Why we have to forget to remember

When we forget something, it often feels like a failure.

But according to psychologist Oliver Hardt, if we lost the ability to forget, we might also lose the ability to remember.

In the moment, the brain can't tell which experiences are important and which are useless — so as we go through our days, it records everything it can.

"We believe the brain is some form of promiscuous encoding device. It just forms memories of basically anything you pay attention to," Hardt told The Sunday Edition's host Michael Enright.

"If that goes on unchecked for days and days, the brain will be flooded with an army, almost, of useless memory demons that distract you in any way possible."

Hardt, an assistant professor at McGill University who specializes in cognitive neuroscience, said scientists weren't the first ones to identify this problem.

In his 1942 short story Funes the Memorious, Argentine writer Jorge Luis Borges wrote about a man who is tormented by his inability to forget.

"That character Funes is basically unable to operate normally during the day. If Funes sees a glass of red wine, immediately anything that is associated with this glass of wine is remembered automatically, like grapes, the process of harvesting, events, and stuff like that," Hardt said.

At the end of the day, the brain needs to free up space to make room for new memories.

That's where the brain's automatic forgetting process comes in.

Hardt explained "neuromodulatory events" help the brain figure out which experiences are important.

"If you get excited, or afraid, or you have a moment of surprise, or there's something novel in it you didn't expect, these experiences cause the release of certain substances in the brain [like dopamine and norepinephrine]. They improve the memory-making process that is going on in the moment," he said.

If there is a strong emotion associated with a memory, there's a greater chance it will withstand the brain's natural forgetting process.

"You can imagine that during the day all these new connections are formed, because you have all these experiences. Some of these connections get a special kind of flag," he explained. "Anything gets weakened that doesn't have that protective little flag attached to it."

In a wide-ranging interview, Hardt spoke with Enright about why it's so hard to intentionally forget something, why "flashbulb" memories of big news events are unreliable, and the relationship between normal forgetting and the pathological forgetting experienced by people with Alzheimer's and dementia.

Click 'listen' above to hear the interview.