EPV 8. Thalamic and subthalamic deep brain stimulation evoke distinct and consistent patterns of cortical responses

Abstract

Recent research revealed that cortical areas are substantially modulated by deep brain stimulation (DBS). To better understand the spatial and temporal pattern of cortical modulation, we recorded and localized responses evoked by low-frequency DBS using magnetoencephalography (MEG). We investigated nine patients suffering from Essential Tremor (ET) and 11 patients with Parkinson’s disease (PD) following DBS surgery. The DBS target area was the subthalamic nucleus (STN) in PD patients and the ventral intermediate nucleus of the thalamus (VIM) in ET patients. We applied unilateral, bipolar DBS with a frequency of 5 Hz at clinically effective amplitude, using an external stimulator and externalized leads. Dipole fitting was applied to MEG data to estimate the anatomical origin of evoked responses. Evoked responses were observed in 7 of 9 ET patients, and 7 of 11 PD patients. The temporal profile of responses was very consistent within groups. The response to VIM stimulation was best explained by a dipole which alternated between anterior and posterior orientation periodically (peaks around 13, 40, 77, and 116 ms). It localized to the central sulcus ipsilateral to DBS in all cases. Three patients showed an additional response in the contralateral cerebellum. STN DBS evoked responses around 4, 11 and 27 ms in sensorimotor channels, which were an order of magnitude smaller than those evoked by VIM DBS. Localization results were variable across subjects. Ipsilateral precentral gyrus was the most frequently estimated origin among a number of cortical and subcortical areas. Finally, we observed very short latency responses around 1 ms in individual ET and PD patients. We conclude that MEG enables localization of cortical responses evoked by DBS. Our results suggest that sensorimotor cortex is primarily modulated. The response in sensorimotor cortex is larger for VIM than for STN stimulation, which is characterized by a distinct spatio-temporal profile of responses. Deeper source estimates, lower sensor amplitudes and earlier peaks point towards stronger subcortical contributions compared to VIM DBS.