Sleep and Mood

Ever felt like you “woke up on the wrong side of the bed”? You probably know that sleep affects our psychological state, as after a rough night’s sleep you may be feeling tired, irritable, grumpy and lack concentration. Getting enough sleep is critical for our overall health and function, and that includes our emotional wellbeing.

Research has shown that sleep loss is associated with negative mood [1]. Even sleeping 1.5-2 hours less than usual increases impulsivity and reduces the experience of positive mood [2]. But the relationship between sleep and mood is not one-way. Sleep affects mood, and mood affects sleep.

## **Stress and Sleep**

Can you recall a time when you felt anxious and found it easy to drift off? Stress leads to the release of the hormone cortisol, which also plays a role in regulating our sleep-wake cycle. During the second half of our sleep, cortisol levels begin to rise which allows us to feel awake and alert. When we are awake during the day, cortisol levels gradually decline allowing other hormones that are related to our sleep drive, such as melatonin, to rise and facilitate our drift off to sleep. When we are stressed, our cortisol levels rise which throws off the balance with other hormones that promote our sleep. Interestingly, poor sleep can also increase cortisol production, showing that the relationship between stress and poor sleep is reciprocal.

## **REM Sleep and Emotion Regulation**

The science and meaning of dreams has captivated and interested many for hundreds of years. Dreaming occurs during rapid eye movement (REM) and non-rapid eye movement (NREM) sleep, although they are typically most vivid and emotional during REM sleep. Research has suggested that REM sleep is critical in processing and consolidating emotional events [3]. The content of our dreams tends to be associated with experiences we have had while awake.

REM sleep is crucial for emotion regulation, but how does it all work? The science suggests that during REM sleep there are two major interactions contributing to emotional functioning.

1. The emotional tone of our experiences is lessened due to neurological processes decoupling the affective tone from our memory

2. The memory of the experience itself is strengthened due to the reprocessing of the event while asleep

This neurological theory (Sleep to Remember, Sleep to Forget) suggests REM sleep acts as a form of “overnight therapy”, allowing us to process the emotional events we experience while awake, without re-living the emotion attached to them. The next day when we recall these memories, we are able to do so without experiencing the emotion elicited at the time of the memory.