Ashvin Shah

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To execute a movement, the CNS must appropriately select and activate the set of muscles that will produce the desired movement. This problem is particularly difficult because a variety of muscle subsets can usually be used to produce the same joint motion. The motor system is therefore faced with a motor redundancy problem that must be resolved to produce(More)
In executing a voluntary movement, one is faced with the problem of translating a specification of the movement in task space (e.g., a visual goal) into a muscle-recruitment pattern. Among many brain regions, the primary motor cortex (MI) plays a prominent role in the specification of movements. In what coordinate frame MI represents movement has been a(More)
Change in behavior and neural activity in skill acquisition suggests that control is transferred from cortical planning areas (e.g., the prefrontal cortex, PFC) to the basal ganglia (BG). Planning has large computational and representational requirements but requires little experience with a task. The BG are thought to employ a simpler control scheme and(More)
Many tasks, such as typing a password, are decomposed into a sequence of subtasks that can be accomplished in many ways. Behavior that accomplishes subtasks in ways that are influenced by the overall task is often described as "skilled" and exhibits coarticulation. Many accounts of coarticulation use search methods that are informed by representations of(More)
Animals, interacting with the environment, learn and exploit the consequences of their movements. Fundamental to this is the pairing of salient sensory input with recent motor output to form an action-outcome pair linking a performed movement with its outcome. Short-latency dopamine (DA) signalling in the basal ganglia has been proposed to support this(More)
Redgrave and Gurney [1] have recently proposed a theory of action discovery in which the occurrence of an unexpected salient sensory event causes short-latency phasic dopamine (DA) neuron activity. Due to conver-gent projections from DA neurons and cortical neurons onto the striatum, the DA signal reinforces (i.e., biases the animal to repeat) preceding(More)
Exploit excess DOFs to best solve multiple subtasks in sequence or concurrently For a given subtask, the coarticulated strategy may q q Coarticulation Often, a complex motor task can be decomposed into a set sequence of subtasks. When there is redundancy in how each subtask is performed, we choose a way that tends to be best for the overall task. This(More)
Often, when animals encounter an unexpected sensory event, they transition from executing a variety of movements to repeating the movement(s) that may have caused the event. According to a recent theory of action discovery (Redgrave and Gurney, 2006), repetition allows the animal to represent those movements, and the outcome, as an action for later(More)
Animals are able to discover the minimal number of actions that achieves an outcome (the minimal action sequence). In most accounts of this, actions are associated with a measure of behavior that is higher for actions that lead to the outcome with a shorter action sequence, and learning mechanisms find the actions associated with the highest measure. In(More)