NEW ORLEANS, LOUISIANA—Books and educational toys can make a child smarter, but they also influence how the brain grows, according to new research presented here on Sunday at the annual meeting of the Society for Neuroscience. The findings point to a "sensitive period" early in life during which the developing brain is strongly influenced by environmental factors.

Studies comparing identical and nonidentical twins show that genes play an important role in the development of the cerebral cortex, the thin, folded structure that supports higher mental functions. But less is known about how early life experiences influence how the cortex grows. To investigate, neuroscientist Martha Farah of the University of Pennsylvania and her colleagues recruited 64 children from a low income background and followed them from birth through to late adolescence. They visited the children's homes at 4 and 8 years of age to evaluate their environment, noting factors such as the number of books and educational toys in their houses, and how much warmth and support they received from their parents.

More than 10 years after the second home visit, the researchers used MRI to obtain detailed images of the participants' brains. They found that the level of mental stimulation a child receives in the home at age 4 predicted the thickness of two regions of the cortex in late adolescence, such that more stimulation was associated with a thinner cortex. One region, the lateral inferior temporal gyrus, is involved in complex visual skills such as word recognition.