Subdivisions and connections of inferior temporal cortex in owl monkeys

Patterns of cortical connections and differences in architectonic appearance were used to subdivide inferior temporal cortex of owl monkeys into four main regions. These regions were named by location: ITC (the caudal subdivision of inferior temporal cortex), ITR (the rostral subdivision of inferior temporal cortex), ITP (the polar subdivision of inferior temporal cortex), and ITM (the medial subdivision of inferior temporal cortex). Two of these regions may contain further subdivisions--ITC, separate dorsal and ventral areas, and ITM, medial and lateral areas. The most caudal subdivision, ITC, was defined in an earlier report (Weller and Kaas: J. Comp. Neurol. 234:35-59, '85) as the projection zone of the dorsolateral visual area (DL). ITC occupies roughly the caudal half of the architectonic zone temporal area E (TE) (after von Bonin and Bailey: The Neocortex of Macaca mulatta. Urbana: University of Illinois Press, '47). TE is characterized by a dense, broad layer IV of granule cells and a dark inner band of myelination. Injections of 3H-proline in ITC demonstrated major projections to a more rostral division of the temporal lobe, ITR. Other projections were to the frontal eye field (FEF), a more ventral region of frontal cortex (FV), and a medial division of inferior temporal cortex, ITM, on the ventral surface of the temporal lobe. Feedback projections of ITC were to DL and adjoining temporal-parietal cortex (TP), while interhemispheric projections were to ITC and ITR. Connections between dorsal and ventral ITC, together with earlier evidence for two projection zones of DL in ITC (Weller and Kaas: ibid., '85), suggest that dorsal and ventral sectors of ITC are separate visual areas. The rostral division of inferior temporal cortex, ITR, was defined as the projection zone of ITC. ITR occupied the rostral half of the architectonic region TE. Slight differences in cortical architecture between ITC and ITR were noted, but an architectonic border between the two fields could not be reliably distinguished. Injections in ITR demonstrated projections to the rostral pole of temporal cortex, ITP, feedback projections to ITC, and inputs to FEF, FV, dorsomedial frontal cortex, and the rostroventral superior temporal gyrus. Interhemispheric projections were to ITR and ITP. The projections of ITR to the rostral pole defined ITP. ITP has broad, less distinct layers of cortex and appears to correspond to temporal area G (TG) of von Bonin and Bailey (ibid., '47). The only known input to ITP is from ITR, and its projections have not yet been determined.(ABSTRACT TRUNCATED AT 400 WORDS)