Neurophysiological evidence for cerebellar dysfunction in primary focal dystonia

Recent studies have suggested that there may be functional and structural changes in the cerebellum of patients with adult onset primary focal dystonia. The aim of this study was to establish whether there is any neurophysiological indicator of abnormal cerebellar function, using the classic eyeblink conditioning paradigm. This paradigm at short intervals is dependent on the olivo-cerebellar circuit and does not require cerebral and basal ganglia structures. Eyeblink conditioning was performed by pairing an auditory tone with a supraorbital nerve stimulus with a delay interval of 400 ms in 12 patients with primary focal dystonia (seven cervical dystonias, five focal hand dystonias) and eight healthy controls. Healthy controls produced more conditioned eyeblink responses than patients with focal dystonia, indicating an abnormality of associative learning in this patient population. This study provides neurophysiological evidence for functional changes in the olivo-cerebellar pathway of patients with primary focal dystonia. Further work needs to be done to determine if these changes are primary, secondary or epiphenomenal to the disease.