Interhemisphere asymmetry of the neocortex and hippocampus during orientational-investigative behavior and freezing in rabbits.

Cross-correlation histograms were used to study the discharges of cortical neurons in symmetrical leads in both hemispheres (visual and parietal areas) and in hippocampal field CA1 on the right and left sides in rabbits in conditions of free behavior during exposure to emotionally significant stimuli. During active orientational-investigative responses to stimuli, as compared with baseline, the neocortex showed increases in left-sided influences on cells in the right hemisphere, with delays of up to 100 msec, which led to the appearance of asymmetry in the interhemisphere interaction, with left-sided dominance. On freezing, the left-sided influence weakened and the right hemisphere became dominant. Interhemisphere asymmetry in hippocampal neuron activity was seen, and was reciprocal to the asymmetry observed in the neocortex. The active investigative response increased right-sided influences in the hippocampus with delays of up to 200 msec, leading to right-sided dominance. Freezing was associated with increases in left-sided influences, such that the left side was dominant. The interaction of cells in the hippocampus was largely at the frequencies of the theta rhythm during active movement and in the delta range on freezing. These data lead to the conclusion that the active or passive nature of behavioral movement reactions to emotionally significant stimuli correlates with changes in the asymmetry of interhemisphere neuron interaction at the levels of the cerebral cortex and hippocampus.