Fear conditioned potentiation of the acoustic blink reflex in patients with cerebellar lesions

Objective-To investigate whether the human cerebellum takes part in fear co nditioned potentiation of the acoustic blink reflex. Methods-A group of 10 cerebellar patients (eight patients with lesions invo lving the medial cerebellum, two patients with circumscribed lesions of the cerebellar hemispheres) was compared with a group of 16 age and sex matche d healthy control subjects. The fear conditioned potentiation paradigm cons isted of three phases. During the first, habituation phase subjects receive d 20 successive acoustic blink stimuli. In the subsequent fear conditioning phase, subjects passed through 20 paired presentations of the unconditione d fear stimulus (US; an electric shock) and the conditioned stimulus (CS; a light). Thereafter, subjects underwent the potentiation phase, which consi sted of a pseudorandom order of 12 trials of the acoustic blink stimulus al one, 12 acoustic blink stimuli paired with the conditioned stimulus, and si x conditioned stimuli paired with the unconditioned stimulus. The EMG of th e acoustic blink reflex was recorded at the orbicularis oculi muscles. The potentiation effect was determined as the difference in normalised peak amp litude of the blink reflex evoked by pairs of CS and acoustic blink stimuli and evoked by the acoustic stimulus alone. Results-In the habituation phase, short term habituation of the acoustic bl ink reflex was preserved in all cerebellar patients. However, in the potent iation phase, the potentiation effect of the blink reflex was significantly reduced in patients with medial cerebellar lesions compared with the contr ols (mean (SD) potentiation effect (%), patients: -6.4 (15.3), controls: 21 .6 (35.6)), but was within normal limits in the two patients with lateral l esions. Conclusions-The present findings suggest that the human medial cerebellum i s involved in associative learning of nonspecific aversive reactions-that i s, the fear conditioned potentiation acoustic blink reflex.