The long-range goal of the studies funded by this grant is to provide functionally-relevant, anatomical descriptions of the patterns of divergence and convergence of the central nervous system pathways involved in somatic sensation. Because of the complexity of the interrelationships between the elements in these pathways, these descriptions are necessary before an understanding of the neural mechanisms underlying various aspects of somatic sensation, such as touch, pain and kinesthesia can be achieved. The work proposed for the next grant period is focused upon two regions---the odrsal column nuclei (DCN) and the zona incerta (ZI). The results obtained so far on DCN tentatively indicate that the DCN are involved in at least two independent systems. One is the previously well-known dorsal column-DCN-ventrobasal complex (VB)-somatic sensory cortex relay pathway with its associated """"""""lemniscal"""""""" characteristics. The other, previously unrecognized system consists of a separate set of DCN neurons (of unknown characteristics) and the interconnections of these neurons with other targets besides VB. Studies in the next grant period will continue ongong experiments in which multiple labeling strategies are being used to obtain as complete a description as possible of the spatial, morphological and collateralization characteristics of DCN's multiple efferent systems. If time permits, additional electrophysiological studies will be initiated to investigate the somatic response properties of some of the differentially-projecting neurons in DCN. One of DCN's major diencephalic targets besides VB is the zona incerta. The ZI in addition receives dense input from the reticular formation and cerebellum. Although these and other results indicate that ZI is a diencephalic region that, like VB and the intralaminar complex, has some function in somatic sensation, ZI has been relatively ignored in this regard. Accordingly, other studies proposed for the next grant period will use multiple labeling strategies and electrophysiological techniques to examine the connective anatomy of ZI together with the somatic response properties of its neurons.
The aim of the studies is to provide anatomical and physiological data that will increase our understanding not only of DCN's and ZI's specific somatic sensory functions, but also how their functions relate to those of other parts of the somatic pathways.
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