Why the brains of humans are bigger

The largest structure in the brain, the cerebral cortex is the headquarters of our intellect -- often referred to as "gray matter." The large surface area of the cortex houses two-thirds of the brain's 100 billion neurons in a thin layer, only slightly thicker than the peel of an orange. In order for this expanded surface area to fit within the confines of the human skull, the cortex folds in on itself, resulting in a series of ridges and grooves that give the brain its "wrinkled" appearance. This characteristic is unique to humans. "This study looked at how the cerebral cortex develops and the role of the beta catenin protein in cortical growth," explains senior author Christopher A. Walsh, a neurogeneticist at Beth Israel Deaconess Medical Center who has been studying cortical development and its role in mental retardation and epilepsy for nearly 10 years. Walsh, who is also the Bullard Professor of Neurology at the Medical School, and Anjen Chenn, a research fellow in Walsh's laboratory and a pathologist at Brigham and Women's Hospital, worked together on the investigation into how and why the human cortex grows so large.