DIRECT TEMPORAL-OCCIPITAL FEEDBACK CONNECTIONS TO STRIATE CORTEX (V1)IN THE MACAQUE MONKEY

Although there have been reports of sparse projections from temporal a reas TE, TF, and even TH to area V1, it is generally believed that cor tical afferents to V1 originate exclusively from prestriate areas. Inj ections of anterograde tracers in anterior occipital and temporal area s, however, consistently produce labeled terminals in area V1. In orde r to confirm these results and display the full range of foci projecti ng to V1, we injected V1 in two monkeys with the retrograde tracer fas t blue. Feedback connections were found, as expected, from several pre striate areas (V2, V3, V4, and MT), These originate from neurons in la yers 3A and 6. Connections were also found from several more distal re gions, namely, areas TEO, TE, TF, TH, and from cortex in the occipitot emporal and superior temporal (STS) sulci. Filled neurons occurred in two small foci in the caudal intraparietal sulcus. These more distal f eedback connections tend to originate only from layer 6. An additional injection of the retrograde tracer diamidino yellow in area V2 of one animal revealed a similarly widespread network of feedback connection s. In some areas (in the STS and in TEO), 10-15% of fluorescent neuron s were double-labeled. These results indicate that feedback connection s to early visual cortex derive from a widespread network of areas, in cluding limbic-associated cortices. These connectional patterns testif y to the massive recursiveness of anatomical pathways. As there are no reports of projections from V1 to anterior temporal cortices, our res ults also indicate that some cortical feedback connections may not be strictly reciprocal.