A cornerstone in PD and ET research is the investigation of neurophysiological changes as potential bio-markers that could help in tracking disease progression and response to therapy. Electroencephalography (EEG) could provide a non-invasive and relatively inexpensive tool for identification of such bio-markers. In this study the investigators will use high-density electroencephalographic (EEG) recordings, in order to develop a platform of sensitive and reliable bio-markers for disease progression and response to MR-guided Focused ultrasound thalamotomy (FUS-T) intervention for tremor.