Unlocking the role of sleep in emotional health

Resume: A new study highlighted the mechanisms by which sleep helps process emotional memories, crucial for mental health. The research combines more than two decades of data to reveal how neurotransmitters such as serotonin and norepinephrine, which are inactive during REM sleep, facilitate the recalibration of emotional experiences.

The study highlights the role of the hippocampus and amygdala in converting new, emotionally charged memories into familiar ones without the physical stress responses typical of wakefulness. These insights argue for targeted sleep interventions to support emotional and mental health, especially for people with sleep disorders.

Key Facts:

1. Neurochemical activity during sleep: Inactivity of serotonin and norepinephrine during REM sleep is essential for processing emotional memories, allowing the brain to process emotional information without the usual “fight or flight” response.
2. Brain areas involved: The hippocampus stores new data every day, while the amygdala, active during emotional experiences, works with the hippocampus during sleep to reorganize these memories.
3. Implications for sleep disorders: Disrupted REM sleep, which is common in sleep disorders, can prevent this necessary processing, increasing the risk of mental health problems and highlighting the need for effective sleep therapies.

Source: Macquarie University

A study published in Nature Reviews Neuroscience by an international team, including Woolcock’s Dr. Rick Wassing, spent more than twenty years researching sleep disorders to prove that a good night’s sleep is the perfect remedy for emotional problems.

Nothing we haven’t known forever, some would argue, but Dr. Wassing, who has been working on the project for the past two years, says there’s a lot more to it than that.

“What we have done with this study is to explain why. We looked at studies in neurobiology, neurochemistry and clinical psychology to really understand the mechanisms underlying how sleep helps us deal with our emotional memories.”

What the team of researchers believes, after accumulating more than two decades of scientific knowledge, is that the way certain neurochemicals (e.g. serotonin and noradrenaline) are regulated during sleep is crucial for the processing of emotional memories and our mental health at the long-term.

Chemistry and circuits

Serotonin is involved in many, if not almost all, aspects of learning emotional experiences. It helps us assess and understand the world around us. Norepinephrine is all about ‘fight or flight’; it allows us to assess and respond to danger.

Both shut down during REM (Rapid Eye Movement) sleep and that creates this “really nice opportunity for the brain to engage in processes that otherwise wouldn’t be possible when we’re awake,” explains Dr. Wash off.

There are two main ways we process emotional memories during sleep, he says, and they involve the brain’s hippocampus and amygdala.

Our brains store what we learn every day. This learning is determined by the hippocampus collecting and cataloging this new information into its ‘novelty’ memory store as we process it. At the same time, if that new experience is emotional, the amygdala is very active and linked to the autonomic nervous system – think of a beating heart, knots in your stomach, crawling skin.

During REM sleep, our brains reactivate these new memories. It’s as if the brain is repeating a summary of what happened when we experienced the memory. But during REM sleep, when the noradrenergic and serotonergic systems are turned off, these memories can be moved to ‘trusted’ storage without experiencing the physical ‘fight or flight’ response.

That can’t happen while we’re awake or – as is the case with people with sleep disorders – when we don’t get consistent REM sleep blocks.

Shining a light on the brain

Much of what we now know about how information is processed by the brain comes from the relatively new field of optogenetics, which is used to activate or inhibit very specific cell types in a neuronal network. This allowed researchers to see which cell types and brain areas are involved in encoding emotional memories.

According to Dr. Wassing has made real breakthroughs in terms of our understanding of brain circuits and neurobiology.

It’s all well and good, he says, to look at neurons, receptors and circuits, but the researchers also reviewed clinical psychology studies and found that their findings, especially regarding uncoupling the amygdala’s reactivity and shutting it down autonomic nervous system, were confirmed.

“All three levels of neuroscience align and reach the same conclusion: the way the brain functions during REM sleep is important for processing emotional memories.”

Creating ‘good sleepers’

So, where to go next?

“We know that with insomnia or other sleep disorders where people wake up a lot, we see an increased risk of developing mental health problems.

“Our hypothesis would be that this awakening from sleep results in the noradrenergic system not turning off for a longer period of time (in fact they could even show increased activity) and that is why these people may not be able to maintain their sleep to regulate. emotional memories.”

“The solution is to try to get a good night’s sleep, yes, but the problem is: how do we do that? We know that two in three people with insomnia benefit from cognitive behavioral therapy for insomnia (CBTI), but that is largely based on subjective assessments.

“There is less evidence for objective sleep measurements. The insomnia patient after CBTI is not necessarily a good sleeping individual. He still suffers from sleep disorders, but CBTI allows him to cope better.”

“We need to think critically about the mechanisms that regulate sleep. It’s very difficult to target one system because sleep is very dynamic: the noradrenergic system turns off during REM sleep, but it actually needs to be active during non-REM sleep, so you can’t just switch it off during turning off the entire sleep cycle.”

“We need really creative ideas about how we can design an intervention or a drug that can target the dynamics that happen during sleep and allow those systems to renormalize. We need to focus on objective sleep and help people with insomnia become good sleepers again.”

About this sleep and mental health research news

Author: Caroline Pierce
Source: Macquarie University
Contact: Caroline Pierce – Macquarie University
Image: The image is credited to Neuroscience News

Original research: Closed access.
“Overnight Neural Plasticity and Adaptation to Emotional Problems” by Yesenia Cabrera et al. Nature Reviews Neuroscience

Abstract

Overnight neuronal plasticity and adaptation to emotional distress

Expressions such as ‘sleep on it’ refer to the resolution of disturbing experiences during a night of restful sleep.

Sleep is an active state in which the brain reorganizes the synaptic connections that form memories. This perspective proposes a model of how sleep modifies emotional memory traces.

Sleep-dependent reorganization occurs through neurophysiological events in neurochemical contexts that determine the fate of synapses to grow, survive, or be pruned.

We discuss how low levels of acetylcholine during non-rapid eye movement sleep and low levels of norepinephrine during rapid eye movement sleep provide a unique opportunity for plasticity in neuronal representations of emotional memories that resolve associated distress.

We integrate sleep-facilitated adaptation at three levels: experience and behavior, neuronal circuits and synaptic events.

The model generates testable hypotheses about how failed sleep-dependent adaptation to emotional problems is key to mental disorders, especially anxiety disorders, depression and post-traumatic stress with insomnia as a common cause.