Sleep Deprivation: What Happens To The Human Body After Just 4 Hours Of Sleep

This question originally appeared on Quora. Answer by Edward Claro Mader, associate professor of neurology and electroencephalography at LSU-NOLA.

It is now clear that most humans require on average 7.5 hours of sleep per night. What's not clear yet is if there are lucky mutants who can get by with 4 to 5 hours of sleep per night without taking some hit on daytime performance. If there are any, these alert freaks are difficult to identify because: (1) the brain has subtle ways of paying back (usually by installment) any sleep debt incurred from the previous nights and (2) every person has developed ways to cope with the cumulative effects of partial sleep deprivation.

The waking EEG of sleep-deprived individuals will show evidence of sleep debt repayment in the form of intrusions of slow waves during the waking state. Except in cases of extreme sleep deprivation, the EEG changes can be quite subtle. Thus, routine visual inspection of the EEG may not reveal the subtle slow wave intrusions, but spectral analysis and measurements of EEG slow wave power (amount of waves in the theta and delta frequency bands) may reveal an increase in the amount of slow waves in the waking EEG. In other words, the EEG will reveal physiological markers of sleep intruding into the person's waking state even if the person appears awake and has no behavioral manifestations indicative of sleep or sleepiness (e.g. droopy eyelids, yawning, etc).

Individual coping abilities also vary and what may be effective for one person may not be for another. Most people will take caffeinated beverages or other stimulants just to get by through the day. Without coffee and rock music, I doubt I would have graduated from med school. Add to that my caring roommate who woke me up in the morning by throwing shoes on my face and my audacity to miss classes when they don't monitor attendance. What also worked well for me is a mandatory long nap during the weekend. At this age, the only coping mechanism that works for me is the mandatory catch-up weekend sleep. I also acquired the ability to work half-asleep — fortunately I don't operate machinery or do surgery.

The point is that everyone brags about their proverbial prowess to "defeat the sleep drive" in school or while in training. While you may be able to cope to a certain extent, you will always reach a point when the somnolence gets overbearing and you have no choice but to drop dead. Sleep deprivation — whether acute or chronic — can be disastrous. Beware!

Here's an article that is relevant to the question you posted: Neurobehavioral Dynamics Following Chronic Sleep Restriction: Dose-Response Effects of One Night for Recovery. LINK: Page on nih.gov -