Contents lists available at ScienceDirect NeuroImage journal homepage: www.elsevier.com/locate/neuroimage Primary motor cortex contributes to the implementation of implicit value- based rules during motor decisions Gerard Derosiere ⁎ ,1 , Alexandre Zénon, Andrea Alamia, Julie Duque Institute of Neuroscience, Université catholique de Louvain, Brussels, Belgium ARTICLE INFO Keywords: Action selection Action value cTBS Decision-making Reward ABSTRACT In the present study, we investigated the functional contribution of the human primary motor cortex (M1) to motor decisions. Continuous theta burst stimulation (cTBS) was used to alter M1 activity while participants performed a decision-making task in which the reward associated with the subjects’ responses (right hand finger movements) depended on explicit and implicit value-based rules. Subjects performed the task over two consecutive days and cTBS occurred in the middle of Day 2, once the subjects were just about to implement implicit rules, in addition to the explicit instructions, to choose their responses, as evident in the control group (cTBS over the right somatosensory cortex). Interestingly, cTBS over the left M1 prevented subjects from implementing the implicit value-based rule while its implementation was enhanced in the group receiving cTBS over the right M1. Hence, cTBS had opposite effects depending on whether it was applied on the contralateral or ipsilateral M1. The use of the explicit value-based rule was unaffected by cTBS in the three groups of subject. Overall, the present study provides evidence for a functional contribution of M1 to the implementation of freshly acquired implicit rules, possibly through its involvement in a cortico-subcortical network controlling value-based motor decisions. 1. Introduction When one decides how to behave in the physical world, the neural activity in primary motor cortex (M1) displays modulatory changes that seem to encode the competition between potential action plans (Cisek and Pastor-Bernier, 2014; Thura and Cisek, 2014, 2016). For instance, transcranial magnetic stimulation (TMS) studies in humans have revealed that changes in M1 activity reflect the impact of parameters that guide action selection in the context of decision- making (Bestmann and Duque, 2015; Quoilin and Derosiere, 2015). Motor evoked potentials (MEPs) elicited by TMS over M1 are influenced by the value (Klein-Flugge and Bestmann, 2012; Klein et al., 2012; Mooshagian et al., 2014) or the biomechanical require- ments of actions to be chosen between (Cos et al., 2014), and reflect the cost of having to select a response in a conflicting setting (Klein et al., 2014; Michelet et al., 2010; van Campen et al., 2014). Traditional approaches have viewed these cognitively driven varia- tions in motor activity as reflecting the unfolding of the outcome of a decision process taking place upstream (Donner et al., 2009; Fecteau et al., 2005; Gail et al. 2009; Hare et al., 2011). Following this view, the observed decision-related changes in M1 activity would reflect the accumulated evidence towards a choice but would not be crucial for the decision process itself. These early adjustments could serve to bias the activation of competing motor plans, allowing for a prompt initiation of the selected action(s) at the time of commitment (O’Shea et al., 2007). However, a recently emerging theoretical framework posits that motor decisions may emerge directly, at least in part, from the regulation of M1 activity by cognitive variables (Bijleveld et al., 2014; Gluth et al., 2013, 2014; Hare et al., 2011). More specifically, M1 would belong to a distributed brain network (involving fronto-basal-ganglia loops; Balleine and O’Doherty, 2010) whose goal would be to con- tinuously specify potential motor actions. Based on this hypothesis, activity in M1 would be critical for decision-making as it would represent the information on the basis of which some actions are selected over others (Cisek, 2007; Cisek and Kalaska 2010; Cisek, 2012; Cisek and Pastor-Bernier, 2014; Thura and Cisek, 2014, 2016). In daily life, human decisions are constantly guided by explicit and implicit biases. For instance, when choosing a restaurant on a Saturday night, one typically compares the content and the price of different menus. Besides, the choice will also depend on less conscious features such as previous experience, the type of people sitting inside, as well as the atmosphere, the odor and the music played in the restaurant. http://dx.doi.org/10.1016/j.neuroimage.2016.10.010 Received 26 July 2016; Accepted 5 October 2016 ⁎ Correspondence to: CoActions Lab, Institute of Neuroscience, Université catholique Louvain, Av. Mounier, 53 - Bte B1.53.04, 1200 Bruxelles, Belgium. 1 https://www.coactionslab.com/. E-mail address: gerard.derosiere@uclouvain.be (G. Derosiere). NeuroImage 146 (2017) 1115–1127 Available online 11 October 2016 1053-8119/ © 2016 Elsevier Inc. All rights reserved. MARK