HIGH-FREQUENCY-GAMMA ELECTROENCEPHALOGRAM ACTIVITY IN ASSOCIATION WITH SLEEP-WAKE STATES AND SPONTANEOUS BEHAVIORS IN THE RAT

The occurrence of high-frequency gamma activity (30-60 Hz) and its rel ationship to other frequency band activities were examined by spectral analysis of the electroencephalogram in association with sleep-wake s tates and spontaneous behaviors in the rat. In the electroencephalogra m, gamma wave activity was evident in unfiltered and high-frequency fi ltered recordings, in which it was prominent during attentive or activ e Wake episodes and during Paradoxical Sleep, when theta-like activity was also apparent. In amplitude spectra from these episodes, multiple peaks were evident within the gamma frequency band, indicating broad- band high-frequency activity, in association with a single low-frequen cy peak in the theta band. gamma peaks were attenuated during quiet Wa king, in association with a low-frequency peak between theta and delta , and during Slow Wave Sleep, in association with a low-frequency peak in the delta band. In coherence spectra from ipsilateral cortical lea ds, peaks were also present within the gamma range and were significan tly higher in Waking moving and Paradoxical Sleep than in Waking quiet and Slow Wave Sleep. In measures of Frequency band amplitude, gamma a ctivity (30.5-58.0 Hz) varied significantly across the sleep-waking cy cle, being similarly high during Wake and Paradoxical Sleep and lowest during Slow Wave Sleep. Across these stales, gamma was negatively cor related with delta (1.5-4.0 Hz). In contrast, high beta (19.0-30.0 Hz) was significantly lower in Wake than in Slow Wave Sleep and was posit ively correlated with delta. gamma differed significantly across speci fic behaviors, being highest in Paradoxical Sleep with twitches and du ring Waking eating and moving behaviors, slightly lower in Waking atte ntive, lower in Waking grooming and as low in Waking quiet as during S low Wave Sleep. These results indicate that the reciprocal variation o f high-frequency gamma activity (and not beta) with low-frequency delt a activity reflects the sleep-waking cycle of the rat. Moreover, gamma activity reflects the degree of behavioral arousal, since it is high during active Waking, when the electromyogram is high, and low during quiet Waking, when the electromyogram is low. II also reflects cortica l arousal, independent of motor activity, since it attains high levels in association with attentive immobility and maximal levels only duri ng particular active behaviors (eating and moving and not grooming), a nd it also attains maximal levels during Paradoxical Sleep, when the n uchal electromyogram is minimal, but small twitches evidence dreaming. The co-variation of gamma and a slow oscillation in the theta band ac ross states and behaviors suggests that a common system may modulate t hese fast and slow electroencephalogram rhythms, and that such modulat ion, potentially emanating from the basal forebrain, could predominate during certain states or behaviors, such as Paradoxical Sleep. Copyri ght (C) 1996 IBRO.