Spontaneous activity of cat hippocampal neurons in sleep and wakefulness

Abstract

Spontaneous activity of the hippocampal pyramidal cells in chronically prepared cats was recorded for extended periods, thus allowing analysis of temporal patterns of neuronal discharges in relation to the behavioral states of the animal. When the animal was aroused or in REM sleep, neuronal activity was increased, showing discharge patterns characterized by marked reduction in the number of long intervals (>200 msec) and by an increase in moderately long intervals (150–200 msec). When the animal was quietly awake or drowsy, the level of neuronal activity decreased moderately with more numerous long inactive periods. In intermediate sleep with cortical spindle bursts. or in deep sleep with dominant high-voltage slow-wave activity, neuronal activity was considerably decreased. The discharge pattern was then characterized by enhanced irregularity and by frequent interposition of very long inactive periods. Discharge of hippocampal neurons in relation to the phase of local theta waves was neither fixed nor enduring. When two adjacent neurons were observed simultaneously, the firing probability with respect to the phase of the theta waves differed, as a rule, from one cell to the other.