When you rifle through your memories, what details stick out to you? If you could travel to Paris, would you be more likely afterwards to vividly recollect biting into soft, warm baguettes, or reflect on the knowledge that you enjoyed the bread without reliving it?
Not everybody remembers their life the same way. In fact, just like personality traits, people have different memory styles. Some tend to rely more on detailed sensory information when forming their memories, while others incorporate a lot of factual knowledge instead.
Scientists might be able to guess which style you favor by looking at your brain. In a recent study, researchers found that distinct activity patterns among several brain areas were associated with different ways of experiencing the past. These differences were present even when people were not trying to remember anything.
Beyond just shaping the feel of their memories, these different styles also direct people's planning and predictions for the future, and may correspond to other aspects of their personality, brain structure, or other cognitive abilities.
"Memory is really the root of a lot of what we do in life," said Signy Sheldon, a coauthor of the new research and psychological researcher at McGill University in Montreal, Canada. "It's not just that the way we remember affects how we recall that dinner that we had last summer when we were in Paris," Sheldon said. "That we're seeing these individual differences in memory style also has implications for individual differences in how people approach planning and problem solving."
Episodic or semantic?
Memories come in several types, two of which are episodic and semantic. Episodic memory is our memory of experiences and life events tied to specific times and places. Semantic memory, on the other hand, is a record of more abstract facts and knowledge we have learned about the world.
The autobiographical account that we record in our brain often incorporates both episodic and semantic memories: You remember your prom night, the people, the music. You also know what a prom night is and why you had one.
But the balance between these two ingredients in the autobiographical memory varies among people. Some people are best considered as episodic rememberers. When they think back on their experiences, they summon an imagery-rich memory full of sensory and perceptual details, and can call to mind more elaborate scenes than their fact-oriented counterparts, the semantic rememberers. If asked to think back on a sumptuous dinner they had, episodic rememberers will remember where they were sitting, what they wore and what the food tasted like.
"Somebody else might remember a dinner like that just as well, but they'll remember it more on a implicational level," Sheldon said. "They'll remember what happened, they'll remember where they were, who they were with, what they ate—but they won't have those rich details associated with that memory."
In rare cases, people have extreme abilities or deficiencies of these styles. Some people have "Highly Superior Autobiographical Memory," meaning they can remember what happened to them in the past in extreme detail. "If you ask them what happened January 24, 2014 they'll be able to tell you what they ate for dinner that night and whether it was raining or not," Sheldon said.
At the other end of the spectrum there are people with "Severely Deficient Autobiographical Memory." These are people who cannot relive their past at all. They can't remember what happened to them from a first-person perspective, and build their own past narrative relying only on facts they've learned about themselves.
Where do you land on the memory spectrum?
"What we wanted to do was see if these variations exist even within individuals who don't meet those extremes," Sheldon said. She and her colleagues asked 66 young adults to fill out a questionnaire called the Survey of Autobiographical Memory that the team had developed previously. The survey establishes whether someone relies more on episodic or semantic remembering, and you can take it online on memoryinventory.com, a website the scientists set up as part of their research.
The study participants then had their brains scanned at rest, when they were not trying to remember anything in particular. "We wanted to see if there was any inherent difference in the way the brain is connected in relation to these different styles," Sheldon said. "Even without the influence of [remembering] demands, you see predictable patterns in the brain in relation to different forms of remembering."
Sheldon and her colleagues measured how activity in the medial temporal lobe, part of the brain that contains structures critical for processing memories, synched up with activity in the rest of the brain. "This is a measure of how particular parts of the brain inherently talk to one another," Sheldon said.
What brain areas the medial temporal lobe talked most with depended on memory style. For people with more of an episodic memory style, the medial temporal lobe was more connected to areas of the brain that are involved in visual processing and perception. In people with a semantic slant, the medial temporal lobe was more connected to areas that help strategize and organize information.
"These findings suggest that the tendency to engage in episodic autobiographical remembering is associated with accessing and constructing detailed images of a past event in memory, while the tendency to engage in semantic autobiographical remembering is associated with organizing and integrating higher-order conceptual information," wrote Sheldon and her team, who published the findings November 19 in the journal Cortex.
Image: In episodic rememberers, the medial temporal lobe is more connected to visual processing-related regions in the occipital and parietal lobes (warm colors). In semantic rememberers, this area is more connected to areas in the frontal and temporal lobes that help organize information (cool colors). Credit: Sheldon et al. (2015).
The researchers don't know yet which style is more common. In future, they want to find out how the brain activity of people with different memory styles varies when they are actually trying to recall information.
Different diseases can primarily affect different memory systems, so knowing someone's style might be helpful if they ever develop a condition that causes memory loss. "If we know their memory traits, then perhaps we can design interventions that are going to gear more towards their way that they approach remembering in the real world," Sheldon said.