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.
Changes in the P100 latency of the visual evoked potential and the saccadic reaction time during isometric contraction of the shoulder girdle elevators
We investigated changes in the P100 latency of the visual evoked potential (VEP) and the saccadic reaction time (SRT) in relation to the degree of activity of the shoulder girdle elevators. Muscle force was set in 10% increments from 0% to 50% of the maximal voluntary contraction (MVC). The VEP was derived from a midline occipital electrode with reference electrodes on the ears when the right retina was stimulated through the eyelid by light emitting diodes while the eyes were closed. The P100 latency of the VEP was defined as the time from the stimulus onset to the main positive peak. The SRT was defined as the latency until the beginning of eye movement toward the lateral target, which was moved at random time-intervals. P100 latency was shortened until 30% of the MVC, and which it lengthened. The SRT changed in a pattern similar to that observed for the P100 latency. The ratio of the shortening in P100 latency relative to that of the SRT was approximately 20%. All data is presented as the mean value, plus the standard deviation. We believe that the information processing time in the neural pathway from the retina to the visual cortex was shortened up to a certain muscle force of the shoulder girdle elevators, and then this processing time lengthened. These findings indicate that shortening of information processing time in the neural pathway beyond the visual cortex is included in the shortening of the SRT.
A note on the characteristic response pattern in primary sensory projection cortex of the cat following a synchronous afferent volley.
Abstract Electrical stimulation of the thalamic relay nuclei (ventralis posterior, medial geniculate, lateral geniculate) or their immediate prethalamic projection tracts, elicits in the appropriate sensory cortices a characteristic polyspike positive and negative wave. This response may also be elicited by direct cortical stimulation in striate cortex, but not in suprasylvian association cortex. The polyspike patterns are not elicited via the corpus callosum or other pathways. The cortical excitability cycle and the variation with stimulus intensity are described for these responses. Their mechanisms and nature are discussed.