Say you’re walk up to a podium in front of a large, cavernous room that seats 2,000 people. You get up to the podium, nod nervously and take out any notes you have, placing them carefully on top of the podium. There’s a glass of water to the left; you notice it because you’ll probably need it later. You actually need it now — your throat has become dry with fear.
Flash forward a few months, when you’re remembering that experience. The cards, the glass, the color of the podium — they all stand out.
But what stands out the most, according to Anne McLaughlin, an assistant professor of psychology, is the way you felt.
“There’s a trace when that memory is recalled,” she said. “The thinking is that you’re actually recalling a memory every time you bring it up. When you remember those feelings, you’re actually recreating them. There’s no thing in your brain that holds memories, something that you can actually take out. You’re recreating the experience in the memory in the same way you created it the first time.”
And as exams are peeking around this week’s corner, understanding a memory’s creation could be an important guide to figuring out which studying techniques work, and which don’t.
The idea that recalling a memory is actually recreating an event is not a novice theory. But in a study released in the journal Science in September, scientists used electrodes to track brain cells — in this case, neurons — as they fired off when a memory was being created. When the scientists asked patients to relive the experience, they knew what memory the patients would recall even before the patient said it.
The same neurons that had fired off when the memory was created were the same ones that fired off upon recalling it.
In the study, American and Israeli scientists threaded electrodes through the brains of 13 epilepsy patients who were preparing for surgery. Patients then watched multiple 5- to 10-second video clips of popular sights and television shows. As they were watching, the electrodes recorded the activity of 100 neurons, located in or near the hippocampus, in each patient.
For certain videos, some neurons became highly active; these same neurons were, during other videos, either slightly less active or not active at all.
Scientists then distracted the patients, then asked them to recall something they had seen.
Neurons that had fired quickly during a certain video lit up again with the same frequency, even before patients spoke the name of the video.
This experiment provides evidence for what scientists have been trying for years to prove.
“We know a lot about what will likely become a memory and what will often disappear before becoming a memory,” McLaughlin said. “When you have a memory, it usually means you can retain that information in your brain. But there are many pieces of information that never make it into there — like a phone number, unless you really encoded it and commit it to memory. And there’s not some memory cell that represents your grandmother. There’s not a particular cell that means one thing.”
McLaughlin mentioned a study researchers performed on rats, in which they attempted to halt the rats’ memory as it was forming.
“They would have rats learn something and then interrupt the chemical transmissions that were happening,” she said. “They could control whether that memory got formed and then test later to see if it did. We don’t really know what really affects memory in the brain, why dome people can have a large part of their brain taken out and it has very little effect on memory. The brain is still a very huge mystery to us.”
