (5) rhythm reproduction. In this study, we will utilize Braingame Brian , a game-The inhibition training task, also based on , focusesThe diagnosis questionnaires and cognitive evaluation tools are used to analyze the associations between the RAT results and the clinical problems seen in children with ADHD. Through these diagnosis questionnaires and cognitive evaluation tools, information on externalization problems, impulsivity and hyperactivity, inattention, and WM in children with ADHD will be collected.The child behavior checklist (CBCL) is a standardized child behavior assessment tool that allows parents to evaluate various aspects of child behavior based on their observations . In thisThe disruptive behavior disorder scale (DBDS) is a psychiatric assessment scale based on the DSM-IV diagnostic criteria to rate attention deficit/hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), and conduct disorder (CD) . The KorThe inattention/overactivity with aggression (IOWA) conners rating scale is one of the widely used measures to evaluate the therapeutic effectiveness of ADHD children and has the advantage of being reliable in evaluating various externalizing behaviors such as aggression and rebellious behaviors in ADHD children as well as hyperactivity . The IOWKorean version of ADHD rating scale-IV (K-ARS-IV) will be used to identify the severity of ADHD symptoms for each participant. The original scale was developed by The Korean version of the wechsler intelligence scale for children: 4th ed. (K-WISC-IV) was used to assess the intellectual and cognitive abilities of the children. The Wechsler intelligence scale is the most widely used tool to assess the intellectual functioning of children and adolescents, and the Korean version was standardized on a sample of 2,448 Korean children, aged from 6–16 years . The K-WStroop color and word test (SCWT) is a neuropsychological assessment tool for evaluating the efficiency of the prefrontal lobe, especially attentional and executive functioning . This toThe children’s color trails test (CCTT) is a neuropsychological test that can evaluate frontal lobe function of child psychiatric disorders, including attention and executive function . Based oIn this study, we will use the advanced test of attention (ATA), a computerized continuous performance test  to assesThe comprehensive attention test (CAT), a Korean version of a computerized continuous performance task will be administered . For eac1 Artifacts will be excluded using an independent component (ICA) analysis after visual inspection. The EEG data are analyzed with MATLAB® and Simulink® software. The pre-processed EEG data will be used to calculate the power spectral density (PSD) and phase locking value (PLV) for raw and z-scored values.The EEG will be recorded during resting and the RAT assessment sessions. The Nihon Kohden Neurofax EEG device  using 19ch Ag/AgCl electrodes is intended for use in this study. The researchers will observe and record participants’ behavior during the EEG for artifact control, and the records will include the participants’ body movements and eye blinks. Data pre-processing and analysis will use the EEGLAB toolbox for MATLAB.Power spectral density analysis is performed for each frequency band, and absolute power is used to calculate topography, especially alpha and beta. For topography, especially the upper alpha range (8–40 Hz), we expect that activation in the frontal and posterior regions will differ depending on the type of rhythmic sequence and the type of task. Topography will visually explore the increase or decrease in spectral power. We expect the spectral power to increase, especially in the posterior region, as the rhythmic sequence and task become more complex. Studies have reported an increase in posterior alpha activity during music perception and imagination and have revealed that alpha activity increases with the complexity of music  and the Phase locking value analysis has been widely used as a robust method for quantifying functional connectivity between brain regions . Comparet-tests on the change of each sequence for all crossover endpoints . The study will undertake a comparative analysis of two intervention sequences and investigate the existence of carry-over effects. This will involve conducting ndpoints . For varThe current study aims to develop RAT as a tool for assessing and training the time-related abilities of children with ADHD using a wide range of auditory stimuli organized in various types of rhythmic sequences. Additionally, the study will validate rhythm-based attention training for children with ADHD and its correlations with the behavioral diagnostic questionnaire and scores of cognitive evaluation tools for ADHD. In addition, they study will examine the efficacy of the training in comparison with general cognitive training. The use of EEG will aid in uncovering the nature of auditory rhythm processing in ADHD and in revealing the therapeutic mechanism of auditory rhythm at various levels of complexity. The present findings will contribute to the potential of rhythm-based training as a supplementary or alternative method for behavioral symptoms and cognitive functions of ADHD. The multifaceted data collected will provide valuable insights into the development of a computerized rhythm-based cognitive training program for ADHD and will enable tailored training agendas based on individual developmental stages and prognoses.The RAT might capture a more comprehensive picture of an individual’s timing ability and potentially lead to more personalized and effective interventions in various clinical and educational contexts. Firstly, the present study could potentially establish the RAT as a new music-based intervention for managing timing-related problems in ADHD. The specific study protocol enables music therapists to measure and quantify musical responses and clearly indicates how changes in musical responses are related to and can lead to symptom-related changes and cognitive enhancement. The behavioral data collected in this study could enable more tailored music-based interventions and, thus, improve the effectiveness of interventions and patient outcomes. Also, by using EEG measurements, the study may provide novel insights into the underlying neural mechanisms of how auditory rhythm can impact cognitive functioning for children with ADHD. This would expand the therapeutic arsenal available to clinicians, offering a non-pharmaceutical intervention that could be used either independently or in conjunction with other treatments. Given the mutual enhancement of WM and cognitive flexibility through rhythm and verbal tasks, an inclusive strategy could improve a deeper understanding between rhythm-related timing ability and cognitive functions.The studies involving human participants were reviewed and approved by the Institutional Review Board of Hanyang University Medical Center . Written informed consent to participate in this study was provided by the participants’ legal guardian/next of kin.HS and EJ developed the protocol, conducted the literature review, and drafted the manuscript. EJ, JK, HL, and DK advised on the experimental design, ethics, and clinical training. JK facilitated the hosting of the study and advised on recruitment sites and procedures. All authors provided critical feedback and edited the manuscript.


