Study shows that characteristic surface wrinkles of the human brain are due to physical forces

Guardian : Forty years ago a theory was proposed that the wrinkles on the outer layer, or cortex, of the human brain formed during fetal development because of differential growth rates and the constraints of the size and shape of the skull. A team led by Tuomos Tallinen of the University of Jyväskylä, Finland, has tested the theory for the first time. The researchers used a 3D printed model of a 22-week-old fetal brain before any wrinkling had occurred. The model was made of a soft polymer core coated with an absorbent elastomer gel that represented the cortex. When placed in a solvent, the elastomer swelled and buckled because of its attachment to the core, which restrains the expansion. The result was short furrows that elongated and then formed into the characteristic junctions and bends seen in real brains. When Tallinen and his team members modelled the process mathematically and compared the model with images of different stages of fetal brain development, they saw a distinct similarity. Although the process doesn’t match the volume or surface-area increases seen in real brains and doesn’t account for the external limitations imposed by the skull, it does provide potential insight into the mechanics of brain growth.