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Why You Can’t Think Straight When You’re Sleep Deprived

After a bad night of sleep, we feel off our mental game.

l i g h t p o e t/Shutterstock
Source: l i g h t p o e t/Shutterstock

After a bad night of sleep, we all typically feel distracted and off our mental game. But do you really know all the ways a lack of sleep interferes with your cognitive performance? Most of my patients are surprised to learn just how broadly it affects their ability to think at their best.

It’s difficult to identify a cognitive skill that isn’t affected by sleep and compromised by sleep deprivation. That’s how pervasive the effects of insufficient sleep are on the brain.

Thanks to recent research, we know that sleep deprivation interferes with brain function at a cellular level. A study by scientists at UCLA found that sleep deprivation interferes with the ability of some brain cells to function and communicate with one another. We’ve got billions of neural cells working on our behalf, enabling us to make decisions, process information, focus on important information—and remember it down the road. Sleep deprivation slows that work down, compromising our mental performance.

Less robust brain-cell activity isn’t the only way poor sleep hampers our ability to think. Other recent discoveries have told us more about how a lack of sleep changes brain function and cognitive performance.

Sleep deprivation:

  • disrupts levels of chemicals, including serotonin, dopamine, and cortisol, that affect thought, mood, and energy.
  • leaves key areas of the brain in an “always-on” state of activation.
  • activates genes that interfere with optimal brain activity.

Because genetic makeup is different from one person to the next, the effects of sleep deprivation on brain function can be, as well—so, some people will experience the negative cognitive and mood effects of sleep deprivation more than others.

We’ve still got much to learn about the full effects of poor and insufficient sleep on cognitive performance and health. But as you’re about to see, what we know already offers many compelling reasons to make getting plenty of sleep a top priority.

You can’t focus well.

Attention is especially sensitive to the effects of sleep deprivation. You know this through experience when you have trouble focusing on tasks after a night of poor sleep. Unfortunately, “a night of poor sleep” is often a series of nights of poor sleep, leading to chronic sleep debt and continually compromised attention.

New research suggests that as many as 75 percent of people with ADHD may have a chronic, underlying sleep problem stemming from a disruption to their circadian rhythms.

Attention is about focus and concentration—your ability to stay with tasks long enough to make meaningful progress. For most of us, focus is key to both our performance and our sense of purpose, in and away from work. Sleep deprivation makes focus harder to achieve.

Your reaction time slows down.

Attention isn’t only about focusing on big, thought-intensive tasks. It’s also about focusing on—and making sense of—what’s important right now. Remember those sluggish brain cells that result from being sleep deprived? Scientists in that recent study found that sleep deprivation slowed down neural cells’ ability to absorb visual information and translate that visual data into conscious thought. Research shows reaction times are dulled as much by sleeplessness as they are by alcohol.

Reacting to changing circumstances around us is a critical skill that helps keep us—and others—safe. And it can be significantly compromised by sleep deprivation.

You have trouble making—and storing—memories.

Research shows just how important sleep during middle age can be to memory and cognitive health in later years. A new study found that disrupted sleep during middle age, including insomnia, is connected to cognitive decline a decade or more later. (It isn’t just sleeping too little during middle age that is linked to greater risk for cognitive decline later on—the study found sleeping 9 or more hours a night was also associated with later-in-life cognitive problems.)

We know sleep is deeply critical to memory in all its phases—from acquiring memories, to storing them, to recalling them. All phases of memory are complex and involve multiple areas of the brain that are affected by lack of sleep.

Sleep deprivation impairs learning and the ability to create new memories. Poor sleep also diminishes your capacity to recall memories you’ve already made, whether you made them a month ago or 10 years ago. That’s why, when you’re short on sleep, you’re more apt to forget the name of your high-school crush or one of those many passwords you need to keep track of.

Both memory acquisition and memory recall take place, of course, when you’re awake. It’s the middle stage of memory—known as consolidation—that actually happens when you’re sleeping. Memory consolidation is the brain’s process of storing new memories for long-term retrieval. It’s a complex, multi-phase process, and it’s one part of the important work the brain undertakes while you’re snoozing. It frees up bandwidth in the brain to tackle the next day’s work of acquisition, making new memories through learning and exposure to stimuli.

