PATIENTS WITH CEREBELLAR LESIONS CANNOT ACQUIRE BUT ARE ABLE TO RETAIN CONDITIONED EYEBLINK REFLEXES

The purpose of these experiments was to examine the role of the human cerebellum in the acquisition and retention of conditioned reflexes. N ormal human subjects and patients with cerebellar lesions were tested for their capacity to acquire, retain and express conditioned eyeblink responses. In acquisition tests, subjects were trained in a delay cla ssical conditioning paradigm using a tone conditioned stimulus and a m idline forehead tap as an unconditioned stimulus. While normal subject s developed anticipatory eyeblinks to the tone in one session, patient s with cerebellar lesions failed to acquire conditioned responses in f our consecutive training sessions. The conditioning deficit was bilate ral even in patients with a unilateral cerebellar pathology. The same groups of subjects were tested for the presence of eyeblinks to a visu al threat. in these experiments, both normal subjects and patients wit h cerebellar lesions exhibited a high level of responding when they sa w an object approaching their face. These eyeblinks to the visual thre at are probably naturally acquired conditioned responses because they extinguish in normal subjects if they are not reinforced by the uncond itioned cutaneous stimulus. in addition, the stimulus of seeing an app roaching object blocks the acquisition of classically conditioned eyeb links to a new conditioned stimulus in normal subjects. These data imp ly thar patients with cerebellar lesions who cannot acquire new classi cally conditioned responses are able to retain and express conditioned eyeblinks which were acquired before the onset of the pathology. Cons equently cerebellum-dependent neural substrates which are involved in learning new conditioned reflexes do not seem to be required for the s torage of naturally learned conditioned responses.