V1 to V2 Projections in Normal Vision and Amblyopia

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In primates, visual information passes from the primary visual area (V1) to the second visual area (V2) before distribution to higher cortical areas. An accurate description of the projections linking V 1 and V2 is crucial for understanding how the brain deciphers visual images. Prior studies have shown that V2 is partitioned into three compartments, known as pale, thin, and thick stripes, defined by their content of a metabolic enzyme called cytochrome oxidase (CO). Our principal goal is to describe the anatomical projections from V1 to each V2 stripe compartment. In Specific Aim #1 we will make injections of a retrograde tracer into single CO stripes in V2 of normal macaques. The resulting pattern of labeled cells in V1 will be correlated with the V2 stripe that received the injection. Our preliminary data indicate that, contrary to a previous report, layer 4B and interblobs both project to thick stripes and pale stripes. In Specific Aim #2 we will make paired injections of two different tracers into adjacent thick stripes and pale stripes to determine if different subpopulations of cells in layer 4B and interblobs project to these V2 compartments. In Specific Aim #3 we will make injections of [3H]proline into V1 to correlate patches of efferent projections with CO staining patterns in V2. In Specific Ai/s #4 we will examine the V1->V2 projections in animals raised with early monocular deprivation. These experiments will advance our knowledge of the mechanisms underlying amblyopia, an important cause of visual loss that affects 2% of the American population. We hypothesize that a selective loss of V1->V2 projections emanating from the ocular dominance columns serving the deprived eye contributes to the loss of vision in amblyopia.