gyri

Gyri, plural of gyrus, are the raised ridges on the surface of the cerebral cortex. They are bounded by sulci (grooves) and together with the sulci create the folded, highly convoluted outer layer of the cerebrum. The folding increases cortical surface area, enabling a greater density of neurons within the limited volume of the skull. Gyrification—the process that forms gyri and sulci—begins in fetal development and continues after birth. It is influenced by genetic factors and mechanical constraints; abnormalities can lead to conditions such as lissencephaly (a smooth brain) or pachygyria (broad, poorly formed gyri).

Anatomically, many gyri are named for their locations. The precentral gyrus hosts the primary motor cortex; the postcentral gyrus contains the primary somatosensory cortex. Frontal lobe gyri include the superior, middle, and inferior frontal gyri; the temporal lobe contains the superior temporal gyrus, involved in auditory processing. The inferior temporal gyrus participates in higher-level visual tasks, while the parahippocampal gyrus lies near the hippocampus. The cingulate gyrus runs along the medial aspect of the brain, and the calcarine sulcus in the occipital lobe marks the primary visual cortex along the banks of surrounding gyri (cuneus and lingual gyrus).

Functionally, gyri host specialized cortical regions underpinning movement, sensation, language, memory, and perception. Variations in gyral patterns are common among individuals and across species; humans typically exhibit extensive cortical folding compared with less convoluted brains in some other mammals. Clinically, atypical gyrification has been associated with developmental disorders and certain neuropsychiatric conditions, and cortical atrophy can accentuate sulci as gyri become less defined.