Fusiform gyrus

The fusiform gyrus, also known as the temporo-occipital gyrus is a structure that lies on the basal surface of the temporal and occipital lobes. It forms part of Brodmann area 37, along with the inferior and medial temporal gyri. As its name suggests, it is composed of a temporal or anterior portion (T₄) and an occipital or posterior portion (O₄). It is delineated superiorly by the collateral sulcus and inferiorly by the occipitotemporal sulcus ¹.

Relations of the two sections of the fusiform gyrus to adjacent structures are as follows:

• temporal portion:
  • the most anterior aspect usually lies at the level of the cerebral peduncles and is typically curved or pointed in shape
  • sits inferior to the parahippocampal gyrus and superior to the inferior temporal gyrus
• occipital portion:
  • sits inferior to the lingual gyrus

Blood supply

Blood is supplied to the fusiform gyrus by the posterior temporal artery and the occipitotemporal arteries; branches of the posterior cerebral artery ^{2, 3}.

Function

The fusiform gyrus is primarily involved in the higher functions of vision. Several have been identified and a couple are linked with specific named areas of the fusiform gyrus:

• the fusiform gyrus forms part of the the ventral stream and plays a role in differentiating between different categories of objects; a degree of lateralisation has been observed in fMRI studies with greater activity in lateral regions for objects with greater similarity and increased medial activation for more dissimilar objects ⁴.
• the fusiform face area (FFA) located on the lateral aspect of the mid-fusiform gyrus is involved in the perception and recognition of faces including recognising onesone's own face ^{5, 6, 7}; however, it appears that the FFA on its own is insufficient for facial recognition and a functioning network of face-sensitive regions, including the occipital face area (OFA), is required ^8-9; a body-selective region in the fusiform gyrus located close to the FFA that responds selectively to human bodies has also been identified in fMRI studies ¹⁰.
• the visual word form area (VWFA) is located in the left lateral fusiform gyrus and contributes to the recognition of visual words and reading. fMRI studies have shown increased activation in the VWFA as subjects learned to read ^{11, 12}.

Related pathology

Lesions of the fusiform gyrus result in a visual agnosia for objects, prosopagnosia and pure alexia (the inability to read) ^{12, 13, 14}.

The fusiform gyrus has also been implicated in the pathogenesis of synesthesia (a condition in which stimulation in one sensory modality results in a secondary experience in another sensory modality). Grapheme-colour and tone-colour synesthetes have been found on voxel-based morphometry to have increased grey matter volume in the left posterior fusiform gyrus and decreased grey matter volume in the left anterior fusiform gyrus ¹⁵.