Cortical connections of inferior temporal area TEO in macaque monkeys

In macaque monkeys, lesions involving the posterior portion of the inferior temporal cortex, cytoarchitectonic area TEO, produce a severe impairment in visual pattern discrimination. Recently, this area has been shown to contain a complete, though coarse, representation of the contralateral visual field (Boussaoud, Desimone, and Ungerleider: J. Comp. Neurol. 306:554-575, '91). Because the inputs and outputs of area TEO have not yet been fully described, we injected a variety of retrograde and anterograde tracers into 11 physiologically identified sites within TEO of seven rhesus monkeys and analyzed the areal and laminar distribution of its cortical connections. Our results show that TEO receives feedforward, topographically organized inputs from prestriate areas V2, V3, and V4. Additional sparser feedforward inputs arise from areas V3A, V4t, and MT. Each of these inputs is reciprocated by a feedback projection from TEO. TEO was also found to have reciprocal intermediate-type connections with the fundus of the superior temporal area (area FST), cortex in the most posteromedial portion of the superior temporal sulcus (the posterior parietal sulcal zone [area PP]), cortex in the intraparietal sulcus (including the lateral intraparietal area [area LIP]), the frontal eye field, and area TF on the parahippocampal gyrus. The connections with V3A, V4t, and PP were found only after injections in the peripheral field representations of TEO. Finally, TEO was found to project in a feedforward pattern to area TE and to areas anterior to FST on the lateral bank and floor of the superior temporal sulcus (areas TEm, TEa, and IPa, Seltzer and Pandya: Brain Res. 149:1-24, '78), all of which send feedback projections to TEO. Feedback projections also arise from parahippocampal area TH, and areas TG, 36, and possibly 35. These are complemented by only sparse feedforward projections to TG from central field representations in TEO and to TH from peripheral field representations. The results thus indicate that TEO forms an important link in the occipitotemporal pathway for object recognition, sending visual information forward from V1 and prestriate relays in V2-V4 to anterior inferior temporal area TE.