Effects of lesions of the cerebellar vermis on VMH lesion-induced hyperdefensiveness, spontaneous mouse killing, and freezing in rats.

In a series of independent experiments, we showed that lesions of the vermis of the cerebellum in rats blocked the hyperdefensiveness induced by lesions of the ventromedial hypothalamus (VMH), attenuated spontaneous mouse killing, and reduced unconditioned freezing and other signs of fear in the presence of a cat. The vermal lesions did not significantly affect foot-shock conditioned freezing. Control lesions of the cerebellar hemispheres did not affect VMH lesion-induced hyperdefensiveness or freezing in the presence of a cat. The hemispheric lesions did attenuate foot-shock conditioned freezing. The data are discussed in terms of the striking similarities and differences between the behavioral effects of cerebellar vermal lesions and amygdala lesions and the interaction of a number of brain areas in modulating agonistic behaviors. The results leave no doubt that the medial cerebellum is significantly involved in the control of species-specific agonistic behaviors. The specific dimension of agonistic behaviors and the details of the interactions with other brain areas remain a puzzle which we approached here by expanding the behavioral profile of animals with lesions of the cerebellar vermis.