Contribution of the primary motor cortex to perceptual and reward-based decision processes
(2015) Department of Psychology of Ghent’s University; INVITED CONFERENCE — Location: Ghent - Belgium
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- When one makes the decision to act in the physical world, the neural activity in primary motor cortex (M1) encodes the competition between potential action choices. Traditional approaches have viewed this activity as reflecting the unfolding of the outcome of a decision process taking place upstream. However, a recently emerging theoretical framework posits that the motor neural structures directly contribute to the decision process. Following this view, the selection of any behavior would directly emerge from the top-down regulation of M1 activity allowing the integration of cognitive variables that drive decisions such as the evaluation of the potential reward associated with each competing action. Here, we tested this hypothesis by assessing the effect of M1 disruption on the ability of human subjects to make action choices based on both perceptual and value-based decision processes. Participants were instructed to select between index and middle finger key-presses with the right hand as quickly as possible according to the color of an imperative signal presented on a computer screen. The colors ranged from clearly green to clearly red with, in between, a set of more ambiguous tints with lower saturation levels. Importantly, this finger choice was biased such that, to earn more money, the subjects also had to take into consideration the shape of the stimulus (circle or square, undisclosed manipulation). As such, the motor response depended on both a perceptual decision process – i.e., discriminating the color of the stimulus according to instructed rules - and a value-based decision process relying on reinforcement learning. The experiment extended over two sessions occurring at 24-hours interval. Each experimental session consisted in six blocks of 4-minutes duration. Continuous theta burst stimulation (cTBS) was exploited to disrupt left or right M1 activity in two different groups of subjects. It was applied after the third block of the second session (i.e., at the middle of the second session), once subjects had learned the task and reached a plateau in their performance (pilot data). Based on our hypothesis, we predicted that left (and maybe right) M1 disruption would alter the operation of the (learned) perceptual and/or value-based processes. The experiment also involved a control condition in which cTBS was applied over the right somatosensory in a third group of subjects. Preliminary data collected in the control group reveal a progressive acquisition of the perceptual decision process throughout the first session, as reflected by an increase in the proportion of correct responses in accordance with the explicit instructions. Interestingly, the operation of the value-based decision process was not evident in the first session but was present from the first block of the second session. We will present data showing the impact of M1 cTBS on the operation of these perceptual and value-based decision processes.
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Derosiere, G. (2015). Contribution of the primary motor cortex to perceptual and reward-based decision processes. Department of Psychology of Ghent’s University; INVITED CONFERENCE, Ghent - Belgium. https://hdl.handle.net/2078.5/122267