If you've been experiencing poor sleep over a period of time, whether it's from burning the midnight oil, insomnia, or habitual tossing and turning, you might wonder what that sleep deprivation is doing to your brain. Adults need an average of eight to nine hours of sleep a night, according to the National Sleep Foundation, and while there are rare people who do function well on less, chances are you're in the majority. If you've been cutting into your sleep time recently, there can be some pretty substantial neurological consequences.
It's important to remember that many studies on sleep loss focus on the chronic end of sleep deprivation, where humans and animals are kept awake or have their sleep restricted repeatedly over days or weeks. That's what happened, for example, in a study in 2017 that revealed that mice with severe sleep deprivation saw an uptick in the activity of immune cells in the brain (not good news in the long term). If you experience enough sleep deprivation, you can start experiencing hallucinations and become vulnerable to psychosis; there's a reason that stopping prisoners from sleeping is a torture technique. When it comes to sleep deprivation and the brain, it's all a matter of degree — but a single night can in fact make a difference.
"Sleep changes the physical structure of the brain on a microscopic level," Dr. Avram R. Gold, a sleep disorders expert at Stony Brook University, tells Bustle. And studies have shown the effects are wide-ranging. "Functional neuroimaging has revealed that frequent and progressively longer cognitive lapses, which are a hallmark of sleep deprivation, involve distributed changes in brain regions including frontal and parietal control areas, secondary sensory processing areas, and thalamic areas," researchers wrote in 2009. However, it's not just about separate areas: it's also about the brain's own overall functioning.
Memory processing is an example. "Sleep deprivation causes the undoing of synapses in the hippocampus that were formed to store short-term memory," Dr. Gold says. "During sleep, short term memory is transferred to long-term memory storage in the other parts of the cortex, the synapses that stored the memory in the hippocampus are undone, and the hippocampus has space to store new short-term memory." The problem? "Sleep deprivation gets in the way of this undoing of synapses. They remain intact in the hippocampus keeping the memory current," he says.
"A number of studies confirm the effects of sleep deprivation on long-term memory, and it is believed that this effect may be partially related to impaired synaptic plasticity, which can alter the number and function of cerebral neurons involved in memory," Dr. Heidi Moawad wrote in Neurology Times in 2017. Synaptic plasticity refers to the brain's ability to produce new neurons, or brain cells, and make connections between them — a crucial aspect of memory creation while we sleep. If you're not sleeping, that process is hampered, with consequences for what you can remember in the future.
Sleep deprivation also affects how brain cells communicate. In a study from UCLA in 2017, people with epilepsy who also had sleep deprivation showed "sluggish" communication between their brain cells — and that impaired how they interpreted visual stimuli and performed on various tasks. This finding has been mirrored in studies in other people; a review of sleep deprivation studies in 2017 found that electrical signals within and between different parts of the brain — which are how neural cells communicate — tend to be much lower in sleep-deprived people. Cells stop talking effectively both to the cells in their vicinity and to those in other areas of the brain. That's why complex tasks that involve multiple areas of the brain tend to be much more difficult when you're sleep-deprived.
"We now know that sleep deprivation interferes with brain function at a cellular level," sleep doctor Dr. Michael Breus tells Bustle. "We’ve got billions of neural cells working on our behalf, enabling us make decisions, process information, focus on important information—and remember it down the road. Sleep deprivation slows that work down, compromising our mental performance."
Various areas of the brain also seem to become hyper-sensitive when you're sleep-deprived. One example is the regions of the brain that related to rewards, or the good feelings we get when we do something fun. The review in 2017 found that some of these regions "seem to become hypersensitized by the state of acute sleep deprivation" — and that makes us less capable of judging risks and rewards in situations like gambling. When we're sleep-deprived, we become much worse at assessing our odds in gambling tasks, which means we're likely to bet wildly and take big risks.
Part of sleep deprivation's effect on the reward system is explained by what lack of sleep does to dopamine. Researcher Nora Volkow, speaking at Harvard in 2018, noted that dopamine, the neurotransmitter that carries communications between various brain cells, is affected by sleep deprivation over time. Brain cells in a sleep-deprived person, she explained, could release dopamine, but not receive it. That can seriously destabilize the normal neurological activity of dopamine — and that's a problem.
Dopamine levels in the brain influence everything from movement to motivation levels and sensations of reward, and the effect of sleep deprivation on dopamine receptors explains why our motivations and judgements of risk can be so scrambled after a few nights of impaired rest. One night of sleep deprivation has actually been shown to boost dopamine levels artificially, though they may decline over time. This explains why some people feel euphoric or punchy when they're sleep deprived.
Hyper-sensitivity in sleep deprivation also occurs in another area of the brain: the amygdala, which is often responsible for regulating our emotions. When we're sleep-deprived, the part of the brain responsible for calming the amygdala down stops working so well, leading to a very over-active amygdala and "emotional instability," according to research published in 2018. A hyper-sensitive amygdala means we're more vulnerable to mood swings, will respond with more intensity to emotional triggers, and will be more afraid, depressed, fearful, and anxious; the 2017 review study noted that one night of sleep deprivation amped up the amygdala's response to scary images by 60%. "Even a single night of sleep deprivation sets us up to react more strongly and impulsively to negative or unpleasant situations, according to research," Dr. Breus tells Bustle.
Sleep is also important for the brain's internal cleaning. "There is a system for the elimination of possibly harmful proteins such as abnormal variants of amyloid," Dr Michael S. Jaffee of the University of Florida's Department of Neurology wrote for The Conversation in 2018. "This waste removal process, using what is known as the glymphatic system, relies on sleep to effectively eliminate these proteins from the brain. These are the same proteins found to be elevated in patients with Alzheimer’s disease. Studies show that older adults with less sleep have greater accumulations of these proteins in their brains." If you're vulnerable to this kind of protein build-up, sleep deprivation hobbles the system that attempts to clean it up.
Fortunately, one night isn't going to cause lasting damage. "A single night of sleep may alter alertness and emotional control, transiently. But it is unlikely that it does any specific damage to the brain," Dr. Gold tells Bustle. However, if you're perpetually in need of some shut-eye, you're not just stumbling around because your muscles are tired. Your brain itself may be changing, and it's a good idea to give it some rest.