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 well understood. The connectivity of the VIM has so far not been studied functionally. It was hypothesized that VIM stimulation would exert an effect primarily on VIM projection areas, namely motor and parietoinsular vestibular cortex.

METHODS

Six patients with essential tremor who had electrodes implanted in the VIM were studied with PET. Regional cerebral blood flow was measured 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 motor cortex ipsilateral to the side of stimulation. Right retroinsular (parietoinsular vestibular) cortex showed regional cerebral blood flow decreases with stimulation.

CONCLUSIONS

Beneficial effects of VIM stimulation in essential tremor are associated with increased synaptic activity in motor cortex, possibly due to nonphysiologic activation of thalamofrontal projections or frequency-dependent neuroinhibition. Retroinsular regional cerebral blood flow decreases suggest an interaction of VIM stimulation on vestibular-thalamic-cortical projections that may explain dysequilibrium, a common and reversible stimulation-associated side effect.