When You’re Drowsy, Is Your Brain Partly Asleep?

By Neuroskeptic | January 28, 2017 2:28 am

When we’re feeling very tired, we sometimes remark that we’re “half-asleep”. But is this more than just a figure of speech? A new paper suggests that parts of our brain may actually ‘fall asleep’ even while we’re still awake.

According to researchers Jeremy D. Slater and colleagues of the University of Texas, “local sleep” occurs throughout the human brain, with each brain region passing into and out of a sleep-like state over time. What’s more, local sleep becomes more and more common in the brain over the course of the day, suggesting that the tiredness we feel at the end of the day may reflect the fact that much of our brain is inactive.

Slater et al. studied six patients who’d each had about 100 electrodes implanted in their brains as part of a program of treatment for severe epilepsy. Here’s an example of the electrode locations:


Recordings from the electrodes were constantly acquired over a period of several days and nights, so Slater et al. were able to determine which features of the brain activity were most characteristic of sleep as opposed to wakefulness.

It turned out that across the brain, sleep was strongly associated with two things: an increase in the amplitude of delta waves, and a fall in the peak frequency of alpha waves. This isn’t a new finding, but Slater et al. went on to examine whether each electrode was showing activity more characteristic of sleep or waking at any given time.

The result is what they call a “restgram”:

restgramThis restgram shows that over the space of about an hour, this patient (“SC553”) gradually went from being awake to being asleep. But the sleep-like “inactive” pattern of activity (blue) didn’t arrive all at once. Some points in the brain (i.e some electrodes) ‘fell asleep’ before others. And most electrodes went through several cycles of ‘waking’ and ‘sleeping’ over the course of the 50 minutes.

This is an interesting study. However, it relies on the assumption that all brain electrical activity can be classified into just two states: “active” and “inactive”. But a closer look at the data in this paper reveals that there’s a smooth continuum between high delta, low alpha frequency “sleep” and low delta, high alpha frequency “wake” activity, as seen in this scatterplot of the activity from one particular electrode over time:

UntitledThe datapoints are grouped into two classes (red and blue, wake and sleep) but this seems arbitrary. We could just as well decide to view the data as one cluster, or three, or more. This is because Slater et al. used an algorithm, K-means clustering with a fixed K=2, which is guaranteed to partition a dataset into two clusters.

My concern is that this binary approach all but guarantees that some electrodes will show “sleep” activity during waking, because “sleep” here means only that the activity is closer to the average for sleep than to the average for waking – a rather broad definition.

ResearchBlogging.orgSlater JD, Chelaru MI, Hansen BJ, Beaman C, Kalamangalam G, Tandon N, & Dragoi V (2017). Focal Changes to Human Electrocorticography With Drowsiness: A Novel Measure of Local Sleep. The Journal of Neuropsychiatry and Clinical Neurosciences PMID: 28121257

CATEGORIZED UNDER: EEG, papers, select, Top Posts
  • JuliusCaesar

    This is really interesting. It seems that people’s interpretation of whether they are awake or asleep can vary – Apparently, many insomiacs are actually half-asleep or in light sleep; they think they are awake, but their spouses report them as asleep.

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  • Psycology Student

    I think it is fascinating when our brains are in sleep there is a decrease in the frequency of alpha waves and an increase in delta waves. It is also interesting that our brains cannot always be classified fully in an “inactive” or “active” state. It had never occured to me that the tiredness we feel at the end of the day could be do to the fact that parts of our brains our “inactive” or asleep. I can imagine how frustrating insomnia is when part of the brain could appear to be half asleep. Insomniacs can appear to be sleeping when they really feel awake.

  • Rohan Wickramasinghe

    I have been told that certain birds, e.g. geese, which migrate long distances without stopping for a rest, may be ‘asleep’ while they are actually in the air flying.

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  • Holly Bumpus

    I think that the idea of being awake and asleep can be so similar that a person has no idea if they really are or not is so fascinating. Personally, I know the feeling of how it feels to feel like you are moving while you are asleep. Our brains make things feel so realistic, it is amazing.

