2.2.1. Patients

Eight consecutive patients treated with bilateral DBS for medically refractory ET participated in the study. Prior medical treatment included propranolol, primidone and topiramate, or a combination of the three. The e fficacy of the treatment has been thoroughly reviewed before deeming the patient therapy-resistant and discussed multi-disciplinarily to establish the indication for DBS. All patients were implanted (Medtronic model 3387 lead, contacts 1.5 mm in length, spaced 3 mm center-to-center; Medtronic, Inc.) using the Leksell G frame (Elekta, Stockholm, Sweden). Accurate electrode positioning was tested using intra-operative macrostimulation (up to 5 V, with 60 μs pulses and a frequency of 185 Hz) and was confirmed by postoperative MRI (Philips Intera, Eindhoven, the Netherlands) and/or CT-scanning (Sensation 64, Siemens, Erlangen, Germany). The post-implantation CT images were fused with preoperative 3T-MRI images using BrainLAB software (BrainLAB, Heimstetten, Germany). The electrode configurations and stimulation parameters had been reviewed at length and optimized by using Medtronic's 8840 N'Vision Clinician Programmer (Medtronic, Inc., Northridge, CA, USA), according to the best current practice [19]. None of the patients were on any medication for tremor following DBS. Patients were recruited at the outpatient neurological department at the University Medical Centre Groningen (UMCG). The experimental procedure was approved by the medical ethical review board of the UMCG (registration number 2017406) and deemed "care as usual". Under these circumstances, written informed consent was not required.
