This application seeks funding for a coordinated research program consisting of experiments on anesthetized squirrel monkeys and simulation studies of a neurobiologically-faithful neural network. The animal experiments will focus on the anterior parietal (SI) cortical response to constant-velocity brushing stimuli applied to the monkey hand, and will employ a newly-developed functional imaging technology (near-infrared - IR - optical imaging). The IR imaging method will be used (l) to observe and characterize development of the large-scale spatiotemporal patterns of SI activity produced by such stimuli and, in the same experiments, (2) to direct the placement of microelectrode penetrations so that the discharge activity of single neurons and small neural aggregates is sampled from different functionally characterized regions of the stimulus-evoked global activity pattern. The stimulus conditions to be employed were selected because of their previously demonstrated capacity to produce (1)- modifications of human subjects' judgements of moving stimulus attributes such as the on/off locus, traverse length, and direction of movement; (2) short-term changes in SI neuron response to tactile motion within the receptive field; and/or (3) large-scale reorganization, with repetitive stimulus application, of the stimulus-evoked global SI activity pattern. Mechanistic explanations for the neurophysiological and IR imaging observations obtained in the animal experiments will be sought through coordinated simulation studies of a model neural network which includes explicit formulations of (l) a recently described manner of SI topographical organization (the "segregate" plan of organization), (2) the radial and lateral intrinsic connectivity of SI, (3) the "classical" fast- acting GABAergic and glutaminergic neurotransmitter systems, as well as the cholinergic neuromodulatory system whose actions are of longer time course, (4) a subset of the repertoire of cellular/molecular mechanisms (including voltage- and/or agonist-gated membrane ionophores) characteristic of neocortical neurons, and -(5) the non-linear interactions between the different dendritic compartments of individual SI neurons.