Most people assume the effects of exhaustion are a broad dilution of the mind a dimming of the light bulb

We believe that after sleepless tosses and turns, we’ll forget how to solve the spreadsheet or mumble through the vocabulary test

But when morning comes, somehow you are able to complete complicated analytical tasks with grace, balancing the budget and reviewing the contract. Then you read a simple email query, get cut off in traffic, or find a coffee mug stuck in the kitchen sink and suddenly find yourself seething with irrational annoyance.

Your analytical facilities were spared the night’s slumber, but your emotional brakes burned rubber the moment you woke.

The Disconnect

This pattern of selective impairment is no personality defect

rather, it’s a feature of your mammalian hardware.

In a landmark fMRI study out of UC Berkeley, Matthew Walker’s team charted what happens to default connectivity in the brain after a night of restricted sleep.

When presented with a progressive series of emotionally valanced stimuli, sleep deprived test subjects showed a shocking 60% increase in amygdala activation when compared to their well rested counterparts

The amygdala is the brain’s alarm system, constantly on the lookout for salient features in the environment, be it food or danger. In a healthy sleeping brain, the amygdala is constantly cross-talk with the prefrontal cortex (mPFC), which acts as a regulatory filter, assessing each incoming signal for threat or priority. This is your brain saying “is that really a bear in the woods, or is that my neighbor’s labrador chasing away a raccoon?”

But the top-down regulation from the prefrontal is disconnected during periods of sleep loss

And so the ability to perform controlled, structured tasks (performing calculations, balancing a budget) are largely unaffected, since they rely on alternate, compensatory networks within the cortex.

But it becomes exceptionally difficult to suppress your knee jerk reactions to simple annoyances.

The brake line is cut before the engine dies.

Useful Distinction: Processing Capability vs Interpretive Threshold

When you feel particularly moody or hot headed after a night of poor sleep, you might be tempted to label the feelings as processing fatigue

You might find yourself thinking “I just need more time to think about how I’m feeling right now”

But a more accurate model is an altered interpretive threshold

When the brakes from your prefrontal are disconnected from your amygdala, emotionally charged events feel much more intense than they otherwise would. The knee-jerk amygdala is now issuing full-throttle reactions to minor snafus across the day. Neutral statements are interpreted as insults and minor inconveniences as deliberate attacks.

The capacity to work through your problems is still intact, but the intake of emotional information is misfiled as a crisis.

A Test

If you’re feeling particularly annoyed today (a likely state given the circumstances), avoid trying to “think your way into a better mood” or “force yourself to feel better about your current situation” (your amygdala isn’t listening)

Instead, try a behavioral quarantine:

1. Recognize that the spike in annoyance is a false positive spike of threat detection in your amygdala

2. Postpone judgment on any interpersonal disputes, and impose a 24 hour moratorium on any reactionary emails or comments.

3. Close the loop

Stick to closed-loop projects or rule-based analyses during your waking hours, to avoid getting sucked into unproductive interpersonal sparring matches that require nuanced emotional evaluation.

Caveat

It’s worth noting that fMRI studies that demonstrate these spikes in amygdala reactivity under total sleep deprivation are usually looking at total loss of sleep, or keeping subjects awake for 24-36 hours straight

Chronic partial sleep restriction (losing 90 minutes a night for three weeks) has similar consequences on a more gradual scale.

While waking up after a night of no sleep produces those striking spikes in amygdala reactivity seen on the fMRI, long standing reductions in sleep quality produce a steady baseline of annoyance.

You’re not likely to perceive a sudden 60% increase in amygdala activation (that would be a panic attack) but your day-to-day baseline for frustration and annoyance is going to be much lower than it was a few weeks ago.

Takeaway

When you’re having a sleepless night, expect your frustration to arise not as a sense of mental fogginess, but as a sudden wave of impatience with the world around you

When the world seems suddenly unfair, angry, and obstructive, double check your state before jumping to conclusion about the intentions of others. The likely culprit is not a hidden strike at you, but rather a night of insufficient rest.

The research

Yoo, S. S., Gujar, N., Hu, P., Jolesz, F. A., & Walker, M. P. (2007). The human emotional brain without sleep-a prefrontal amygdala disconnect. Current Biology, 17(20), R877-R878.

Walker, M. P. (2009). The role of sleep in cognition and emotion. Annals of the New York Academy of Sciences, 1156(1), 168-197.

Krause, A. J., Simon, E. B., Mander, B. A., Greer, S. M., Saletin, J. M., Goldstein-Piekarski, A. N., & Walker, M. P. (2017). The sleep-deprived human brain. Nature reviews neuroscience, 18(7), 404-418.