The University of Massachusetts Amherst

Feature Stories

Why Do We Sleep?

Rebecca Spencer investigates the cognitive function of sleep and its impact on health and behavior
  • Female child sleeping with stuffed animal

Spencer and her group are interested in sleep's effects on cognitive performance such as memory, decision making, emotion processing, and learning; and how those functions change across the lifespan from preschool children to older adults.

It’s time to challenge our assumptions about the function of sleep. Long thought to be a way for muscle and bone to get much needed rest, there is mounting evidence that the brain, and its many functions, stand to benefit the most from sleep. Rebecca Spencer, Professor of psychological and brain sciences at the University of Massachusetts Amherst asks us to think twice before cutting ourselves short on sleep, as it can have serious implications for learning, decision-making, and other cognitive functions.

“While we are sleeping our bodies are still but our brains are super active,” says Spencer. Researchers in Spencer’s Cognition and Action (COGNAC) lab investigate the function of sleep as it relates to cognitive performance; such things as memory, decision making, emotion processing, and learning. They look at the brain activity of sleeping children and adults using EEG while building on the work of others who use fMRI (functional Magnetic Resonance Imaging) to measure sleeping brain activity related to cognitive function. Their findings are revealing what happens in the brain when we sleep that drives the way we behave when we’re awake.

Spencer and her colleagues are also interested in how those functions change across the lifespan from preschool children all the way up to older adults. Does the nap benefit learning in preschools? Do the changes in memory and cognition that occur in aging parallel the well-known changes in sleep that also occur as we age? Spencer’s research begins to address these large, complex questions, while giving decision-makers a growing, research-based set of tools with which to make informed public policy.

What Happens in the Brain During Sleep?

“During sleep the brain is packing memories away” says Spencer. She compares the brain to a desktop that is filling up with papers. Spencer asks us to imagine various people coming in during the day and putting different types of papers in different categories on our desk. There might be books, stacks of email, there may be notes from a class today, dozens of personal interactions. “All of these different things, every episode we have during our day is piling up on our mental desk,” she explains.

Spencer’s research suggests that during the first part of sleep (slow wave) the brain is replaying all the memories of the day and, in doing so, filing all that material from our mental desk away in its appropriate storage space. “If you can imagine trying to store away all these pieces of paper while someone’s coming in and putting more papers on, your brain will be less efficient in acquiring new information. Our data shows that the early slow wave sleep is important because it helps you file away memories without interference. This process gives us stabilized memories and an emotional clean slate,” says Spencer.

Spencer says this explains why when young children come back from a nap they are less moody, and better able to process their emotions.

“Their desks are tiny, smaller than an adult’s, and they are filled with a lot of emotional ups and downs: somebody stole their cookie, or somebody hit them, or somebody looked at them the wrong way, or got angry at them. They have these heaps of emotional load. But when they come back from a nap where they’ve filed that all away they have a clean emotional slate. So when someone is throwing something emotional at them, such as taking their ball, they are now less dysregulated about it because they can take it on with less emotional baggage,” says Spencer.

Battling “Sleep Bias”

In many ways what’s driving Spencer’s interest in this area of neuroscience is something called sleep bias—a culturally accepted wave of sleep deprivation that has global populations, both children and adults, burning the candle at both ends.

“You see kids overscheduled and teens with too much homework late in the day and into the evening having to get up early in the morning,” says Spencer. It’s common, she says, to find the extra time we need to manage our overscheduled lives by sacrificing sleep. “Setting of this new bar challenges us as a culture to be sleep deprived –it’s like a badge of honor. Our research looks at the risks—the emotional, physical, and social costs—of this behavior,” says Spencer.

Because of this trend, Spencer is concerned about the lack of sleep research that has been tapped to develop health and education policy around sleep. Her research shows, for example, that naptime for young children can improve learning outcomes.

 “As adults, we all know what we are like when we are sleep deprived. But policy-makers look at preschool kids and think it’s not worth their time or money to let them nap during preschool,” says Spencer.

Placing a Value on Sleep

To counter that thinking, Spencer refers to one of President Obama’s state of the Union addresses which touts the advantages of universal preschool. The President points out that for every one dollar invested in preschool education a seven dollar savings is realized in the long run in terms of health and other benefits that a preschool experience gives a child.

“There’s this known value to preschool. Children who attend do better in education, and they will have a higher income as an adult. Our research shows that naps enhance the learning process by about 15% versus skipping naps. So if the investment return for attending preschool is $7 for every $1 of investment, napping can turn that $1 investment into a $9 return. So if learning is really what underlies the long term benefits [of preschool] then we should be supporting the nap,” says Spencer.

The Compromised Brain: Age and Trauma

Along with her findings about memory and learning, Spencer’s research addresses how changes in sleep relate to changes in cognitive ability as we grow older. Research shows that as people age they experience changes in their sleep stages and sleep quality.

“The ability to file away memories in slow wave sleep is compromised in older adults and this seems to be related to some changes in their memory and cognitive abilities,” says Spencer. “It’s not about how much sleep older adults get but rather the quality of that sleep when they are sleeping. If we can help adults improve their sleep hygiene with things like practicing good sleep promotion habits and creating a good culture around sleep we could help to improve their cognitive performance –their memory and their decision-making capabilities,” says Spencer.

Spencer’s research has also shown that sleep is related to mood, which may shed light on a mysterious set of symptoms elderly patients with dementia and Alzheimer’s can experience called sundowning –a state of confusion in the early evening that can cause a variety of unstable behaviors such as anxiety, irritability and aggression.

Younger adults and specialized populations, such as those who have suffered brain trauma, are also studied in Spencer’s group in order to gather both baseline data on normal cognitive function and changes to cognitive function that may occur due to atypical stress on the brain. One of Spencer’s most recent findings regarding Traumatic Brain Injury (TBI) and cognition were quite surprising; the brains of TBI subjects actually IMPROVED the type of deep, slow-wave sleep that helps with cognition.

“This is a compensatory mechanism that the body/brain does to accommodate the TBI. They were able to accomplish the same amount of memory consolidation over sleep as non-TBI subjects with this additional compensation. The TBI brains had to kick it up a notch to get the same level of performance. Our research is full of surprises,” says Spencer.

Karen J. Hayes '85