Probing movement decision processes with transcranial current stimulation techniques

In decision making experiments with humans, a typical approach is to monitor behaviour and brain activity in reference to sensory input. In this thesis we explore the possibility of using electrically based non-invasive brain stimulation techniques such as transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS) and transcranial random noise stimulation (tRNS) to probe ongoing decisions regarding movement as they are being developed. We attempt to do this in a principled way by rooting our approach in the field of perceptual decision making, relying heavily on models of evidence accumulation to bounds. In this manner, we address decisions relating to self-initiated movement, where we show that tACS can modulate the probability of self-initiated key-presses in a phasic manner and discuss this in the context of mechanistic explanations of the readiness potential such as the threshold crossings of an Ornstein–Uhlenbeck process, and a biophysically plausible neural network model. In a second study, we examine the development of a decision variable in the long-latency stretch reflex during a typical random dot motion discrimination task while tDCS is applied. Finally, we also show that tRNS can reduce reaction times while responding to stimuli during the 'Simon effect' task in a manner consistent with modulation of thresholded accumulators but unrelated to stimulus-response conflict.Open Acces