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New research has shed interesting light on human memory.
Imagine a video camera recording, say, the cash register at a convenience store. It records and re-records the day’s mundane transactions until something important happens – say, a robbery. At that point, the recording can be pulled out and the moments before the robbery occurred can be scrutinized. Boring days just get recorded over and forgotten.
It turns out memory may be something like that. A slightly traumatic event – in this case a little, electric shock – helped people better remember pictures they had looked at just moments before the shock.
“It is like the memory system has evolved to find a way to capture something meaningful and then replay this information,” says psychology professor Lila Davachi of New York University, who oversaw the experiments.
The findings, published in the journal Nature, suggest there could be a good way to improve peoples’ memories – perhaps people who are beginning to forget things, like early Alzheimer’s patients, says Davachi.
Her team was surprised by the findings. They were trying to figure out if an upsetting event – in this case an electric shock – would change the way people remember things.
“What is interesting about emotion and what we do know about memory is memory does get distorted with emotion,” Davachi told NBC News. People believe they remember details well when they are associated with a traumatic event, such as a car accident.
“People tend to report that they remember a lot of details with high confidence but it turns out they don’t accurately remember those details,” Davachi said.
Davachi’s team set up an experiment with 119 volunteers, who knew they might be getting a little shock. They showed the volunteers a series of pictures of either animals or tools. “Then they entered the next phase of the experiment, about five to 10 minutes later, where we attached leads to their wrists so we could administer a mild shock,” she said.
It was a conditioning phase – the volunteers were being trained, without knowing it, to associate either the tools or the animals with the shock. Some volunteers got shocked only with tool images; others were shocked only with animal images.
“What I am learning is there is a high probability I might get shocked if there is an animal on the screen,” Davachi explained.
Then they were shown more pictures – some old, some new. The volunteers were asked to remember which pictures they had seen before.
“What we expected to see was the animals that were paired with the shock, you would remember better,” Davachi said. And that was the case. “What was surprising was that we found that memory for the animals they saw before they were shocked was better than the memory for the tools,” Davachi said. And the same was true for people shocked while looking at tool images – they remembered the tools they saw before anyone had been shocked.
“Memory was selective and retrospective,” Davachi said.
So the shocks were enhancing some memories, but not others. And it took several hours for this effect to kick in, something that tells brain experts about the process that underlies this memory encoding.
It’s not entirely clear what this means, Davachi says. “The question is figuring out which ones are and which ones aren’t (accurate),” she said.
But there may be uses for helping people with memory loss. “In the early stages of cognitive decline, when people are just starting to lose memories for parts of their day, you could potentially think about developing a training program,” Davachi said.
She also plans more experiments, using functional magnetic resonance imaging to see what’s going on in the brain while the memories are being laid down, and seeing how long the effects of enhanced memory last.
“It would be important to know whether you could update and change memory that already had a chance to consolidate,” she said.