Thalamic stimulation for essential tremor activates motor and deactivates vestibular cortex

Background: The functional effects of deep brain stimulation in the nucleus ventralis intermedius (VIM) of the thalamus on brain circuitry are not wel l understood. The connectivity of the VIM has so far not been studied funct ionally. It was hypothesized that VIM stimulation would exert an effect pri marily on VIM projection areas, namely motor and parietoinsular vestibular cortex. Methods: Six patients with essential tremor who had electrodes impl anted in the VIM were studied with PET. Regional cerebral blood flow was me asured during three experimental conditions: with 130 Hz (effective) and 50 Hz (ineffective) stimulation, and without stimulation. Results: Effective stimulation was associated with regional cerebral blood flow increases in m otor cortex ipsilateral to the side of stimulation. Right retroinsular (par ietoinsular vestibular) cortex showed regional cerebral blood flow decrease s with stimulation. Conclusions: Beneficial effects of VIM stimulation in e ssential tremor are associated with increased synaptic activity in motor co rtex, possibly due to nonphysiologic activation of thalamofrontal projectio ns or frequency-dependent neuroinhibition. Retroinsular regional cerebral b lood flow decreases suggest an interaction of VIM stimulation on vestibular -thalamic-cortical projections that may explain dysequilibrium, a common an d reversible stimulation-associated side effect.