The fusiform gyrus
is a long, narrow gyrus that lies at the bottom of the brain (only the inferior temporal gyrus
lies beneath it) and which extends from the base of the occipital lobe
along the entire length of the temporal lobe
. It is involved in high-level visual processing
, and contains much of Brodmann area 37
While this gyrus serves many functions, it is most centrally involved in color processing, face recognition, and the recognition of complex visual images, including letters. It is sometimes involved in dyslexia, although dyslexia refers to a large range of disorders in visual processing, print recognition, and print processing. It may also be involved in cases of face blindness and some forms of synesthesia.
One of the more localized functions of the fusiform gyrus is facial identification and recognition, from the basic level of "that cloud looks like it's smiling" all the way up to "hey, it's Bob!". However, this area has been found to help experts of many types identify relevant objects (e.g., for birdwatchers, it activates when they see birds), and it may simply be the case that all humans are experts when it comes to human faces. This may also explain why it is involved in letter recognition, as in recent centuries most humans have become 'experts' in reading.
Different recognition systems are physically separated within the gyrus, so it's possible to suffer severe object agnosia but not facial agnosia, or for a bilingual stroke victim to have aphasia in English but not in Chinese. Some functions are highly lateralized, meaning that damage on one side may interfere in specific splinter skills while leaving others untouched, as in some cases of face blindness, in which you may be able to perceive and process faces in full detail, but can't recognize the person.