Sleep Health and Emotional Reactivity
Post by Anastasia Sares
The takeaway
In a study of over 26,000 participants, emotional reactivity was associated with sleep duration, a result that adds to the conversation on sleep hygiene and mental health.
What's the science?
Previous research has established a relationship between sleep patterns and mental health issues like depression and anxiety. People with insomnia have shown altered processing of emotional stimuli, and a similar effect can be found in people who are temporarily deprived of sleep in an experimental setting. However, there are a number of ways to measure sleep quantity and quality, which are not applied consistently.
This week in Biological Psychiatry, Schiel and colleagues used a massive dataset to test whether emotional reactivity was related to different aspects of sleep health.
How did they do it?
The authors used data from the UK Biobank, a large study that has been collecting MRI data since 2014. Before accessing the data, they preregistered the study—meaning they submitted a publicly accessible document that outlined their hypotheses and planned analyses. Preregistering is a modern process that is increasingly recommended to counteract publication bias: either publishing results that were not hypothesized as if they had been, or failing to publish hypothesized results because they do not turn out to be true.
The authors were interested in the activity of the amygdala, a small almond-shaped region deep in the brain that responds to fearful or negative stimuli. Biobank participants had done an experiment while in the MRI where they were shown images of negative facial expressions (like anger). The authors isolated the amygdala and measured its reactivity to these negative stimuli, and then tried to see if any aspects of the participants’ sleep health correlated with this reactivity. Measures of sleep health included duration of sleep, insomnia, daytime sleepiness, and chronotype (see a previous brainpost for details on what chronotype is).
What did they find?
In this large sample, only sleep duration over the long term was associated with amygdala reactivity—people with shorter sleep duration had lower reactivity. This result was not intuitive, and it contradicted the authors’ original hypothesis, which was based on previous studies about amygdala reactivity (these other studies found that short-term sleep deprivation results in increased amygdala reactivity). The authors proposed that the decrease in emotional reactivity could be a sort of blunting effect—that is, people who habitually get less than 7 hours of sleep lower their overall amygdala reactivity so that they won’t suffer emotional fatigue. Interestingly, insomnia was not related to amygdala reactivity in this large sample, though previous studies with fewer people had found this association.
What's the impact?
This study confirmed that there is a link between sleep and emotion regulation, however, the exact nature of the relationship was unexpected given the previous literature. This shows why it can be beneficial to preregister research, so we can see when the results of a study diverge from our predictions.