第35回生理研コンファレンス / 統合脳 国際シンポジウム/日本神経科学会大会サテライトワークショップ(岡崎)2006.7.24-26

Functional and Anatomical Architecture of the Inferior Temporal Cortex

Ichiro Fujita

Lab Cognitive Neuroscience, Osaka University, Osaka, Japan

     Neurons in the inferior temporal cortex (IT), an area critically involved in visual object recognition in monkeys, respond selectively to shape, color, texture, and binocular disparity. Each neuron responds to a particular range of stimuli, and the preferred stimuli of the IT cell population are diverse. How are these cells with different stimulus selectivities arranged in the IT?

IT cells that prefer the same shape stimuli tend to be arranged vertically across the layers of the cortex, suggesting the presence of functional columnar structures for shape preference. No convincing evidence that shows any particular visual parameter is continuously represented across the cortical surface has been reported. Available evidence suggests that the map in the IT is patchy; neighboring columns respond to distinct shapes. Mapping high-dimensional features, such as shape, onto the two-dimensional sheet of cortex may inevitably invoke discontinuities. The cross-sectional diameter of the shape columns is estimated to be 0.4 mm, a larger value than that for orientation columns in V1. IT cells with similar disparity selectivity are also clustered. It is unknown how these disparity clusters spatially relate to the shape columns.

Some anatomical characteristics of the IT are distinct from those in earlier cortical areas, and parallel the nature of the functional architecture of the IT. For example, layer III pyramidal cells in the IT have larger basal dendritic fields and more dendritic branches and spines than the cells in earlier visual areas, such as V1, V2, and V4. The size and distribution of the horizontal axonal arbors are also larger and more irregular in the IT than in earlier areas. IT cells are thus capable of integrating a larger population of afferents from widely distributed regions and process a more diverse set of inputs than neurons in earlier areas. In newborn monkeys, rudimentary, yet conspicuous differences already exist between the IT and area V1 in the morphologies of dendrites and axons. These two areas then undergo drastically different developmental processes to attain the structural differences observed in adults.