Intrinsic Connections in the macaque inferior temporal cortex

Area of Science:

• Neuroscience
• Primate Brain Anatomy
• Cortical Connectivity

Background:

• The inferior temporal cortex (area TE) in primates is crucial for visual processing.
• A functional columnar organization has been previously demonstrated in the dorsal part of area TE.
• Understanding intrinsic connections is key to deciphering cortical processing modules.

Purpose of the Study:

• To investigate the intrinsic connections within the dorsal part of the inferior temporal cortex (area TE) in Japanese macaques.
• To analyze the laminar and tangential organization of axonal projections.
• To correlate the observed anatomical patterns with functional modularity.

Main Methods:

• Extracellular injections of biocytin in the dorsal area TE of Japanese macaques.
• Analysis of both coronal sections for interlaminar connections and tangential sections for intralaminar connections.
• Microinjections were performed at various depths to trace axonal and cell body distributions.

Main Results:

• Axons and cell bodies exhibited a columnar appearance above and below injection sites.
• Layer 3 axons projected towards white matter, with collaterals in layer 5; ascending axons from deeper layers to layer 3 were observed.
• Horizontal axons in layers 2 and 3 formed patchy terminal fields (0.5 +/- 0.1 mm) spanning multiple layers, distributed anisotropically.
• Similar patchy organization was found in area TEO, with smaller patch sizes.
• Patch size and spacing in area TE correlated with columns of similar stimulus selectivity.

Conclusions:

• Intrinsic horizontal axons in area TE and TEO form patchy arborizations, consistent with other cortical areas.
• The observed patchy structure in area TE aligns with functional modularity and shared stimulus selectivity within columns.
• Vertical connections and cylindrical horizontal axon patches likely contribute to columnar functional organization.