Does brain white matter growth expand the cortex like a balloon? Hypothesis and consequences.

Horrobin (2001) has proposed that phospholipid metabolism is linked to human brain growth, and that deviations in the metabolism may be linked to creativity as well as mental disorders. The present literature review leads to a framework or model which states that brain white matter growth causes the overlying cortex to expand tangentially, like a balloon, and that this expansion affects the cortex's capacity to differentiate afferent signals. The neuroanatomical description of this model is based on publications linking human white matter growth and mass to the thickness of the overlying cortex, and of some linking cortical thickness and surface area (inversely). The link between the surface area of a cortical region and its differentiation capacity is based on previous work on hemispheric differences and functional lateralisation in the human auditory cortices. The link between differentiation capacity and inappropriate responses or "loose associations" is based on publications linking perceptual deficits and abnormal cortical structure, especially abnormal laterality. Finally, perceptual deficits have been linked to aspects of schizophrenia or other "disorders".