Does the Direction of Current Flow Using Transcranial Direct-Current Stimulation (tDCS) Affect One’s Ability to Perform Motor Tasks?

Transcranial direct-current stimulation (tDCS), is a non-invasive, painless brain stimulation treatment that uses direct electrical currents to stimulate specific parts of the brain. This is achieved by placing two electrodes--one positive (the anode) and one negative (the cathode)--on the scalp and running current across them. Altering the cortical excitability in this manner has been associated with changes in a variety of cognitive and motor tasks, those thought to be controlled by the underlying regions. While most of the existing literature has focused on the effects of placing the anode over the target region (often benefitting the associated performance), there is some evidence suggesting that switching the polarity and placing the cathode over the target region reverses the behavioral effect, such that an improvement might turn into a decrement. For my Senior Project, I conducted an experiment manipulating the polarity of the electrode placed over my target region of interest (the left dorsolateral prefrontal cortex (L DLPFC) in order to test whether cathodal stimulation temporarily impairs motor skill performance. As far as I am aware, all previous tDCS work targeting this region has focused exclusively on anodal stimulation as it pertains to motor skill performance. I compared the accuracy and reaction times involved in a standard motor task (using a finger-tapping task) across three different (within-subject) conditions: (a) anodal stimulation (b) cathodal stimulation and (c) sham stimulation on the L DLPFC. In contrast to anodal stimulation, which I predict will replicate an improvement in motor performance, I predict that cathodal tDCS will lead to a relative decrease in reaction time from baseline. These conditions should be distinct from the sham condition, for which no reliable change from baseline is expected, save for any changes reflecting expectancy effects. The result revealed an unexpected reversed effect of Cathodal tDCS in RT which suggests that Cathodal tDCS may also have the ability to improve motor ability. Potential possibilities and limitations of this study were discussed