Zapping away tremors: scientists probe how electrical stimulation calms shaky hands

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria for Healthy Participants: * Age from 18 to 80 years * No history of a brain and/or skull lesion * Normal hearing and (corrected) vision * Able to understand and give informed consent * No neurological disorders, no tremor * Absence of pathology that could cause abnormal movements of extremities (e.g., epilepsy, stroke, marked arthritis) * Able to understand and speak English Inclusion Criteria for Patients: * Age from 18 to 80 years * No prior history of skull lesions or craniotomy * Normal hearing and (corrected) vision * Able to understand and give informed consent * Diagnosis of ET (Tremor Research investigation Group criteria) or diagnosis of PD (UK PD Society Brain bank diagnostic criteria) by a physician * Tremor in at least an upper limb with pure flexion-extension wrist tremor with posture (ET) and rest (PD). * Tremor at least moderate-severe by clinician judgment and tremor scales (Fahn Tolosa Marin Tremor Rating Scale (TETRAS), Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS)) * Absence of pathology that could cause abnormal movements of extremities (e.g., epilepsy, stroke, marked arthritis, moderate to severe dyskinesias in PD) * Stable medication doses for at least 30 days prior to study enrollment * Able to understand and speak English Exclusion Criteria for Healthy Participants: * Cardiac pacemaker or pacemaker wires; neurostimulators; implanted pumps * Metal in the body (rods, plates, screws, shrapnel, dentures, IUD) or metallic particles in the eye * Surgical clips in the head or previous neurosurgery * Any magnetic particles in the body * Cochlear implants * Prosthetic heart valves * Epilepsy or any other type of seizure history * Any neurological diagnoses or medications influencing brain function * History of significant head trauma (i.e., extended loss of consciousness, neurological sequelae) * Known structural brain lesion * Significant other disease (heart disease, malignant tumors, mental disorders) * Significant claustrophobia; Ménière's disease * Pregnancy (ruled out by urine ß-HCG if answers to screening questions suggest that pregnancy is possible), breast feeding * Non prescribed drug use * History of current substance abuse (exception: current nicotine use is allowed) * Recreational marijuana * Tremor, parkinsonism; neurological diseases; medical (cardiological, renal, hepatic, oncological) or psychiatric disease that would interfere with study procedures for asES, HD-EMG, TMS, or EEG * Dementia; severe depression; or prior neurosurgical procedures * Failure to perform the behavioral tasks or neuropsychological evaluation tests * Prisoners Exclusion Criteria for Patients: * Cardiac pacemaker or pacemaker wires; neurostimulators; implanted pumps * Metal in the body (rods, plates, screws, shrapnel, dentures, IUD) or metallic particles in the eye * Surgical clips or shunts in the head * Any magnetic particles in the body * Cochlear implants * Prosthetic heart valves * Epilepsy or any other type of seizure history * Significant claustrophobia; Ménière's disease * Pregnancy, breast feeding * Medications increasing risk for seizures * History of current substance abuse (exception: current nicotine use is allowed) * Failure to perform tasks (e.g., follow instructions to stay still in the scanner) or fill in safety screening forms * Prisoners * Atypical or secondary parkinsonism * Co-existence of other neurological diseases * Mixed or complex tremors * Inability or unwillingness to discontinue medications for tremor on the day of study assessments * Medical (cardiological, renal, hepatic, oncological) or psychiatric disease that would interfere with study procedures for asES, HD-EMG, TMS, or EEG; dementia; severe depression; prior neurosurgical procedures