Scientists have discovered which brain cells are responsible for memories
Researchers have discovered two types of brain cells that play an important role in the formation of our memory. These cells play a significant role in dividing continuous conscious experience into different segments that we remember in the future.
Moving from the past, through the present to the future, we form autobiographical memories-reference points of ourselves in a certain place and time. These memories are charged and have clear beginnings and ends, and we connect these threads and form an uninterrupted narrative about ourselves.
Similar to how we perceive objects and entities in the world around us, our memories have clear boundaries, and in a new study, neuroscientists have tried to figure out whether the neurophysiological formation of memory reflects the character of memory in our conscious experience.
The team collected data from patients with epilepsy whose electrodes were surgically implanted in the brain to determine in which part of the brain the seizure occurs.
With consent, patients with epilepsy often participate in neuroscience studies because of these useful intracranial electrodes. They allowed the researchers to record the activity of individual neurons while watching film footage with “cognitive boundaries”.
Boundary cells and event cells
Although these boundaries in our daily lives may be nuanced and less obvious, scientists have focused their research on what they have called “hard” and “soft” boundaries.
“An example of a soft border would be a scene where two people walk down the hall and talk, and in the next scene a third person joins them, but it’s still part of the same narrative,” explains Juli Ruthauser, a neurosurgeon at Los Angeles Hospital, director of the Center for Neuroscience and medicine and co-author of the study.
“The difference between hard and soft borders is in the size of the deviation from the ongoing narrative. Is it a completely different story or a new scene from the same story? “
The researchers were able to find two types of cells that responded to these cognitive boundaries: “borderline cells”, which responded to both soft and hard boundaries, and “event cells”, which responded exclusively to hard boundaries.
Ruttishauser and his team believe that when the activity of events and boundary cells reaches a peak, after a solid boundary when both cells are activated, the brain enters a state of creating new memories.
“The limit response is like opening a new folder on your computer,” adds Ruthauser. “Then you can insert data into it. And when you reach a certain limit, you close the first one and open a new folder. “
You need to find the right folder
When the brain tries to find that information, the peak of neural activity takes place at the boundaries of finding the right folder.
“When we try to remember something, it causes brain cells to burn. The memory system then compares this pattern of activity with all previous peaks of brain activity that have occurred at certain limits. If it finds something similar, it opens that folder. You go back to that point in time for a second, and the things that happened then come into focus” says Ruthauser.
The researchers then tested their theory by asking participants whether or not they had seen certain images in film clips. Confirming the researchers’ assumptions, participants were more likely to recall images that closely followed a hard or soft border, at the site of new memory formation.
In the second test, participants were asked which picture of the two offered first they saw while watching movie clips. It was harder for participants to remember the exact sequence if the images appeared on opposite sides of a solid border, suggesting that the brain segmented those images into separate memories.
“Together, these findings suggest that boundary cells and event cells play two roles in episodic memory — they structure memories during coding and serve as markers for time periods that are later re-established” the authors state.
When event cells are activated in time with one of the brain’s internal rhythms, theta rhythm — a waveform of neurological activity associated with learning, memory, and orientation — participants were able to better remember the sequence of images they saw.
“Theta rhythms are considered to be ‘time glue’ for episodic memory,” said Qi Zhang, lead author of the study from Harvard Medical School.
“We think that activating event cells in sync with theta rhythm builds time-based connections in different memory folders.” Therefore, it seems that event cells help to establish the time order of our memories, while border cells are more involved in recognizing the contents of memories.
