SYNCHRONIZING RETINAL ACTIVITY IN BOTH EYES DISRUPTS BINOCULAR MAP DEVELOPMENT IN THE OPTIC TECTUM

Spatiotemporal correlations in the pattern of spontaneous and evoked r etinal ganglion cell (RGC) activity are believed to influence the topo graphic organization of connections throughout the developing visual s ystem. We have tested this hypothesis by examining the effects of inte rfering with these potential activity cues during development on the f unctional organization of binocular maps in the Xenopus frog optic tec tum, Paired recordings combined with cross-correlation analyses demons trated that exposing normal frogs to a continuous 1 Hz of stroboscopic illumination synchronized the firing of all three classes of RGC proj ecting to the tectum and induced similar patterns of temporally correl ated activity across both robes of the nucleus. Embryonic and eye-rota ted larval animals were reared until early adulthood under equivalent stroboscopic conditions. The maps formed by each RGC class in the cont ralateral tectum showed normal topography and stratification after str obe rearing, but with consistently enlarged multiunit receptive fields , Maps of the ipsilateral eye, formed by crossed isthmotectal axons, s howed significant disorder and misalignment with direct visual input f rom the retina, and in the eye-rotated animals complete compensatory r eorientation of these maps usually induced by this procedure failed to occur, These findings suggest that refinement of retinal arbors in th e tectum and the ability of crossed isthmotectal arbors to establish b inocular convergence with these retinal afferents are disrupted when t hey all fire together, Our data thus provide direct experimental evide nce that spatiotemporal activity patterns within and between the two e yes regulate the precision of their developing connections.