The fusiform gyrus, also known as the temporo-occipital gyrus, is a large spindle shaped gyrus that spans across the basal surface of the temporal and occipital lobes of the cerebral hemispheres.
This region of the brain has been implicated in higher processing of visual information, including visual processing and recognition of faces, body, color and words, although the functions of the fusiform gyrus have not been fully defined.
In this article we will outline the primary anatomical features of the fusiform gyrus and discuss its known functions. At the end we will discus the clinically association of the fusiform gyrus in various neurological phenomena, including prosopagnosia, synesthesia and dyslexia.
Location & Characteristics
The fusiform gyrus lies between the parahippocampal gyrus and the lingual gyrus medially, and the inferior temporal gyrus laterally on the basal temporal and occipital cortex. The term fusiform (spindle shaped convolution) reflects the shape of the gyrus, which is wide in the middle, and tapers off at both ends. The fusiform gyrus is composed of an anterior temporal portion and and posterior occipital portion. The most anterior part of the temporal portion of the fusiform gyrus lies close to the cerebral peduncles and is usually curved or pointed, while the occipital portion lies inferior to the lingual gyrus.
The collateral sulcus separates the fusiform gyrus from the parahippocampal gyrus and the occipitotemporal sulcus separates it from the inferior temporal gyrus. Being the largest gyrus of the ventral temporal lobe, the fusiform gyrus forms part of Brodmann area 37, along with the inferior and medial temporal gyri.
A shallow mid-fusiform sulcus divides the mid-part of the fusiform gyrus into a lateral and medial part. The mid-fusiform sulcus serves as a landmark for an important functional region of the fusiform gyrus believed to play a role in face processing, called the fusiform face area.
The fusiform gyrus is supplied by branches of the posterior cerebral artery, i.e. the occipitotemporal arteries and posterior temporal artery.
In general, the function of the fusiform gyrus entails higher processing of visual information, including the identification and differentiation of objects. In addition to high-level visual processing, the fusiform gyrus is involved in memory, multisensory integration and perception. Several functions have been linked with specific cortical areas of the fusiform gyrus.
While the exact functional significance of the fusiform gyrus remains unclear, it has been implicated in the following neurologic systems related to processing and recognition of visual information:
- Color processing
- Face recognition
- Body recognition
- Word recognition
- Identification of features within each category
The fusiform gyrus appears to have a tight functional relationship with the angular gyrus. The angular gyrus is involved in the higher processing of colors. The fusiform gyrus communicates with the visual pathway and angular gyrus, allowing the association of colors and shapes.
Fusiform Face Area
The fusiform face area (FFA) lies on the lateral surface of the middle of the fusiform gyrus. It’s name reflects that it plays a critical role in the identification of faces, including recognition of one’s own face. This region is not the only area which facilitates face identification. Although the FFA is an important component, a network of face-recognizing regions of the cortex are required, including adjacent areas of the occipital lobe.
In addition to recognizing faces, the fusiform gyrus is also involved in the perception of emotions in facial stimuli. Close to the FFA is a body recognition region, which is important for recognizing the form of the human body.
Visual Word Form Area
Another region of the fusiform gyrus is identified as the visual word form area (VWFA). This is located on the dominant hemisphere (left side), and contributes to the recognition of written (visual) words, which enables reading.
The fusiform also appears to be involved in within-category identification of other stimuli (e.g. the ability to discriminate a rose from other types of flowers).
Prosopagnosia (or face blindness) is condition characterized by an inability to recognise familiar faces (even one’s own face). It may result from isolated lesions to the FFA of the fusiform gyrus. Other higher cortical functions involved in visual processing, such as word processing remain intact in patients with prosopagnosia. There are two types of prosopagnosia. Acquired prosopagnosia usually results from injury to the fusiform gyrus, and typically occurs in adults, while congenital prosopagnosia the ability to recognize faces nerve develops.
This is a neurological condition where stimulation of one sensory pathway leads to involuntary experience of second sensory pathway, for example seeing colours when you hear certain sounds. A common subtype of synaesthesia is called grapheme-colour perception; when the individual reads numbers and letters, they experience colours. These types of synesthetic associations can occur in various combinations with any number of senses or cognitive pathways.
Two types of synesthesia have been described. In projective synesthesia, the patient will actually see colors, forms or shapes, while in associative synesthesia, the patient will feel a very strong association between a stimulus and a particular sense that they feel.
Dyslexia is characterized by a difficulty reading. Developmental dyslexia affects about 10-20% of the population and is associated with abnormalities in both visual and auditory processing. Studies have shown that the fusiform gyrus is under active in patients with dyslexia and the amount of gray matter in the fusiform cortex is reduced