An emerging movement within cognitive neuroscience posits that many cognitive processes are a product of goal-directed interactions between actors and environments. A complementary view is the theory of "motor facilitation", which maintains that viewing an object activates the appropriate movements for interacting with it. Thus hypothesized is a strong bi-directional link between conceptual representations of objects and goal- directed actions. Due in part to the novelty of this area of investigation, relevant theories are for the most part highly unconstrained. This proposal makes use of our conceptual model of object-related actions, the 2 Action System model, to frame a theoretically- driven set of predictions that will be tested in an interdigitated series of studies with patients with stroke and cortico-basal ganglionic degeneration syndrome, both of whom exhibit high-level action disorders, healthy subjects, detailed neuroimaging analyses, and transcranial magnetic stimulation. One of the critical hypotheses to be tested is that different types of action representations may be activated under different task demands, with differing predicted time courses, and based upon distinct neuroanatomic substrates. Also to be tested are predictions related to a hypothesized set of constraints on the relationship of motor competence and conceptual organization. Finally, several experiments will relate individual differences in the current status of the motor system, and underlying integrity of brain structures involved in motor planning and execution, to a) activation of previously-existing, natural conceptual representations and b) the ability to develop artificial conceptual object and action representations. These studies will test the hypothesis that the competence of the motor system has highly circumscribed and predicted relevance for both natural concept retrieval as well as artificial concept learning. The proposed work is expected to have broad significance for theories of "selection for action" and "embodied cognition", as well as for accounts of higher-level disorders of motor control. Specifically, the proposed work will 1) provide critical constraints on the contexts in which bidirectional links are observed at the conceptual- motor interface, 2) elucidate the precise representational structure and time-course of activation of object and action representations, 3) anchor relevant constructs in a detailed cognitive-neuroanatomic model, and 4) clarify the nature of conceptual-motor impairments of patients with high-level (cognitive) action disorders.
The proposal describes a series of studies with neurological patients and transcranial magnetic stimulation (TMS) having broad significance for our understanding of clinical disorders of object-related action (apraxias). These disorders are extremely common and disabling in both stroke and degenerative dementia, yet have been the subject of comparatively little research. The proposed experiments will focus on clarifying the mechanisms and interactions of neural systems responsible for coding different types of object-related action, and are a critical missing step in the design of theoretically and empirically informed approaches to treatment.
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