UBC Theses and Dissertations
Light-based mapping of mouse sensorimotor cortex Harrison, Thomas Clarke
The motor cortex controls voluntary, skilled movements. It possesses a basic somatotopic organization, but its fine structure remains controversial. Although the reorganization of motor cortex after brain injury is believed to be a critical part of behavioral recovery, our understanding of this process has been constrained by technical limitations. Conventional methods for mapping the motor cortex rely on the insertion of intracortical stimulating electrodes into the brain. We developed a new method for light-based motor mapping that is faster, less invasive, and better suited to repeated mapping in both acute and longitudinal studies. Using this technique, we identified a functional subdivision of the mouse forelimb motor representation according to the direction of movement. Pharmacological and anatomical experiments revealed that the expression of complex movements requires the intact function of the intracortical circuitry, whereas the basic topography of movement in motor cortex may arise primarily from the arrangement of output projections. We also refined methods for intrinsic optical signal sensory imaging, which can be combined with light-based motor mapping to obtain a more complete map of sensorimotor cortex. Performing light-based mapping of sensorimotor cortex for weeks before and after targeted photothrombotic stroke allowed us to monitor cortical reorganization on an unprecedented timescale. We found that if forelimb somatosensory cortex was destroyed by targeted stroke, the forelimb motor cortex was able to incorporate a reorganized sensory map. As a consequence of this increased integration of sensory and motor function after stroke, however, the structure of the motor map was altered, evidenced by a decrease in spatial autocorrelation. Strokes in motor cortex caused increased motor output in peri-infarct cortex, but had no effect on the location or sensitivity of the forelimb somatosensory representation. Light-based motor mapping has provided new insights into both the functional organization of motor cortex and its capacity for spontaneous reorganization after stroke.
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