A new hypothesis, published this year in Limits in Network Physiology, states that the human mind is not meant to be awake after midnight. The researchers behind the study claim that an awake mind pays more attention to negative emotions than positive ones after midnight. They emphasize that the mind may even find ideas of self-harm more appealing if it stays awake long after bedtime. The research suggests that the human circadian rhythm — the body’s internal natural process that synchronizes the sleep-wake cycle every 24 hours — plays an important role in these fluctuations.
Previous studies have looked at the consequences of fragmented or insufficient sleep, such as increased stress, cardiovascular disease and dopamine fluctuations that can even lead to addiction. In addition, uninterrupted sleep during the night results in better cognition and overall healthier functioning the following night. The researchers took this into account and sought to investigate whether nighttime wakefulness, or choosing to stay up during the circadian or biological night, leads to maladaptive behaviors — behaviors that go against a person’s self-interest — such as violent crime, substance use, and even suicidal thoughts. In their study, the scientists state that they evaluated “how mood, reward processing and executive function differ during nighttime wakefulness.”
The researchers examined empirical data from existing studies on sleep and its effects on cognition and functioning. They suggest that the human body and mind follow a circadian clock — it’s meant to act and feel in certain ways at certain hours. So while molecular and brain activities are in full swing during the day, the body seeks rest at night.
There may also be an evolutionary rationale for explaining how nighttime wakefulness affects maladaptive behavior. When humans evolved in the wild, there was a high risk of being hunted at night; as a result, the brain increased its attention to negative stimuli during this time. Today, in the absence of such external risks, this hyperfocus on the negative has resulted in an altered reward/motivation system and consequently made people more susceptible to risky behavior. Therefore, during nighttime insomnia, people are in heightened consciousness and may feel encouraged to engage in more harmful behaviors.
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Citing a personal experience at the Mass General Research Institute — an affiliate of Harvard Medical School — the study’s lead author Elizabeth Klerman talked about her ordeal sleeping in Japan after severe jet lag. “While part of my brain knew I would eventually fall asleep, laying there watching the clock go tick, tick, tick – I was beside myself,” she recalled, adding “Then I thought, ‘ What if I was a drug addict? I’d be on drugs right now.’ I later realized that this can also be relevant when it comes to suicidal tendencies, substance abuse or other impulse disorders, gambling, (or) other addictive behaviors. How can I prove that?” This thought led her to work with her colleagues to formulate what they called the “Mind After Midnight” hypothesis.
Key evidence that helped shape the hypothesis was a 2016 study published by the National Library of Medicine, USA, which found that, statistically speaking, suicide was most likely to occur at night. That study found that suicide rates tripled from midnight to 6 a.m. than at any other time of the day. Another study, at a controlled drug consumption center in Brazil, found an almost five times higher risk of opioid overdose at night.
Existing evidence on shift workers – medical personnel, pilots, firefighters, etc. – shows that their unusual sleep patterns lead to health problems such as insomnia, caffeine addiction and a general feeling of restlessness. Klerman and her colleagues’ hypothesis, if properly researched, could provide clues that could be taken to explore how these workers, and several others, might be protected from the harmful effects of nighttime wakefulness.