Abstract
Rewards associated with actions are critical for motivation and learning about the consequences of one’s actions on the world. The motor cortices are involved in planning and executing movements, but it is unclear whether they encode reward over and above limb kinematics and dynamics. Here, we report a categorical reward signal in dorsal premotor (PMd) and primary motor (M1) neurons that corresponds to an increase in firing rates when a trial was not rewarded regardless of whether or not a reward was expected. We show that this signal is unrelated to error magnitude, reward prediction error, or other task confounds such as reward consumption, return reach plan, or kinematic differences across rewarded and unrewarded trials. The availability of reward information in motor cortex is crucial for theories of reward-based learning and motivational influences on actions.
Highlights
How the brain learns based on action outcomes is a central question in neuroscience
We recorded from two 96-channel microelectrode arrays (Fig 1B, Blackrock Microsystems), chronically implanted in the primary motor cortex (M1) and the dorsal premotor cortex (PMd)
We asked if the premotor and motor cortices, implicated in planning and executing movements, might represent the reward associated with those movements
Summary
How the brain learns based on action outcomes is a central question in neuroscience. Theories of motor learning have usually focused on rapid, error-based learning mediated by the cerebellum, and slower, reward-based learning mediated by the basal ganglia (for a review, see [1]). Different combinations of reward and sensory feedback result in different learning rates. Positive and negative rewards influence motor learning differently [2, 3]. When reward is combined with sensory feedback, it can accelerate motor learning [4]. Reward is a fundamental aspect of learning [5, 6, 7, 8]. Various reward signals have been characterized in the midbrain, prefrontal and limbic cortices [9, 10, 11, 12, 13]. We do not know how neurons in the motor system obtain the reward information that could be useful for planning subsequent movements
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