| Abstract: | Spontaneous and evoked unit activity of the superior colliculus was studied in cats immobilized with gallamine or with the spinal cord divided (encephalé isolé). Statistical parameters of unit activity were calculated in light and darkness and in the presence of a moving photic stimulus. Spontaneously active neurons were divided into four main groups: 1) with a mean interspike interval of about 300 msec, coefficient of variation 1.9, and with two modes in the autocorrelation histogram; 2) with similar statistical parameters but distinguished by correlation with saccadic eye movements; 3) histogram of interspike intervals exponential in type, autocorrelation histogram flat, mean interval and standard deviation about 100 msec; 4) with symmetrical distribution of interspike intervals, mean interval about 50 msec, coefficient of variation 0.4–0.5. Spontaneous activity in light and darkness differed only in the neurons of the second group. Comparison of the statistical parameters of the spontaneous and evoked activity shows that encoding of the stimulus could be carried out by neurons of groups 3 and 4. In some cases the mode of the histogram of interspike intervals and the standard deviation changed significantly and activity appeared regularly in the autocorrelation histogram. |
