While You Were Sleeping
The body may be at rest during sleep, Weinberg College researchers say, but the mind surely isn’t.
In his relentless quest to drive innovation, Thomas Edison felt success came only to those who stayed awake.
Sleep, the inventor reasoned, was time lost — “an absurdity, a bad habit.” He eschewed a clock in his workroom and boasted of working 20 hours a day, inspiring a cult of followers — as well as his exhausted
lab staff — to push themselves to similar lengths.
But even the inventor of the light bulb saw the value in a little shut-eye now and then.
When facing a complex problem in his lab, Edison was known to saunter over to an easy chair. He would hold a stainless steel ball in each hand and allow his body to relax. As he drifted off, the balls would crash to the floor. An awakening Edison would then scramble to record all of the immediate thoughts in his mind.
The man who famously bellowed that “genius is 99 percent perspiration and 1 percent inspiration” believed that sleep might actually be the key to that final drop of genius.
A century later, Weinberg College researchers agree that Edison was onto something. Sleep, they say, can be a prime time to activate memories, strengthen skills, solve problems, reset our internal clocks, and even reduce our racial and gender biases.
“The workings of our conscious mind while we are awake are but a small part of what our brains do,” says Professor of Psychology Ken Paller, who directs Northwestern’s Cognitive Neuroscience Program. “Sleep is an example of how a lot of mental activity is hidden from us, but is nevertheless critically affecting our behavior, our personality and how we store memories.”
During sleep, the brain is busily consuming energy as it cycles between different stages — from light sleep to deep sleep to the vivid, dream-inducing phase of rapid eye movement (REM) sleep. “Sleep is not a passive process,” observes Ravi Allada, chair of Weinberg College’s Department of Neurobiology, “but rather a time when the brain shifts into a different and complementary mode of activity.”
Indeed, many of us can cite an anecdote about a problem we solved while we slept — a dream that yielded a clue to a conundrum, or an answer that suddenly seemed obvious upon awakening. But how and why we do that remains rather mysterious.
“In this unresponsive, unconscious state, we can’t eat, mate or protect ourselves,” Allada muses. “And yet we spend one third of our lives in this stasis.
“Why? That question is incredibly intriguing.”
Allada, Paller and other Weinberg researchers, including Professor of Psychology Mark Beeman, are intent on solving that riddle.
Sleep, memory and biases
As a graduate student in neuroscience in the 1980s, Paller focused much of his research on memory. Whenever he approached the subject of sleep, however, he found a convoluted mess of conflicting findings, and he retreated from the topic.
But Paller returned to the subject in 2008, motivated by a growing body of research suggesting that memories are reinforced during sleep. Working with colleagues, he conducted research that affirmed that our brains are not only active while we are asleep, but are, in fact, performing an intriguing process of memory consolidation. The end result of that process: improved memory skills when we are awake.
Those findings inspired Paller and his research team to take a closer look at sleep’s impact on memory, which he says is “just one of the many functions of the sleeping brain.” They found that sound and odor interventions during sleep might enhance skills that rely on memory — such as the capacity to recall the locations of various objects, or the ability to deliver a musical performance that one has practiced just prior to sleeping.
Most recently, Paller’s team investigated whether cues played during sleep could reinforce prior learning that sought to reduce a sleeper’s unconscious racial and gender biases.
Paller and his team conducted an experiment in which the participants were told to focus on faces that were paired with words that were counter to a stereotype. Female faces, for example, could appear with words associated with math or science, and African-American faces could appear with words such as “sunshine.” Distinctive sounds were linked strongly with each pairing during the training.
Later, the participants took a nap. While they were in deep sleep and without their knowledge, either one sound or the other was played repeatedly. The volume was set low enough to avoid disturbing their sleep.
Paller and his team later found a notable reduction in the participants’ biases, an effect that remained evident a full week later.
“The usual expectation is that a brief, one-time intervention is not strong enough to have a lasting influence,” says study co-author Xiaoqing Hu MS ’11 PhD ’14. “But our results show how learning, even this type of learning, depends on sleep.”
Such findings point to the possibility of using sleep to help people combat phobias, negative self-perceptions and habits such as smoking and unhealthy eating.
