You Must Remember This
In asking why we forget, it’s worth stepping back to ask what memory actually does for us. It’s not so warm recollections of our childhood or spouse enrich us emotionally, it’s to help us survive long enough to reproduce by remembering the sensory and emotional signals that lead to food, predators, sex, shelter, etc.
We all lament our awful powers or memory at some stage, but neuroscience actually shows the memory is a near-perfect mechanism for what it evolved to achieve. “We need to forget because we remember too much,” Hardt says. “Our brains are promiscuous memory makers. Most of these memories are completely useless, but there’s no way of figuring out what may be or may not be important in the moment, so the best strategy is to form a memory now and ask questions later.”
In fact, the superhuman memory we’d all like does actually exist, but people with highly superior autobiographical memory (HSAM, also known as “hyperthymesia” — from the Greek for “excessive remembering”) tend not to be particularly accomplished and have an increased tendency for obsessiveness.
As you can imagine, being overloaded with so much useless information we don’t really need in day to day life ends up crippling, rendering us completely inert as we try to sift through infinite signals.
Instead, many neurologists and psychologists believe memory is about the gist and not the details. Protohumans learned which waterhole attracted wild game, not the time of day they first visited, who might have vocalized the directions to them or whether the water was cold. Today you might remember a linguini recipe but not whether you got it from a book or online, who you first cooked it for or what color sweater you were wearing last time you made it.
Davis talks about a kind of snowballing effect memories might have when they take root in the brain, one which ends with the pruning of those extraneous details but retains the important stuff: “A memory might be represented by x number of neurons. The first ‘station’ might be the olfactory bulb where there could be 10 or 100 neurons that become part of learning about a given odor. Then it goes to the next portion of the circuit, the primary olfactory cortex, where there might be another hundred neurons, etc.
“So there are multiple stations each with perhaps 100 or more neurons in successive nodes within in a circuit, which means you may have 1,000 neurons that represent a memory. A major question then is, how many neurons have to drop out of that representation in order to forget? How many need to drop out to lose an engram? Might it be just one critical neuron?
“Maybe there’s a scaffold of neurons within that subset so you could start whittling away the ones that are responsible for the details of the memory, and be left with the neurons that represent the gist. If you’re talking about visual versus olfactory versus taste memories, for instance, there are going to be dozens of different ways the brain uses to forget.”
In fact, Hardt found just that in his lab rats. “You basically teach a rat that one particular box is bad news because it gives the rat a light electric shock, making it afraid of that box. If you put that rat in a new box it won’t be afraid because it remembers this isn’t the nasty box.
“But if you wait two weeks or so it won’t be able to distinguish between them and will fear any box that’s similar to the nasty box. It’s called ‘contextual fear generalization,’ and it happens because the rat forgets exactly how the nasty box looked, so it simply retains the gist that being put in a rectangular box is generally bad news.”
But something different happened when Hardt and his team stopped active forgetting of spatial memories for two weeks after the box experience. The rats that could no longer forget spatial details remembered what the nasty box looked like, so they were more afraid of the nasty box than of a new box. Their knowledge of what the nasty box looked like was preserved and they didn’t generalize their fear to new boxes.
In order to generalize knowledge about boxes and shocks and form a general rule like “these kind of boxes are bad news,” the rats needed to forget details about the box which taught them to expect the shock.
What’s more, remembering the gist but not the details has a parallel from a surprising area — artificial intelligence and machine learning, which gives us the concept of “overfitting,” where a memory process gets hung up on a particular (and irrelevant) detail and misses a big picture event it should have spotted.
“[AI has] regularization processes, which essentially make a memory fuzzier,” says Frankland. “The benefit is that you want to predict new situations, and that generalizes more readily to unseen data or a new situations. It’s something we’re actually working on — the idea that a regularized or fuzzy memory is much more useful than an overly detailed memory.”
In The Real World
And so, armed with knowledge about how memories build and how the brain very decisively targets and removes them using neurotransmitters, the next logical question is how that might help us?
Some of the most crippling and heartbreaking maladies of our time are either the premature and chronic degradation of memory (like Alzheimer’s) or the focused and emotionally traumatic retention of memories we don’t want, as with post-traumatic stress disorder (PTSD).
And now, active forgetting is opening up a new frontier in treatment possibilities. To Hardt, the focus on making memories biased our view a little, romanticizing memory as an automatic diary meticulously recording our lives. “It’s a view that promoted the idea that we have to look for ways to improve the making of memories instead of how to regulate the forgetting system,” he says.
Of course, there’s a long winding road leading from the activity of neurotransmitters (neurology) to the complexity of human emotional experience (psychology). Frankland reminds us that we still don’t understand how the brain works and cautions that it’s going to take a lot of difficult steps from there to treatments. But he adds you can measure and maintain a healthy level of neurogenesis to produce “good levels” of forgetting, which might be adaptive in weakening traumatic memories.
When it comes to Alzheimer’s disease, Hardt and his lab have wondered if it might not be a disease not of memory formation but excess forgetting, the neurotransmitters, enzymes, and other chemicals that regulate forgetting in a healthy brain run amok. Maybe the characteristic amyloid plaques and tangles found around neurons in Alzheimer’s sufferers are deposits caused by an excess activity of natural forgetting.
But he reminds us that engram is a philosophical and not a biochemical term. We can’t at present isolate and pluck out a memory, thus removing an episode or semantic fact from our brains like the fictional Lacuna, Inc. did in the film “Eternal Sunshine of the Spotless Mind.”
In referring to using the forgetting machinery to treat PTSD Hardt says: “I’m not sure it’d be in the interest of the individual to wipe out the entire PTSD episode but rather somehow dampen or reduce the emotional aspect of it.
“Targeting specific memories is the challenge and the best method for it presently is using the fact that when memories are being remembered they can be modified shortly thereafter, something called the ‘reconsolidation’ effect. For drug-based treatments it’s a challenge to target specific brain areas only — forgetting happens in many, if not all, brain regions, and if you speed it up with a drug you speed it up everywhere, so you’re at risk of losing all kinds of memories [not just harmful ones].”
Still, our new awareness that the brain works just as hard to forget as it does to remember represents what Davis calls a “huge leap forward.” And in upgrading what we’ve long thought of an irritating glitch to an essential mental process, he says there’s going to be much more activity in the area. “It’s a frontier that needs to be explored.”
More From Brain World
- All in Your Head? Why Some Memories Last a Lifetime
- The Art of Remembering Everything: A Q&A with Memory Champion Joshua Foer
- Fine-Tuning Your Instrument of Memory
- Memories in the Night: How Your Brain Comes Alive While You Sleep
- Not-So-Total Recall: The Elusive Story Behind What We Remember and Forget
- What “Tip of the Tongue” Tells Us About How Memory Works
