Functional Brain Network Changes in Patients Undergoing Deep Brain Stimulation for Essential Tremor

DRUG

Alcohol

Alcohol consumption is shown to reduce tremor in individuals with essential tremor. The alcoholic beverage will be dispensed by the a clinician study investigator, and the participant will be administered the alcoholic beverage until their tremor is decreased, as determined by the clinician. Individual sensitivity to the tremor-mitigating effects of alcohol varies, but it is anticipated that only light (1-2 40% ABV drinks, containing 1-2 units of absolute alcohol \[10 mL. or 8 g of pure ethanol\]) consumption will be necessary. Participants will then repeat motor task and data collection while the alcohol is effective at controlling tremor, beginning approximately 15-20 minutes after consumption.

DRUG

Alprazolam

Alprazolam is shown to reduce tremor in individuals with essential tremor. The primary investigator will select the appropriate dose for the patient (0.5mg for patients with a body weight of up to 75kg, and 0.75mg for participants with a body weight of 75kg and higher). Participants will swallow the drug with a glass of water in the presence of the research team. If participants have not reached a sufficient level of tremor improvement, a subsequent dose of up to a total of 1.0mg of alprazolam per participant will be requested. Participants will then repeat motor task and data collection.

DEVICE

Cold Therapy

One or both of the participant's upper limbs will be wrapped with pre-chilled ice packs or a cold water circulating device such as a cryomanchet (e.g., the Breg PolarCare Glacier), and the skin temperature monitored until it lowers to 15-25°C. Participants will then repeat motor task and data collection while the limb is cool.

PROCEDURE

Peripheral Nerve Stimulation

Electrical stimulation will be applied using techniques similar to those applied during standard somatosensory evoked potential testing. Specifically, adhesive surface electrodes will be placed above the median and radial nerves at the wrist. Stimulation paradigms will be tailored to each participant based on the frequency characteristics of their tremor. Participants will receive between 20-60 minutes of stimulation, then will repeat motor task and data collection. Transcutaneous peripheral nerve stimulation may help mitigate tremor, with effects lasting beyond cessation of stimulation1-3.

CTCM Coherence

Time frame: up to 8 hours in-lab during experiment

Coherence, a unitless measure of correlation between signals, calculated across the cerebellothalmocorticomuscular (CTCM) circuit, will be computed from neurophysiological recordings including electroencephalography (EEG), electromyography (EMG), magnetoencephalography (MEG), and/or local field potential (LFP), using data collected at rest, during tremor-eliciting tasks, with DBS OFF, with DBS ON (when available), and when using non-DBS tremor interventions (limb cooling and/or peripheral nerve stimulation and/or alprazolam or alcohol).

Power of oscillatory activity across the CTCM network in response to tremor interventions

Time frame: up to 8 hours in-lab during experiment

Power of tremor-related oscillatory activity, in the form of mean power in the 4-12Hz frequency band with units in mV\^2, will be computed from neurophysiological recordings including electroencephalography (EEG), electromyography (EMG), magnetoencephalography (MEG), and/or local field potential (LFP), using data collected at rest, during tremor-eliciting tasks, with DBS OFF, with DBS ON (when available), and when using non-DBS tremor interventions (limb cooling and/or peripheral nerve stimulation and/or alprazolam or alcohol).

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