Measuring Expectancy Effects of Transcranial Direct Current Stimulation on Motor Learning

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PROJECT SUMMARY/ABSTRACT Transcranial direct current stimulation (tDCS) is a type of non-invasive brain stimulation that applies constant, low levels of direct electrical current to the scalp to modulate brain excitability. While tDCS is used in neurorehabilitation to augment motor learning, the evidence supporting this use is somewhat inconclusive, with many reports of null findings. Current study designs do not adequately control for participants’ expectations about tDCS, which may exert a powerful placebo effect on motor learning (as well as cognition, pain, or anxiety). The long-term goal is to maximize motor learning by considering person-centered perceptions of brain stimulation in addition to the effects of electrical stimulation itself. The overall objectives in this R21 application are to demonstrate that expectations about tDCS (i) play a significant role in enhancing motor learning, independent of any real stimulation (i.e., an expectancy effect vs. a treatment effect of tDCS) and (ii) can be leveraged to maximize the benefits of tDCS in enhancing motor learning. The central hypothesis is that higher expectations about the efficacy of tDCS are associated with more skill improvement following motor practice, even in placebo conditions (sham tDCS). The rationale for this project is that considering people’s expectations about tDCS will not only improve the reproducibility and rigor of future tDCS research, but will also maximize the overall benefit of tDCS for improving and restoring health. The central hypothesis will be tested by pursuing two specific aims: 1) Determine the extent to which priming expectations of tDCS will modulate motor skill learning and 2) Determine the extent to which sham tDCS improves motor skill learning. For the primary aim, suggestive information will be used to prime participants’ expectations to be more positive or more negative prior to motor training with sham stimulation. For the secondary aim, the effects of unprimed tDCS during motor training will be compared to a control group with no exposure to the tDCS device at all (motor training only). The research proposed in this application in innovative, in the applicant’s opinion, because it is a major departure from the status quo of tDCS research by considering and measuring how participants’ expectations of tDCS affect motor learning and rehabilitation, independent from any effect of the stimulation itself. The proposed research is significant because it is expected to shift current research and clinical practice paradigms that use tDCS for treatment. Ultimately, adopting an integrative health approach that considers how people’s perceptions and expectations of tDCS (and other non-invasive brain stimulation techniques) will have a greater impact on health and health care than simply focusing on parameters of the electrical stimulation itself.