Northwestern Medicine investigators have discovered a tight-knit relationship between eye movements and memory, finding that memories retrieved from the brain’s hippocampus influence what we choose to look at and when, according to findings published in the journal eLife.
The hippocampus, located deep within the brain’s temporal lobe, is essential for learning and episodic recall, or the retrieval of memories from the past. The challenge in studying these processes, however, has been understanding how these two mechanisms work when they occur simultaneously in the hippocampus, according James Kragel, PhD, a postdoctoral fellow in the Department of Medical Social Sciences and first author of the study.
For the current study, the investigators decided to track eye movements to determine whether memory retrieval or novel information guides visual behavior.
“We rapidly move our eyes three or four times per second, and because they happen so fast, they typically fall under our radar. Eye movements provide one of the fastest behavioral measures to be able to track neural processes,” said Donna Bridge, PhD, a former faculty investigator in the Department of Medical Social Sciences and senior author of the study.
Participants with a medical history of epilepsy were asked to complete an object location association task, which required them to learn where objects appeared on a screen. Each object was shown multiple times, but the location of the object could vary in location each time it was shown on screen. Participants were tested on their memory for the original location, requiring episodic recall.
While completing this task, the investigators recorded the neural activity of each participant to differentiate the neural correlation of memory recall versus learning in the hippocampus.
One type of neural activity observed was the theta oscillation, an increase in rhythmic activity in the hippocampus. When a participant used memory to remember the original location of the object on the screen, the investigators noticed eye movements to this location occurred in sync with theta oscillations.
“This theta oscillation might be a way the hippocampus can coordinate when it’s learning new things or when it’s retrieving memories,” Kragel said.
Currently, Kragel is studying what eye movements are made when exploring and remembering novel environments, and how the hippocampus supports memory-guided exploration.
This work was supported by the National Institutes of Health National Institute of Mental Health grant R21MH115366, the National Center for Advancing Translational Sciences grant UL1TR001422 and the National Institute of Neurological Disorders and Stroke grant T32NS047987.