Which leads to an even bigger question: what might people accomplish in their lives with the ability to change such deeply rooted attitudes and behaviors?
Paller is energized by the possibilities.
“We now have so many new questions to try to answer,” he says. “That’s what makes the research so exciting.”
Sleep and breakthrough thinking
Beeman, the current chair of Northwestern’s Department of Psychology, is exploring how sleep and memory contribute to our ability to solve problems. Or as Beeman describes it, “targeted problem reactivation.”
“We’re building upon [Paller’s] paradigm and applying it to a new domain,” Beeman says.
In his current experiment, Beeman is providing his subjects with brainteasers while producing a specific sound, such as the Jeopardy theme song, in the background. Later, while the subjects are asleep, a computer monitors their brain waves and cues the aforementioned sound when they hit deep sleep.
When the subjects return to the brainteasers the following day, Beeman checks to see if their ability to solve the problems has improved. His work builds on the idea that daily slumber helps humans sift through knowledge and organize data in their minds, enabling them to connect unrelated items.
“We’re curious if the sound they hear cues them to think about a problem from different angles, essentially restructuring the problem during sleep so they can better see how it fits together,” Beeman says.
This approach could help people solve problems in novel or unconventional ways, a process Edison himself employed every time he ventured over to his easy chair.
“After all, we humans are not just computers that store information,” Beeman says. “Memory is an active, reconstructive process.”
If the subjects do indeed solve their brainteasers faster and more easily, then Beeman’s team will try to determine which stages of sleep are most conducive to problem solving. They will also look to identify the pre-sleep processes that could lead to more beneficial results during one’s waking hours.
“The more we learn about how the brain works during sleep, the more we learn about how sleep contributes to daily thoughts,” Beeman says. “We might be shut off from external stimuli during sleep, but we’re not shut off from processing.”
An additional question is whether this cueing-up approach can enhance all types of problem solving, or whether, as Beeman suspects, it will be most effective with those that require a “Eureka!” type of solution.
“That’s something we’ll continue to explore,” he says.
Addressing disrupted sleep
Neurobiologist Ravi Allada is exploring the relationship between sleep, learning and memory by studying the molecular and cellular underpinnings of those processes.
“Ultimately, we’re asking, ‘Why do we sleep and why do we need to sleep?’” he says.
It’s a mystery Allada is unraveling with the help of fruit flies — who, like humans, sleep. “We’re using this rather simple organism to understand a complex issue,” he says.
In his efforts to understand which parts of the brain promote sleep, Allada has used a genetic tool to turn off various sets of neurons in fruit flies’ brains as they slept. As he shut off different sets of neurons, the fruit flies remained asleep — until he unplugged one particular set and the flies awoke.
“And that is the same set of neurons important for learning and memory, which suggests that sleep and learning and memory are connected,” Allada says.
This past summer, Allada and colleagues built upon their findings to explore why we wake up and go to bed at similar times each day. They studied the sleep-wake cycles of two different species — mice, who are nocturnal, and fruit flies, who active during the day. The team discovered that the cycles of both species are controlled in the same way.
“This suggests that the control of sleep is an ancient mechanism conserved across hundreds of millions of years of evolution,” Allada says.
The researchers discovered a “bicycle mechanism” that conveys important information about time to both species: when the sodium current in their neurons is high, the animals awaken; when the potassium current is high, the animals sleep.
“Like two pedals on a bicycle: when one goes up, the other goes down,” Allada says.
These findings have the potential to inspire new pharmaceuticals to address not only sleep disorders but also issues such as jet lag and shift work, thereby allowing people to reboot their internal clocks to fit their individual situations and curtail sleep deprivation. It’s a particularly critical line of inquiry, given that disrupted sleep is linked to debilitating afflictions such as Alzheimer’s and depression.
“If we can discover how sleep is accomplished, then we can design drugs and therapies specifically to improve the process of sleep or restore it to a healthy level,” Allada says.
And with that, we can capture all the potential benefits of sleep in a way that helps our minds and our bodies perform at optimal levels, perhaps even to the point that Edison might desire a nap.