Hypothalamo-cerebellar and cerebello-hypothalamic pathways: a review and hypothesis concerning cerebellar circuits which may influence autonomic centers affective behavior.

Experimental data which have suggested the probability of connections between the cerebellum and hypothalamus are reviewed. Early studies relied mainly on physiological methods and, in general, concluded that such connections were multisynaptic being relayed via an undetermined number of synapses in the bulbar reticular formation. Recent studies, using horseradish peroxidase techniques, have identified direct connections between cerebellar nuclei and the hypothalamus and between several regions of hypothalamus and the cerebellar cortex. It is proposed that the cerebellum, by way of direct nucleo-hypothalamic projections and the resultant descending hypothalamic projections to visceral centers, has a variety of specific circuits through which it can directly influence autonomic centers. It is further noted that autonomic centers, as exemplified by hypothalamo-cerebellar projections, may have equally specific feedback loops to cerebellar cortex. Direct cerebello-hypothalamic projections and the subsequent diffuse pathways from hypothalamus into a number of forebrain areas may represent circuits responsible for the affective responses seen as a result of cerebellar ablation and/or stimulation.