Neuroimaging evidence implicating cerebellum in Support of sensory/cognitive processes associated with thirst

Recent studies implicate the cerebellum, long considered strictly a motor c ontrol structure, in cognitive, sensory, and affective phenomenon. The cere bellum, a phylogenetically ancient structure, has reciprocal ancient connec tions to the hypothalamus, a structure important in vegetative functions. T he present study investigated whether the cerebellum was involved in vegeta tive functions and the primal emotions engendered by them. Using positron e mission tomography, we examined the effects on the cerebellum of the rise o f plasma sodium concentration and the emergence of thirst in 10 healthy adu lts. The correlation of regional cerebral blood flow with subjects' ratings of thirst showed major activation in the vermal central lobule. During the development of thirst, the anterior acid posterior quadrangular lobule, li ngula, and the vermis were activated. At maximum thirst and then during irr igation of the mouth with water to alleviate dryness, the cerebellum was le ss activated. However, 3 min after drinking to satiation, the anterior quad rangular lobule and posterior cerebellum were highly activated. The increas ed cerebellar activity was not related to motor behavior as this did not oc cur. Instead, responses in ancient cerebellar regions (vermis, fastigal nuc leus, archicerebellum) may be more directly related to vegetative and affec tive aspects of thirst experiences, whereas activity in neocerebellar (post erior) regions may be related to sensory and cognitive aspects. Moreover, t he cerebellum is apparently not involved in the computation of thirst per s e but rather is activated during changes in thirst/satiation state when the brain is "vigilant" and is monitoring its sensory systems. Some neocerebel lar activity may also reflect an intentionality for gratification by drinki ng inherent in the consciousness of thirst.