It is well documented that attention‐deficit hyperactivity disorder (ADHD) often presents with co‐occurring motor difficulties. However, little is known about the biological mechanisms that explain compromised motor skills in approximately half of those with ADHD. To provide insight into the neurobiological basis of poor motor outcomes in ADHD, this study profiled the development of white matter organization within the cortico‐spinal tract (CST) in adolescents with ADHD with and without co‐occurring motor problems, as well as non‐ADHD control children with and without motor problems. Participants were 60 children aged 9–14 years, 27 with a history of ADHD and 33 controls. All underwent high‐angular resolution diffusion MRI data at up to three time points . We screened for motor impairment in all participants at the third time point (≈14 years) using the Developmental Coordination Disorder Questionnaire (DCD‐Q). Following pre‐processing of diffusion MRI scans, fixel‐based analysis was performed, and the bilateral CST was delineated using TractSeg. Mean fiber density (FD) and fiber cross‐section (FC) were extracted for each tract at each time‐point. To investigate longitudinal trajectories of fiber development, linear mixed models were performed separately for the left and right CST, controlling for nuisance variables. To examine possible variations in fiber development between groups, we tested whether the inclusion of group and the interaction between age and group improved model fit. At ≈10 years, those with ADHD presented with lower FD within the bilateral CST relative to controls, irrespective of their prospective motor status. While these microstructural abnormalities persisted into adolescence for individuals with ADHD and co‐occurring motor problems, they resolved for those with ADHD alone. Divergent maturational pathways of motor networks  may, at least partly, explain motor problems individuals with ADHD. Children with ADHD showed atypical microstructure within the cortico‐spinal tract (CST) at 10 years, regardless of motor ability later in life. These CST abnormalities persisted into adolescence when ADHD co‐occurred with motor problems, yet resolved for those with ADHD alone. Maturation within motor networks may explain motor difficulties in ADHD. These symptoms lead to functional impairments in daily living, psychosocial disadvantage, and poorer academic performance  during childhood is thought to be particularly important , 54 months , and 72 months  follow‐up. The total number of MRI scans included in the present set was 115. During the final wave of assessments (approximately 14 years of age), participants were screened for motor difficulties using the DCD‐Q (see below for details).This study reports on a longitudinal community sample of 60 children aged between 9 and 14 years, 27 with and 33 controls without a history of ADHD , rather than as having DCD.Children at Wave 3 were also administered the DCD‐Q . A reverse phase‐encoded image was acquired to correct for magnetic susceptibility‐induced distortions during EPI acquisition. High resolution T1‐weighted, multi‐echo MPRAGE images were acquired in the sagittal plane with in‐scanner motion correction .Diffusion and T1‐weighted images were acquired using a 3T Siemens scanner across all three time‐points. While Waves 1 and 2 were acquired on the Tim Trio scanning system, following an upgrade, Wave 3 was captured on a the MAGNETOM Prisma system. As a result, scanner was included as a nuisance covariate in our statistical modeling. High‐angular resolution diffusion imaging (HARDI) data were acquired in the transverse plane with an anterior–posterior phase encoding direction. Sixty gradient directions, b‐value = 2800 s/mm3. Group average response functions for gray matter, white matter, and CSF used to generate individual FOD maps using single‐shell three‐tissue constrained spherical deconvolution  to account for repeated observations per participant.Analyses first compared null (1), linear 2), and quadratic (3) models to identify the most parsimonious developmental model for the left and right CST , ADHD, and ADHD + MI groups, analyses tested whether the inclusion of group and the interaction between age and group improved model fit beyond the best fitting developmental model  and right (p = .003) CST, the interaction model (5) demonstrated the best model fit. As shown in Figure p = .039) and right (p = .046) CST across the study period. The rate of fiber development did not differ between the ADHD + MI and TD groups , those with ADHD presented with lower FD within the bilateral CST relative to those without ADHD, regardless of their prospective motor status . These microstructural abnormalities persisted for those individuals who presented with co‐occurring motor problems at adolescence (ADHD + MI). Conversely, the atypical CST microstructure observed in children with ADHD resolved in those individuals who presented with typical motor skill levels at adolescence. Divergence in the maturational profile of the CST between those with ADHD + MI and ADHD supports the view that atypical development of motor networks may explain, at least partly, the presence of motor difficulties in a substantial sub‐set of those with ADHD. It also lends weight to argument that poorer motor skill in ADHD is distinct from the core ADHD symptom profile.In‐keeping with earlier accounts  from late childhood into adolescence, may offer insight into the presence of motor difficulties in a sub‐set of adolescents with ADHD. Though recent work has mapped the development of microstructure of the CST in those with ADHD  intervention, an effect not observed in those with DCD + ADHD , and direct intervention for motor symptoms . This raises the question as to whether greater inattention in the ADHD + MI group might explain the differential profile of CST maturation observed in this group relative to the ADHD group, rather than MI. We note that were inattention the primary driver of CST microstructural abnormalities in those with ADHD + MI, then it would be expected that the ADHD group would have also maintained some degree of CST abnormality relative to the TD group across development, since they too experienced elevated inattention relative to controls. This was not the case. We can therefore be confident that inattention does not, at least entirely, explain the divergent CST maturational profile of those with ADHD + MI and ADHD.We acknowledge several limitations of the present study, which warrant consideration. We only assessed motor outcomes in our sample once they reached adolescence (Wave 3). Without motor assessments in earlier waves of assessment, we are unable to verify the motor status of our sample in childhood. Even still, our data are the first to demonstrate that atypical development of the CST  from late childhood to adolescence presages MI in those with adolescent ADHD. In doing so, it provides novel insight into the role of maturation within the CST in motor outcomes in ADHD. Future work should monitor motor status in those with ADHD longitudinally in order to determine whether motor status fluctuations across childhood might impact the contribution of CST microstructure to motor outcomes in those with ADHD. Finally, while the DCD‐Q is often used to screen for the presence of motor difficulties, we note that a formal diagnosis of DCD would typically require a follow‐up assessment including a standardized battery of movement function  time points , and did not (ADHD), present with co‐occurring motor difficulties. More specifically, while those adolescents with ADHD + MI showed persistent reductions in CST microstructure between 10 and 14 years, those with ADHD alone “caught up” to their neurotypical counterparts across the same time period, an effect also observed in non‐ADHD adolescents who presented with low motor ability. We argue that the maturational profile of the CST may provide a window into the mechanisms by which many children with ADHD present with co‐occurring motor problems.This project is funded by Project Grants from the Australian National Health and Medical Research Council (NHMRC) .The research was supported by the Murdoch Children’s Research Institute, the Royal Children’s Hospital, the Royal Children’s Hospital Foundation, the Department of Paediatrics at the University of Melbourne, and the Victorian Government’s Operational Infrastructure Support Program.Data S1: Supporting Information.Click here for additional data file.


