Lack of sleep causes us to have intrusive thoughts

Some people find it difficult to get rid of emotionally uncomfortable thoughts or memories, while others can do so more easily. Typically, these thoughts or memories appear suddenly, involuntarily and intrusively, often persistently, and interfere with their mental or emotional activity. They tend to be negative, worrying or stressful in content, and can be difficult to control or ignore. Intrusive thoughts are characteristic of various psychological illnesses such as anxiety, post-traumatic stress disorder and obsessive-compulsive disorder; and, at the same time, having them promotes mental states of sadness, anxiety, anguish and depression. On a neuropsychological level, there is still not much data on why some people have many more intrusive thoughts than others, especially with regard to the ability we can have to block them consciously.

British psychologist Scott A. Cairney and his colleagues from various universities and research centres in the United Kingdom have analysed the relationship between sleep quality and the recurrence of intrusive thoughts, especially with regard to the ability to inhibit them in a voluntary manner. As published in the Proceedings of the National Academy of Sciences, A good night's sleep helps activate the areas of the brain that allow us to correctly manage intrusive negative thoughts and avoid them. According to them, this discovery may allow for improved behavioural and pharmacological therapies for people who are affected on a recurring basis, which can seriously affect their mental health.

Amygdala, hyperactivated

Before starting this study, it was already known that both intrusive thoughts and rumination, which is the tendency to think repeatedly and persistently about negative experiences or worries, are due to an imbalance between the neural circuits of the prefrontal cortex and the amygdala. Hyperactivation of the amygdala, which is the brain structure responsible for processing negative emotions, combined with poor connectivity with the prefrontal cortex, which is what allows us to reflect and manage emotional states consciously, hinders emotional regulation, making it difficult for the brain to interrupt the flow.

In this study, Cairney and his colleagues took a group of 85 healthy adult volunteers and separated them into two sociodemographically equivalent subgroups. Members of one of the subgroups were allowed to have normal sleep while being monitored to see how well they slept. Others were not allowed to sleep, to achieve a condition that was radically opposite. They had previously shown all of them a series of faces of people linked to images of emotionally uncomfortable situations, such as accidents or assaults.

After they had slept well through the night or alternatively had been awake, they were shown their faces again but without the uncomfortable images. For some of the faces they were asked to recall the traumatic scene initially associated with it, while for others they were asked to make an effort not to remember it. During this process, their brain activity was scanned using functional magnetic resonance imaging.

The differences between the two subgroups were clear. When asked to avoid thinking about the traumatic scenes, the people who had slept well showed much greater activity compared to those who had been awake in the dorsolateral prefrontal cortex, which is where the neural networks that allow us to control thoughts, actions and emotions are located. They also showed decreased activity in the hippocampus, which is the area that allows us to retrieve memories, indicating that they were inhibiting them correctly. In other words, a good night's sleep helps prevent intrusive thoughts and rumination, making it possible for us to inhibit them more efficiently.

They also found that people who had slept well and had a more active REM phase were more efficient at inhibiting emotionally unpleasant thoughts. The REM phase is a stage of sleep characterized by rapid eye movements and brain activity similar to that of the previous night, and serves to consolidate memory, process emotions and restore cognitive functions, making it essential for mental and emotional health.

In their work, these researchers point to another key factor: the involvement in intrusive thoughts of the so-called default mode of the brain, a system of brain regions that is especially active during states of rest or introspection. When the default mode of operation is hyperactive, especially in people with anxiety or depression, the brain is more likely to focus on internal worries or uncomfortable memories, which facilitates rumination. This hyperactivity is often associated with a decreased ability to redirect attention to external stimuli, a function that depends on the cognitive control of the dorsal prefrontal cortex. Hence the crucial importance of promoting a restful night's sleep for emotional and mental health.