THERE are few things more frustrating than trying to recall a fact or memory and finding it has gone missing. You might ask yourself whether it is the start of mental decline or the onset of a degenerative brain condition. What you probably don’t think is that forgetting is a good thing. But it can be. New research into memory suggests that it is actually a healthy and necessary brain function – and one that is becoming increasingly important in our rapidly changing lives. “You want to be able to adapt to your environment because your environment is always changing. But if you’re overly fixated on your first experience, you’re not going to behave adaptively,” says at Trinity College Dublin in Ireland. Intriguingly, his research also hints that forgotten memories remain in the brain, so could, if necessary, be restored.
Everyday forgetting – like not being able to recall what you ate for dinner last week – is called natural forgetting. This is in contrast to pathological forgetting, which results from brain injuries or conditions such as Alzheimer’s. Far from being a problem, natural forgetting underpins one of our most unique and powerful traits – our ability to generalise. Though there are times when having an ultra-detailed memory is invaluable, like when revising for exams or acting as a witness to a crime, we can’t generalise without playing fast and loose with specifics, says at the University of Glasgow, UK. “For a chair to be thought of as a chair, it doesn’t necessarily have to have wood or leather upholstery, it only requires a few features. Remembering the exact details of a chair is potentially unhelpful because it prevents you from generalising across all instances of a chair.”
But natural forgetting may have another advantage. “It’s easy to come up with behaviours that you can train an animal or human to do, and then in two weeks’ time they have forgotten it,” says Ryan. “We’ve let ourselves think that’s just because of time going by and the memory degrading. But actually, over that two-week period, the individual is experiencing all kinds of things and, as a result of those things it’s experiencing, it’s actually changing its expectations.” That matters because expectations play a key role in an emerging picture of the brain as a prediction machine, where conscious experience consists of predictions about what the brain expects to perceive based on what it detects via the senses. This wouldn’t work unless the brain could tweak and update its predictions in the form of forgetting, says Ryan.
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What’s more, research by Ryan and his colleagues challenges the idea that our outdated memories become lost for good. Each memory is thought to be stored in the brain in a suite of physical and chemical changes in groups of neurons called engrams. Using drugs to block the formation of specific proteins in engram cells, the researchers were able to prevent recently formed memories in mice from being stored as long-term ones. Later, when the researchers stimulated the original engrams using optical light stimulation or by presenting the animals with information similar to that which formed them, . This suggests that even memories that aren’t stored long term still exist in the brain somehow and can be retrieved given the right circumstances.
Stimulating dormant engrams could be a promising route for restoring memory in people who have experienced pathological forgetting. One day, these new insights might even help us to optimise our natural forgetting. For now, they should make us more forgiving of forgetting, says Ryan, because it signifies that you are adaptive to your environment.