Abnormal functional brain asymmetry and deficient response inhibition are two core symptoms of attention deficit hyperactivity disorder (ADHD). We investigated whether these symptoms are inter-related and whether they are underlined by altered frontal excitability and by compromised interhemispheric connectivity.We studied these issues in 52 ADHD and 43 non-clinical adults by comparing: (1) stop-signal reaction time (SSRT); (2) frontal asymmetry of the N200 event-related potential component, which is evoked during response inhibition and is lateralised to the right hemisphere; (3) TMS-evoked potential (TEP) in the right frontal hemisphere, which is indicative of local cortical excitability; and (4) frontal right-to-left interhemispheric TMS signal propagation (ISP), which is reversely indicative of interhemispheric connectivity.Compared to controls, the ADHD group demonstrated elongated SSRT, reduced N200 right-frontal-asymmetry, weaker TEP, and stronger ISP. Moreover, in the ADHD group, N200 right-frontal-asymmetry correlated with SSRT, with TEP, and with symptoms severity. Conversely, no relationship was observed between ISP and N200 right-frontal-asymmetry, and both TEP and ISP were found to be unrelated to SSRT.Our results indicate that abnormal frontal asymmetry is related to a key cognitive symptom in ADHD and suggest that it is underlined by reduced right-frontal excitability. Attention deficit hyperactivity disorder (ADHD) is a common neuropsychiatric disorder characterised by excessive inattention, hyperactivity, and impulsivity; either alone or in combination. ADHD, affecting ~7.2% of children worldwide , had preWhile ADHD has been associated with a multitude of cognitive, neurobiological, and genetic factors, its precise neuropsychological underpinnings are currently unclear –11. A laCommonly, response inhibition is studied using the stop-signal task (SST) , 19, in Response inhibition is a lateralised function that requires the specialisation of the right frontal cortex , 21–32. One influential account of ADHD is the right-hemisphere account, which implicates a right-hemispheric deficit in this disorder, and states that its symptoms arise from the disruption of lateralised right-hemispheric processes related to response inhibition, as well as to the regulation of attention and arousal –42. HoweWhile previous asymmetry studies of ADHD have mainly focused on spontaneous Alpha-band oscillations, the role of asymmetry abnormalities in ADHD-related cognitive and clinical symptoms is yet to be understood; most prominently with regard to a deficit central to its pathology as response inhibition, reflected by the right-lateralised N200 SST component. To investigate this, we hypothesised, drawing from the asymmetry account, a direct link between aberrant frontal N200 asymmetry and a response inhibition deficit in ADHD. Consequently, we expected to find reduced N200 right-asymmetry among ADHD than in non-clinical individuals, which is positively correlated with response inhibition performance, measured as SSRT. Similarly, as asymmetry abnormalities have been indicated as central to ADHD neuropathology, we expected to observe a relationship between N200 asymmetry and ADHD clinical symptoms severity.While suggested as central to ADHD neuropathology, the underlying mechanism of asymmetry abnormalities in ADHD is currently not-well-understood. Relevantly, functional asymmetry has been indicated to arise when an area in a given hemisphere is strongly activated, leading to the transmission of interhemispheric inhibitory signalling to the homologous region of the contralateral hemisphere through the corpus callosum (CC), the main neural pathway connecting the two cerebral hemispheres –51. HencIn order to measure cortical excitability and functional interhemispheric connectivity, we used the combination of EEG with transcranial magnetic stimulation (TMS), a non-invasive neuromodulation technique able to depolarise neurons and trigger action potentials –60. FirsHere, we measured EEG responses to single TMS pulses delivered to the right-frontal cortex of both ADHD and non-clinical individuals. We expected to find reduced TEP in the ADHD than in the control group, indicative of diminished right-frontal excitability. We also expected to observe increased ISP in the ADHD group, indicative of reduced frontal interhemispheric connectivity. Lastly, in order to investigate the underlying role of these possible neuromarkers of ADHD in asymmetry abnormalities, we examined their relationships to the asymmetry of the N200 SST component. To the best of our knowledge, this is the first attempt to examine a relationship between ERPs measured during task performance, and TEPs, measured in a non-task-related context. Furthermore, by measuring ISP, this study is one of the first to use TMS-EEG for examining functional interhemispheric connectivity in ADHD, and the first to do so outside of the motor cortex.To conclude, while previous studies have indicated abnormal functional asymmetry in ADHD, its relationship with response inhibition deficiency, a core cognitive symptom of this condition, as well as with ADHD clinical symptomology, is yet to be understood. To investigate this, we combined EEG measures with the SST to examine whether the asymmetry account can describe deficient response inhibition in adult ADHD, as well as the severity of clinical symptoms in this condition. Furthermore, to study the currently not-well-understood neuronal basis of asymmetry abnormalities in ADHD, we combined TMS with EEG to investigate frontal cortical excitability and interhemispheric connectivity abnormalities in adult ADHD, and evaluate their relationship with compromised frontal asymmetry in this disorder.https://clinicaltrials.gov/ct2/show/NCT01737476, ClinicalTrials.gov identifier NCT01737476. A few of the findings presented here, which are not related to this study’s main subject , were previously published elsewhere [Fifty-two ADHD and 43 control participants were recruited to this study by distribution of ads throughout the Ben-Gurion University of the Negev campus and via mass university e-mail. Participants were a part of a larger, clinical study; trial registration: Trial to Evaluate the Efficacy of the HLPFC Coil Deep Transcranial Magnetic Stimulation System in Treating Attention Deficit and Hyperactivity Disorder (ADHD) in Adults, lsewhere , 68. ParFour ADHD and one control participant were excluded from the study due to either poor SST EEG data quality  or poor performance of the SST . Overall, 48 ADHD  participants, aged 21–46 years , and 42 non-clinical control participants , aged 22–32 years  were included in this study. For the TMS-EEG analysis, three ADHD and four control participants were additionally excluded due to poor data quality.Severity of ADHD symptoms was assessed using the Conners’ Adult ADHD Rating Scales Self-report Long-version (CAARS-S:L) , and ADHAll participants filled a demographic questionnaire and the CAARS-S:L. Next, EEG was measured during: (1) 3 minutes of resting-state (eyes closed), followed by (2) performance of a computerised SST task (~20 min), and finally (3) administration of single-pulse TMS (~10 min).The computerised visual SST was conducted similar to as previously described , 19. In In each trial , a visuaThe task began with 12 practice trials, for which the first six trials did not include a “Stop” signal , while 75% and 25% of the last six trials were “Go” and “Stop” trials, respectively. During practice, participants received feedback at the end of each trial, presented on the