The primary sensory areas of neocortex perform complex transformations of the information flowing into them. They are essential for normal perception and behavior, and it is generally agreed that the capabilities that are uniquely human, and uniquely mammalian, derive from the circuits of the neocortex. Under pathological conditions, such as a decrease in synaptic inhibition, the normal activity of a local neocortical circuit can be usurped by large, synchronized burst of epileptiform excitation in all of its neurons. In the primary somatosensory (SmI) area of the rat, neural operations are carried out by discrete, repeating units of interconnected neurons; each unit can be visually identified by a barrel-shaped aggregate of small cells in cortical layer IV. Cortical barrels are representative of a nearly ubiquitous property of neocortex in all mammals: a strongly vertical, or columnar, neuronal organization. The proposed research will investigate the morphological and physiological properties of neurons and their synaptic connections within rat barrel cortex. A method has been devised for visualizing individual barrels in living cortical slices in vitro. Specific investigation include: 1) Intracellular recordings plus dye injections to correlate distinctive membrane properties with the somadendritic shape and axon patterns of neurons, 2) Electrophysiological techniques and axonal labelling methods to delineate interlaminar and interbarrel connections, 3) Direct measurement of the characteristics of unitary synaptic potentials (the influence of one neuron upon one other neuron), 4) A test of the hypothesis that a subpopulation of middle layer bursting neurons initiates and disperses synchronized epileptiform activity. This interdisciplinary approach should provide a uniquely detailed view of the functional properties of a local neocortical area. The data obtained will contribute to the formulation of theories of cortical information processing, as well as suggest mechanisms for the genesis and control of partial seizures.