The belief that a good night’s sleep boosts memory has been shown in countless tests.
But up until now, direct evidence has been lacking on how exactly sleep strengthens the brains’ neural connections.
Now researchers in New York have, for the first time, provided clear physical evidence that sleep fortifies learning.
The finding adds to research that a lack of shut eye causes rogue proteins to build up in the eye, increasing the risk for Alzheimer’s disease.
Using a microscope, scientists looked inside the brains of mice to see what happened when they were either asleep, or sleep-deprived, after being trained to walk on top of a rotating rod for the first time.
They found learning led to the formation of new dendritic spines – tiny structures that project from the end of nerve cells and help pass electric signals from one neuron to another – but only in the mice left to sleep.
The study, published in Science, provides the first physical evidence of how sleep helps to consolidate and strengthen new memories.
It revealed learning and sleep cause changes in the motor cortex area of the brain, a region responsible for voluntary movements.
Professor Wen-Biao Gan, of New York University, said: ‘We have known for a long time sleep plays an important role in learning and memory. If you do not sleep well you will not learn well.
On the cellular level, sleep is anything but restful.
Brain cells that spark as we digest new information during waking hours replay during deep sleep, also known as slow wave sleep.
This is when brain waves slow down and rapid-eye movement, as well as dreaming, stops.
The researchers trained one set of mice to sleep for seven hours and another to stay awake for the same period of time, after both groups practised for 60 minutes.
The mice lacking in sleep experienced significantly less dendritic spine growth than the well rested ones.
Furthermore, 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 it, suggesting learning specific tasks causes specific structural changes in the brain.
Dr Gan said: ‘Now we know when we learn something new, a neuron will grow new connections on a specific branch.
‘Imagine a tree that grows leaves on one branch but not another branch. When we learn something new, it is like we are sprouting leaves on a specific branch.’
