University of California, San Francisco researchers are reporting direct evidence that sleep in early life may play a crucial role in brain development.
Their study, the cover story in the April 26 issue of Neuron, indicates that sleep dramatically enhances changes in brain connections during a critical period of visual development in cats, says the lead author of the study, Marcos G. Frank, PhD, a postdoctoral fellow in the laboratory of senior author Michael P. Stryker, PhD.
The capacity for "change," or growth and strengthening, of connections between nerve cells is the basis of development in the brain. The elaboration and refinement of neural circuitry continues to a lesser extent in the adult brain. The process of growth, known as plasticity, is believed to underlie the brain's capacity to control behavior, including learning and memory. Plasticity occurs when neurons are stimulated by events, or information, from the environment.
In their study, the researchers examined the effect of sleep on brain plasticity after cats experienced an environmental challenge. They determined that animals allowed to sleep for six hours after the period of environmental stimulation developed twice the amount of brain change as those cats kept awake during that time. The animals that were allowed to sleep even had slightly more brain change than the animals whose environmental challenge continued during the additional six hours.
The findings provide strong evidence, says Stryker, UCSF professor and chair of the Department of Physiology and a member of the UCSF Keck Center for Integrative Neuroscience, that a function of sleep is to help consolidate the effects of waking experience on cortical plasticity, converting memory into more permanent and/or enhanced forms.
"This is the first direct evidence that sleep modifies the effect of environmental stimuli on the development of new brain connections," says Frank.