screen for 1,000 ms. Following, participants underwent 480 experimental trials. All trials were presented in random order. To eliminate anticipation, each experimental trial ended with a variable inter-trial interval of either 1,100, 1,300, 1,500, 1,700 or 1,900 ms, appearing in pseudo-random order, each occurring in one fifth of trials. In “Go” trials in which the participant failed to respond, a beep sound was presented at the end of the trial , reminding the participant to remain focused on the task.Only participants which demonstrated a percentage of erroneous responses given a “Stop” signal in between 35–65% of “Stop” trials were included in the analysis, as large deviations from 50% successful inhibition are in violation with the assumptions of the independent horse-race model, on which the stop-signal task is based upon . The perTMS was applied using a Magstim-Rapid Stimulator  inducing biphasic pulses via a figure-eight coil, with a 70-mm diameter of each wing. Participant’s resting motor threshold (RMT) was determined by stimulation of the contralateral abductor pollicis brevis (APB) muscle and finding the minimal intensity that produces visible muscle responses following at least 5 out of 10 pulses, separated by 5 seconds . ThereafTM cap and amplifier , and data were acquired using ASA™ version 4.7.3 . The Cz electrode was used as a common reference (re-referenced offline to the average), and the PO6 electrode as ground. Impedance was kept below 10 kOhm in all electrodes. The signal was digitised at 2048 Hz using a 24-bit AD converter.EEG was recorded via a TMS-compatible 64-channel WaveguardAll EEG data was processed offline using the EEGlab toolbox for MATLAB  and custFirst, data was down-sampled to 512 Hz. Then, a bandpass (1–100 Hz) and a notch (45–55 Hz) finite impulse response (FIR) filters were applied (EEGlab function pop_eegfiltnew); the second of which used to eliminate 50 Hz AC main power supply interference. Next, data of successful and unsuccessful “Stop” trials was segmented from −1000 to 1000 ms relative to “Stop” signal onset. Following, baseline correction was applied . Then, noisy channels and segments were removed using both automatic algorithms  and manual inspection. Following, eye blinks and vertical eye movements were removed using infomax independent component analysis , as described in . Then, aOverall, preprocessing included the removal of noisy channels  and trials , as well as ICA components .First, Data of the first 40 ms post-pulse (0 to 40 ms) was discarded, because it contains a massive electrical artefact as well as dominant lateral muscle activation . Next, d1,81 = 6.37, p < .05, ηp2 = .073) and segments , as well as ICA components .Overall, preprocessing included the removal of noisy channels  were chosen based on previous literature on the SST N200 component , 76 and symmetry , 85.The N200 component was calculated as the mean voltage amplitude of electrodes in the right side of the Task-ROI. N200 asymmetry was quantified by calculating the relative amplitude at each homologous electrode pair , and repFor this measure, positive scores are indicative of right-asymmetry while negative scores are indicative of left-asymmetry, and higher absolute values represent stronger asymmetry. Importantly, this method provides a degree of correction for overall power, as large individual differences may be confounded with the magnitude of the asymmetry, as well as mitigates the impact of individual differences  on signal amplitude . FinallyTEP was calculated as the average AURC in the right electrodes directly under the TMS figure-eight coil intersection, i.e., the right electrodes of the Stim-ROI. ISP was calculated similarly to the right-asymmetry measure, with two exceptions: (1) since TMS was delivered to the right hemisphere, the ratio of the contralateral left hemisphere and the ipsilateral right hemisphere was calculated; (2) a 10-ms delay was used for the contralateral left hemisphere to account for the time required for the induced signal to propagate from the site of the stimulation to the contralateral hemisphere , 87. TheFor this measure, negative scores are indictive of greater TMS-induced activation in the ipsilateral than in the contralateral hemisphere, while higher scores signify increased signal propagation between the hemispheres. Finally, TEP and ISP were averaged separately in the corresponding time windows, and grand-averaged for the ADHD and control groups.Symptoms severity, TEP, and ISP were compared via a one-way analysis of variance (ANOVA) with Group (ADHD vs. control) as a between-subject factor. A similar analysis was used for group comparison of SST behavioural measurements: “Go” trials error rates and reaction time (RT), and “Stop” trials SSRT. N200 amplitude and right-asymmetry were analysed via a mixed-design two-way ANOVA, with Group (ADHD vs. control) as a between-subject factor and Stopping (successful vs. unsuccessful stops) as a within-subject factor.2 value showing relationships of reverse directionality between the activation in each side and the dependent variable  represents a significant relationship between N200 asymmetry and that dependent variable. To further investigate group differences in observed relationships between N200 asymmetry and a given dependent variable, the difference in the partial correlation between the left ROI and that dependant variable, controlling for the right ROI, in the ADHD and control groups was analysed via a Z-test between the Fisher-transformed correlation coefficients. Bivariate correlation analyses were conducted to examine the relationships between SSRT and TEP and between SSRT and ISP.The relationships between N200 right-asymmetry and SSRT, ADHD symptoms severity, TEP, and ISP, were assessed using multiple regression analyses for successful and unsuccessful “Stop” trials, with averaged N200 amplitude in the right and left sides of the Task-ROI used as independent measures. Thus, a model with significant RDescriptive statistics of clinical and neuropsychological study variables are presented in F1,88 = 127.70, p < .001, ηp2 = .592).As expected, CAARS total symptoms scores in the ADHD group were higher than that of controls , but correct “Go” RT was not significantly different between the groups . As expected, SSRT of ADHD participants was significantly longer than that of controls .“Go” error rates in the ADHD group were marginally higher than that of controls  and Stopping , but no Group X Stopping interaction . That is, N200 amplitude was larger in the control (relative to the ADHD) group, and in unsuccessful (relative to successful) “Stop” trials.The spatiotemporal distribution of the N200 component is presented in F1,88 = 5.06, p = .027, ηp2 = .054), but no main effect for Stopping , nor a Group X Stopping interaction . That is, N200 right-frontal-asymmetry was reduced in the ADHD group across stopping success conditions.Analysis of N200 right-frontal-asymmetry  revealed3.3.2.1 Relationship between N200 frontal-asymmetry and response inhibition. Relationships between response inhibition performance and N200 amplitude are presented in Z = -1.21, p = .226). For both groups, no relationship between SSRT and N200 asymmetry in unsuccessful “Stop” trials was observed. These results indicate that while the performance of successful response inhibition is marginally related to stronger right-frontal-asymmetry in the ADHD group, and marginally related to frontal right-sided amplitude alone in the control group, the groups do not statistically differ with respect to the relationship between N200 