  • Kristina

    The fact that this study showed some parts of the brain falling asleep before other parts is very fascinating. When you are going into REM sleep you can even feel your body doing this. As you drift off into sleep it’s like you are slowly going down this slope. I know it seems hard to think about, especially when you are falling asleep but just try it- you’ll be out before you know it.

  • Cayley

    This article is really interesting!! It is amazing how we can be awake, but our brains can be asleep. With that being said, it also makes so much sense! How overtime our brain can slowly fall asleep, which I can personally associated with the feeling of not being able to concentrate on something longer than a certain amount of time. This could be because my brain is slowly going to sleep. It was amazing that this study showed that certain parts of your brain fall asleep before others. This relates to REM sleep when you can feel your body going into these stages.

  • Jake M

    I did not realize that when feeling “half-asleep” parts of your brain were literally asleep. The author of the article makes a good point in being concerned with the data from this article being purely binary (meaning the neurons were reported as being either “active” or “inactive”). As shown in the figure above, the data of the neuronal wave activity would be more accurately classified if it wasn’t limited to two states that are arbitrary in meaning.

  • Evan

    This is an incredibly interesting study that examines the experience of being half-asleep. I had no idea that parts of one’s brain could sleep while other parts remain active. I thought that sleep was always an all-or-nothing act—this study shows that being asleep is more of a continuum. In addition, it is interesting that some neurons cycle between being active and inactive. The author does have reason to be concerned with the study’s data being binary. Essentially, the study accounts for neurons being fully active or inactive. In reality, neurons have different levels of activity. The results from this study could have interesting real-world applications. For example, this study could explain how sleep affects daily performance. If half of one’s brain is asleep, then it is easy to explain why he will not perform as well on various tasks as one who if fully awake.

  • Rachel

    I found this post extremely interesting. I am currently in an ornithology class and have learned that birds can actually participate in unihemispheric sleep. This occurs when one side of the brain “falls asleep” while the other side awake. This is useful during times of migration and foraging. It has long been believed that mammals and, therefore, humans have lost this ability when they diverged evolutionarily. It is extremely interesting to now find out that humans also do this in some way. I also agree with the author that this may not be a strictly binary system but that neurons are on a continuum from sleep to wake. It would be interesting to see what can be uncovered with additional research!

  • Hannah Gonder

    I am curious to see if active vs. inactive means being awake vs. sleeping or if it means a certain part of the brain is just simply not being used to a certain extent. I think this is an interesting concept and a possibility, especially since several animals have brains that can be asleep while they are awake. I would like to see if any studies have been done that compare the brains of humans to the brains or those animals who have brains that can “sleep” while they are awake. It would be interesting to see this concept being researched further.

  • Haley Ulrich

    I would like to know if the brain goes through REM cycles as parts of the brain or if it is an entire process that happens all at once. This article makes it seem like some areas may reach that deep sleep first. Do you all think it is one process, or that it could be different parts at a time?

  • Morgan

    This is extremely interesting. There are several different animals that have the ability to shut off or not use areas of the brain at all times and this is exciting to discover and hopefully learn more about. I wonder if the inactive parts can be associated with the activation-synthesis theory in a way. The brain turns inactive to digest the information it has collected over the day. I also wonder if it effects REM sleep at all. In terms of how quickly in the day or how often the brain goes through the active to inactive stages.

  • Candy Meadows-Daily

    It’s interesting that so much of the brain starts to become inactive before we even go to sleep! It makes sense though, since one of the main functions of sleep is to conserve energy. Towards the end of the day, our brain forces us to be less active and alert. It would be harder to do complex tasks around bedtime because the parts of the brain required for that are not as active. I wonder what insomniacs experience with their brain activity. Are they “stuck” in a state of partial brain activity and feel drowsy, but cannot fully shut down? Or is the brain too active, and not lowering the activity in the parts that it should?

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Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.


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