Abstract
Hominoid-specific brain structures are of particular importance in understanding the evolution of human brain structure and function, as they are absent in mammals that are widely studied in the extended neuroscience field. Recent research indicates that the human fusiform gyrus (FG), which is a hominoid-specific structure critical for complex object recognition, contains a tertiary, longitudinal sulcus (mid-fusiform sulcus, MFS) that bisects the FG into lateral and medial parallel gyri. The MFS is a functional and architectonic landmark in the human brain. Here, we tested if the MFS is specific to the human FG or if the MFS is also identifiable in other hominoids. Using magnetic resonance imaging and cortical surface reconstructions in 30 chimpanzees and 30 humans, we show that the MFS is also present in chimpanzees. The MFS is relatively deeper and cortically thinner in chimpanzees compared to humans. Additional histological analyses reveal that the MFS is not only present in humans and chimpanzees, but also in bonobos, gorillas, orangutans, and gibbons. Taken together, these results reveal that the MFS is a sulcal landmark that is shared between humans and other hominoids. These results require a reconsideration of the sulcal patterning in ventral temporal cortex across hominoids, as well as revise the compensation theory of cortical folding.