asymmetry and response inhibition.Z = -2.97, p = .003), supporting the conclusion that the groups differed in the extent to which the left ROI had a unique contribution to CAARS total symptoms scores, and thus that the relationship between N200 asymmetry and CAARS total symptoms scores magnitude, obtained in the ADHD group, is significantly different between the groups. These results indicate that stronger right-frontal-asymmetry during unsuccessful “Stop” trials is related to more severe symptoms in the ADHD group.Relationships between CAARS total symptoms scores and N200 amplitude are presented in F1,81 = 7.95, p = .006, ηp2 = .089; F1,81 = 4.97, p = .029, ηp2 = .058; The analysis revealed that TEP in the ADHD group was significantly weaker than that of the control group  and N200 amplitude (in the Task-ROI) are presented in Z = 2.01, p = .044), supporting the conclusion that the groups differed in the extent to which the left ROI had a unique contribution to TEP, and thus that the relationship between N200 asymmetry and TEP magnitude, obtained in the ADHD group, is significantly different between the groups. These results indicate a positive relationship between N200 frontal right-asymmetry during successful stops and the excitability of the right frontal cortex in the ADHD group.Interhemispheric signal propagation. Relationships between ISP (in the Stim-ROI) and N200 amplitude (in the Task-ROI) are presented in r = -.06, p = .697 and r = .22, p = .177 for the ADHD and control groups, respectively) or between SSRT and ISP . These results indicate no direct relationship between response inhibition behavioural performance and neither the excitability of the right frontal cortex or interhemispheric connectivity.For both the ADHD and control groups, the analysis revealed no correlation between SSRT and TEP  by showing that adult ADHD individuals demonstrate diminished response inhibition performance  and processing  then non-clinical controls. Next, we found that the ADHD group demonstrated reduced N200 right-asymmetry, right-frontal excitability , and frontal interhemispheric connectivity . Finally, we showed that in the ADHD group, N200 right-asymmetry was positively related to response inhibition performance  and to TEP magnitude , and reversely related to symptoms severity . However, we did not find a relationship between ISP and N200 asymmetry, while response inhibition was not found related to either TEP or ISP. As such, our results indicate that abnormal frontal asymmetry is related to a key cognitive symptom in ADHD and suggest that frontal asymmetry deficits in this disorder are underlined, at least partly, from reduced right-frontal excitability, indicated by TEP. Importantly, this result pattern favours the asymmetry hypothesis over the right-hemispheric account for ADHD, further suggesting that frontal hemispheric asymmetry deficiencies provide a more comprehensive neuromarker of ADHD and can thus better explain its symptomology than diminished right-frontal activation alone.Across stopping success conditions, the ADHD group demonstrated diminished N200 amplitude and right-asymmetry, as well as elongated SSRT. A marginal positive relationship between increased N200 asymmetry during successful “Stop” trials and better response inhibition performance (indicated by shorter SSRT) was also observed in the ADHD, but not the control group, for which such a relationship was obtained for only right-sided N200 amplitude. However, the groups did not significantly differ with respect to the relationship between N200 asymmetry and SSRT. Taken together, these results suggest that both right-sided activation (as in controls) and hemispheric asymmetry are related to response inhibition deficits in adult ADHD. This suggests that compromised N200 frontal asymmetry is related to an inhibitory deficit specifically characteristic to this disorder. This notion is in line with previous studies supporting the brain asymmetry account of ADHD by showing increased spontaneous Alpha-band right-frontal-asymmetry in this disorder , 44, 46.Given that response inhibition is a lateralised function, which requires specialisation of the right frontal cortex , 21–32, As expected, symptoms severity was higher for the ADHD group than for controls. Importantly, it was found to be inversely related to N200 right-frontal-asymmetry during unsuccessful “Stop” trials in the ADHD, but not in the control group, and a significant difference between the groups was observed with respect to this relationship. This stands in some contradiction with the marginal, positive relationship found for the ADHD group between N200 asymmetry during successful stops and more efficient response inhibition . Taken together, these results suggest a dissociation between N200 asymmetry during successful and unsuccessful response inhibition in relationship to ADHD pathology: while its enhancement during successful stops is related to more efficient response inhibition processing, thus to a less severe core cognitive deficit, its enhancement during unsuccessful stops is related to more severe clinical symptomatology.This dissociation may be explained by the added presence of error processing during unsuccessful stops. Across groups, N200 activation in the right hemisphere was stronger for unsuccessful than for successful stops. This is a typical finding in the SST , 77–79, Since asymmetry reflects the ratio between the activation of the two hemispheres, the addition of symmetric activation, affecting both hemispheres to a similar extant, is expected to result in reduced asymmetry. This implies that the observed relationship between stronger unsuccessful “Stop” N200 right-frontal-asymmetry and increased ADHD symptoms severity indicates that individuals showing weaker symmetrical, error processing are characterised by more severe pathology. This notion is in line with previous studies suggesting compromised error monitoring, and reduction of corresponding EEG signals , in children and adults with ADHD –98.The presence of error processing may also explain why no relationship was observed between right-sided activation or asymmetry of the N200 component during unsuccessful stops and SSRT for either group, as unlike for successful stops, it is not prominently reflective of response inhibition processing. Future studies should systematically examine both the unique, as well as potentially accumulating, contributions of abnormalities in both error processing and response inhibition in ADHD to the severity of its symptoms.Our results demonstrate seemingly contradictive effects, with the ADHD group showing weaker right-frontal excitability but greater signal propagation. TEP reflects the summation of excitatory and inhibitory activation over stimulated neuron populations, and has been indicated to signify local cortical excitability , 61–64. ISP following a suprathreshold stimulation , as measured here, has been shown to be negatively correlated with the integrity of CC fibres . ImportaOur results indicate that TEP, but not ISP, is related to right-frontal N200 asymmetry in ADHD adults, but not in non-clinical controls. This relationship was found to be significantly different between these groups. Relevantly, the 50–150 ms time window used here for both TEP and ISP is considered to represent the expected duration of interhemispheric inhibitory mechanisms relevant to the formation of functional asymmetry , 85. DimInterestingly, left-frontal negative deflection during unsuccessful stopping was found to be inversely correlated with ISP in the control group, thus