Epicranial Direct Current Stimulation Suppresses Harmaline Tremor in Rats

Essential tremor (ET) is the most common neurologic movement disorder worldwide. It is characterized by a postural tremor, mostly in the upper extremities, causing difficulties in daily activities that may lead to social exclusion. Some patients with ET do not respond well to or do not tolerate medication. Thus, deep brain stimulation can be offered. In a recent study, we proposed a novel neuromodulation technique called epicranial current stimulation (ECS) that works in a minimally invasive way by placing the electrodes subcutaneously under the skin and directly over the skull. In this study, we investigated the feasibility of using epicranial direct current stimulation (EDCS) to suppress tremor in a rat harmaline ET model.

In experiment 1, seven Sprague Dawley rats were implanted with ECS electrodes placed over the motor cortex (MC) and the cerebellum to investigate whether stimulating between them could suppress tremor. In experiments 2 and 3, eight rats were implanted with ECS electrodes placed over the MC, cerebellum, and the rostral skull to separate the effects on tremor caused by stimulating each target. During each experiment, the rats were injected with harmaline, which induced tremor that was quantified using an accelerometer. EDCS was then applied through the different electrode configurations to evaluate their tremor suppression effectiveness.

Results from experiment 1 showed that MC_cathode-Cerebellar_anode suppressed tremor compared with stimulation-OFF but MC_anode-Cerebellar_cathode did not. Furthermore, experiments 2 and 3 showed that it was the cerebellar anodal electrode that was driving tremor suppression.

Cerebellar EDCS suppressed harmaline tremor in rats in a polarity-dependent manner. EDCS could be a promising neuromodulation method for patients with ET.