How Does Sleep Affect Memory and Stress in PTSD?

What you need to know

The study looked at how sleep patterns called “sleep spindles” affect memory and anxiety after seeing stressful images in people with varying levels of PTSD symptoms.
People with more PTSD symptoms had a greater increase in sleep spindles after seeing stressful images compared to a control condition.
More sleep spindles were linked to worse memory of the stressful images but greater reduction in anxiety in those with high PTSD symptoms.
The findings suggest sleep may prioritize reducing emotional distress over forming memories of stressful events in PTSD.

What are sleep spindles and why study them in PTSD?

Post-traumatic stress disorder (PTSD) is a mental health condition that can develop after experiencing or witnessing a traumatic event. People with PTSD often have intrusive memories of the trauma, feel on edge, have negative thoughts and moods, and experience sleep problems.

Researchers are very interested in understanding how the brain processes memories and emotions related to stressful or traumatic events, especially during sleep. One particular sleep pattern they focus on is called “sleep spindles.”

Sleep spindles are brief bursts of brain activity that occur during certain stages of sleep, particularly stage 2 non-rapid eye movement (NREM) sleep. They show up as short, spindle-shaped patterns on a sleep study recording. Sleep spindles are thought to play an important role in memory formation and emotional processing during sleep.

In people with PTSD, intrusive memories of trauma and heightened anxiety are key symptoms. So researchers want to know: How might sleep spindles be involved in processing memories and emotions related to stressful events in people with PTSD? This study aimed to shed light on that question.

How the study worked

The researchers recruited 45 participants who had all experienced some form of trauma in their lives. The participants had varying levels of PTSD symptoms, from very low to very high.

Each person completed two different study visits:

A stress visit: In the morning, participants viewed a series of negative, emotionally distressing images. In the afternoon, they took a 2-hour nap while their brain activity was recorded. After the nap, they did a memory test about the images they saw.
A control visit: Participants followed the same schedule but did not view any stressful images before the nap.

The researchers measured participants’ anxiety levels at different points during both visits. They also analyzed the sleep spindle patterns in participants’ naps and looked at how they related to memory of the images and changes in anxiety.

Key findings

More sleep spindles after stress exposure

Overall, participants had more sleep spindles during their nap after viewing the stressful images compared to the control nap. This suggests that being exposed to emotional stress may trigger changes in sleep patterns.

Importantly, people with higher levels of PTSD symptoms showed an even greater increase in sleep spindles after stress exposure compared to those with lower PTSD symptoms. This could indicate that those with more PTSD symptoms have a stronger sleep response to emotional stress.

Sleep spindles linked to worse memory in high-PTSD group

When looking at memory of the stressful images, an interesting pattern emerged. For participants with low PTSD symptoms, having more sleep spindles was associated with slightly better memory of the images.

However, for those with high PTSD symptoms, more sleep spindles were actually linked to worse memory performance. This was contrary to what the researchers expected, as sleep spindles are often associated with better memory formation.

Sleep spindles linked to anxiety reduction in high-PTSD group

While more sleep spindles seemed to impair memory in the high-PTSD group, they were associated with a greater reduction in anxiety levels from before to after the nap.

This effect was not seen in the low-PTSD group. For them, sleep spindles did not seem to have much relationship to changes in anxiety.

What might this mean?

The researchers suggest these findings point to sleep having a dual role in processing emotional information, which may work differently in people with higher levels of PTSD symptoms.

For those with low PTSD symptoms, sleep spindles may help consolidate memories of stressful events in a relatively normal way. But for those with high PTSD symptoms, sleep processes may prioritize reducing emotional distress over forming accurate memories of stressful experiences.

In other words, in people with more severe PTSD, sleep may favor calming emotions over remembering details. This could potentially be an adaptive response to help cope with trauma and stress.

Potential mechanisms in the brain

While this study only looked at sleep patterns recorded from the scalp, the researchers speculate about what might be happening in deeper brain structures to explain these effects.

Key brain regions involved in memory and emotion include:

The hippocampus: Important for forming and consolidating memories
The amygdala: Plays a central role in processing emotions, especially fear and anxiety
The neocortex: The outer layer of the brain involved in higher-order thinking and memory storage

During sleep, these regions communicate with each other to process information from our waking experiences. Sleep spindles may help coordinate this communication.

The researchers suggest that in people with PTSD, the “dialogue” between these brain regions during sleep may focus more on regulating emotions via the amygdala, rather than on accurately consolidating memories via the hippocampus.

However, this is still speculative. More research would be needed to confirm what’s happening in these deeper brain structures during sleep in people with PTSD.

Limitations to keep in mind

This study provides intriguing findings, but there are some limitations to consider:

It used a relatively small sample size, which can make results less reliable.
The naps were short (2 hours), so effects might be different with full nights of sleep.
The stressful images, while negative, are not the same as real-life trauma. The effects of actual traumatic experiences could be different.
PTSD symptoms exist on a spectrum, and this study did not specifically compare people with diagnosed PTSD to those without.

More research is needed to confirm and expand on these findings. Studies looking at overnight sleep in people with clinically diagnosed PTSD could provide additional insights.

Conclusions

Sleep spindles increase after viewing stressful images, especially in people with higher levels of PTSD symptoms.
In those with high PTSD symptoms, more sleep spindles are linked to worse memory of stressful images but greater anxiety reduction.
Sleep processes may prioritize emotional regulation over memory accuracy in PTSD.
Understanding how sleep affects emotional processing could lead to new approaches for treating PTSD and other stress-related conditions.

This research sheds new light on how sleep may be involved in processing stressful experiences differently in people with PTSD symptoms. It highlights the complex relationship between sleep, memory, and emotion. Further studies in this area could potentially lead to new strategies for addressing trauma-related sleep issues and PTSD symptoms.