Why It's Vital to Empty Your Head Every Night
The brain literally flushes most of our life away. Lucky for us.
Posted April 22, 2015
Pay close attention to your butt.
As you sit reading this, feel your posterior—and the back of the top of your thighs—press into your chair. Now notice that, until I called attention to it, you weren’t aware what was happening with your butt and thighs.
This same lack of awareness applies to the majority of sensations pouring into your brain. You don’t focus on the feel of your clothes against your body or background sounds like the hum of your refrigerator or the change in temperature of your breath each time you breathe in and out (the air going in always feels cooler than the air going out). Similarly, while you read, a tremendous amount of visual information in your peripheral vision goes unnoticed.
Your brain automatically chucks all this sensory information into a mental trash can so that you don't accumulate clutter that will get in the way of perception, thought or memory.
Tomorrow, you might remember the sensations on your butt and thighs or the feel of your breath today because I made you pay attention to these things, but you don’t remember years and years of similar sensations because your brain flushed them away before they could be stored.
Raw sensations are not the only information your brain relegates to the re-cycle bin.
Think back over your life: If you pick any random day—say, August 12, 2013—it’s very unlikely that you can remember the events that happened that day, unless you check a calendar and think hard about where you were and what you were doing. Even after going through this exercise, you probably can only recall vague facts: "That particular day was a Monday so I was probably at work and probably commuted back and forth," etc.
The sad truth is that you don’t remember the vast majority of your life because—like the pressure on your butt—your brain has thrown most of your life experiences into a trash can, then emptied that can.
Yes, you remember the day you graduated high school, got married, had a child, lost a parent or watched the events of 9/11—some things do escape the trash bin. But most days of your life are either a vague haze or gone entirely.
How does your brain decide what to keep and what to throw away?
A quick experiment will provide clues: Grab a pencil and paper, then scan your eyes quickly over each of the 9 images below, allowing no more than 3 seconds to look at the full set, or 1 second per row of images. Next, close your eyes, count to 20, then open your eyes and—without looking back at the images—write down a brief description of each photo you remember.
Odds are that you won’t remember all of the pictures, but even if you do, the photos at the top of your list will probably be: the rabbit with a waffle on its head, the cheetah on a branch, the building with a tree growing out of its side, and the 17th-century musician with a guitar.
Why? Because those images represent a departure from “normal," whereas it’s not unusual to see objects in the remaining images. You recall details surrounding births, marriages, deaths, and major news stories precisely for the same reason: They represent a major departure from the normal flow of your life
In other words, your brain likes to hang on to information that’s “abnormal," and trash information that’s "normal.”
Your brain does this because retaining “abnormal” data keeps you out of trouble. Events that are everyday occurrences rarely cause you problems because you can predict and prepare for things like rush-hour traffic, winter weather, and even reckless drunk New Year’s Eve drivers. What could threaten your well-being most are unpredictable events for which you are unprepared, such as a mugging in a “safe” part of town, a sudden rainstorm on a sunny day...or a cheetah lounging on a neighborhood tree.
So it makes perfect sense for your brain to remove “normal” memories so that they don’t interfere with “abnormal” information that could prevent nasty surprises. As amazing as our brains are, they can only store, and quickly retrieve, limited amounts of information; so it’s a good idea for that stored information to maximize our odds of survival.
Recent research suggests that mental trash removal is so important that it does not happen passively by gradual decay, but is an active process in which your brain selectively erases memories it believes are of little value. Neuroscientist Oliver Hardt and colleagues at McGill University recently found that this process of selective active memory erasure takes place while we sleep.
It seems that we go to bed knowing more than when we wake up the next day, but what we remember in the morning is the important stuff.
If you think your brain is erasing more memories than you’d like, you don’t have to let it make automatic “trash removal” decisions. You can intervene to retain more memories by “manually” telling your brain to store them. The simplest way to do this is to pay close attention to details you want to recall. Your brain won’t throw out data—such as the fact that your breath is cooler going in than coming out—that you take time to actively notice. Your brain will also keep information that you repeat over and over (like a phone number someone has given you). Finally, if there are particular memories—say, of a pleasant vacation—that you want to keep, revisit those memories often. Each time you call up a memory, your brain takes notice, and will avoid erasing it while you sleep.
One way or another, you can best preserve memories by telling your brain that they're important.
Ron Davis of the Scripps Research Institute has examined the neurotransmitters involved in memory formation and forgetting and concluded that dopamine plays an active role in erasing unimportant memories almost as soon as they are formed. According to Davis:
"The study suggests that when a new memory is first formed, there also exists an active, dopamine-based forgetting mechanism—ongoing dopamine neuron activity—that begins to erase those memories unless some importance is attached to them, a process known as consolidation that may shield important memories from the dopamine-driven forgetting process."
Now…since I’d like your brain to avoid erasing this article from memory with dopamine (or while you sleep) I’ll leave you with a thought that is (hopefully) sufficiently abnormal, and so I’ll end the article the same way I began it, with your butt—specifically, that by erasing memories about your rear end, your brain is in the best position to save it.