We’re all familiar with the feeling of running on fumes after a night of little to no sleep. Sleep deprivation doesn’t just feel terrible, though: It also can hamper your ability to form and recall memories.
Even just one night of less than six hours of sleep can impair your short-term memory the next day, said Dr. Richard Castriotta, a sleep medicine specialist at Keck Medicine of the University of Southern California. Not everyone responds to sleep deprivation in the same way, but generally speaking, the longer you go without adequate rest, the greater the burden on your brain. Extreme sleep deprivation — being awake for 24 hours or more — can even make people behave as if they’re intoxicated, he said.
“If we go without sleep,” said Dr. Indira Gurubhagavatula, a sleep specialist at Penn Medicine, “we ourselves are aware that the next day we have a hard time remembering things: ‘Where did I leave my keys? What’s that person’s name?’”
As a person rests, the brain strengthens and synthesizes the connections between neurons that were formed during the previous day, which helps store memories — a process known as consolidation. Some researchers think that rapid eye movement sleep, or REM sleep, plays a particularly powerful role in locking in memories and helping us process emotions, Dr. Gurubhagavatula said.
“Sleep is not a passive process,” she added.
When people wake up before they are fully rested, they get less sleep overall and also may get less REM sleep, Dr. Gurubhagavatula said. They may also miss out on the last and longest period of REM sleep, which happens in the final hours of rest.
Because of that, “you might notice you can’t remember things as well,” she said. “You might be a little bit more edgy or irritable or anxious, just not in your best state.”
If you haven’t slept well, you also may struggle to fully pay attention to what’s in front of you, which makes you less likely to remember it later. The same goes if you’re feeling emotionally overwhelmed, anxious or preoccupied — your mind isn’t fully present. This can limit how much information our brain encodes, said Dr. Sharon Sha, a clinical professor of neurology and neurological sciences at Stanford University.
As a result, people may have trouble remembering details from conversations or events that happened while they were deprived of sleep. Your brain might not encode where you parked, for example, Dr. Sha said.
A lack of sleep can also lead to what Dr. Sha calls a “retrieval deficit,” which may mean people need an extra nudge to recall short-term memories. Maybe your brain did store the details of a meeting you recently sat through after a sleepless night, but you need a reminder — the topic of the conversation, or the joke your boss made midway through — to jog your memory.
Short-term sleep deprivation does not affect more deeply entrenched information, known as remote memories, Dr. Sha said. Even if you’re extremely fatigued, most people can remember biographical details they’ve known for many years, like the names of the streets they grew up on.
In most people, “remote memory is really, really sharp,” Dr. Sha said. “And it’s more recent information, or when we were having that sleep deprivation, where we tend to have more difficulty.”
Getting less than a sufficient amount of sleep can negatively impact the frontal lobe of the brain. It’s an area involved in memory retrieval and executive function (a set of skills that includes the ability to multitask and make decisions), said Dr. Michael Rosenbloom, a behavioral neurologist at the University of Washington School of Medicine.
One large study of more than 479,000 adults between the ages of 38 and 73 found that people who said they typically slept between three and six hours performed worse on cognitive tests that measured their executive function than people who slept between six and eight hours. These tests included tasks involving working memory, which refers to the brain’s ability to hold and use a small amount of information, like remembering the content of a sentence you just read or what was on your grocery list.
The researchers controlled for age, smoking status and other health factors that are known to predict cognitive performance. The study found that the cognitive performance of those who reported regularly sleeping between three and six hours declined with every additional hour of sleep that was missed.
It may take several nights of solid sleep to offset the effects of a bad night, Dr. Gurubhagavatula said. It may get more difficult with age to bounce back from sleep deprivation, she said, but “all of us are vulnerable to this.”
