The goal of this proposal is to determine how posterior parietal cortex (PPC) of primates is organized and functions in sensorimotor behavior. Posterior parietal cortex is currently thought to play a critical role in the planning and the initiation of various sensory guided behaviors such as reaching, grasping, and looking, while providing outputs to premotor and motor cortex that organize the motor behaviors. Over the last grant period we have greatly extended this important framework by providing clear evidence that approximately 7-8 different subregions or domains of PPC initiate different classes of movements when electrically stimulated in monkeys and other primates (grasping, reaching, looking, head defense, body defense, aggressive expression, climbing). Moreover, we defined functionally matching domains in premotor cortex and primary motor cortex where matching classes of complex movements are evoked by electrical stimulation. We have identified anatomical connections between matching domains, and visual and somatosensory inputs to PPC domains. We now plan experiments to reveal the functional relationship between matched PPC and motor domains, how domains of different types interact, and how domains differ in the proportions and types of visual and somatosensory inputs they receive to guide motor behaviors. We also expect to determine if matching or electrically evoked behaviors recover after we lesion specific domains, and if so, how the brain reorganizes to mediate behavioral recoveries. Our methods of investigation include electrical microstimulation of domains, the chemical inactivation or potentiation of domains, the reversible inactivation of domains with a cooling probe, behavioral studies after lesions of domains, the recordings of neural activity with arrays of microelectrodes, and the use of anatomical and histological methods to reveal brain connections and structural subdivisions of the cortex. The results are expected to produce a new and greatly expanded understandings of the functional organization of PPC in primates, how functional domains in PPC interact with each other, how they are guided by sensory information, and how they mediate different classes of behaviors by activating matching parts of frontal motor fields. The results will lead to a better understanding of the impairments that resul in humans after PPC damage, and indicate the levels and time courses of recovery. The results will also suggest modes of clinical treatment that are open to experimental validation.
The goal of our project is to determine how subregions of posterior parietal cortex mediate classes of useful behaviors, such as reaching and grasping food. These studies will reveal neural networks for such behaviors and provide an understanding that will have clinical relevance for treatments and recoveries after stroke or other damage to posterior parietal cortex.
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