⏰ How a Lack of Sleep Leads to Intrusive Thoughts

The link between REM sleep, brain function, and unwanted memories

Without enough sleep, it’s hard to function well during the day. Our ability to solve problems can feel like it’s lagging, our concentration can feel dispersed, and our emotions can be challenging to control. When you’re going through a difficult time with your mental health, one of the first and most valuable questions you can ask yourself is: “am I sleeping enough?”.

At various points in your life (maybe even daily if you’re unlucky), you’ve probably experienced intrusive thoughts. These are often mental images related to unwanted memories or anxiety-inducing future events you have no control over. Often, the less you want to think about something, the more likely it is to pop into your mind.

New research is looking into how a lack of sleep interacts with this basic control over our own minds. If you frequently experience intrusive thoughts, here’s why it might be a good idea to examine your sleep habits.

🧠 The thought control problems of a sleep-deprived brain

In a study published on New Year’s Eve 2024, researchers recruited 87 participants aged 18-30. Half of those participants had to go a full 24 hours without sleep while the other half were asked to have a regular night of restful sleep.

On the evening before and the morning after sleep deprivation/restful sleep, all participants completed two demanding cognitive tasks:

1. Shape task: participants had to indicate the location of a particular shape on a screen either by immediate vision (easy) or by memory (more difficult). During this task, participants also answered questions about how much their thoughts were focused on the task itself rather than distracted.

2. Memory suppression: participants were trained to memorize links between specific faces and specific visual scenes. After these links were reliably established in memory, they saw those faces appear individually on a screen surrounded either by a green or red box. In the green condition, participants were asked to mentally visualize the scene associated with that face. In the red condition, participants were asked to suppress any mental images of the associated scene by trying to keep their minds blank. After each condition, participants reported back on how much the scene appeared in their minds.

When completing these tasks in the morning (after the night of regular sleep or sleep deprivation), participants also underwent an fMRI brain scan to assess how a lack of sleep affected their brain function.

So what did the results show?

When participants were sleep-deprived, they were less able to stay focused on the first shape task. In the evening test before any sleep deprivation took place, participants in each group were equally good at keeping their thoughts and attention focused on the shapes. But in the morning, sleep-deprived participants showed less task-related thinking.

Similarly, when researchers looked at how effectively participants suppressed mental images in the second memory suppression task, they found that sleep-deprived participants struggled more than rested participants did. Over the course of the experiment, a full night of restful sleep allowed participants to suppress intrusive thoughts more and more effectively. Sleep-deprived participants showed significantly less progress in their ability to suppress unwanted mental images.

But how did sleep deprivation cause these intrusive thought problems? The brain imaging data showed that sleep-deprived participants had significantly less activity in their right dorsolateral prefrontal cortex when suppressing mental images compared to participants who had a good night’s sleep.

This area of the brain is involved in inhibiting unwanted thoughts and is important for cognitive control more generally. During memory suppression, it can target the hippocampus (a crucial area for memory formation and recall) to prevent unwanted memories. Indeed, compared to rested participants, participants in the sleep deprivation condition showed higher hippocampus activity during memory suppression, consistent with the idea that their prefrontal cortex was less effective at regulating memory recall as needed.

In other words, when you don’t get enough sleep, your prefrontal cortex may be impaired in the way it controls your thoughts and memories. Less capable control in the prefrontal cortex and a consequently hyperactive hippocampus mean that unwanted memories are more likely to make an intrusive appearance.

REM sleep was particularly restorative for prefrontal memory control. The more REM sleep participants had in the sleep condition, the less impaired their dorsolateral prefrontal cortex was during memory suppression.

So if you’re someone who experiences a lot of intrusive thoughts—perhaps related to awkward memories or worries about upcoming events—prioritizing your sleep quality is one effective way to boost your prefrontal thought regulation system.

⭐️ Takeaway tips

#1. Prioritize sleep quality to reduce intrusive thoughts

• There are already many reasons to sleep well, but the research above highlights one additional benefit: encouraging better thought and memory control. Without sufficient sleep, your day is more likely to be burdened by unwanted memories, intrusive thoughts, and ongoing distractions. Night-time REM sleep is particularly important for restoring your prefrontal control systems, so if you use a sleep tracker, you can keep an eye on how your levels of REM sleep compare to ideal benchmarks.

#2. Optimize your pre-sleep routines

• If you’re someone who struggles with sleep, it’s likely that you’ve already tried many things to improve your sleep quality. One of my favorite strategies has been to maintain a regular pre-sleep routine and bedtime. When your evenings are unpredictable or inconsistent, it can be difficult for your body to settle into sleep mode at the right time. On the other hand, when you adopt all the same triggers around the same time each night, there are much clearer signals for your body to use. You can read more about these kinds of sleep rituals and find other good sleep tips online.

#3. Be aware of your weaknesses when you’re sleep-deprived

• All of us will have a bad night’s sleep on occasion, so rather than worrying about it, be aware of how it might affect your day and plan ahead to mitigate some of the risks. Some obvious things to watch out for would be any strenuous physical activities or life changing decisions. Based on the research above, it’s also important to be aware of the added risks of intrusive thoughts. When you feel more anxious than normal or less in control of your thinking, reflect on how well you slept. It may just be a temporary sleep-related blip in your daily function that you can ride out until the next day.

“Sleep the sleep that knows not breaking,
Morn of toil, nor night of waking.”

~ Walter Scott

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