Most of what happens to you every day vanishes without a trace. Countless walks, interactions, meals, and discussions have little or no long-term impact on your brain. You will have no memory of many of the people you pass when you walk by them, or of particular words that someone spoke to you (even if you recall the gist of what they were saying).
What determines which events and interactions create memories? There are several ways to address this question, and they each lead to different perspectives on how to answer it.
The brain’s economy
One approach to thinking about the memories the brain stores is based on economics. The currency of the realm in the brain is energy. The brain itself is an energy-hungry organ. It is 2% to 3% of your body weight, but uses 20% to 25% of your daily energy supply. That is the physiological cost of generating electrical signals, processing the variety of chemicals neurons use to communicate, and creating subtle changes in the growth of brain structures.
In general, the brain uses about the same amount of energy per hour regardless of what it is doing. That is, the overall energy cost associated with generating all that chemical and electrical activity is about the same whether you’re thinking hard or mindlessly scrolling Instagram. That means that the brain is trying to minimize the amount of time that it devotes to any given task, because the more time you do something, the more energy the brain is allocating to that task.
Building a new memory has a physiological cost, because structures have to grow that influence the neurons in the pathway that is storing that memory to ensure that the pattern of brain activity associated with that memory can be created again.
Memories are more likely to be stored when the cost of creating the new connection is likely to reduce the amount of time the brain will have to spend doing something in the future. The brain is investing energy now to reduce future costs.
For example, if you have an important and deep conversation with a colleague, there is likely to be a future time savings to storing a memory of that conversation. When you see that colleague again, remembering that conversation will make the next discussion more efficient.
What kind of memory?
The word memory is inaccurate here. There are many different memory systems that the brain uses. The things we usually call memories are part of the episodic memory system, which stores memories of episodes of your life (like having a conversation with a colleague or going to the grocery store). You also have procedural memories, which are your memories of how to carry out a task like typing or tying your shoe. One other important memory system for your work life is semantic memory, which is your knowledge about what words and concepts mean.
All of these memory systems have the same basis in the brain’s economy. You will create physiological changes if it is likely that this will save you time later. Your procedural memory develops habits so that you can perform actions more quickly. In contrast, your semantic memory system refines the meanings of concepts to make you faster at understanding situations and communicating with others. Finally, your episodic memory system stores information when those situations are likely to be important enough that you will need that information again in the future to navigate a similar situation.
It’s important to keep these distinctions in mind, because you may not be able to recall a particular situation, but it still may have influenced your ability to carry out a procedure or it may have affected your knowledge of the world. So, just because you don’t remember doing something later doesn’t mean that it had no impact on any of your memory systems.
Desirable difficulty
One principle about memory that is valuable to know is the concept of the desirable difficulty, articulated by Bob Bjork and Elizabeth Bjork. You might wonder how the brain determines whether storing something is likely to make you faster at engaging with the world in the future. The brain uses the effort and engagement associated with an event as part of that calculation.
Both parts of the phrase desirable difficulty matter.
Let’s think first about difficulty. When you engage in intense and productive thinking, then you spend a lot of time and focused attention on that work. Because of that effort, the brain calculates that storing the results of that work is likely to make you faster at dealing with similar information in the future. So, if you work hard to solve a problem, then remembering the solution to that problem later is probably going to allow you to deal with that situation more quickly when you encounter it again.
What makes a difficulty desirable is that the work is ultimately productive. That is, you think hard or work hard with a colleague, and feel like you’re making progress. Storing a memory of that situation is likely to make life easier in the future. You have probably had situations, though, in which you encounter a problem so hard to solve or so far beyond your capacity that the engagement is frustrating rather than productive.
Frustration is an emotion that signals that your brain doesn’t want to keep working on it, because you’re wasting its precious energy on something that is not valuable. When you get frustrated in this way, you’re not likely to store much of the information you were thinking about, because it’s not likely to make you more efficient in the future.
Intensity of emotion
One other signal the brain uses to store information is the intensity of the emotion associated with it. You’re more likely to form a memory when a situation is particularly exciting, shocking, painful, or upsetting than when it elicits only a mild emotional response. The intensity and energy associated with the event influences the brain’s calculation that this information is likely to be useful later.
One reason that intensity matters is that intense emotions are often associated with important events or surprising events. You are elated because you have completed a significant goal. Or you are shocked because a highly surprising (and potentially dangerous) thing has happened. Or you are angry because someone or something has blocked you from doing something important.
Storing that information may be valuable in many ways. For example, when you experience a great shock, you may not have much of a chance to analyze what happened (and potentially what went wrong) in the moment. By storing a memory of the event, it gives you information you can think about later to help prevent you from experiencing a similar unpleasant surprise in the future.
There is much more to be said about what gets the brain to remember things. Whole books could be written on the topic (and indeed, several have). But the principles here give you at least some way of thinking about how to make it more likely you’ll remember things later (even if you don’t recall reading this particular article in the future).
