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The time-travelling brain

Tuesday 3rd May 2016 12:17 pm

What would it be like to only live in the moment? Or to relive the past over and over again? Dr Karl explores the extreme range of memory.

Without memories, it would be hard to remember who we are.

But there are at least three people living now (that we know of) who cannot recall any memories of their individual past lives. Each is a healthy, high-functioning adult.

One (AA, retirement specialist) is married, one (CC, with a PhD) is in a relationship, and one (BB) is single. Their memory gaps are not due to trauma nor degenerative diseases — they’ve always been that way. The condition is called severely deficient autobiographical memory (SDAM).

It’s not that they have no memory at all. They can learn, and remember, the history of World War II, the fall of the Berlin Wall, or the death of Princess Diana. But they cannot lay down those memories that integrate what they feel, with time and location details, in a movie-like fashion.

You and I can remember how delightful the ocean felt on our last holiday when we dived into it. We can retrieve and relive the feelings of the warmth and the saltiness of the moment. But these three with SDAM cannot.

AA can remember that she recently walked onto the stage to sing an old English folk song. But she has no idea how she felt on stage. She quickly forgets arguments and cannot hold a grudge — because she can’t remember what caused it. She can’t remember any books she’s read or movies she’s seen — each re-reading or re-watching is effectively her first experience of it, each and every time.

Certain parts of the brain are critical for us to lay down memories so we can ‘time travel’ into our past to relive it — and perhaps to understand ourselves better.

These regions include the left medial prefrontal cortex (mental projections of one’s self back through time) and the right precuneus (visual memory).

The three people with SDAM have reduced brain activity in these regions.

Some of us who ruminate on the past a lot might think it would be weirdly liberating to be living only in the here and now — in a state of easy-going eternal mindfulness.

But the rest of us probably love all our little golden memories, even if they are inaccurate and hazy — and wouldn’t want to give them up for the world.

Reliving the past over and over and over …

But as a complete contrast, there are some people who can remember most days of their lives as though they happened just a month ago. They have HSAM (highly superior autobiographical memory).

If you ask them what happened on June-the-something, 15 years ago, they’ll tell you it was a Wednesday, and that the day started off sunny, but there was a storm in the afternoon. On the way home, the train got delayed because a tree had fallen across the railway tracks. And sure enough, the public record agrees with their private recollection.

The first person with HSAM emailed a psychologist in the year 2000. Today, some 50 more people with this quirk of memory have been documented.

As compared to you and me, they have the same recall for events and personal experiences up to about a month ago. But then, as the months and years and decades roll by, their memories stay fairly constant, whereas ours relentlessly fade away.

Often, their HSAM began around the age of 11.

In most cases, they have a strong tendency to obsessive behaviours. They might keep a very detailed diary, or just before they go to sleep, they might pick a day at random and try to remember what happened on that day in successive years. They are more likely to fantasise about events that relate to themselves.

They are slightly better than the rest of us when tested for recall of visual objects, and associating names with faces.

But in other aspects of their lives, they are completely average. They might have five keys on their key ring, but not be able to say what each key is for.

Surprisingly, they are also slightly more prone to false memory. For example, in a specific test for false memory, they might remember seeing footage of a real news event — for which no footage at all exists.

I wonder what happens after an argument. Sure, they can forgive, but what about forget?

 

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This blog first appeared on Dr Karl's Great Moments in Science

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