Let’s talk about heartbreak due to the end of a relationship. By all means, I’m no expert on this topic, having only experienced one romantic breakup before marrying my husband, lol. Still, I need a “based on a true story” backdrop for the neuroscience stuff I’m exploring today. So, let’s just continue.

There was this guy who sat next to me on an eight-hour overnight train. We had engaging conversations, felt a connection, and exchanged phone numbers. That’s how it all began. At the time, I was obsessed with the movie Before Sunrise, so you can imagine my excitement over the idea of two people magically finding each other on a random train trip, like Jesse and Celine.

Unfortunately (or fortunately), the relationship didn’t work out. Mostly because I wasn’t in love with him, but with the idea of him that I built from my imagination. Just like one of the quotes from the movie, I was more captivated by “the well-crafted representation of life than life itself.” I was in love with the idealized version of him that I created in my mind, rather than with him in reality.

The conflict during our relationship stemmed from my struggle to accept that he wasn’t the fictional character I had envisioned. While everyone has their good and bad sides, I simply couldn’t accept him as he was. Most of the time we were together, I made him feel unaccepted and underappreciated. I know I was mean and immature. But for better or worse, we were just not right for each other.

Nevertheless, the breakup still hurt. Not because he hurt me—he was a decent man and did nothing wrong—but because I was dealing with my own internal struggles. Essentially, I hurt myself. The early days after the breakup were the worst, as they often are, filled with tears and the typical post-breakup misery.

But as time went by, everything got better. A few months later, I was fortunate to reconnect with my old high school friend, who is now my husband. Maybe it was destiny; everything felt so easy with him, and we got married not long after.

The Role of REM Sleep in Healing Heartbreak

So, how exactly does our brain manage to heal from heartbreak or any kind of emotional trauma? That’s the topic of today’s post.

I’ve written before about the emotional tagging hypothesis, which explains how we tend to remember emotionally charged events better than neutral ones. Since sleep is what I’m trying to study now, I’ve also discussed briefly the function of REM sleep (where dreams typically occur) in the consolidation of emotional memory.

But we don’t just remember everything; we also forget things, which can be beneficial. Otherwise, how could we heal from negative experiences if we just stored everything? 

This brings us to the “Sleep to Forget, Sleep to Remember” hypothesis, suggested by Matthew Walker, the renowned sleep scientist and author of the bestselling book Why We Sleep.

doi: 10.1111/j.1749-6632.2009.04416.x

This hypothesis centers on the dual function of sleep, especially during REM sleep, which helps consolidate emotional memory while also stripping away its emotional intensity. You can still remember the experience, but if it’s a negative event, it becomes less painful as you now view it in a more neutral tone. This mechanism helps you ‘learn your lessons’ and then gracefully move on.

When you form a new emotional memory, especially during a stressful situation, it’s initially encoded in a state of high adrenergic tone. This means your body’s adrenaline and noradrenaline levels are high, helping the brain wrap the memory in a strong emotional “blanket.”

Then, at night, you go to bed. During REM sleep, something amazing happens. This stage helps consolidate the memory, transferring it from your hippocampus to the neocortex, etching the memory traces into your long-term memory.

But here’s another magic occurring. Over multiple nights of sleep, the strong emotional charge surrounding that memory starts to fade. This means the information of the event (the memory) is still there, stored in your brain, but without the intense emotions originally attached to it. Eventually, you’re left with just the ‘important lessons’ from a traumatic event, but relatively free from the overwhelming emotional weight. This process is known as “emotional forgetting.”

How Exactly Does REM Sleep Enable All These Processes?

Several core mechanisms in REM sleep contribute to these processes. First, during REM sleep, your brain’s emotional circuits light up with activity, even more than when you’re awake. This heightened activity allows your brain to reactivate previously encoded emotional experiences, setting the stage for emotional memory consolidation.

Two critical pathways come into play within this emotional network during REM sleep. One is the fear expression pathway, which includes connections between the amygdala, hippocampus, and dorsal anterior cingulate cortex (dACC). The other is the fear extinction pathway, involving the hippocampus and the ventromedial prefrontal cortex (vmPFC). These pathways work together to balance fear expression and fear extinction, the remembering and the forgetting parts.

Second, during REM sleep, theta brain oscillations dominate, creating a connection between subcortical and cortical regions. This large-scale network cooperation allows your brain to integrate recent emotional events into your existing memory schema stored in your cortices, ensuring that your emotional experiences are smoothly woven into your life’s narrative.

Third, REM sleep has a distinct neurochemical environment that creates an ideal setting for the ‘Sleep to Forget, Sleep to Remember’ mechanism. Levels of the cholinergic neurotransmitter acetylcholine peak, even higher than during wakefulness. This helps enhance synaptic plasticity and memory consolidation. Conversely, levels of aminergic neurotransmitters, such as serotonin, are almost absent. This reduction is crucial because it minimizes interference, allowing the brain to process memories without the immediate stress responses these neurotransmitters can provoke.

When the Process Fails: PTSD, Anxiety, and Mood Disorders

Unfortunately, in disorders like PTSD, anxiety, and mood disorders, the “Sleep to Forget, Sleep to Remember” mechanism doesn’t work as it is supposed to. In people with these disorders, we can see hyperactivation of the fear expression pathway and hypoactivation of the fear extinction pathway. This imbalance disrupts the “emotional forgetting” process, making it difficult for the mind to release the weight of past negative experiences.

The reason for this imbalance is complex and still not fully understood by science. To make matters even more complicated, there appears to be a positive feedback loop between sleep quality and the disrupted emotional forgetting mechanism. People with poor sleep quality are at greater risk of developing PTSD and anxiety disorder when exposed to extreme stressful events. Meanwhile, traumatic experiences can make it difficult for individuals to achieve restful sleep, often due to recurring nightmares. The poorer the sleep quality, the fewer opportunities there are for emotional forgetting, creating a vicious cycle that perpetuates emotional distress.

https://doi.org/10.1111/j.1749-6632.2009.04416.x

In answering the question of “Why Do We Sleep,” Matthew Walker suggests that the timeless maternal wisdom of our mothers may hold the key: you should sleep on a problem, and when you’re troubled, go to bed; you’ll feel better in the morning. The “Sleep to Forget, Sleep to Remember” hypothesis beautifully encapsulates this advice. Sleep is not just a passive state but an active, essential process for emotional healing and well-being. So if you’re dealing with a troubled heart these days, just cry it out, talk to people, write down your thoughts, and then get a good night’s sleep. You’ll feel better eventually.