In this TED-ED lesson, Shai Marcu shows how sleep restructures your brain in a way that’s crucial for how our memory works.
TED-ED Lesson TRANSCRIPT:
It’s 4 a.m., and the big test is in eight hours, followed by a piano recital. You’ve been studying and playing for days, but you still don’t feel ready for either.
SO, WHAT CAN YOU DO?
Well, you can drink another cup of coffee and spend the next few hours cramming and practicing. But believe it or not, you might be better off closing the books, putting away the music, and going to sleep.
Sleep occupies nearly a third of our lives, but many of us give surprisingly little attention and care to it. This neglect is often the result of a major misunderstanding.
Sleep isn’t lost time, or just a way to rest when all our important work is done. Instead, it’s a critical function, during which your body balances and regulates its vital systems, affecting respiration and regulating everything from circulation to growth and immune response.
That’s great, but you can worry about all those things after this test, right? Well, not so fast.
It turns out that sleep is also crucial for your brain, with a fifth of your body’s circulatory blood being channeled to it as you drift off. And what goes on in your brain while you sleep is an intensely active period of restructuring that’s crucial for how our memory works.
At first glance, our ability to remember things doesn’t seem very impressive at all. 19th century psychologist Herman Ebbinghaus demonstrated that we normally forget 40% of new material within the first 20 minutes, a phenomenon known as the forgetting curve.
But this loss can be prevented through memory consolidation, the process by which information is moved from our fleeting short-term memory to our more durable long-term memory.
This consolidation occurs with the help of a major part of the brain, known as the hippocampus. Its role in long-term memory formation was demonstrated in the 1950s by Brenda Milner in her research with a patient known as H.M.
After having his hippocampus removed, H.M.’s ability to form new short-term memories was damaged, but he was able to learn physical tasks through repetition.
Due to the removal of his hippocampus, H.M.’s ability to form long-term memories was also damaged. What this case revealed, among other things, was that the hippocampus was specifically involved in the consolidation of long-term declarative memory, such as the facts and concepts you need to remember for that test, rather than procedural memory, such as the finger movements you need to master for that recital.
Milner’s findings, along with work by Eric Kandel in the 90’s, have given us our current model of how this consolidation process works. Sensory data is initially transcribed and temporarily recorded in the neurons as short-term memory.
From there, it travels to the hippocampus, which strengthens and enhances the neurons in that cortical area.
Thanks to the phenomenon of neuroplasticity, new synaptic buds are formed, allowing new connections between neurons, and strengthening the neural network where the information will be returned as long-term memory.
SO WHY DO WE REMEMBER SOME THINGS AND NOT OTHERS?
Well, there are a few ways to influence the extent and effectiveness of memory retention. For example, memories that are formed in times of heightened feeling, or even stress, will be better recorded due to the hippocampus’ link with emotion.
But one of the major factors contributing to memory consolidation is, you guessed it, a good night’s sleep.
Sleep is composed of four stages, the deepest of which are known as slow-wave sleep and rapid eye movement. EEG machines monitoring people during these stages have shown electrical impulses moving between the brainstem, hippocampus, thalamus, and cortex, which serve as relay stations of memory formation.