The Effects of Transcranial Direct Current Stimulation (tDCS) on Training During a Complex Procedural Task

There is a growing body of literature suggesting transcranial direct current stimulation (tDCS) is effective in accelerating certain types of memory including working memory, language learning, and object recognition. Recent studies have provided new evidence that non-declarative memories such as motor skill acquisition may be enhanced through direct stimulation of motor cortex. Additionally, Galea and Celnik (J Neurophysiol 102:294–301, [10]) showed that inhibition of the prefrontal cortex following motor training led to enhanced procedural memory consolidation. This effort examined the effects of excitatory transcranial direct current stimulation (tDCS) over the primary motor cortex on memory acquisition and inhibitory tDCS over dorsolateral prefrontal cortex in memory consolidation. Thirty-six Air Force members volunteered to participate. They were divided into four groups: anodal tDCS over motor cortex, cathodal stimulation over dorsolateral prefrontal cortex (DLPFC), both anodal tDCS over motor cortex and cathodal tDCS over DLPFC, or sham tDCS over motor cortex and DLFPC. All participants received their stimulation condition while training on a procedural task that required them to identify incoming aircraft as friend or foe. Twenty-four hours after the training session, participants returned to the lab for retention testing. When comparing the day 1 (training) scores to the day 2 (test) score, the results showed the cathodal tDCS group performed 2× better than sham and all real tDCS groups exhibited scores significantly higher than sham. The evidence suggests that inhibition of the prefrontal cortex leads to the greatest improvement in performance. We hypothesize that this is a result of a shift in dominance of the declarative memory system to the non-declarative procedural system, which improves consolidation of the procedural memories gained during training.