P160 Enhanced biasing effect of prior knowledge on perceptual decision processes following continuous theta burst stimulation of motor cortex

Abstract

Introduction Separate interneuron circuits in human motor cortex (M1) have been suggested to subserve different forms of motor behaviour, but it is not clear what role they play in other aspects such as decision-to-action processes. Objectives We tested whether two distinct interneuron networks in M1 play different roles in perceptual decision-making. Materials & methods 10 participants completed 3 blocks of a decision making task in each of 2 measurement sessions. Participants responded to a left/right visual imperative cue with left/right hand key presses. A random dot kinetogram (RDK) with 2 levels of coherent motion (low, high) preceded the visual cue. In 80% of trials the motion direction of the dots was congruent with that of the imperative cue, and thus could be used to prepare a response in advance. Accuracy and reaction time (RT) associated with correct responses in congruent trials were measured. A controllable pulse parameter transcranial magnetic stimulation (cTMS; Rogue Resolutions Ltd.) device was used to target distinct interneuron circuits in M1 by changing the coil orientation (posterior-anterior, PA; anterior-posterior, AP) and pulse width (45–75 μ s). A continuous theta burst stimulation (cTBS) protocol was applied with AP45 or PA75 pulses, in separate sessions, to the left M1 following the first block of the decision-making task. Results Accuracy of responses was typically ⩾95%, therefore we focus on RTs. As expected, RTs were faster with high versus low RDK coherence (Fig. 1A–D). There was no effect of pulse type on RTs, but ANOVA revealed an interaction of hand, block and coherence (P = 0.029). Calculating the percentage change in RT from low to high coherence trials (Fig. 1E and F) revealed an improvement in RTs for right, but not left, hand responses in high, but not low, coherence trials immediately after cTBS. Conclusion Irrespective of the pulse type, and thus M1 interneuron circuits targeted, cTBS over left M1 enhanced the bias effect for corresponding right hand responses, but only following high coherence RDK. cTBS may have altered the integration in M1 of the sensory evidence from the bias and imperative cue, giving more weight to the bias which normally has a relatively minor influence. Download : Download high-res image (772KB) Download : Download full-size image