London, Jan 21 : Researchers from the University of Wisconsin School of Medicine and Public Health have found that sleep plays a crucial role in brain's plasticity which is in turn an important foundation in learning and memory.
The study conducted over rodents revealed that synapses, nerve cell connections central to brain plasticity were very strong during waking hours and weak during sleep.
Chiara Cirelli, study author and associate professor of psychiatry lucidated that human brain uses up to 80 percent of its energy on synaptic activity, constantly adding and strengthening connections in response to all kinds of stimulation.
"We need an off-line period, when we are not exposed to the environment, to take synapses down," Nature Neuroscience quoted Cirelli, as saying.
"We believe that's why humans and all living organisms sleep. Without sleep, the brain reaches a saturation point that taxes its energy budget, its store of supplies and its ability to learn further," she added.
While conducting both molecular and electro-physiological studies in rats to evaluate synaptic potentiation, or strengthening, and depression, or weakening, the findings showed that rats had about 50 percent receptor increase after a period of wakefulness compared to rats that had been asleep.
"Recent research has shown that as synaptic activity increases, more of these glutamatergic receptors enter the synapse and make it bigger and stronger," she added.
Cirelli and colleagues also carried out experiments on live rats assessing the electrical signals reflecting synaptic changes at different times where in the team stimulated one side of each rat's brain with an electrode following waking and sleeping and determined the "evoked response."
The findings showed that responses were stronger following a long period of waking and weaker after sleep.
"Taken together, these molecular and electro-physiological measures fit nicely with the idea that our brain circuits get progressively stronger during wakefulness and that sleep helps to recalibrate them to a sustainable baseline," said Cirelli.
The study appears in journal Nature Neuroscience.