Effects of transcranial direct current stimulation on cortical and subcortical persistent activity

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The ability to guide our responses on the basis of plans and goals is a fundamental facet of human behaviour. Working memory (WM) - the ability to temporarily retain information- such as when one holds in mind a phone number one wishes to dial, is one of the most studied aspects of cognition. Two brain areas, the prefrontal and posterior parietal cortex, have been most closely linked to WM performance. Non-invasive experimental techniques that allow temporary modifications of brain activity have the capability to add greatly to our understanding of WM, since they allow establishment of a direct relationship between activity in a particular brain area and WM ability. Transcranial direct current stimulation (tDCS) is a safe, non-invasive method of brain stimulation that is rapidly gaining in popularity. In this technique, weak electrical currents are applied to surface of the head, which are believed to lead to subtle, long-lasting changes in excitability of the brain. tDCS of both prefrontal and parietal cortex has been shown to influence WM performance in humans but our understanding of the changes in brain activity responsible these cognitive changes is limited by our lack of animal models of tDCS. Non-human primates can be readily trained to perform WM tasks, and have similar cortical areas to humans. The objective of this research is to advance our understanding of the effects of tDCS on brain activity by combining tDCS and recordings of brain activity in the prefrontal and posterior parietal cortex of rhesus macaques performing a WM task.