positively correlated with interhemispheric connectivity. This may suggest that, when intact , increased interhemispheric connectivity during performance of a lateralised function  may be related to errors; or alternatively, to increased activity related to non-lateralised functions observed during unsuccessful, but not successful stop trials .While our results did not indicate a significant relationship between functional interhemispheric connectivity and abnormal frontal asymmetry in ADHD, it should be noted that this may be influenced by the fact that the participants in our study were adults. Such a relationship may still be obtained in children with ADHD, as CC abnormalities in this disorder have been suggested to partially normalise during development , congrueCurrent ADHD treatments commonly involve chronic administration of psychotropic drugs; most commonly psychostimulants, such a methylphenidate  and amphetamine . Importantly, these treatments can only provide temporary alleviation of ADHD symptoms, without producing long-term therapeutic changes in relevant brain functions. Moreover, these treatments are ineffective for about 30% of patients, have various adverse effects, are intolerable by some patients, and have a potential for abuse –115. ForThe results of the current study indicate a direct link between functional frontal asymmetry abnormalities and both clinical symptoms severity and a core cognitive deficiency in adult ADHD , suggesting it may constitute an endophenotype of this disorder. Moreover, our results indicate reduced right-frontal excitability and aberrant frontal interhemispheric functional connectivity in ADHD adults. Thus, the development of novel treatments aimed at modulating these abnormalities may prove beneficial for the treatment of ADHD. Specifically, treatments that can normalize deficient functional asymmetry by facilitating interhemispheric connectivity, which has been indicated to subserve the transmission of interhemispheric inhibitory signalling required for the initiation and sustainability of functional asymmetry –51.One example of such treatment is the use of paired associative stimulation (PAS), a TMS protocol involving pairing the stimulation of two regions through the coordination of two coils. This technique is based on Hebbian plasticity, according to which neuronal connections are strengthened or weakened depending on whether the firing of the presynaptic region precedes or follows the firing of the postsynaptic region, respectively , 117. ImLate TMS evoked brain activations, like the ones used here, are known to be contaminated by somatosensory and auditory saliency artifacts which may hinder the validity of our results . Thus, oWhile the sample of ADHD adult participants in this study was comprised of individuals with various levels of medium to very high symptoms severity, as indicated by CAARS total symptoms scores, this sample was entirely comprised of university undergraduate students. Therefore, the generalizability of this study’s findings to the general population might be limited, an issue which can be addressed by future studies examining their replication in different adult ADHD populations.To conclude, our results support the initial hypothesis regarding the existence of abnormal N200 asymmetry in ADHD and relate it to a response inhibition deficiency and clinical symptoms severity in this disorder. Thus, this study supports the asymmetry account of ADHD in suggesting that aberrant frontal functional brain asymmetry may subserve behavioural and cognitive aspects of ADHD, and therefore constitute an endophenotype of this disorder. Relevantly, our results add to the accumulating evidence indicating that frontal asymmetry abnormalities pose a more comprehensive explanation for ADHD than right-frontal deficiencies alone, and are directly related to response inhibition deficiency—a key endophenotype in this disorder. By combining TMS with EEG, we showed that this abnormality is likely underlined by reduced excitability of the right frontal hemisphere in ADHD, as well as evidence for reduced frontal interhemispheric connectivity in this condition.Our conclusions encourage future studies to further investigate the mechanisms underlying comprised functional asymmetry in ADHD, as it is indicated here and elsewhere as central to the neuropathology of this disorder, and their importance to the cognitive and clinical symptomatology of this disorder. For example, the role of structural abnormalities in callosal interhemispheric pathways can be examined in both children and adults with ADHD by incorporating structural imaging methods such as DTI. Importantly, while the current study is focused on response inhibition, future investigations should include examination of other cognitive deficits relevant to ADHD, such as in sustained and selective attention, cognitive control, working memory, arousal, motivational processes, and processing efficiency. Moreover, our conclusions call for examination of the possibility of modulating frontal interhemispheric asymmetry as a treatment for ADHD. Future studies may explore the possibility of facilitating interhemispheric connectivity in individuals with ADHD via methods such as brain stimulation or cognitive training, and examine its relationship with alleviation in symptoms severity and/or improvement in cognitive functions related to this disorder, such as response inhibition.


Attention deficit hyperactivity disorder (ADHD) is one of the most common neurodevelopmental disorders, although the aetiology of ADHD is not yet understood. One proposed theory for developing ADHD is N-methyl-D-aspartate receptors (NMDARs) dysfunction. NMDARs are involved in regulating synaptic plasticity and memory function in the brain. Abnormal expression or polymorphism of some genes associated with ADHD results in NMDAR dysfunction. Correspondingly, NMDAR malfunction in animal models results in ADHD-like symptoms, such as impulsivity and hyperactivity. Currently, there are no drugs for ADHD that specifically target NMDARs. However, NMDAR-stabilizing drugs have shown promise in improving ADHD symptoms with fewer side effects than the currently most widely used psychostimulant in ADHD treatment, methylphenidate. In this review, we outline the molecular and genetic basis of NMDAR malfunction and how it affects the course of ADHD. We also present new therapeutic options related to treating ADHD by targeting NMDAR. Attention deficit hyperactivity disorder (ADHD) is one of the most frequent disorders in child and adolescent psychiatry . AccordiExecutive deficits in ADHD are associated with widespread changes in several brain regions, such as the prefrontal cortex (PFC), temporal region, basal ganglia, and hippocampus ,10,11. CThe International Multi-centre ADHD Gene (IMAGE) project provided comprehensive analysis of over 50 candidate genes that substantially contribute to ADHD susceptibility. The majority of these genes are involved in the regulation of dopaminergic, noradrenergic, and serotonergic pathways . HoweverNMDARs are tetra-heteromers composed of the GluN1, GluN2, and GluN3 subunits. The subunits of NMDAR include two mandatory GluN1 subunits and, depending on the specific anatomical location within the brain, an additional two GluN2 or a combination of GluN2 and GluN3 subunits. There are four different types of GluN2 subunits  that can combine with the GluN1 subunit to form diverse receptor configurations . Each ofTwo extensively studied NMDAR-dependent forms of synaptic plasticity associated with learning and memory