Several stages of sleep—including both deep, slow-wave sleep and REM sleep—are important to memory consolidation. And new research provides more evidence that multiple stages of non-REM sleep–when the brain generates bursts of electrical activity known as sleep spindles—are also critical to our ability to store memories and recall them later.

Bottom line: If you shortchange yourself on sleep, and deprive yourself of the four to five sleep cycles that a full night’s rest provides, you risk compromising your memory. That matters to your performance tomorrow—and to your memory and cognitive health down the road.

Your decision making and judgment skills suffer.

The prefrontal cortex—the area of the brain that handles planning and complex decision making and enables you to make complicated, nuanced judgment calls that balance risk and reward—is especially hard hit by sleep deprivation. Low on sleep, you’re more likely to be impulsive in your decision making. Impulsive decisions tend to favor immediate rewards, rather than the best outcomes over time. You’re also more likely to engage in risky behavior, according to research. The self-control that the prefrontal cortex enables us to exert becomes diminished when we’re sleep-deprived, and that can have consequences on everything from your relationships to your health to your finances.

Recent research showed the impact of moderate, chronic sleep deprivation on financial decision making. Two groups of sleepers—who slept either 5 or 8 hours a night—were given a choice, repeated daily for a week: They could take a certain amount of money guaranteed, or take a risk, receiving a higher sum of money or nothing at all. Over the course of the week, the 5-hour-a-night, sleep-deprived participants increasingly gravitated toward the riskier option. Especially interesting and important was this detail: As their decision-making grew riskier, the sleep-deprived subjects were unable to perceive that change happening in themselves. This suggests that not only will sleep deprivation make us less adept at sound decision making, we won’t have the self-awareness to catch ourselves making shaky decisions as they happen. There’s also fascinating research suggesting that sleep deprivation makes us more likely to cheat.

Sound judgment, solid planning, thoughtful decision-making—these are the bedrock cognitive skills that help us thrive, succeed at work and in relationships, create stable, prosperous lives, and help us live out our ethical values. Sleep deprivation makes these important, grown-up life skills more difficult.

You’re less creative.

The science of how sleep affects creativity is really interesting. When we’re distracted, unfocused, and fatigued, just when our other cognitive abilities are struggling, creativity perks up. Anyone who’s struggled to come up with an inspired solution—whether it’s a design issue at work or the perfect birthday gift for your mother-in-law—only to have the answer present itself just as you’re falling asleep knows how mysterious our creative thinking can be. These are what I call “moments of groggy greatness,” when our mental fatigue opens up pathways of innovative thinking, and they happen to all of us.

Does this mean going without sleep boosts creativity? No. Very much to the contrary. REM sleep in particular appears to be especially important to creative thinking and inspiration. (Remember, REM is the time when we dream most actively and vividly.) You get REM in segments throughout the night, each time you move through a complete sleep cycle. But periods of REM become longer as the night progresses, and your heaviest doses occur in the last third of a night’s sleep. If you shortchange your sleep time, you risk missing out on the creativity-boosting effects of REM.

Rather than depriving yourself of sleep, pay attention to the times of day when you tend to be on the groggy side. For most people, that’s first thing in the morning and near the end of the day. Let your brain roam during these times, and see what surprising, innovative ideas spring to mind.

Women multitask more—and that takes more energy, and more sleep.

Science tells us that women are more robust multitaskers than men are. Women’s ability to handle a bunch of thought projects at once means their brains expend more energy than men’s—and that means they need more sleep, according to recent research. Scientists found women’s multitasking brains need an average of about 20 additional minutes of sleep a night. It’s not just multitasking where men’s and women’s brains differ in their needs for sleep—and the effects of sleep deprivation. I led a study a few years ago that looked at the mental and physical effects of insufficient sleep on men and women. Among other interesting results, we found women who are sleep deprived experience greater degrees of anger, hostility, and depression early in the morning. I’ll talk more soon about the emotional consequences of sleep deprivation. The effects are just as complex, and just as important to your performance and quality of life.

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