Why a Lack of Sleep Makes You Anxious

A poor night’s rest can cause your brain to overreact

SSome consequences of a bad night’s sleep are obvious — fatigue, difficulty concentrating, a yearning for bed. But some other effects, such as a weaker drive to be social the next day, are frequently overlooked because they’re unexpected or misunderstood. In a study published late last year, a team of scientists from the University of California, Berkeley focused their attention on another hidden problem of limited sleep: anxiety.

It turns out there is a close relationship between how long people sleep and how they experience the world. The longer people go without sleep, the more distressed they begin to feel. Sleep disturbances are also a common symptom of major mood disorders such as depression. Improving sleep quality is an early target for many approaches to therapy, because when people sleep better, they feel better.

It could be that sadness and worry are simply consequences of feeling tired, but it could also be that there are direct links between sleep and mood regulation systems in the brain. To answer this question, the Berkeley researchers surveyed people’s anxiety levels both after a normal night of sleep and after a second night of total sleep deprivation. In addition, they recorded each person’s brain activity while they watched videos that made them uncomfortable (for example, witnessing a young child cry).

As expected, people felt more anxious when they were deprived of sleep than when they were allowed to sleep. When the researchers looked inside people’s heads with a brain scanner, they found that a brain area known as the medial prefrontal cortex — an area linked to emotional control — reduced its activity when people were sleep deprived. More specifically, this area of the brain was less active in response to the stress caused by watching uncomfortable videos. This suggests that a sleep-deprived brain is less able to control its reaction to momentarily stressful events.

Feelings of stress and anxiety after a bad night’s sleep appear to be driven by a weakened emotional control system in the brain.

In contrast, the amygdala area of the brain showed the opposite pattern: stronger reactivity following sleep deprivation. Unlike the medial prefrontal cortex, which is involved in regulating emotions and actions, the amygdala is closely linked to the actual experiences of emotion, most notably the feeling of fear.

The more the medial prefrontal cortex reduced its activity following sleep deprivation, the more anxious people reported feeling. Rising anxiety also correlated with impaired connections between the prefrontal cortex and the amygdala. In other words, feelings of stress and anxiety after a bad night’s sleep appear to be driven by a weakened emotional control system in the brain. Without the rejuvenating effects of sleep, the prefrontal cortex is less able to control how the amygdala processes anxiety, allowing fear to spiral to unhealthy levels.

But what is it about sleep itself that actually helps to relieve anxiety? The researchers investigated different stages of sleep to see whether some phases were more helpful than others. They found that one’s amount of slow-wave sleep during the night — the deepest phase of sleep occurring soon after falling asleep — predicted how much their anxiety levels would drop overnight. Simply put, more slow-wave sleep led to less anxiety in the morning.

The links between anxiety and sleep often flow in both directions. Higher anxiety during the night stops people from sleeping, and sleep deprivation makes them more anxious. That said, the researchers found that poor sleep made anxiety worse regardless of how anxious people felt the night before. To prevent the cycle from starting, it’s therefore important to make time for a full night’s sleep even after a good day with little stress.

Overall, the harmful effects of poor sleep run deeper than just feeling tired the next day. Good-quality sleep — in particular robust deep sleep — restores the ability of the prefrontal cortex to monitor and regulate emotional systems in the brain. Poor sleep damages how these systems process emotional information, which opens the door to hypersensitivity.

When people are anxious, they often see threats where none exist. Fortunately, sleep helps to boost the brain networks that prevent these overreactions. Sufficient shut-eye allows people to focus their energy on the tangible problems in their life instead of the toxic thinking patterns and manufactured worries that can make life seem overwhelming.

Neuroscientist writing about brains, behavior, & health. “Understand more, so that we may fear less” — Marie Curie.

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