What Facial Features Activate Face Neurons in the Inferotemporal Cortex of the Monkey?

Single neurons were recorded in the inferotemporal cortex (IT) of a monkey trained to discriminate three selected human faces from a large number of different faces. Neurons which were not responsive to non-face visual stimuli used in the task but were responsive to certain sets of faces were found in the gyrus of the IT. The correlation analysis between the quantified facial features and the responses has revealed that face neurons detect the combination of the distances between facial parts such as eyes, mouth, eyebrows, hair, and so on. One of the face neurons detected the combination of the degree that the forehead above the left eye covered with hair and the distance between the eyes and the mouth. The results of this analysis have given appropriate reason for naming the neurons as the face neurons.