| Abstract: | Although there have been reports of sparse projections fromtemporal areas TE, TF, and even TH to area V1, it is generallybelieved that cortical afferents to V1 originate exclusivelyfrom prestriate areas. Injections of anterograde tracers inanterior occipital and temporal areas, however, consistentlyproduce labeled terminals in area V1. In order to confirm theseresults and display the full range of foci projecting to V1,we injected V1 in two monkeys with the retrograde tracer fastblue. Feedback connections were found, as expected, from severalprestriate areas (V2, V3, V4, and MT). These originate fromneurons in layers 3A and 6. Connections were also found fromseveral more distal regions, namely, areas TEO, TE, TF, TH,and from cortex in the occipitotemporal and superior temporal(STS) sulci. Filled neurons occurred in two small foci in thecaudal intraparietal sulcus. These more distal feedback connectionstend to originate only from layer 6. An additional injectionof the retrograde tracer diamidino yellow in area V2 of oneanimal revealed a similarly widespread network of feedback connections.In some areas (In the STS and in TEO), 10–15% of fluorescentneurons were double-labeled. These results indicate that feedback connections to early visualcortex derive from a widespread network of areas, includinglimbic-associated cortices. These connectional patterns testifyto the massive recursiveness of anatomical pathways. As thereare no reports of projections from V1 to anterior temporal cortices,our results also indicate that some cortical feedback connectionsmay not be strictly reciprocal. |
