In the space of just a few seconds, a person walking down a city block might check their phone, yawn, worry about making rent, and adjust their path to avoid a puddle. The smell from a food cart could suddenly conjure a memory from childhood, or they could notice a rat eating a slice of pizza and store the image as a new memory.
For most people, shifting through behaviors quickly and seamlessly is a mundane part of everyday life.
For neuroscientists, it's one of the brain's most remarkable capabilities. That's because different activities require the brain to use different combinations of its many regions and billions of neurons. How it manages to do this so rapidly has been an open question for decades.
In a paper published March 8 in Nature Human Behaviour, a team of researchers, led by Joshua Jacobs, associate professor of biomedical engineering at Columbia Engineering, shed new light on this question. By carefully monitoring neural activity of people who were recalling memories or forming new ones, the researchers managed to detect how a newly appreciated type of brainwave—traveling waves—influences the storage and retrieval of memories.
“Broadly, we found that waves tended to move from the back of the brain to the front while patients were putting something into their memory,” said the paper's co-author Uma R. Mohan, a postdoctoral researcher at NIH and former postdoctoral researcher in the Electrophysiology, Memory, and Navigation Laboratory at Columbia Engineering.
“When patients were later searching to recall the same information, those waves moved in the opposite direction, from the front towards the back of the brain,” she said.
In the brains of some of the study's 93 participants, waves traveled in other directions.
“There was a lot of diversity across patients, so we implemented a framework based on the direction an individual's oscillations ‘preferred' to travel,” Mohan said.
The researchers say these findings advance fundamental neuroscience research and point toward diagnostic and therapeutic approaches for memory-related disorders.
“We think the work may lead to new approaches for interfacing with the brain. By measuring the direction that a person's brain waves move, we may be able to predict their behavior,” Jacobs said.
Brain waves are patterns of electrical oscillations that reflect the state of hundreds or thousands of individual neurons at a particular moment. One major question, which remains unsettled, is whether brain waves drive activity or simply occur as a byproduct of neural activity that was already happening. Researchers who study brain waves have tended to treat them as a stationary phenomenon that occurs in a particular region, noting when oscillations in multiple regions seem synchronized.
In this study, Mohan and her colleagues contribute to a growing understanding of these oscillations differently, as “traveling waves” that spread across the brain's cortex, the outermost layer that supports higher cognitive processing. Mohan compares the traveling waves to the ripples that would spread outward after a pebble was thrown into a pond.
Source: Columbia University School of Engineering and Applied Science