Animal studies, published in Nature Neuroscience, found molecular and electro-physiological measures taken on rats showed the neurochemical processes underlying learning -- synapses -- actually weaken during sleeping hours.

The findings support the synaptic homeostasis hypothesis proposed by the study 's lead researchers Chiara Cirelli and Giulio Tononi of the University of Wisconsin, Madison. They said that during sleep the synapses actually "downsize" in preparation for a new round of learning during waking hours.

"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," Cirelli said in a statement.

Cirelli found the amount of enzymes and other signs of synaptic activity in the brain slices of rats increased 50 percent after a period of wakefulness compared to rats that had been asleep. An experiment in live rats showed responses to the same level of stimulation were stronger following a long period of waking and weaker after sleep, again suggesting synapses grow stronger during waking hours.