THE INFLUENCE OF TDCS INTENSITY ON DECISION-MAKING TRAINING AND TRANSFER OUTCOMES.

Transcranial direct current stimulation (tDCS) has been shown to improve single- and dual-task performance in healthy participants and enhance transferable training gains following multiple sessions of combined stimulation and task-practice. However, it has yet to be determined what the optimal stimulation dose is for facilitating such outcomes. We aimed to test the effects of different tDCS intensities, with a commonly used electrode montage, on performance outcomes in a multi-session single/dual-task training and transfer protocol. In a pre-registered study, 123 participants, who were pseudorandomised across four groups, each completed six sessions (pre- and post-training sessions and four combined tDCS and training sessions) and received 20 minutes of prefrontal anodal tDCS at 0.7 mA, 1.0 mA, 2.0 mA, or 15-second sham stimulation. Response time and accuracy were assessed in trained and untrained tasks. The 1.0 mA group showed substantial improvements in single-task reaction time and dual-task accuracy, with additional evidence for improvements in dual-task reaction times, relative to sham performance. This group also showed near transfer to the single-task component of an untrained multitasking paradigm. The 0.7 mA and 2.0 mA intensities varied in which performance measures they improved on the trained task, but in sum, the effects were less robust than for the 1.0 mA group and there was no evidence for the transfer of performance. Our study highlights that training performance gains are augmented by tDCS, but their magnitude and nature are not uniform across stimulation intensity.