Scientists at Cedars-Sinai Medical Center have found two types of brain cells that are instrumental in slicing up the human stream of consciousness into discrete memories that can be recalled later. This breakthrough discovery could potentially benefit those suffering from memory disorders such as Alzheimer’s disease.
“One of the reasons we can’t offer significant help for somebody who suffers from a memory disorder is that we don’t know enough about how the memory system works,” said Dr. Ueli Rutishauser, senior author of the study.
To carry out the research, the experts recruited 19 participants with drug resistant epilepsy. The volunteers had electrodes implanted in their brains, which allowed the researchers to locate the location of seizures.
The electrodes also made it possible for the scientists to watch how the brain reacted as the participants were shown videos with soft and hard cognitive boundaries.
“An example of a soft boundary would be a scene with two people walking down a hallway and talking, and in the next scene, a third person joins them, but it is still part of the same overall narrative,” said Dr. Rutishauser. “The difference between hard and soft boundaries is in the size of the deviation from the ongoing narrative. Is it a totally different story, or like a new scene from the same story?”
When the volunteers viewed the film clips, the scientists noticed that certain brain cells increased in their activity after hard or soft boundaries, so they named these “boundary cells.” Other cells were called “event cells.” The scientists hypothesized that both of these types of cells are important in finding and demarking different memories.
“A boundary response is kind of like creating a new folder on your computer,” said Dr. Rutishauser. “You can then deposit files in there. And when another boundary comes around, you close the first folder and create another one.”
After viewing the film, the volunteers were shown still images and asked whether or not they were part of the film. The scientists found that participants were more likely to remember an image that occurred right after either hard or soft boundaries.
The research subjects were also more likely to remember the order of images correctly, if they were separated by hard or soft boundaries. This may be due to the brain partitioning the different scenes into different memories.
“When you try to remember something, it causes brain cells to fire,” explained Dr. Rutishauser. “The memory system then compares this pattern of activity to all the previous firing peaks that happened shortly after boundaries. If it finds one that is similar, it opens that folder. You go back for a few seconds to that point in time, and things that happened then come into focus.”
The scientists believe that memory therapies which increase this sort of event partitioning could possibly benefit patients suffering from memory disorders but more research is needed.
The study is published in the journal Nature Neuroscience.