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I’ve stayed up all night to study ancient philosophy and binge-watch 'tween dramas. I’ve stayed up all night to mourn and to celebrate, by bar-light and moonlight. I’ve stayed up all night in a rudderless daze and on a mission, pacing my apartment and stalking down city streets. I have no shortage of up-all-night experiences, a mess of half-stories that don’t share much in common: different states, years, supporting characters.

But, across the board, nights of no sleep have left me in some exaggerated emotional state the next day. Often, that state is unpleasant: I’m anxious, sad or irritable. But sometimes, exhaustion sends me into a dim-witted euphoria, marked by giggle fits over nothing. I get downright giddy. And, when I pass on sleeping, I don’t know which way my emotional pendulum will swing, or why it goes the direction it does. My bleary-eyed split personality isn't only confusing to me. Sleep-deprived silliness is real and so is the struggle to make sense of it. 

Most studies depict sleep-starved people as pessimistic, thin-skinned creatures. In experiments, sleep loss is associated with homing in on signs of threat, interpreting neutral facial expressions as negative and struggling to keep calm and carry on. But this research trend is undermined by one, well-documented phenomenon: Exhaustion can act as an antidepressant. For decades, doctors have used short-term sleep deprivation to rescue patients from the belly of unyielding sadness, without understanding quite how it works.

“We find that in healthy people, sleep deprivation generally makes them feel more depressed, anxious, and paranoid, said William D. Killgore, a professor at the University of Arizona and Harvard Medical School. “Sleep deprivation has the paradoxical effect of improving mood in depressed people.” 

Lack of Sleep: The Original Upper?
grinning creepy lady

Studies on sleep, emotion and mood often analyze how study participants in well-rested and sleep-deprived states respond to images, sounds, social situations and other emotional triggers. In some cases, researchers use neuroimaging tools to see what's happening inside their brains, too. Sleeplessness appears to alter activity in and between brain regions that process and control emotion.  

Exhaustion can act as an antidepressant. For decades, doctors have used short-term sleep deprivation to rescue patients from the belly of unyielding sadness.
 

In the well-rested brain, the rational-thought center known as the prefrontal cortex is highly connected to the amygdala, an almond-shaped structure in the limbic system. The amygdala fires up in response to emotional cues in the environment — it's our neuronal alarm bell. By regulating amygdala activity, the prefrontal cortex keeps kneejerk feelings in check. When people skip sleep, this buddy system seems to malfunction: The amygdala becomes more active and less connected to its babysitter, leaving it free to blare when it should (monsters, robbers, photos of cheating boyfriends) as well as when it shouldn't (meaningless sighs, resting bitch face, lightly sarcastic text messages). Additionally, studies have reported increased connectivity between the amygdala and visual-processing brain regions, which suggests that an underslept person is more likely to get worked up over whatever happens to catch their eye. Greenpeace canvassers, beware. 

Over the years, negative mood has hogged the scientific spotlight, presumably because researchers are more interested in cheering people up than understanding why they're jazzed. But the focus on emotional valence (i.e., whether emotions are positive, negative or neutral) may be misplaced. More recent work suggests that exhaustion primes us to pick up on high-arousing cues across the color wheel of emotions. For example, one 2011 study from UC Berkeley and Harvard Medical School assessed the impact of sleep deprivation on positive emotional responses. Researchers found that, compared to study participants who hit the sack, those who stayed up all night were more likely to see neutral images as positive. So, the study-based evidence is slim, but it’s there: People seem to get low and high when they don’t sleep.

Granted, these sorts of studies take place in a lab. As Killgore (of Arizona and Harvard) pointed out, “filling out a simple mood scale is not the same as getting into a heated argument with your partner, hearing that a family member has passed, or getting giddy when joking with friends about a shared experience.”

More recent work suggests that exhaustion primes us to pick up on all high-arousing cues, across the color wheel of emotions.

The prevailing evidence of sleep deprivation as a mood-booster, however, comes from a real-world environment: the hospital. A substantial proportion of patients with major depression exhibit “fast-acting alleviation of depressed mood in response to total or selective sleep deprivation,” according to the 2011 study. The antidepressant effect isn’t permanent. In fact, it reverses once people make up the sleep they missed.

The phenomenon plays out under less-dire circumstances, too. “This beneficial mood-elevating effect is paralleled by reports of emotional lability in healthy adults under conditions of sleep loss, commonly describing episodes of inappropriate euphoria and giddiness, and oscillating periods of lopsided positive emotional reactivity,” study authors wrote, referencing studies dating back to the ‘50s.

A healthy adult with inappropriate euphoria and giddiness? Hi, that's me. 

The Giddiness Effect
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It's not clear why sleep deprivation affects mood in such contradictory ways, but Killgore floated a few explanations. The first goes back to the idea of reduced function in the prefrontal cortex, which, as explained above, regulates emotion. We might assume regulating emotion means regulating negative emotion, the implication being that positivity isn’t something we need to control. But the prefrontal cortex can regulate good vibes, too, said Killgore.

"Giddiness" isn't a defined scientific designation; it's just my way of describing the state of hyper-LOLsy mania into which I occasionally slip when I say no thanks to bedtime.

A core symptom of major depression is anhedonia, meaning the inability to feel pleasure. There’s some evidence that depressed people inadvertently suppress positive emotions in an attempt to block out negative ones, said Killgore. Skipping sleep may undo this process, in a way. “By sleep-depriving the individual,” said Killgore, “I think that we may be releasing this inhibition of both types of emotion.”

This form of emotional disinhibition, Killgore said, may let depressed people experience more positive emotions than they would on solid sleep. The effect looks like a net increase in happiness, even if it’s more like uncovering dormant happiness. For people who aren’t depressed, on the other hand, emotional regulation mostly comes in the form of suppressing negative feelings. So, their outlook turns sour when they give up sleep and, as a result, lose their ability to muzzle their yappy amygdalae.

Other researchers similarly pointed to the prefrontal cortex. Increased stress levels, coupled with a “breakdown of the brain’s control centers” (i.e., the prefrontal cortex), might leave someone “at the mercy of their immediate instinctive and emotional response to whatever is going on in the environment,” said Kalina Rossa, a PhD student at Queensland University of Technology. Rossa compared resulting giddiness to behavior seen in people with mild prefrontal brain damage and mental illness.

A healthy adult with inappropriate euphoria and giddiness? Hi, that's me.

Additionally, Killgore mentioned a brain system called the default mode network (DMN), which takes over when we daydream, space out or otherwise go on autopilot. The ability to suppress the DMN from kicking into gear varies from person to person, said Killgore. People who have trouble suppressing the DMN when they’re well-rested seem to have trouble with mood regulation when they’re sleep-deprived, according to Killgore’s not-yet-published research. Individual differences in DMN-suppression ability might determine whether or not someone is susceptible to positive or negative mood shifts, but Killgore hasn’t specifically looked at the issue yet.

These intriguing ideas come with caveats aplenty: They're just ideas, not tested or certified theories. And "giddiness" isn't a scientific designation; it's just my way of describing the state of hyper-LOLsy mania into which I occasionally slip when I say no thanks to bedtime. 

In the end, I didn't get the clarity I was looking for. I want to use my sleep-deprived mood as a barometer of my mental wellbeing. I want to understand what it means if I yawn through a grin versus a grimace. But I know that emotions elude precise capture and calculation, even with brain scans and psychometric tests at our disposal. All I can really do is pay attention to how I feel and take note of patterns between missed sleep, trembling lips and laughing fits. And, then, I can sleep on it.