COLUMNAR AND HORIZONTAL CONNECTIONS IN THE MONKEY INFEROTEMPORAL CORTEX: ANALYSIS OF ANTEROGRADE LABELING AFTER BIOCYTIN INJECTION.
Neurosci. Res.Suppl. 18: s181.
In area TE of the monkey inferotemporal cortex, neurons with similar stimulus selectivities are clustered in multiple columns separated by those with distict selectivities. To advance our understanding of the anatomical substrate and the functioning of this organization, we studied intrinsic connections of area TE by analyzing anterograde labeling after extracellular injections of biocytin. Biocytin (4%) was injected into single or restricted layers (1-2,2-3, 3, 3-4, 4, 5 or 6) in area TE of seven Japanese monkeys. Labeling appeared most strongly in a vertical alignment of the injection site. Axons from the superficial layers ran in bundle towards the white matter. They made a prominent arborization in layer 5 on their way. Axons from the deeper layers towards the pia were present but obscured by massive apical dendrites of labeled cells. In addition to these vertically running axons, there were axons running roughly parallel to the cortical layers. These horizontal axons, particularly those in layers 2-4, produced patches of terminal arborizations 0.5±0.2 mm in size at a center-to-center interval of 0.7±0.3 mm. These patches often spanned layers 1 to 4. Single axon tracing confirmed that these terminal arbors belonged to horizontal axons from the injection site, and were not recurrent collaterals of the retrogradely labeled cells. A single injection could label more than 15 patches which were distributed in an elongated way parallel to the superior temporal sulcus. We suggest that the radial connections across layers and the patchy horizontal connections may provide an anatomical basis for the functional columnar system in area TE.