Gyrification

In brain anatomy, gyrification refers to the folding of the cerebral cortex during brain development in reptiles and mammals, e.g. in turtles, cetaceans and primates. In this process, gyri (ridges) and sulci (fissures) form on the outermost surface of the brain. The term gyrification is also sometimes used instead of the more common term foliation to describe the folding patterns of the cerebellum, which is highly convoluted in other taxa, too, e.g. in birds.

While the extent of cortical folding has been found to be partly determined by genetic factors, the underlying biomechanical mechanisms are not yet well understood. The overall folding pattern, however, can be mechanistically explained in terms of the cerebral cortex resembling a gel that buckles under the influence of non-isotropic forces. Possible causes of the non-isotropy include thermal noise, variations in the number and timing of cell divisions, cell migration, cortical connectivity, synaptic pruning, brain size and metabolism (phospholipids in particular), all of which may interact.

This multitude of underlying processes has rendered the concept of gyrification increasingly important for clinical diagnostics in recent years, since gyrification in some areas of the human brain appears to correlate with measures of intelligence , and disturbances in the folding pattern — as determined by non-invasive neuroimaging — can be taken as indicators of neuropsychiatric diseases. Patients with schizophrenia or Williams syndrome, for example, can be readily distinguished from healthy control populations on the basis of gyrification measures.