Neuronal responses to passive movement in the globus pallidus internus in primary dystonia

Abnormal sensory processing has been implicated in the pathophysiology of primary dystonia. In the globus pallidus internus (GPi), the primary output structure of the basal ganglia, many neurons respond to sensory (proprioceptive) stimulation. Here we have characterized GPi neuronal responses to passive movement of the contralateral limbs in 22 patients with primary dystonia undergoing microelectrode recording for placement of deep brain stimulator leads. We plotted coordinates of cells responding to limb movement in a common space. We observed distinct representations of leg and arm movement localized to the dorsal and ventral part of the posterior GPi, respectively. Comparing patients with generalized dystonia versus patients with segmental craniocervical dystonia, there was no difference in the volumes or separations of leg and arm related territories. In contrast to parkinsonism, only a small minority of units were responsive to movement across multiple joints. Abnormally increased directional selectivity was found in units responding to dystonic limbs compared with nondystonic limbs. Some affected GPi neurons therefore appear to have altered proprioceptive tuning for movement direction. There is an apparent preservation of GPi somatotopic organization in dystonia in comparison with prior studies of GPi somatotopic organization in non-human primates and humans with Parkinson's disease.