A number of functional properties of cells in the cat's area 17 are dependent on short pathways contained entirely within the gray matter. Because of the importance of these intrinsic circuits, it would be worthwhile to analyze their anatomical organization. However, standard neuroanatomical tracer methods are not suited to this task. I propose to develop an alternative method suitable for tracing intracortical connections. A small group of cortical neurons will be excited by continuous iontophoretic application of L-glutamate. Simultaneously, (14C) 2-deoxy-D-glucose (2DG) an agent taken up by active cell bodies and processes, will be administered systemically. It is hoped that 2DG will label not only the neuronal cell bodies directly activated by L-glutamate but also their distant axon terminals, which will be activated indirectly as a result of spike conduction along the axons. I will apply this method to area 17 in the cat, with the intention of asking whether projections arising from small sets of functionally similar neurons radiate uniformly into the surrounding cortex or are distributed in a patchy pattern. The findings should throw light on mechanisms underlying the stimulus selectivity of cortical cells. As a pilot study of a technique which, if it proves feasible, will have broad applications, this project qualifies for support under the Small Grant Program. In accord with the aims of the Small Grant Program, the principal investigator is at the beginning of his independent research career and is not currently being supported by other grants. The project conforms to a current NEI objective, viz. "to define how neurons or neuron sets are interconnected" in the visual system (Vision Research, A National Plan: 1983-1987, p.34).