The researchers found that the sleep-deprived mice experienced significantly less dendritic spine growth than the well-rested mice.

Furthermore, they found that the type of task learned determined which dendritic branches spines would grow. Running forward on the spinning rod, for instance, produced spine growth on different dendritic branches than running backward on the rod, suggesting that learning specific tasks causes specific structural changes in the brain.

"Now we know that when we learn something new, a neuron will grow new connections on a specific branch," said Gan. "Imagine a tree that grows leaves (spines) on one branch but not another branch. When we learn something new, it's like we're sprouting leaves on a specific branch."

The researchers also showed that brain cells in a brain region called motor cortex that activate when mice learn a task reactivate during slow-wave deep sleep.

Disrupting this process prevents dendritic spine growth, Gan said. Their findings offer an important insight into the functional role of neuronal replay -- the process by which the sleeping brain rehearses tasks learned during the day -- observed in the motor cortex.

"Our data suggest that neuronal reactivation during sleep is quite important for growing specific connections within the motor cortex," Gan said.

"The findings are especially important for children," he said. "Sacrificing sleep to study only causes significantly less dendritic spine, thus you will not be able to remember what you have learned."