Using transcranial direct current stimulation (tDCS) to improve working memory in schizophrenia and healthy controls: investigating the role of current strength

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Working memory is essential for key cognitive processes including reasoning, language comprehension and learning. Many neurological and psychiatric disorders result in working memory impairments and any technique that may enhance working memory would be very useful. For example cognitive dysfunction is a core feature of schizophrenia. The main areas affected include attention, memory and executive functioning; with working memory in particular frequently affected. These difficulties have been shown to negatively influence patients’ psychosocial functioning. Traditional treatment approaches have resulted in small gains at best. It is therefore essential that novel treatment approaches are explored. Recent research has suggested that brain stimulation, and in particular transcranial Direct Current Stimulation (tDCS), may have a role to play in improving cognition. While tDCS has been shown to improve working memory in a number of conditions, to date there have been no tDCS studies looking at the enhancement of working memory in schizophrenia. tDCS has been shown to be safe, with very few side effects. It involves the application of a very weak electrical current (1-2mA) using two surface electrodes (anode and cathode) to the head. The use of tDCS on the cortex has been shown to alter the how likely nerve cells are to fire and the effect generally has been shown to last up to 1 hour after stimulation. To date, a number of studies have examined the effect of tDCS on working memory, with some mixed results. While some studies have shown improvements in working memory during a session of tDCS (Boggio et al., 2006), other recent research has found no significant improvement (Marshall et al., 2005). A recent study has shown significantly better performance in a working memory task completed during an application of tDCS to the dorsolateral prefrontal cortex (DLPFC), a part of the brain associated with this type of thinking activity (Fregni et al., 2005). However, despite the breadth of tDCS research being undertaken, many questions remain regarding the most effective stimulation parameters, particularly with respect to optimal current strength (i.e. 1 or 2 mA). The current study aims investigate this in healthy participants and patients with schizophrenia.

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