Limb flexion reflex-related areas in human cerebellum.

Numerous studies have shown that the cerebellum is involved in classical conditioning of specific aversive reactions. Only few studies, however, have examined the exact localization of cerebellar areas involved in the control of unconditioned reflex responses. The present study investigated cerebellar areas, which are activated during eliciting of the limb flexion reflex in healthy controls using [15O]H2O PET. Limb flexion reflex related areas were found in vermal lobules III-VI with the local maximum in vermal lobule V. Areas of activation were more widespread compared to a voluntary foot movement and a sensory foot stimulation condition. Limb flexion reflex areas probably reflect efferent reflex modulation as well as sensory inputs from the stimulus itself and/or the reflex response.