Sensory-specific Peripheral Stimulation for Tremor Management

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