We’ve all been guilty of cramming for a midterm the night before so we regurgitate as much information needed to pass the next day — all on four hours of sleep.

Researchers at the University of Wisconsin are conducting a study that reveals exactly how hitting the sack instead of the stacks may help you pass the exam through a process they refer to as the synaptic homeostasis hypothesis.

Chiara Cirelli and Giulio Tononi, sleep psychiatrists at the UW Center for Sleep and Conscious, discovered sleep is the price we pay for brain plasticity, which is the ability to continue to learn new information throughout our lives. This is a function we cannot maintain during what they refer to as “quiet wake,” such as resting awake on the couch.

“Any idea about why we sleep has to answer this fundamental question: [Is there] a function that cannot be easily accomplished in quiet wake that has to require this disconnection?” Cirelli said. “Otherwise, I would do it during quiet wake, because quiet wake is a much less dangerous condition to be in.”

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While awake, our neurons, which are the railway network of brain cells that intertwine as we learn new information, only connect when necessary, such as during class or reading a book. As more information travels through those connected networks, the stations between them, called synapses, become stronger, Cirelli said. This enables us to recall information quicker and with less energy over time.

Yet while our synapses strengthen as we learn throughout the day, an “energy-expensive” process, they reach a point where they can no longer get any stronger.

“At one point there is a saturation issue,” Cirelli said. “You can’t just keep going up and up in strength, you need to renormalize.”

So Cirelli and Tononi hypothesized our minds must have to recover, or renormalize, from all this synaptic stretch that occurs during the day in some way through sleep, so our minds can continue to stretch and get stronger over time.

Measuring this change in strength, however, was not easy, Cirelli said.

In the early stages of their study, Cirelli and Tononi used a variety of methods for measurement, such as quantifying the amount of proteins in the brain associated with synaptic strength, she said, or measuring if the brain responds strongly to certain simulations – a sign of strong synaptic connections.

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Ultimately, they found using a high-powered electron microscope yielded the most accurate results in measuring synaptic strength, which strongly correlates with changes in synaptic size, Cirelli said. A larger synapse indicates a stronger synapse.

To test their synaptic homeostasis hypothesis, Cirelli and Tononi assigned 6 to 7 hours of sleep to lab mice and compared their synaptic plasticity to that of mice who were awake for 6 to 7 hours, Tononi said.

“Changes in synapse size, and thus strength, are believed to be at the basis of synaptic plasticity – the mechanisms by which we learn and remember,” Tononi said. 

They used the electron microscope to capture images of the mice’s synapses, no larger than a grain of sand, which they compiled into stacks of 500 to 1,000 images to construct blueprints used to measure changes in synaptic strength – a task that took four years to complete with five to six people working full-time, Cirelli said.

Through comparing the blueprints, Cirelli and Tononi discovered the size of mice’s synapses noticeably fluctuated between periods of rest and wake, proving their hypothesis that our synapses grow in strength during the day when we learn and weaken during the night when we sleep – the price we pay for sustaining our brain’s plasticity.

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A worthwhile investment, but only if you respect it, Tononi said.

“Sleep is very important, for many reasons,” he said. “And [students] should respect their sleep. Learning, remembering, being able to speak fluently, being able to integrate a lot of complex information all heavily depend on sleep.”

Cirelli said the most effective way to learn and remember is through spaced learning as opposed to massed learning. This means you divide your study material over a period of time, for example over a few days or weeks, as opposed to all at once like an all-nighter.

Contrary to the 7 to 9 hours of sleep the National Sleep Foundation suggests college students receive every night, Cirelli believes it varies highly from person to person. Some people, she said, can recover after sleeping for just a few hours.

“There isn’t a time that works for everybody,” Cirelli said. “The best judge is you, you have to sleep as many hours as necessary for you when you wake up to feel restored.”