The Trans-cutaneous Effects on Physiological Tremor Entertainment During tACS

Transcranial alternating current stimulation (tACS) is a noninvasive neuromodulation method that works by passing alternating electric current between electrodes where at least one of them is attached to the head. This has been shown to have effects on the motor system, cognition and behavior. The exact mechanism by which tACS causes such effects is not fully understood. Some studies suggests a contribution from the stimulated peripheral nerves present in the scalp rather than direct brain effects. To test this hypothesis two arms will be done. First, 12 subjects (arm 1) will be stimulated using focused 4x1 montage with gel-filled cup-electrodes over the motor cortex and the effects will be compared between anesthetized and non-anesthetized scalp. The effects of anesthetizing the scalp will be tested on three different stimulation amplitudes off (0 mA), low (0.5 mA) and high (2.5 mA). Then, 10 subjects (arm 2) will be stimulated over the contralateral arm to exclude any direct brain stimulation effects and to test if peripheral nerve stimulation can entrain the tremor. Three outcome measurements will be measured during the experiments which are: tremor entrainment, sensation intensity and sensation threshold.

Each subject will be stimulated at two different days. One day with the presence of topical anesthetic cream on the scalp above the MC and in the other day with absence of the anesthetic cream. Stimulation frequency is set similar to that of the tremor. Three stimulation amplitudes will be tested (0 mA, 0.5 mA and 2.5 mA -reduced if not uncomfortable). A set of 4*1 gel-filled cup-electrodes is placed over each of motor cortex. Each subject follows three sessions of 12 min length each day. During each session the tremor is measured while interleaving between low amplitude stimulation, high amplitude stimulation and No stimulation. By the end of each session we get 3 min of Low amplitude stimulation, 3 min of high amplitude stimulation and 6 min of No stimulation.

Each subject will be stimulated on only one day. Stimulation frequency is set similar to that of the tremor. Three stimulation amplitudes will be tested (0 mA, 0.5 mA and 2.5 mA -reduced if not uncomfortable). A set of 2*1 gel-filled cup-electrodes is placed over the contralateral arm. Each subject follows three sessions of 12 min length. During each session the tremor is measured while interleaving between low amplitude stimulation, high amplitude stimulation and No stimulation. By the end of each session we get 3 min of Low amplitude stimulation, 3 min of high amplitude stimulation and 6 min of No stimulation.

phase locking value was calculated between the tremor signal measured using accelerometer and the stimulation signal

During session one of 12 minutes length (6 minutes with stimulation ON and 6 minutes with stimulation OFF)

phase locking value was calculated between the tremor signal measured using accelerometer and the stimulation signal

During session two of 12 minutes length (6 minutes with stimulation ON and 6 minutes with stimulation OFF)

phase locking value was calculated between the tremor signal measured using accelerometer and the stimulation signal

During session three of 12 minutes length (6 minutes with stimulation ON and 6 minutes with stimulation OFF)

The subject is asked to rate the sensation intensity during the stimulation at each stimulation amplitude using a visual analog scale from 0 to 10. Zero means the subject doesn't feel the stimulation and the number starts to increase as the sensation perception intensity increases to reach 10 if the subject feels it painful.

Measured up to 5 minutes before the start of the stimulation sessions and lasts for 10 seconds of stimulation after which the subject gives the rating

Stimulation amplitude at which the subject starts to feel the stimulation. Stimulation starts with 0 mA amplitude and then increased gradually until stimulation is perceived (or reaching maximum amplitude).

Measured 3 minutes before the start of the stimulation sessions and lasts up to 2 minutes. Stimulation at each amplitude lasts for 10 seconds

Inclusion Criteria: Above 18 Signed informed consents Exclusion Criteria: Pregnancy History of Epilepsy Family history of Epilepsy