are long-term potentiation (LTP) and long-term depression (LTD). As both LTP and LTD are induced by NMDAR-dependent calcium influx, the suggested differentiating factor is the level of activity or depolarisation in the postsynaptic cell. In contrast to LTP, which is triggered by significantly stronger NMDAR activation and a larger increase in postsynaptic calcium influx, LTD is triggered by modest NMDAR activation and modest increase in postsynaptic calcium influx . AnotherLTP and LTD modulate vastly interconnected neuronal pathways providing a neurochemical foundation for learning and memory. Alterations in synaptic plasticity can lead to structural changes in neuronal networks, contributing to the cognitive and behavioural deficits observed in ADHD. Although the role of synaptic plasticity in ADHD is not fully elucidated, several genes implicated as risk factors for ADHD are linked to synaptic plasticity and neurodevelopment ,63. HereGRIN gene family encodes the following classes of NMDA receptor (NMDAR) subunits: the glycine-binding GluN1, which is the product of GRIN1, glutamate-binding GluN2, which has 4 paralogs (A-D) encoded by GRIN2A, GRIN2B, GRIN2C, and GRIN2D, respectively, and the glycine-binding GluN3, encoded by GRIN3A and GRIN3B [GRIN2 gene expression changes throughout the developmental stages. The GluN2B subunit is strongly expressed during the prenatal phase, and then its expression drops during postnatal stages. When it comes to GluN2A, its expression appears to be low during the prenatal period and rises after delivery [GRIN2 gene expression is exposure to methamphetamine. In rodents, repeated administration of methamphetamine led to a decrease in GRIN2A expression in the hippocampus and decreased GRIN2B expression in the striatum [GRIN gene expression is prenatal nicotine exposure (PNE) [GRIN gene expression, but further research is needed to confirm the association.The d GRIN3B . GluN2A d GRIN3B . There ad GRIN3B . Furtherd GRIN3B ,75. Physdelivery ,77. Presdelivery . One of striatum . Rats prstriatum ,81. Anotre (PNE) . PNE is re (PNE) ,84 and bre (PNE) ,86. All GRIN genes have been found in patients with diverse neuropsychiatric disorders, including ADHD [GRIN mutations. Intellectual disability, epilepsy, and autism spectrum disorder are all much more common in GRIN-mutant patients, but certain GRIN mutations are still strongly linked to ADHD [GRIN2A gene variants that were the first NMDAR-related genes associated with an increased risk of ADHD [GRIN2B variants and ADHD [GRIN2A(N615S) mutation showed hyperactivity and dysregulated attentional levels. Since the asparagine amino acid residue GluN2A(N615) controls the magnesium block, it is suggested that symptoms caused by the GRIN2A(N615S) mutation may result from magnesium block suppression and enhanced calcium permeability [GRIN2B mutations, behavioural tests showed prominent hyperactivity, impulsivity, distractibility, and a short attention span. Patients with ADHD-resembling phenotype carried the following GRIN2B mutations: t, t, (p.R682C) in ABD, (p.A636P) in M3 domain and (p.T268SfsX15) in ATD [GRIN2A and rs2284411 in GRIN2B [Numerous variants and mutations of the ing ADHD ,88. Howe to ADHD . One exa of ADHD ,91. Reseand ADHD . Mutatioand ADHD . Mice wieability . In the ) in ATD ,95. Othen GRIN2B . rs22844n GRIN2B .SorCS2  is a large gene composed of 30 exons, belonging to the VSP10p (Vacuolar Protein Sorting 10 protein)-domain receptors gene family, which encodes SorCS2 protein. SNPs in this gene have been associated with a multitude of neuropsychiatric disorders including bipolar disorder [SorCS2 gene rs4689642 has been recognised as the most relevant ADHD-associated polymorphism [SorCS2 gene methylation (thus silencing) leads to reduced grey-matter volume in precentral and posterior orbital gyri, which induces symptoms of ADHD in affected children [disorder , schizopdisorder , and ADHdisorder . Interesmorphism . Furtherchildren . TherefoSorCS2-deficient mice presented impaired LTP, LTD, neurite outgrowth, and dendritic spines formation. Lack of SorCS2 abolished NMDAR-dependent synaptic plasticity in the mouse hippocampus, resulting in a phenotype similar to ADHD. SorCS2-deficient mice displayed impairment of long-term memory formation and higher tendency to take a risk and stimulus-seeking behaviour, however, this was accompanied by higher stress vulnerability [SorCS2-deficient mice exhibited significant social memory deficits, however, without abnormalities in other hippocampal-dependent behaviours [SorCS2-deficient mice exhibited an altered dopaminergic firing pattern within the ventral tegmental area (VTA). The dopaminergic transmission was shifted from an irregular to a more regular pattern, along with an associated change in dopaminergic receptor sensitivity . Behaviourally, mice presented a general reward deficit, novelty-induced hyperactivity, and yet paradoxical tranquillity in response to amphetamine—a phenotype reminiscent of ADHD [VSP10p act as sorting receptors and regulators of neuronal viability and function by controlling the intracellular trafficking of targeted proteins . Both corability . Furtherhaviours . In addihaviours . Further of ADHD .DRD4 gene located on chromosome 11 at 11p15.5 [DRD4 exhibits numerous polymorphisms in its coding sequence, and the most common polymorphism occurs in a region encoding the third intracellular loop of the receptor. This polymorphism results in variable number of tandem repeats of a 48-base pair sequence in the third exon [DRD4 polymorphism products are D4.2, D4.4 and D4.7, characterized by 2, 4, and 7 repeats of a proline-rich sequence of 16 amino acids, respectively [DRD4 polymorphisms and better response to methylphenidate as compared to placebo [There are five subtypes of dopamine receptors: D1, D2, D3, D4, and D5. The D1 and D5 dopamine receptors belong to the D1-like family, whereas the D2, D3, and D4 receptors belong to the D2-like family . The D4  11p15.5 . DRD4 exird exon ,110. Theectively . D4.7 haectively . In vitrectively , and thiectively . ADHD chectively . Furtherectively . Activatectively . Activatectively . Presumaectively ,115. Thu placebo ,117. How placebo , while o placebo . Factors placebo .BAIAP2 gene, located on the chromosome 17. SNPs within the mentioned gene have been suggested to be involved in ADHD aetiology, as well as abnormal cerebral lateralisation, which is also associated with ADHD-related symptoms [BAIAP2-KO mice showed a selective increase in NMDAR activity, however, without significant changes in AMPAR-mediated transmission. This was followed by a substantial increase in LTP and, functionally, deficits in learning, memory, and social interactions [BAIAP2-deficient mice [BAIAP2-mutant mice resulted in the restoration of NMDAR-mediated synaptic transmission and proper NMDAR/AMPAR ratio in the medial PFC region (mPFC). However, despite improvement in social interactions, the hyperactivity- and anxiety-like behaviour induced by BAIAP2-knockout were not rescued in such conditions [BAIAP2 suppressed neuronal firing variability and dynamics within excitatory mPFC neurons, especially in those encoding social information. Administration of NMDAR antagonist (memantine) restored burst firing in mPFC neurons and rescued social deficits [BAIAP2  is an abundantly expressed, postsynaptic adaptor protein. It is implicated in the regulation of actin filaments assembly during dendritic spines development, as well as the regulation of NMDAR-mediated synaptic transmission and LTP . BAIAP2 symptoms ,122. Theractions ,123. Intent mice . Consistnditions . Additiodeficits . AltogetSNAP-25 deletion, known as coloboma mice [SNAP-25 genes  present mild hyperactivity [SNAP-25 mutations associated with ADHD among humans. Barr et al. genotyped DNA from 122 patients diagnosed with ADHD and found two significant mutations, the MnlI polymorphism and DdeI polymorphism [SNAP-25 and ADHD prevalence [SNAP-25 gene variants were confirmed as ADHD risk genes. These included: rs362987 on intron 4, rs363006 on intron 6, and aforementioned MnlI (3′UTR rs3746544) and DdeI (3′UTR rs1051312) [Synaptosomal-associated protein, 25 kDa (SNAP-25) is a part of the SNARE complex, which is involved in the exocytotic release of neurotransmitters during synaptic transmission. Furthermore, SNAP-25 plays an important role in modifying NMDAR and kainate receptor density in the postsynaptic membrane . Proteinoma mice ,132. Micactivity . The hypmorphism . Both hamorphism ,136. Morevalence ,138. In 1051312) . A subse1051312) . SNAP-251051312) ,142. The1051312) . Another1051312) .SNAP-25 gene variations might be an important predictor for methylphenidate response. The strongest association with pharmacotherapy was seen in children with MnlI polymorphism [morphism ,146. Themorphism ,148,149.ADGRL3 gene , located on chromosome 4. Functional studies have demonstrated that LPHN3 variants were expressed mainly within brain regions associated with attention and activity  and were implicated in both ADHD development and pharmacogenetics [LPHN3 SNPs in susceptibility to ADHD, as well as its predictive role in ADHD severity, associated comorbidities, and drug responsiveness [Latrophilin-3 protein (LPHN3p) is a brain-specific member of a small subfamily of adhesion G protein-coupled receptors. It is encoded by the genetics ,151. Indsiveness ,154,155.siveness ,157,158.siveness . Furthersiveness ,160.PCDH7 is a gene that belongs to the protocadherin gene family and encodes an extracellular protein Protocadherin 7 (PCDH7p). PCDH7p is an integral protein of plasma membrane, which plays role in cell–cell recognition and adhesion. Few variants in PCDH7 have been identified as rare, but at the same time significant risk loci for ADHD development [PCDH7 resulted in elongation of dendritic protrusions beyond typical spine size [PCDH7 constitutes another potential factor affecting synaptic NMDAR function and ADHD risk; however, further research is required to validate this hypothesis.elopment ,162. Intelopment . On the ine size . AltogetRecent advances in high-throughput technologies have enabled mapping and holistic analysis of numerous genetic variants, leading to a more comprehensive understanding of molecular changes in normal development and disease. The utility of integrative approaches is particularly important for diseases such as ADHD, where genetic and environmental factors interact with each other . Multi-oGiven the side effects of commonly used stimulant drugs in treating ADHD, there is a need to explore alternative therapies, especially for children. Hence, the use of drugs targeting NMDAR as a treatment for ADHD is an area of ongoing research.Amantadine and memantine are both adamantane derivatives that act as non-competitive NMDAR antagonists. These drugs have been shown to stabilise NMDAR and inhibit prolonged calcium influx, which protects neurons from excitotoxicity while preserving normal synaptic activity ,175. AmaThere are also other FDA-approved drugs for the monotherapy treatment of ADHD, namely atomoxetine and guanfacine, which have been found to interact with NMDAR. Atomoxetine is a presynaptic norepinephrine reuptake inhibitor that also suppresses dopamine reuptake in particular brain regions, such as the PFC . In the It should also be kept in mind that various genetic mutations may differently affect the expression of NMDAR subunits and, in turn, exert different impact on response to treatment in ADHD patients, as presented in GRIN gene variants. Changes in the expression of GRIN genes directly impair the synthesis of NMDAR subunits and are strongly associated with an elevated risk of developing ADHD. In addition to GRIN, deficiencies in other genes associated with ADHD susceptibility, such as SorC2, D4.7R, SNAP-25, and LPHN3, have also been shown to result in NMDAR hypofunction. For example, SorC2 deficiency leads to impaired NMDAR-dependent LTP, LTD, and synaptic plasticity. The D4.7R variant inhibits the GluN1 subunit of NMDAR via interaction with PSD-95. Downregulation of SNAP-25 reduces NMDAR synaptic density and impairs LTP, whereas LPHN3 knockout leads to early LTP impairment and reduced NMDAR-GluN1 expression. Conversely, BAIAP2 deficiency has been found to increase NMDAR density and NMDAR-mediated synaptic transmission. Interestingly, the most used drugs for treating ADHD, such as methylphenidate and atomoxetine, have been shown to regulate NMDAR function. On the other hand, drugs directly targeting NMDAR, such as amantadine and memantine, have demonstrated effectiveness in alleviating ADHD symptoms in clinical trials.ADHD is a neurodevelopmental disorder commonly attributed to a complex interplay between genetic and environmental factors. Mutations and SNPs in numerous genes, including those associated with NMDAR, have been identified as genetic susceptibility factors for ADHD. These genetic variants have been shown to have regulatory effects on glutamatergic neurotransmission by regulating NMDAR function and distribution, NMDAR-dependent LTP and LTD, and synaptic plasticity. The most compelling evidence is provided by It is noteworthy that, according to proton magnetic resonance spectroscopy studies, glutamatergic imbalance in the context of ADHD differs in terms of particular neural circuits and age. For example, studies in adult ADHD patients have demonstrated reduced levels of a glutamate marker in the medial PFC, ACC, and basal ganglia, while elevated in the cerebellum. On the other hand, studies with children and adolescents suggest increased glutamate markers in the frontal cortex and ACC . Also, cAlthough animal models offer valuable insights into mechanistic data on disease pathogenesis, they face limitations in direct translation of these findings to humans. Currently, there is a lack of substantial clinical data that directly establishes a connection between NMDAR dysfunction and ADHD in human populations. This draws attention to the exploration of non-invasive methods to bridge the gap between basic research and clinical applications. The implementation of advanced neuroimaging techniques and multi-omics studies can potentially aid in the identification of ADHD-related biomarkers  ,195. TheThe NMDAR complex is highly polymorphic, with multiple subunits and splice variants that contribute to the functional diversity of the receptor. Genetic variations in NMDAR genes can influence receptor activity, subunit composition, and synaptic localisation, which in turn affects synaptic plasticity and neurotransmission. The expression of NMDAR subunits varies across different regions of the brain. For example, GluN2A and GluN2B subunits are predominantly expressed in the cortical regions and hippocampus, which are key brain regions involved in the ADHD development. Conversely, GluN2C and GluN2D expression is much weaker in the aforementioned regions . It is tTaking all of this into consideration, attempts to treat ADHD by targeting the NMDA receptor may pose significant challenges. However, gaining a better understanding of its role in the disease development could shed a new light on the complex pathogenesis of ADHD and lead to development of novel therapeutics.