Memory helps us assess situations on the fly, not just remember the past

Scientists have long known that the brain’s hippocampus is crucial for long-term memory. Now, a new study from Northwestern Medicine has found that the hippocampus also plays a role in short-term memory and helps guide decision-making.

Findings shed light on how the hippocampus contributes to memory and exploration, potentially leading to therapies that restore hippocampal function, which is affected by memory-related aging and neurodegenerative diseases such as dementia. , said the study’s authors.

In the study, scientists monitored participants’ brain activity and tracked their eye movements while viewing different complex images. Scientists have found that when we visually scan our surroundings and absorb new information, our hippocampus activates, using short-term memory to better process new visual information to help us quickly reassess situations.

How our memory helps us scan new environments

Imagine walking down the street and noticing a badly parked car on your neighbor’s lawn. Maybe you quickly dismiss it and move on. But when you see an ambulance and a fire engine approaching your position, you connect the dots and look back to see the scene of an accident. By using short-term memory to guide where you look, the hippocampus allows you to reexamine the car and form a lasting memory of the accident.

“At any point in time, your brain is rapidly triggering eye movements that you are usually unaware of,” said corresponding author James Kragel, postdoctoral researcher at Northwestern University Feinberg School of Medicine. “Our results suggest that the hippocampus uses memory to indicate where your eyes are looking, thus preparing the visual system to learn and re-evaluate our environment on the fly.

“If you haven’t looked back and seen the crash, you might not be able to encode this important information, but using short term memory recovery, you can tie these clues together and remember details that bring back greater memories. It all comes down to making connections between these disparate pieces that make it much easier for you to remember them later. “

The study will be published on June 18 in the journal Scientists progress.

“These results underscore that while hippocampal dependent memory is generally considered a thing of the past, in fact, it works in the moment to optimize our behavior and decision making,” said lead author of the report. study, Joel Voss, associate professor of social and medical sciences. , neurology and psychiatry and behavioral sciences in Feinberg. “This is the key to understanding hippocampal function and developing effective treatments for memory impairment.”

“It’s like using your memory to plan out what to expect, then when that doesn’t match up with what’s really going on, your hippocampus is activated to reassess and update your current perception of what’s going on,” Kragel said.

Eye movement tracking to learn more about memory

The study was conducted in patients with epilepsy who underwent neurosurgical monitoring at Northwestern Memorial Hospital to locate the source of their seizures. They had electrodes implanted in their brains to map brain activity related to seizures. While in the Epilepsy Surveillance Unit, participants completed a memory task in which they studied lists of complex scenes with multiple people and objects (for example, someone sitting on a park bench with food on the table, things going on in the background) followed by a memory test.

During the test, participants indicated whether a scene presented was old or new. Throughout the task, the authors simultaneously recorded eye movements and neuronal activity to link hippocampal activity to memory-guided behaviors.

When studying a scene for the first time, participants often returned their gaze to a place they had just seen hundreds of milliseconds before. These “revisits” eye movements improved spatiotemporal memory for scenes (remembering the location of an object or the sequence in which something happened). Brain recordings revealed the brain networks involved in the generation of these “revisitations”, as hippocampal activity changed just before they were performed. Increases of brain activity the ongoing revisits, which, according to Kragel, can form a lasting memory of the scene and its elements.

“This shows that the contribution of the hippocampus to Memory takes place over a few hundred milliseconds during continuous behavior, which is surprising given that the temporal course of its involvement, typically observed in long term memory recovery, is generally considered days to years, ”said Voss.