Losing one's mind is a primal fear.
After cancer, it's perhaps the greatest concern most of us share as we grow older.
The loss of memory doesn't just frustrate those who struggle with it. It also causes them to fret about what life will be like when they no longer remember names, places, and eventually loved ones.
But a new science of forgetting is challenging the way we think about memory loss.
The act of forgetting, experts now say, is not always a sign of decay. It's an essential part of the way the brain functions.
And gaining a greater understanding of the mechanics of forgetting could help us better deal with debilitating conditions like Alzheimer's and post-traumatic stress disorder (PTSD).
The forgotten science
Researcher Oliver Hardt from Canada's McGill University dates the first scientific study of memory to a publication by German psychologist Hermann Ebbinghaus in 1885.
The pioneering psychologist was interested in both memory formation and loss. But during the 20th century, forgetting increasingly became seen simply as a failure of memory, with no biological function of its own, according to Dr Hardt.
But that perception has begun to shift over the past decade.
Dr Scott A. Small, the director of Alzheimer's research at Columbia University, argues that memory and forgetting are intrinsically linked.
"Just like an engine needs an accelerator and a braking system, so too does our mind," he tells ABC RN's Future Tense.
Dr Small says the neurons in our brains have two separate mechanisms: one dedicated to constructing memories and the other to disassembling the components of memory.
"If one revisits neurology, psychology, psychiatry, one can see many examples where we really need our normal forgetting to countervail, to squelch, to sculpt our memories."
Forgetting as a way of prioritising
So, forgetting can be a positive thing, it's not always a marker of deterioration.
Dr Small draws a distinction between what he terms "pathological" forms of forgetting, like Alzheimer's, and "normal" forgetting – not remembering a name or where you put your car keys.
And he says just like memory, our ability to forget varies from person to person.
"It's just like height and weight, there's a normal distribution," he says. "There are some people who have better or worse memory just naturally; there are some people who have better and worse forgetting; and it turns out the one has to be balanced with the other."
But what is its evolutionary purpose?
Dr Hardt believes the process of forgetting is a form of vetting, allowing the brain to better prioritise stored information.
"And forgetting is the process by which the brain decides which of the multitude of memories it encodes every day … can be discarded."
Without that kind of active forgetting process, argues Dr Hardt, our brains would soon be cluttered with useless information.
"That is the context in which our brains evolved, in order to survive, it is best to retain as much as you can of what happens right now and then decide later what to forget."
Dr Small says some memories are "stickier" than others.
"We tend to spray-paint our mind with negative emotions. Our brain tends to record bad memories or fearful memories more than happy memories."
Too much memory
The new science of forgetting is also prompting a medical reassessment of the way in which we think about brain-related disorders and the best strategies for treating them.
Post-traumatic stress disorder (PTSD) is now increasingly being seen as a breakdown of the brain's vetting system.
"PTSD is fundamentally a disorder of too much memory," says Dr Small.
"If you think about any trauma that any of us experience, if we were to re-live the emotional fear of that event over and over again in perpetuity, we would be anxious and distressed. That's PTSD.
"That's an example where memory needs to be turned down by our forgetting mechanisms, our emotional memories. In fact, that is what is being tested right now — think drugs like MDMA [methylenedioxy-methamphetamine] which we now know effectively turn down our fear memories."
Alzheimer's disease is the other major brain disorder now under review.
The Australian Institute of Health and Welfare says dementia is the second leading cause of death in this country, with over 70 per cent of cases involving Alzheimer's.
The institute says in 2021, dementia afflicted somewhere between 386,000 and 472,000 Australians.
Dr Hardt says there has been very little progress in treating Alzheimer's over the past three decades, but he says the science of forgetting, and the new perspective it brings, offers some hope.
"It might actually be that the treatment of Alzheimer's cannot focus on memory formation, it needs to focus on the dysregulated forgetting process."
Alzheimer's, he theorises, could be a lifestyle disease caused by a lack of social stimuli as we get older and thereby throwing the relationship between memory formation and forgetting off-kilter.
"When our lifestyles actually no longer promote these inputs, that's when things get out of balance. Perhaps these forgetting processes are slightly overactive, perhaps they can spiral out of control."
Isolation and lack of social stimuli are also making PTSD worse.
Both Dr Hardt and Dr Small worry about the long-term mental health impacts of the global pandemic.
"And here we have clearly a trauma — the pandemic. And yet our medical recommendation is to socially isolate.
"So, there is an anticipation that there's going to be a very specific form of post-pandemic PTSD because of this sort of double-whammy."
How effectively the world will respond to a massive increase in brain-related disorders is yet to be seen, but Dr Small is looking to governments to start thinking of the medical consequences of this looming problem.
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