Priming Expectations and Motor Learning With tDCS

Transcranial direct current stimulation (tDCS) is currently being investigated by the scientific community as an intervention to improve motor learning in the context of neurorehabilitation (e.g., recover lost motor function after stroke) and performance enhancement (e.g., improve sports or technical skill training). More importantly, consumers believe that tDCS works. The expectation surrounding the benefits of tDCS for skill enhancement is so pervasive that the technology is sold for less than $200 and highly rated by the general public on Amazon.com. At the same time, there is considerable skepticism within the motor control field regarding the efficacy and mechanism of action of tDCS on motor learning, driven by highly irreproducible and equivocal findings between and even within laboratories.

How effective is tDCS, and could the positive effects of tDCS be attributable in part to a strong placebo effect? Placebo effects (i.e., a positive expectation associated with positive treatment outcomes), are well documented in other interventions like surgeries and pharmaceuticals, but have not been investigated in detail for tDCS, particularly in the motor domain. The lack of knowledge or consideration of the placebo effect may therefore explain why tDCS findings are so inconsistent within motor learning. Thus, the overall aim of this project is to determine whether people's expectations about tDCS change as a function of information about tDCS itself, and whether these changed expectations modulate the effects of tDCS on motor learning.

Transcranial direct current stimulation (tDCS) is a noninvasive, safe cortical stimulation technique that has been effectively used for enhancing and inhibiting sensory and motor performance when applied to the responsible cortical areas in healthy adults. For instance, anodal tDCS of primary motor area can improve motor execution. Recent research has investigated whether it is the expectation of receiving tDCS that has a greater impact on behavioral outcomes compared to the actual application of tDCS. This is important as many domains of science are challenged to reproduce previous research demonstrating a positive effect of tDCS on behavior. Thus, to decipher legitimate effects of tDCS on behavior it is important to quantify and compare how changes in behavior are related to tDCS, a key metric related to strength of the placebo effect, and how malleable these placebo effects are.

Individuals may participate in this study for up to four sessions (up to 3 training sessions and up to 1 follow-up visit, as assigned) in the span of approximately one week. The investigators expect that individuals will spend up to one hour during the training sessions, and (if applicable) around 15 minutes to complete the follow-up visit, if assigned. The follow-up visit would occur one week after the final training session.

This is a double-blind study in which participants will be randomly assigned to specific intervention methods.

Inclusion criteria

• Must be 18 or older. Right-hand dominant
• Right-hand dominant

Exclusion criteria

• Mixed-handed or ambidextrous
• Left-hand dominant
• Seizure(s)
• Head injury resulting in a loss of consciousness that has required further investigation (including neurosurgery)
• Migraines
• Current medical diagnosis of a phycological or neurological condition
• Any metal in head (outside of mouth) such as shrapnel or surgical clips
• Any implanted devices (e.g. cardiac pacemaker, brain stimulator)
• Skin condition on scalp (e.g. psoriasis)
• Head wound that has not completely healed
• Adverse reactions to tDCS or any other brain stimulation technique (e.g. TMS, tRNS)
• Pregnant
• Currently taking prescription medications or are self-medicating (including recreational drug use), other than the contraceptive pill?