Eyeblink conditioning in patients with hereditary ataxia: a one-year follow-up study

Delay eyeblink conditioning was examined in patients with genetically-defined heredoataxias and age-matched control subjects. 24 patients with spinocerebellar ataxia type 6 (SCA6), type 3 (SCA3), and Friedreich's ataxia (FRDA) participated. SCA6 affects primarily the cerebellum, whereas extracerebellar involvement is common in SCA3 and FRDA. Testing was performed in three sessions six months apart. Severity of ataxia was defined based on the International Ataxia Cooperative Rating Scale (ICARS). As expected, cerebellar patients were significantly impaired in eyeblink conditioning compared to controls. Signs of retention and further learning across sessions were present in controls, but not in the cerebellar patients. In addition, findings of disturbed timing of conditioned responses were observed. Both onsets and peaks of the conditioned responses (CRs) occurred significantly earlier in cerebellar patients. Shortened CR responses were most prominent in patients with primarily cerebellar cortical disease (SCA6). In the group of all cerebellar patients, the SCA3 and the FRDA group correlations between learning deficits and clinical findings were weak. Moderate-to-strong correlations were found in the SCA6 patients. There was no significant change, however, in clinical ataxia scores and CR incidence across the three sessions. In summary, impaired learning of conditioned eyeblink responses is a stable finding across multiple sessions in patients with degenerative cerebellar disorders. Eyeblink conditioning may be a useful measure of cerebellar impairment in patients with hereditary ataxias that primarily affect the cerebellum (such as SCA6). In other heredoataxias (such as SCA3 and FRDA), extracerebellar involvement not assessed by ICARS likely contributes to eyeblink conditioning abnormalities.