A recent study at the New York University has found that a good amount of sleep after a learning session boosts and strengthens memory.
Researchers said that sleep after learning promotes the growth of "dendritic spines" - tiny protrusions from brain cells that connect to other brain cells and allow information to pass. Deep sleep or slow-wave sleep is required for the growth of dendritic spines.
Neuroscientists have long known about the role of sleep in cementing and strengthening new memories, but the underlying mechanism was not determined until now.
"Here we've shown how sleep helps neurons form very specific connections on dendritic branches that may facilitate long-term memory," Senior Author Wen-Biao Gan said in a press release. "We also show how different types of learning form synapses on different branches of the same neurons suggesting that learning cause very specific structural changes in the brain."
Brain cells that flash during absorption of new information during waking hours replay during deep sleep. Scientists have long believed that this nocturnal replay helps form and recall memories, however, the structural changes have not been well-studied.
For the study, researchers involved mice - genetically engineered to express a fluorescent protein in neurons. Using a special laser-scanning microscope that illuminates the glowing fluorescent proteins in the motor cortex, the scientists tracked the growth of new dendritic spines along individual branches of dendrites before and after mice learnt to balance on a spin rod.
The researchers then studied the role of sleep on dendritic spine growth. One group of mice practised on the rod for an hour and then slept for seven hours, while the second group trained for the same period but stayed awake for seven hours.
The researchers found that the sleep-deprived mice were associated with less dendritic spine growth than the well-rested mice.
Plus, the location of the dendritic spine's growth was based on the type of activity they learnt. For example, running forward on the spinning rod triggered spine growth on different dendritic branches than running backwards.
"When we learn something new, a neuron will grow new connections on a specific branch," Gan said. "We've shown how sleep helps neurons form very specific connections that may facilitate long-term memory."
The finding is published in the journal Science.
