(J Neurol Neurosurg Psychiatry 2001;70:464-470)

DBS of the GPi is a new and promising treatment option for dystonia. Secondary worsening may limit this therapy.

The subthalamic nucleus (STN) has generally been considered as a relay station within frontal-subcortical motor control circuitry. Little is known about the influence of the STN on cognitive networks. Clinical observations and studies in animals suggest that the STN participates in non-motor functions which can now be probed in Parkinson's disease patients with deep brain stimulation of the STN, allowing selective and reversible modulation of this nucleus. Using PET, we studied changes in regional cerebral blood flow (rCBF) associated with a response conflict task (Stroop task) in Parkinson's disease patients ON and OFF bilateral STN stimulation. The Stroop task requires subjects to name the font colour of colour words (e.g. "blue") printed in an incongruent colour ink (e.g. yellow). During STN stimulation, impaired task performance (prolonged reaction times) was associated with decreased activation in both right anterior cingulate cortex (ACC) and right ventral striatum. Concomitant increased activation in left angular gyrus indicative of ongoing word processing during stimulation is consistent with an impairment to inhibit habitual responses. ACC and ventral striatum are part of the ACC circuit associated with response conflict tasks. The decreased activation during STN stimulation in the ACC circuit, while response conflict processing worsened, provides direct evidence of STN modulating non-motor basal ganglia-thalamocortical circuitry. Impairment in ACC circuit function could account for the subtle negative effects on cognition induced by STN stimulation.

Pallidal stereotactic surgery is a well-accepted treatment alternative for Parkinson's disease. Another indication for this procedure is medically refractory dystonia, especially generalized dystonia with abnormal axial and extremity movements and postures. Improvement of dystonia after pallidotomy has been reported in several recent papers. In this report the authors describe three patients with generalized dystonia (two primary, one secondary) and their improvement after bilateral pallidal stimulation at follow-up times of between 6 and 18 months.