A Glimpse Inside Your Head

The gnarled lobes of the cerebral cortex, or the brain’s outer layer, present the most striking feature. (See the diagram on page 4 and the box on page 8.) This convoluted layer of pinkish-gray matter, which is about one eighth inch thick, houses some 75 percent of the brain’s 10 billion to 100 billion neurons (nerve cells). But some scientists say that even this vast quantity cannot account for the brain’s complexity.

Why We Don’t Need a Bigger Head

“If the human brain’s cerebral cortex was smooth rather than wrinkled, the brain would have to be about the same size as a basketball, instead of about the size of two clenched fists held side by side.”—Professor Susan A. Greenfield