Abstract
Electrical responses of the superior colliculus (SC), elicited by single shock stimulation of the optic tract (CT), were studied in unanesthetized immobilized cats and in one chronic preparation. 1) When recorded from deep points of the SC, the electrical response con-sisted of an initial spike complex and a following positive-negative biphasic wave. Among these, the earliest spike with a latency of 0.6 msec was identified as representing a presynaptic volley. The onset latency of the positive wave was 3-6 msec.
2) In response to a single OT shock, units of the SC discharged singly or repetitively. The latency histogram of the unitary responses had two peaks, one at 2-3 msec and the other at 8-9 msec. The configuration of the latency histo-gram was about the same as the positive wave response.
3) Conditioning stimulation of the mesencephalic reticular formation (MRF) enhanced the positive wave response. This effect was maximum at 150 msec and lasted up to 500 msec after the MRF activation. With about the same time course as this, the reactivity of the SC units was increased.
4) The antidromic response of the OT was enhanced following the MRF activation, the maximum being reached at 40 msec. In association with this a slow negative potential change was found to occur at the optic chiasm. Its time course was similar to the facilitation curve of the antidromic CT response.
5) It was seen in one chronic preparation that the SC response was augmented during deep sleep as compared with those during light sleep and resting arousal.
