You Can Choose Your Memories

In the earliest days of research, memory was thought to be populated with socalled engrams, memory traces that were localized in specific parts of the brain. To locate one such engram—for the memory of a maze—psychologist Karl Lashley taught rats to run through a labyrinth. He then cut out various parts of their brain tissue and put them right back into the maze. Though the rats’ motor function declined and some had to hobble or crawl their way woozily through the twists and turns, the animals never altogether forgot their way, leading Lashley to conclude that there was no single location that stored a given memory. Rather, memory was widely distributed in a connected neural network—one that may look rather familiar to Holmes.

Today, it is commonly accepted that memory is divided into two systems, one short- and one long-term, and while the precise mechanisms of the systems remain theoretical, an atticlike view—albeit a very specific kind of attic—may not be far from the truth. When we see something, it is first encoded by the brain and then stored in the hippocampus—think of it as the attic’s first entry point, where you place everything before you know whether or not you will need to retrieve it. From there, the stuff that you either actively consider important or that your mind somehow decides is worth storing, based on past experience and your past directives (i.e., what you normally consider important), will be moved to a specific box within the attic, into a specific folder, in a specific compartment in the cortex—the bulk of your attic’s storage space, your long-term memory. This is called consolidation. When you need to recall a specific memory that has been stored, your mind goes to the proper file and pulls it out. Sometimes it pulls out the file next to it, too, activating the contents of the whole box or whatever happens to be nearby—associative activation. Sometimes the file slips and by the time you get it out into the light, its contents have changed from when you first placed them inside—only you may not be aware of the change. In any case, you take a look, and you add anything that may seem newly relevant. Then you replace it in its spot in its changed form. Those steps are called retrieval and reconsolidation, respectively.

The specifics aren’t nearly as important as the broad idea. Some things get stored; some are thrown out and never reach the main attic. What’s stored is organized according to some associative system— your brain decides where a given memory might fit—but if you think you’ll be retrieving an exact replica of what you’ve stored, you’re wrong. Contents shift, change, and re-form with every shake of the box where they are stored. Put in your favorite book from childhood, and if you’re not careful, the next time you retrieve it there may be water damage to the picture you so wanted to see. Throw a few photo albums up there, and the pictures may get mixed together so that the images from one trip merge with those from another one altogether. Reach for an object more often, and it doesn’t gather dust. It stays on top, fresh and ready for your next touch (though who knows what it may take with it on its next trip out). Leave it untouched, and it retreats further and further into a heap—but it can be dislodged by a sudden movement in its vicinity. Forget about something for long enough, and by the time you go to look for it, it may be lost beyond your reach—still there, to be sure, but at the bottom of a box in a dark corner where you aren’t likely to ever again find it.

To cultivate our knowledge actively, we need to realize that items are being pushed into our attic space at every opportunity. In our default state, we don’t often pay attention to them unless some aspect draws our attention—but that doesn’t mean they haven’t found their way into our attic all the same. They sneak in if we’re not careful, if we just passively take in information and don’t make a conscious effort to control our attention—especially if they are things that somehow pique our attention naturally: topics of general interest; things we can’t help but notice; things that raise some emotion in us; or things that capture us by some aspect of novelty or note.

It is all too easy to let the world come unfiltered into your attic space, populating it with whatever inputs may come its way or whatever naturally captures your attention by virtue of its interest or immediate relevance to you. When we’re in our default System Watson mode, we don’t “choose” which memories to store. They just kind of store themselves—or they don’t, as the case may be.

We can cognitively choose what memories will be stored longterm and which to let go, but we normally operate on autopilot, allowing novelties into our longterm memory-space.