The cerebrum is the largest area of the human brain, and it is divided into several regions called lobes. One region, called the temporal lobe, sits on the outer side of each half of the cerebrum. In the lower part of this lobe, there is an elongated ridge called the fusiform gyrus, located just between two other gyrii, or ridges. These are called the occipitotemporal gyrus and the parahippocampal gyrus. The fusiform gyrus plays several essential roles in high-level visual processing and recognition.
Within this ridged area, there are specialized groups of cells, called neurons, that play a role in facial recognition. These neurons are located on the lower section of the gyrus in the fusiform face area. Individuals with autism show reduced activity among neurons in this area, which may be why some people with autism have difficulties recognizing faces.
This section of the fusiform gyrus is largely responsible just for perceiving the presence of a face. Even non-living objects that resemble faces will cause this region to activate. The fusiform face area does, however, have connections with other brain regions to expand the uses of facial recognition. A circuit between these neurons and the amygdala, another structure in the brain, is activated when a person views facial expressions that portray negative emotions, for example.
Cells of the fusiform face area also seem to assist in differentiating other well-known objects, for example, between different types of cars in a person knowledgeable about them. Groups of other categorized objects, such as animals and sculptures, also seem to be recognized by these cells. Just above this area, a separate group of cells in the fusiform gyrus activates in response to representations of bodies, including stick figures.
Categorization and higher-order visual processing seem to be responsibilities of other groups of neurons in the fusiform gyrus. Studies have shown evidence that this brain region may be involved in the recognition of numbers and words, as well as the conscious recognition of colors. Other cells may assist in differentiating between similar items that fall into a single mental category, and work with fusiform face area cells to accomplish this task.
A rare brain condition known as synesthesia may involve this part of the brain. This condition involves experiencing stimuli with more than one sense. In a specific form, where numbers and letters are perceived as having colors associated with them, neurons within this brain region are activated.