Laminal analysis of visual evoked potentials and unit discharges on visual cortex of albino rat.

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Both visual evoked potentials (VEP) and unit discharges by Xenon flash were recorded with macro- and micro-electrode technique from visual cortex of albino rat adapted to dark environment under very light anesthesia. Some characteristics of VEP and the relation between laminal VEP and unit discharges were investigated. 1. VEP led by ball electrode from cortical surface was individually different in configuration, but it had six wave components statistically. Averaged peak latencies of them were as follows: 1 st 26 msec, 2 nd 36 msec, 3 rd 73 msec, 4 th 91 msec, 5 th 111 msec and 6 th 182 msec in order of from positive to negative. The 4 th to 6 th components were labile in configuration. Especially, the 4 th negative wave appeared separately or was included within the 6 th wave or changed to rhythmic after-discharge in sequential series of recording in some cases. 2. As a microelectrode was inserted into cortex, the amplitude of VEP increased. Especially, the 2 nd negative wave increased in amplitude and had small ripples on it. At the depth of about 1mm in cortex some ripples showed phase reverse in some cases. The peak latencies after the 3 rd wave delayed. 3. Both spontaneous and responding discharges were most frequently observed at the depth of about 1mm, but injury discharges at the relatively superficial layer. 4. Correspondence of responding discharges for repeated stimulation to VEP was apparently complicated and not constant in unit to unit and even in the same one. However, the correlation between the unit discharges and VEP was evident on time-histogram by means of the data processing computer.