Conditioning in identical twins with ataxia-telangiectasia

Evidence has accumulated to indicate an essential role for the cerebellum in eyeblink classical conditioning, with normal acquisition impaired by lesions in the cerebellar cortex. For this reason, eyeblink conditioning was studied in a pair of 16-year-old identical twin females with ataxia-tetangiectasia (AT), a disorder with onset in early childhood characterized by diffuse, almost selective, degeneration of the cerebellar cortex with extensive loss of Purkinje cells. We also tested a pair of 16-year-old identical twin female normal control subjects. Twins with AT produced significantly fewer conditioned responses (CRs). The mean percentages of CRs over 144 trials for each eye were 23.0% (left eye) and 10.2% (right eye) in patients with AT, and 45.9% (left eye) and 45.3% (right eye) in normal control subjects. The magnitude of the eyeblink reflex, assessed as unconditioned response amplitude, was not different between patients with AT and control subjects. The results indicate that patients with AT are impaired in the acquisition of CRs and provide further evidence for the role of the cerebellum in eyeblink classical conditioning in humans.