Updated: Mar 11
“Sleep on it.”
This is one of the most under-appreciated pieces of advice we’ve all received at some point. But rather than being a clichéd adage, research suggests that there is truth behind it and reason to listen.
Sleep has the potential to impart on us some significant emotional and behavioural benefits rooted in fundamental neurological processes. Conversely, we see very notable impairments following a lack of sleep or poor sleep quality.
It is important to remember that not all sleep is created equal. As far as humans are concerned, sleep is divided into two distinct types – Rapid Eye Movement sleep (REM), and non-rapid eye movement sleep. The non-rapid eye movement sleep is further divided into three to four consecutive stages, with the last stage commonly referred to as “deep sleep” or Slow Wavelength sleep (SWL). You can read more about stages of sleep in our other posts.
When looking at the relationship between sleep and our emotional experiences, and stress, we want to pay special attention to REM sleep. REM sleep will be familiar to you as that space where dreams happen. But there is more to it. Studies have found that REM sleep is associated with increased activity in the regions of the brain associated with experiences of emotion and emotional regulation (Dang-Vu, Scabus, et al., 2010; Miyachi, Misaki et al., 2009; Nofzinger, 2005).
REM Sleep is Important for Emotional Processing
Neural structures such as the amygdala, striatum, hippocampus, insula, and the medial prefrontal cortex – all of which are involved in emotional processing – increase in activity during REM sleep. What is even more interesting is that REM sleep is associated with the lowest levels of neurotransmitters or chemicals in our brain that lead to feelings of arousal and stress. In fact, it is during REM sleep that we experience the lowest levels of these chemicals (norepinephrine) at any time in a 24 hour day (Ouyang, Hellman, Abel & Thomas, 2004; Park, 2002; Shouse, Staba, Saquib, & Farber, 2000).
In other words, REM sleep seems to be extremely important to our emotional processing, reactivity, regulation and action. So what happens when we don’t get enough of it?
“Without enough sleep, we all become tall two-year-olds.” JoJo Jensen
It is probably not a surprise that sleep loss is associated with impairments in attention, alertness and memory, as well as with increases in irritability and emotional volatility (Horne, 1985).
Reversing the Downward Spiral
Even small disruptions in sleep, such as a couple of hours decrease in sleep duration per night will lead to significant increases in experienced emotional disturbances and difficulties (Dinges, Pack, et al., 1997). What is more, these negative experiences are likely to accumulate and strengthen over time. In other words, accumulating sleep loss (say, over a week) amplifies subjective negativity in responses to negative events, and blunts the positivity in response to positive events (Zohar, Tzichinsky, Epstein, & Lavie, 2005). Therefore, poor sleep causes us to become more negative, less positive, and overall more impulsive (Minkel, Banks, et al., 2012; Anderson, Platten, 2011).
What is really cool, and perhaps scary about this, is what happens in our brains as a result of even modest sleep deprivation. Even a single night of sleep deprivation increases the activity of the amygdala - a part of the brain heavily involved in experiences of fear and emotional processing – increases by 60% (Yoo, Guraj, Jolesz, & Walker, 2007). This means that when we are deprived of sleep, we are significantly more likely to experience fearful and negative states when we otherwise would not.
As if that was not enough, sleep loss leads to a decreased connection between the parts of our brain associated with consciousness and self-control - such as the medial prefrontal cortex – and the amygdala (Yoo, Guraj, Jolesz, & Walker, 2007; Motomura, Kitamura, et al., 2013), which predicts an increase in subjective anxiety, negative affect and stress (Motomura, Kitamura, et al., 2013). What this means is that we become more likely to experience fear, negativity, anxiety and stress, because sleep loss removes our ability to control and regulate our own emotional and fearful reactions.
“Sleep is the best meditation.” Dalai Lama
On the flip side, of course, a good night of high quality sleep, with ample time spent in those deeper stages, in particular the REM sleep, helps us manage our emotional experiences in a positive and adaptive way.
Sleep is heavily involved in the processing of emotional, stressful or fear-inducing experiences of the day. Negative, painful or traumatic experiences – such as a negative interaction with a colleague at work, experiencing bullying at school, the pain we often experience when going to the dentist – kick start a process of fear conditioning. Here a particular situation or context in which the experience occurred becomes associated with the negative experience.
So, the colleague with whom we have negative interaction, the office or the office building, or the idea of work itself, or the school, or the dentist, or other people in general, may cause us to experience the same negative feelings and reactions as the negative experience itself. This is fear conditioning and it can be more or less specific. For example, we can associate the negative feelings with just the person or the bully or just that specific situation – this is more specific and is an adaptive response. Or, more irrationally, we can associate the negative feelings with all manner of similar and related contexts such as the office, the school, work itself, all dentists everywhere, or people in general – this is less specific and tends to cause a whole lot of problems.
Recovery During REM Sleep
Sleep, in particular REM sleep, has been found to be related to greater specificity of fear conditioning. That is, better sleep helps us better differentiate between actual threatening stimuli and situations that are not actually threatening (Menz, Rihm, et al., 2013). What’s more, is good quality sleep improves fear inhibition – or the unlearning of fearful responses (Spoormaker, Schroter, et al., 2012). This is driven by important processes in our brains, almost the exact opposite to what happens when we lose sleep. The connection between the medial prefrontal cortex – the area associated with conscious executive control – and the amygdala – the area associated with fearful and emotional responses – is strengthened, in effect giving us more control over our own emotional experience (Spoormaker, Schroter, et al., 2012; van der Helm, Yao, et al., 2011).
In addition, a good dose of REM sleep helps us manage our emotional memories. It is in REM sleep that we process our emotional experience, discerning the important from the unimportant, stripping away some of the emotionality, and adequately storing them in our memory (Wagner, Gais, & Born, 2001; Payne, Chambers, & Kansinger, 2012).
This is a good thing and is crucial for navigating life – we can maintain appropriate fear response to the threatening stimuli, while not having the inappropriate fear responses to non-threatening stimuli (Menz, Rihm, et al., 2013; Goldstein, & Walker, 2014). We can also adequately process our emotional memories allowing us to maintain emotional balance (Goldstein, & Walker, 2014). You can see how this can protect us from a whole lot of trauma, negativity, fear and anxiety.
In essence, there is a reason for that ubiquitous piece of advice: “Sleep on it.”
Good sleep, especially REM sleep, helps us manage and navigate our emotional life, both in terms of how we process what has happened, as well as how we deal with what’s to come. When you consider that all life is emotional life, or all experience is emotional experience, this seems quite important.
On the flip side, losing sleep is very damaging to our emotional experience, turning us all into fearful, emotionally reactive, tantrum- throwing, “tall two year olds.” So protect your sleep. Remember that most REM sleep happens in the later portions of the night. And remember to use the restorative power of sleep, especially when you find yourself in the more turbulent and stressful waters of life, such as a global pandemic, for example. Sleep on it.
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