We’ve all experienced sleep-deprived grogginess, the feeling that everything’s hazy and our reaction time is a little slower than normal. Maybe you had a hard time concentrating during a meeting or it took a bit more effort to create your grocery list (What was I just about to write down?). Or, even worse, you got distracted while driving and stopped short at a red light. These are moments that can happen when we don’t get enough sleep.
But the effects our sleep habits have on our brains go beyond concentration and focus. Consider this: What if you couldn’t remember what you ate for dinner the night before? Or how to play your favorite song on the piano? What if you weren’t able to recall the name of your college roommate? The parts of the brain responsible for memories—how they’re processed and stored—and learning and recalling information are greatly affected by the quality of our sleep, which is why it’s so critical to maintaining brain health.
Let’s start with short-term memory, also known as your working memory, which requires your brain to hold on to a piece of information for a few seconds in order to complete a task—like remembering a phone number so you can call it just seconds later, or calculating the tip for your waiter in your head. This type of memory is stored in the front region of your brain, known as your prefrontal cortex, which is particularly vulnerable when you haven’t had enough shut-eye, making tasks like mental math more difficult.
But it’s your long-term memory, and its different forms, that show the biggest benefits from logging a healthy amount of sleep. Your long-term memory can store an unlimited amount of information over a long period of time—anything from a fact you learned in grade school to the moment you watched your child take his first steps. These are the details we want to remember—and are worried about forgetting. So how does sleep help us keep that information readily available, and help protect us from serious diseases like Alzheimer’s? Truly restorative sleep—sleep in which you enter all 4 stages of the cycle—allows your brain to transfer data into a “storage bank,” making room for new information. While you sleep, your brain’s hippocampus sorts and consolidates the information before sending it along to the frontal lobes for long-term storage. And during that process, the communication between your brain’s neurons becomes stronger, allowing you to not only hold on to all those facts, skills and experiences but also to recall them later on.
Now, let’s look at the various forms of long-term memory.
Your declarative memory holds information you know for a fact: your husband’s birthday, the days of the week, the names of all 50 states. When you recall this knowledge, it’s a conscious effort, but you “declare” it because you know it’s true. Your deep sleep—stage 3—becomes essential to your declarative memory. In this slow-wave sleep, often referred to as SWS, your slowest brain waves, known as delta waves, begin to appear, allowing your brain to process and consolidate information so that you can store it and call it up later.
When you enter into rapid eye movement (REM) sleep—stage 4 of the cycle—a structure in your brain called the amygdala is active. This is a part of your limbic system, the area associated with your emotional memory—a more complex type of declarative memory. Your emotional memory holds information associated with a feeling—whether it be a good or bad one. Simply put, REM sleep is strengthening your brain’s ability to feel the associated emotion when you recall that experience.
But REM sleep also plays a critical role in the health of your cognitive procedural memory—what helps you remember how to do things, like make your famous stew or play your favorite song on the piano. Lighter stages of sleep, like stage 2, support your procedural memory too—especially the parts that rely on motor skills, like tying your shoes or riding a bike. In this sleep stage, your brain starts to produce bursts of rapid, rhythmic brain wave activity, known as sleep spindles, which are associated with our ability to learn new tasks. These electrical impulses, often occurring in the top layer of the brain, team up with other regions to make room for more learned skills, which will eventually be stored as well.
While we all aim for a good night’s rest in order to feel energized and alert the next day, a healthy dose of sleep is imperative to maintaining a strong memory as well as the ability to learn and recall skills and tasks—now and in the future. Giving your brain the time it needs to properly transfer and store information will help keep all of that data readily accessible. And as those hardworking neurons continue to communicate, your mind will welcome new information and your memory bank will remain full.