Relationship between the types of behavioral reaction in a conditioned shake-off reflex and neocortical lateralization.

The nature of the spike activity and interhemisphere interactions of neurons in the parietal cortex (somatosensory representation of the ear) during the intersignal period before active shake-off and passive (freezing) reactions to stimuli was studied in rabbits after acquisition of a conditioned defensive escape reflex. Before passive reactions, in contrast to the situation before active shake-off, there were increases in right-sided influences on cells in the left hemisphere with delays of up to 100 msec, leading to asymmetry in interhemisphere interactions with right-sided dominance. Passive reactions were preceded by increases in the extent of frequencies in the delta range in the spike activity of individual neurons and in interactions between pairs of cells. These data provide evidence that the existence and nature of interhemisphere asymmetry before stimulation is one of the factors determining the passive or active type of behavioral reaction and reflecting the level of activation of the cortex.