By guest blogger Freddy Parker

How did you sleep last night? If the answer is “badly” followed by an uninvited pang of anxiety, look no further for an explanation than a study published this month in Nature Human Behaviour.

A lack of sleep is known to lead to feelings of anxiety, even among healthy people. But the new paper reveals that the amount of “deep” or slow-wave sleep is most pertinent to this relationship. That, the authors conclude, is because slow-wave brain oscillations offer an “ameliorating, anxiolytic benefit” on brain networks associated with emotional regulation.

To investigate this link, Eti Ben Simon and colleagues at the University of California, Berkeley, ran a series of experiments. First, the team recruited 18 students to come into the lab: once for a full night of shut eye, and again for a night of no sleep. In the evening and the following morning, participants filled in a questionnaire to measure their anxiety levels. And in the morning they also viewed emotionally-charged, aversive videos while the researchers looked at brain activity using functional MRI.

In contrast to a night of sleep, after the all-nighter scans revealed reduced activity in the medial prefrontal cortex (mPFC), typically responsible for emotional regulation, whereas deeper emotional centres of the limbic system, such as the amygdala, appeared hyperactive. That is akin to the brain pressing “heavy on the emotional accelerator pedal, without enough brake”, suggests senior author Matthew Walker.

Quite remarkably, half of these sleep-deprived students reported anxiety scores that would normally signal a clinical anxiety disorder. In fact, these scores were directly related to changes in brain activity: those with the steepest drop in mPFC activity reported the greatest spike in anxiety.

How was sleep protecting against these changes? In the video-watching session where participants slept beforehand, those who had managed more slow-wave sleep had greater activity in the mPFC, and less in the limbic system. It thus appears that deep sleep had restored the brain’s prefrontal capacity to regulate emotions and prevent the escalation of anxiety.

It doesn’t end there. The team also conducted an online study in which 154 people of all ages recorded their sleep and anxiety levels over four days. Respondents’ data showed that the quality of sleep predicted anxiety levels the following day, with even subtle disruptions during sleep elevating feelings of anxiety.

Given the high prevalence of poor sleep and anxiety disorders in much of the Western world, understanding the mechanisms that link the two is important. By implication the authors support strategies to improve sleep quality in anxious and sleep deprived populations, and suggest sleep could be an overlooked “non-pharmacological intervention for anxiety”. It’s certainly an admirable agenda.

But the knowledge that a lack of sleep worsens anxiety is hardly soporific. Indeed, having read Walker’s eye-opening book Why We Sleep, by passing it to my mother I had unknowingly triggered her own worries about sleep. Regrettably, she now finds it more difficult.

So could it be that, in some cases, research like this inadvertently exacerbates the problems scientists set out to resolve? Reviews suggest that worrying about sleep can do more harm than a lack of sleep itself — so it’s important to consider how we communicate these sorts of findings. As a start, it might be wise to bear in mind the bigger picture: sometimes poor sleep is inevitable and does not necessarily signal disaster. It’s also worth remembering that there are individual differences that buffer against the negative effects of sleep deprivation, while others even have a genetic propensity to need less sleep.

However, these arguments shouldn’t let people, or societies, off the hook. Good sleep serves myriad vital functions, not least keeping anxiety at bay. And future research will doubtless continue to highlight the need to teach people about healthy sleep. It just might also be important to figure out how best to do so.

– Overanxious and underslept

Post written by Freddy Parker for the BPS Research Digest. Freddy is a long-standing reader of the Research Digest and student at the University of Bath, studying for his final undergraduate year in Psychology.

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