Mechanisms of Recovery from Motor Stroke

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Low-frequency (0.1-4 Hz) neural activity during movement, which disappears after injury to motor territory of the rat cerebral cortex, may represent some neural process that is required to accurately reach and grasp pellets. The restoration of this low-frequency signature is associated with recovery, but the calculation or purpose it subserves in the execution of movement remains unknown. We recorded unit activity from Layer V in the bilateral motor cortical areas in the rat during pellet retrievals following an ischemic injury to the homotopic caudal forelimb area (CFA; rodent M1 homolog). Statistically significant changes in the per-channel multi-unit spike counts as a function of movement were identified in a subset of units. In general most units with movement-related correlations in spiking did not exhibit inter-day changes in a stereotyped way that correlated with functional outcomes. By contrast, when we recovered a linear approximation of the first-order system dynamics (i.e. jPCA), we made two interesting findings. First, even the multiple least-squares (MLS) optimal regression did not generally capture dynamics during the first 1-2 weeks after injury, despite the presence of units with movement-related correlations in spiking during this period. Second, the interaction effect for generalized linear mixed-effects model terms for the variance captured by both the MLS and the jPCA system approximations was statistically significant in predicting the likelihood of pellet retrieval success on a given postoperative day. These correlative findings suggest that a stable fixed point structure is required by the dynamical system that relates the cortical neural state to the generation of accurate movements. Preliminary data and simulations are provided to illustrate a simple way that plasticity in sprouting cortical pathways for sensory information could alter the BIBO filter stability of such a system, which may be a key determinant of recovery after stroke.