We often feel more anxious and stressed when we are tired, and scientists may have partly uncovered why. A lack of shuteye may make it harder for our brain to adapt to new, potentially threatening environments, keeping us in a hyperalert state. This might have been an advantage for our ancient human ancestors, who were more vulnerable to predators, but may be less useful in our modern world.
“Our bodies and brain view sleep loss as a reason to turn on the emergency engines in order to survive,” says at the University of Texas at Dallas, who wasn’t involved in the research. “It is a ‘better safe than sorry’ approach we received from evolution to better deal with challenges in tough times.”
at least once a week, with anxiety disorders – – being both a cause and symptom of these issues.
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Previous studies have linked sleep deprivation to increased activity in parts of the brain involved in anxiety, such as the amygdala. One such tested people’s responses to negative images, like mutilated bodies, after they’d been awake for 35 hours. This revealed that the emotional centres of the brain were more than 60 per cent more active after a sleepless night than a well-rested one, suggesting that sleep deprivation causes negative stimuli to affect us more profoundly.
But studies like these tend to expose participants to these images for only a few seconds at a time. “Real-world threats rarely work this way,” says of the University of Melbourne, Australia. “Knowing whether sleep deprivation prevents emotional adaptation in more real-world situations helps provide new insight into the role sleep problems play in the emergence, persistence and resolution of anxiety.”
Sullivan and her colleagues studied 54 adults, aged between 18 and 30, with no known health conditions and no history of neurological, psychiatric, attention or sleep conditions. Half were told to stay awake overnight, confirmed via a sleep tracker, while the others slept for 8 hours in a sleep lab.
The next morning, all the participants entered an , starting in a bright office with gentle music. They were then taken down to a basement, where they had to collect lanterns in dark rooms with ominous music and unsettling sounds, such as crying, footsteps and whispers. The participants spent about 10 minutes moving between these spaces.
Meanwhile, the researchers monitored their heart rates and skin-conductance levels, tiny changes in sweating that reflect whether someone is in the fight-or-flight response.
They found that all the participants showed higher signs of stress when they first entered the virtual basement. But when they re-entered that space, those who had had a good night’s rest showed reduced stress, suggesting that they were able to acclimatise to the ongoing threat. For the sleep-deprived participants, stress levels remained around the same each time they entered the threatening rooms.
“[Sleep deprivation] may result in a state of hypervigilance, which, if it becomes chronic, may take the form of pathological anxiety,” says Sullivan.
When the sleep-deprived people watched recordings of their experience, those with greater heart rate variability – when the time between beats naturally changes, reflecting good heart health – reported not feeling particularly anxious in the intimidating rooms, even though their other measurements reflected a strong response.
In contrast, those with less varied heartbeats reported feeling much more anxious. “Identifying factors that lessen the impact of sleep loss is valuable,” says Sullivan. “Interventions like moderate-to-vigorous exercise have been shown to increase heart rate variability, pointing to a potential intervention target.”
Treating sleep problems may also be useful for relieving anxiety, seeing as they seem to feed off each other, says Ben Simon. For instance, cognitive behavioural therapy, which helps to change how you think and act, can improve both and anxiety, says Sullivan.
What’s more, “if sleep deprivation cannot be prevented for various reasons – e.g. shift work, [being] new parents – napping or scheduled recovery sleep could help partially offset the effects of poor sleep on adaptation to ongoing threat,” she says.
bioRxiv
