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.
Previous studies have linked sleep deprivation to increased activity in parts of the brain involved in anxiety, such as the amygdala. One such study 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. 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 immersive virtual world, 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.
To gain the benefits of sleep, it was thought that the whole brain must switch off. But experiments suggest the right kind of rest can encourage our brain to improve memory and learning while we’re awake. 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. 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.
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