Contribution of primary motor cortex to perceptual and value-based decision processes
(2015) 11th Congress of the Belgian Society for Neuroscience — Location: Mons
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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 (Cisek, 2007). 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 (Klein et al., 2012; Klein-Flügge et al., 2012). Here, we directly 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 (cTBSleftM1 and cTBSrightM1 groups, respectively). 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, just before both perceptual and value-based processes become operational (pilot data). Based on our hypothesis, we predicted that left (and maybe right) M1 disruption would alter the operation of the perceptual and/or value-based processes. The experiment also involved a control condition in which cTBS was applied over the right somatosensory cortex in a third group of subjects (cTBScontrol group). Motor evoked potentials (MEPs) were recorded throughout the second session in the right (cTBSleftM1) or left (cTBSrightM1 and cTBScontrol groups) first dorsal interosseous muscle in order to test for the effect of cTBS in the three experimental groups. Motor activity was altered following cTBS, as reflected by a significant decrease in MEP amplitudes in both the cTBSleftM1 and the cTBSrightM1 groups; such an effect on MEPs was not observed in the cTBScontrol group. Consistent with our pilot data, the value-based process was operational in the second half of the second session in the cTBScontrol group. Interestingly, the emergence of this value-based decision process was not evident in the cTBSleftM1 group while it was enhanced in the cTBSrightM1 group. The latter result may be due to a release of inter-hemispheric inhibitory influences originating in the (inhibited) right M1, resulting in the facilitation of the homonymous left M1. Of note, the perceptual decision process was unaffected by the M1 virtual lesions. Taken together, the results of the present study provide evidence for a direct and causal involvement of M1 in the implementation of value-based processes underlying motor decisions.
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Derosiere, G., Zenon, A., Alamia, A., Klein, P.-A., & Duque, J. (2015). Contribution of primary motor cortex to perceptual and value-based decision processes. 11th Congress of the Belgian Society for Neuroscience, Mons. https://hdl.handle.net/2078.5/122272