A high-intensity, goggle-mounted flash stimulator for short-latency visual evoked potentials.
The few studies that have been done on short-latency, subcortical visual evoked potentials (SVEPs) have all used stroboscopic flashes as the evoking stimulus. The dimensions of the stimulator, the acoustical artifacts and the photic spread to the examination room limited the use of SVEPs to research laboratories. With the advent of high-efficiency light-emitting diodes (LEDs), high-intensity flashes can now be generated from goggle-mounted LEDs. In this study, a goggle-mounted high-intensity stimulator was constructed and its flashes used to evoke SVEPs. The reproducibility of SVEPs across subjects and the ease of using the high-intensity LED flash stimulator make them a promising candidate for testing subcortical visual pathway function in the operating room.
The scalp topography of human visual evoked potentials
Abstract The topography of all identifiable components of the scalp-recorded visual evoked potential (VEP) to unpatterned centrally-viewed light flashes presented in Maxwellian view to the right eye was determined for all scalp electrode locations of the 10–20 system and for locations at the right eye, mastoids, and posterior neck. Twenty-two components were analyzed. Of these, six were regarded as electroretinographic, one as myogenic, and the rest as neurogenic. Supplementary analysis suggested that VEP components and their topography are similar whether evoked by unpatterned flashes presented in Maxwellian view, by unpatterned stroboscopic flashes, or by patterned, flashes, but not by pattern reversal. Potentials thought to originate in periorbital musculature were evoked by somatosensory and auditory as well as visual stimuli. They were larger in inexperienced than in experienced subjects, were larger to unpredictable than to predictable stimuli, but did not differ whether the subject was in a Maxwellian view apparatus or seated in a comfortable chair. These potentials can distort recordings of presumptive neurogenic components in the same latency range. These data should aid in predicting VEP characteristics and in assessing myogenic contamination of neurogenic activity. Components thought to be analogous in the somatosensory, auditory and visual modalities were discussed.
Photoinduced spin-state transition of Co3+ in the layered perovskite manganite thin film
The photoinduced effect, at different temperatures, on layered perovskite manganite La1.2Sr1.8Mn1.8Co0.2O7 thin film deposited on a SrTiO3(100) substrate has been studied using a He–Ne laser (632.8 nm) with the power of output 25 mW at low temperatures. The electrical transport and magnetic properties of the film are investigated systematically in the temperature region from 20 to 300 K. The resistance shows a significant decrease at low temperatures (T<90 K) under laser irradiation, which can be interpreted in terms of the spin-state transition of Co3+ ions. The magnetic field combined with the laser is also used to detect the photoinduced effect of the spin-glass state. The time dependence of the metastable system under several applied fields was also discussed. The system has the ability to keep a persistent memory of the magnetic history imprinted in its zero-field resistance.