Abstract
Transcranial direct current stimulation (tDCS) uses a weak electrical current applied to the scalp to alter neural excitability, whereby anodal stimulation increases and cathodal stimulation decreases the excitability of underlying structures. Excitability changes to the motor cortex have also been linked to changes in motor performance (e.g., reaction time; RT). A previous study used tDCS with electrodes placed over both motor cortices in a choice RT task involving left or right wrist extension. They predicted that RT would be faster contralateral to the anode and slower contralateral to the cathode. However, RT was decreased for both limbs, irrespective of electrode placement. This unexpected finding may have been due to a reversal in the effect of cathodal stimulation resulting in increased excitability under both electrodes. To investigate this possibility, neural excitability was monitored using transcranial magnetic stimulation (TMS) over left motor cortex during a choice RT task following bi-hemispheric tDCS. In seven participants, three tDCS protocols were applied (anode left-cathode right, anode right-cathode left, and sham; counterbalanced), with excitability and choice RT measured at 6-minute intervals for 36 minutes. Preliminary analyses indicate that choice RT was marginally reduced (p=.25) in each hand following only bi-hemispheric tDCS with anode-left. Although non-significant (p=.16), excitability was also largest following tDCS in the anode-left protocol compared to sham. While further data collection is required to confirm these results, they suggest that bi-hemispheric tDCS with the anode over left motor cortex can reduce RT bilaterally through changes in cortical excitability.Acknowledgments: Supported by NSERC and the Ontario Ministry of Research and Innovation and Science