Antisaccade Deficits in Stiff Person Syndrome

The antisaccade task is a clinically useful sign of frontal cortical dysfunction (Hallet,1978). In this task, subjects must make a saccade away from a salient stimulus to a spatial location reflected 180° away. Normal subjects make about 10% errors in this task, but frontal patients make many more. Stiff Person Syndrome (SPS) is a disorder characterized by muscle rigidity, spasm, and ataxia, in which 85% of patients have antibodies against glutamic acid decarboxylase (GAD) an enzyme necessary for GABA synthesis. Previous studies of these patients have identified oculomotor abnormalities, including esotropia (Economides, 2005), multi-component and slow vertical saccades, decreased smooth pursuit gain, downbeat nystagmus (Ances, 2005), and ophthalmoplegia (Pittock, 2006).