Excitability changes in various types of visual cortical units in freely behaving cats

Abstract

Maintained and evoked unit activity was studied in the visual cortex of chronic cats. Recording conditions were differentiated into the 3 states by behavioral and electrical signs: resting arousal (RA), light sleep (LS) and deep sleep (DS or REM). The first and largest group (44.3%) increased neural excitability in the sequence LS → RA → DS. For the second (20.3%) and third group (11.4%) it was RA → LS → DS and DS → RA → LS, respectively. The first had a wide range of discharge rates (0.1–30.0/sec) and the third discharged extremely slowly (<0.1/sec in RA). These 3 main groups corresponded well to the 3 types of units classified on the basis of the correlation function between the mean discharge rate in RA and its changes in LS. Neural excitability was depressed in attentive arousal in comparison to RA. For some units (62.5%) there was noted a significant correlation between the mean discharge rate and the response latency to geniculate stimulation.