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Subdivisions and connections of inferior temporal cortex in owl monkeys
Author(s) -
Weller R. E.,
Kaas J. H.
Publication year - 1987
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.902560112
Subject(s) - temporal cortex , cortex (anatomy) , anatomy , biology , temporal lobe , neuroscience , neocortex , posterior parietal cortex , dorsum , epilepsy
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: IT c (the caudal subdivision of inferior temporal cortex), IT R (the rostral subdivision of inferior temporal cortex), IT p (the polar subdivision of inferior temporal cortex), and IT M (the medial subdivision of inferior temporal cortex). Two of these regions may contain further subdivisions–IT C , separate dorsal and ventral areas, and IT M medial and lateral areas. The most caudal subdivision, IT C , 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). IT C 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 3 H‐proline in IT C demonstrated major projections to a more rostral division of the temporal lobe, IT R . 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, IT M , on the ventral surface of the temporal lobe. Feedback projections of IT C were to DL and adjoining temporal‐parietal cortex (TP), while interhemispheric projections were to IT C and IT R . Connections between dorsal and ventral IT C , together with earlier evidence for two projection zones of DL in IT C (Weller and Kaas: ibid., '85), suggest that dorsal and ventral sectors of IT C are separate visual areas. The rostral division of inferior temporal cortex, IT R , was defined as the projection zone of IT C . IT R occupied the rostral half of the architectonic region TE. Slight differences in cortical architecture between IT C and IT R were noted, but an architectonic border between the two fields could not be reliably distinguished. Injections in IT R demonstrated projections to the rostral pole of temporal cortex, IT P , feedback projections to IT C , and inputs to FEF, FV, dorsomedial frontal cortex, and the rostroventral superior temporal gyrus. Interhemispheric projections were to IT R and IT P . The projections of IT R to the rostral pole defined IT P . IT P 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 IT P is from IT R , and its projections have not yet been determined. The fourth major division of inferior temporal cortex, IT M , is medial to IT C and IT R on the ventral surface of the temporal lobe. Most of area IT M is coextensive with area TF of von Bonin and Bailey (ibid., '47). Area TF has a reduced layer IV of granule cells and a thin and pale inner band of myelination. A small medial portion of IT M , just caudal to entorhinal cortex, was identified as area TH of von Bonin and Bailey (ibid., '47). Area TH is characterized by a fusion of granular and supragranular layers. IT M receives inputs from the dorsointer‐mediate area, DI, and the superior temporal area, ST (Weller et al.: J. Comp. Neurol. 228231‐104, '84). DI projects most densely to lateral IT M , while ST projects most densely to medial IT M . IT c and probably also IT R project weakly to lateral IT M . It is not certain that the differences in connections between lateral and medial IT M correspond to the architectonic distinction between TF and TH, but the results do suggest the existance of two fields within IT M . The major cortical input to IT C cortex is compatible with the proposed role of IT in object recognition (for review see Ungerleider and Mishkin: “Two cortical visual systems.” In D.J. Ingle, J.W. Mansfield, and M.A. Goodale (eds):Advances in the Analysis of Visual Behavior. Cambridge: MIT Press, '82). Thus, the major visual projection to IT c in owl monkeys originates from DL. This input, in turn, depends on relays through V‐11, V‐I, and the parvocellular (X‐like) geniculate laminae. IT c relays to IT R , and IT R provides a major input to IT p . IT c also relates to visuomotor centers in the frontal lobe, while IT R has more widely distributed frontal lobe connections suggesting a broader role in visual behavior. Although lateral IT M receives input similar to that of IT c , medial IT M receives input from ST, which may receive Y‐like visual input via a relay through cells in magnocellular genic‐ulate layers to V‐I and then the middle temporal visual area, MT. Thus, in contrast to other divisions of IT cortex, medial IT M is associated with a subsystem that is also directed to posterior parietal cortex and is generally thought to be important in visual attention (e.g., Ungerleider and Mishkin, ibid., '82).