Involvement of the human cerebellum in fear-conditioned potentiation of the acoustic startle response: a PET study.

Fear-conditioned potentiation of the startle response was used to study the role of the cerebellum in associative learning of non-specific aversive reactions in healthy human subjects using PET. Prior PET scanning initially neutral light stimuli were paired with painful electric shocks (fear-conditioning phase). Four PET-scans each were performed with presentation of acoustic startle stimuli (T), fear-conditioned light stimuli (L) or acoustic stimuli paired with light (LT, potentation phase). As a measure of fear-conditioning subtraction of condition T from LT revealed an increase of regional cerebellar blood flow (rCBF) in the left cerebellar hemisphere. Subtraction of condition L from LT, as a measure of fear-conditioned potentiation, revealed an increase of rCBF in the medial cerebellum. Different parts of the cerebellum appear to be involved in this form of motor associative learning.