Functional architecture in monkey inferotemporal cortex revealed by in vivo optical imaging.

To investigate the functional organization in the monkey inferotemporal cortex, which is the last exclusively visual area along the ventral visual cortical pathway, optical imaging based on intrinsic signals was carried out. We first conducted single-cell recordings with microelectrodes and determined the features critical for the activation of single cells. For the subsequent optical imaging, each critical feature was presented, which evoked multiple dark spots. Individual spots were approximately 0.5 mm in diameter and one of them covered the site of the electrode penetration at which the particular critical feature had been determined. The degree of stimulus selectivity varied from spot to spot, and from region to region even within a spot. Some regions were activated only by one of 12- 16 stimuli, while others by more than three stimuli. There were spots specifically activated by faces, and the position of activation spot changed gradually along the cortical surface as the stimulus face was rotated in depth. The length of the overall region along the direction of shift of these spots was approximately 1 mm. These results confirm the regional clustering of cells with similar stimulus selectivity and suggest larger units in which some parameters of object features are continuously mapped.