Implicit encoding of action values in the human primary motor cortex.
(2016) Neuroscience of Decision-Making Conference — Location: Montreal - Canada (2.May.2016)
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- Abstract
- In the present study, we investigated the functional contribution of the human primary motor cortex (M1) to the implicit encoding of action values during motor decisions. In two series of experiments, continuous theta burst stimulation (cTBS) was exploited to alter activity in left M1 while participants performed a decision-making task in which the reward associated with their responses (right hand finger movements) depended on an implicit (undisclosed) value-based rule. In Experiment 1, subjects were provided with two days of practice and cTBS occurred in the middle of Day 2, once the subjects had learned the implicit rule and were ready to use it in the next blocks to choose their responses, as evident in the control group (cTBS over the right somatosensory cortex). In Experiment 2, subjects were given three days of practice and cTBS occurred either at the beginning of Day 1 (before learning) or in the middle of Day 3, while subjects were proficient in using the implicit rule. Interestingly, the implementation of the implicit value-based rule was absent in the group receiving M1 cTBS in the middle of Day 2 (Experiment 1). Oppositely, disrupting M1 before learning (Experiment 2) led to an early and enhanced encoding of the implicit rule during Day 1. Finally, the use of the implicit rule was unaffected when M1 was disrupted in the middle of Day 3 (Experiment 2). Our results suggest that M1 might belong to the brain network underlying the encoding of action values during motor decisions. In Experiment 1, M1 was left undisrupted during learning (until the middle of Day 2) and could have encoded – in concert with other reinforcement learning-related structures such as the basal ganglia or the medial frontal cortex – the implicit value-based rule. A subsequent disruption of M1 in Day 2 might have then perturbed the whole network, impeding the implementation of the learned implicit rule. Of note, when realized in the middle of Day 3 (Experiment 2), M1 cTBS had no impact on the way subjects used the implicit rule; this indicates that the effect of cTBS was dependent on the phase at which it was applied during learning (i.e., more or less labile/stabilized phase of learning). Finally, the disruption of M1 before learning (Experiment 2) might have led to an over-compensation of the aforementioned reinforcement learning-related structures, leading to an increased reliance on the implicit rule from the very beginning of the decision making task.
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Derosiere, G., Demaret, S., Vassiliadis, P., Zenon, A., & Duque, J. (2016). Implicit encoding of action values in the human primary motor cortex. Neuroscience of Decision-Making Conference, Montreal - Canada. https://hdl.handle.net/2078.5/181041