What All Nighters Do to the Brain

This piece, by Onno Berkan, was published on 04/08/25. The original text, by Holding et al., was published by Frontiers in Behavioral Neuroscience on 04/12/2021.

The timing of this piece may be perceived as a signal from the gods. It is not. Unless you pray to Byte-Sized.

This Karolinska Institute study investigated how sleep deprivation affects cognitive performance at different times of day using a brief smartphone-based test called the Karolinska WakeApp (KWA). The app includes five different 2-minute cognitive tests measuring various mental abilities.

The study involved 182 participants, half sleeping well and half staying awake all night. After sleeping usually or staying awake, participants completed cognitive tests at four different times: 10:30 PM (baseline), 8:00 AM, 12:30 PM, and 4:30 PM the next day.

The researchers found that a night without sleep significantly impaired performance on four cognitive tests. Attention was the most affected ability; sleep-deprived participants showed slower reaction times and made more mistakes. Sleep deprivation also hurts participants' ability to do basic math, remember words, and maintain information in their working memory. Interestingly, the one test that wasn't affected by sleep loss was the Stroop task.

The researchers found that the time of day significantly impacted how sleep deprivation affected performance. For example, sleep-deprived people showed better memory performance around 12:30 PM compared to 8:00 AM or 4:30 PM, amazingly suggesting that there might be optimal times of day to perform specific tasks after an all-nighter. This contrasts with participants who got normal sleep, who maintained relatively stable performance throughout the day, showing much more variation depending on the time of day. This means that, after an all-nighter, you should schedule your memory-intensive tasks for around lunchtime.

One of the study's main points was demonstrating that even very brief 2-minute phone tests can effectively detect cognitive impairments caused by sleep loss. This is significant because it suggests that smartphones could be used to measure mental performance in real-world settings, such as medical, transportation, or military environments, where more extended testing isn't practical. The results could be influenced by factors besides sleep deprivation, such as mental fatigue and mood, but the feedback you get from the test would still be beneficial.

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