Activity of rabbit neocortex and hippocampus neurons in orientational-investigative behavior and freezing.

Autocorrelation histograms were used to study the nature of spike activity in neurons recorded bilaterally from the visual and parietal areas of the cortex and hippocampal field CA1 in rabbits in free behavior during exposure to emotionally significant stimuli. Active movement orientational-investigative reactions to stimuli were associated with grouping of discharges and periodicity in the spike activity of most neurons in the cortex and hippocampus, this being dominated by the theta frequency (predominantly 4-5 Hz in the cortex and 4-5 and 6-7 Hz in the hippocampus). As compared with active movement reactions, freezing in response to stimulation was associated with increased numbers of neurons with uniform discharge distributions, while the spike activity of neurons with discharge periodicity showed increases in the intensity of the delta frequency (predominantly from 2 to 4 Hz), while theta intensity decreased. The number of neurons with periodic frequency in the delta range was greater in freezing than in the baseline state of calmly sitting rabbits.