FUNCTIONAL MODULARITY OF CORTEX

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There are a number of fundamental questions regarding processing of somatosensory information for which there are currently no answers. For instance, Which cortical areas are dependent upon direct projections from the thalamus for their activation? Which areas depend upon direct cortical inputs for activation? What are the serial and parallel cortical pathways by which somatic information is normally processed? In addition, while modular projections between somatosensory cortical areas are known to exist, the contribution of such modular organization to somatic processing is not understood. Finally, earlier studies have demonstrated that somatotopic maps in the cerebral cortex have a remarkable capacity to reorganize in response to perturbations of the peripheral or central nervous system, even in adult primates. However, the mechanisms by which such reorganization occurs is not known. By conducting combined ablation/recording experiments we will determine if direct thalamic projections to the areas (3a, 3b, 1 and 2) comprising anterior parietal cortex (APC) are sufficient to activate neurons in each of these individual areas in the absence of cortical inputs, or alternatively, whether cortical inputs from other APC areas are necessary for somatic activation of these areas. In related experiments within APC, the dependency of one cortical area on another for somatic activation will be determined, and serial and parallel processing pathways identified. Of course knowing the anatomical substrates underlying the functional activation of neurons in APC is essential to obtain a complete picture of how somatosensory information is processed. We plan to conduct combined physiological mapping and anatomical tracing studies in order to determine all cortical and subcortical connections of somatotopically matched portions in each area within APC, determine the convergence or divergence of such connections on projection targets, correlate electrophysiological findings from the ablation/recording experiments with laminar patterns of connections and determine the functional significance, if any, of the interdigitation of projections from each of the areas within APC to the second somatosensory area, SII. Additional anatomical studies will determine if normal projections from brain stem nuclei (trigeminal nucleus or the spinal nucleus of V) to the thalamus can account for expansion of-the face representation in cortex following dorsal rhizotomies. In another study we will determine if the reorganizational capacity of the thalamus, APC and SH is similar, or different, by recording from all three structures in the same animal after peripheral deafferentation of the hand. Understanding the mechanisms responsible for functional reorganization of cortical maps after injury to the central and peripheral nervous system may allow us to harness this immense reorganizational capacity of cortex for therapeutic benefit.