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 four and eight 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 four 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.
Home environment at age eight had a smaller impact on development of these brain regions, whereas other factors, such as the mother's intelligence and the degree and quality of her care, had no such effect.
Previous work has shown that adverse experiences, such as childhood neglect, abuse, and poverty, can stunt the growth of the brain.
The new findings highlight the sensitivity of the growing brain to environmental factors, Farah says, and provide strong evidence that subtle variations in early life experience can affect the brain throughout life.
As the brain develops, it produces more synapses, or neuronal connections, than are needed, she explains.
Underused connections are later eliminated, and this elimination process, called synaptic pruning, is highly dependent upon experience.
The findings suggest that mental stimulation in early life increases the extent to which synaptic pruning occurs in the lateral temporal lobe.
Synaptic pruning reduces the volume of tissue in the cortex.
This makes the cortex thinner, but it also makes information processing more efficient.
"This is a first look at how nurture influences brain structure later in life," Farah reported at the meeting.
"As with all observational studies, we can't really speak about causality, but it seems likely that cognitive stimulation experienced early in life led to changes in cortical thickness."
She adds, however, that the research is still in its infancy, and that more work is needed to gain a better understanding of exactly how early life experiences impact brain structure and function.
The findings add to the growing body of evidence that early life is a period of "extreme vulnerability," says psychiatrist Jay Giedd, head of the brain imaging unit in the Child Psychiatry Branch at the National Institute of Mental Health in Bethesda, Maryland. But early life, he says, also offers a window of opportunity during which the effects of adversity can be offset.
Parents can help young children develop their cognitive skills by providing a stimulating environment.
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