Cerebellar vermis: essential for classically conditioned bradycardia in the rat.

The effects of lesions of the cerebellar vermis on the acquisition of heart-rate conditioning in rats was examined. Lesions of the vermis severely attenuated the acquisition of conditioned bradycardic responses in a simple conditioning procedure in restrained rats. Importantly, the vermal lesions did not affect resting heart-rate, unconditioned heart-rate orienting responses to a tone stimulus or unconditioned heart-rate responses to the shock unconditioned stimulus. It is concluded that the cerebellar vermis is an essential component of a heart-rate conditioned response circuit in the rat. The similarities between these effects and those following manipulations of the amygdala are discussed.