Interhemispheric asymmetry of positive emotional reactions in rats.

Interhemispheric asymmetry of positive conditional reactions in rats were investigated, i.e., reactions of drinking need and self-stimulation satisfaction. A successive hemisphere inactivation was performed by potassium spreading depression. Both right and left hemisphere inactivation were shown symmetrically to affect the total quantity of water consumed by the rats until complete thirst satisfaction, i.e., the need magnitude. At different stages of thirst satisfaction, however, interhemispheric asymmetry was observed: when drinking motivation was strong, the right hemisphere dominated, when it was weak the left hemisphere was dominant. Right hemisphere inactivation caused a decrease in the frequency of lateral hypothalamus self-stimulation, whereas with left hemisphere inactivation it increased, which testifies to right hemisphere dominance in self-stimulation reaction. Self-stimulation reaction was also characterized by the asymmetry of lateral hypothalamus nuclei: reactivity of the right nucleus to hemisphere inactivation (decrease or increase in self-stimulation frequency) was more pronounced than that of the left nucleus.