[Hierarchical functional organization and face representation in inferotemporal cortex of monkeys]

To gain an understanding of object recognition, it is important to identify the neural basis for object recognition. In this review, I have attempted to explain which neural structures are involved in these functions, and how these structures are organized within the brain. Electrophysiological and optical imaging studies suggest that object images are represented by a combination of the columnar activities in the monkey inferior temporal (IT) cortex. Each column represents a visual feature of the object. However, fMRI studies have extracted category-specific activity patches that were formed by neurons responding to the specific object category. These studies suggest that there are 2 functional organization levels, which represent object images and categories in IT cortex. Recently, dense electrophysiological mapping was conducted in a wide range of IT cortex. The results showed that columns that have similar object selectivity are located close to each other, forming functional domains. The selectivity of some domains was related to object category. In a domain found to be selective for faces, columns within the domain showed variability in their selectivity for finer categories, such as human faces or monkey faces. These findings suggest that there are hierarchical functional structures that represent object images and categories. Both structures were embedded in the same IT cortex.