CEREBELLAR ACTIVATION DURING CLASSICAL-CONDITIONING OF THE HUMAN FLEXION REFLEX - A PET STUDY

THE present study investigated the involvement of the cerebellum in cl assical conditioning of the cutaneomuscular flexion reflex in four nor mal volunteers using positron emission tomography (PET). The flexion r eflex was elicited by electrical pulses applied to the medial plantar nerve (unconditioned stimulus, US). A tone was presented as the condit ioning stimulus, which co-terminated with the US. The incidence of con ditioned responses was correlated with changes in rCBF during the acqu isition process of flexion reflex conditioning. Blood flow was signifi cantly increased in an area extending from the ipsilateral cerebellum and hippocampus to bilateral frontal regions (p = 0.009). These data p rovide support for an involvement of the cerebellum as well as hippoca mpus among other neural systems in classical flexion reflex conditioni ng.