Researchers have discovered two types of human brain cells that physically aid memory formation.
These cells are important for segmenting continuous conscious experience into discrete segments that can be remembered later.
How does our brain respond to memories?
We form autobiographical memories – reference points of ourselves in a particular place and time – as we move from the past, through the present, and into the future. We stitch these threads together to form a continuous narrative of ourselves because these memories are chunky, with clear beginnings and ends.
Similar to how we perceive objects and entities in the world, our memories have clear boundaries, and in the new study, neuroscientists ask if the neurophysiological formation of memories reflects the discrete character of memories in our conscious experience.
How was the research conducted?
The researchers gathered information from epilepsy patients who had electrodes surgically implanted in their brains to pinpoint the location of their seizures.
Because of these useful intracranial electrodes, epilepsy patients frequently participate in neuroscientific studies with their consent. They allowed researchers to monitor individual neurons’ activity while patients watched film clips with ‘cognitive boundaries.’
Cognitive Boundaries
While these boundaries may be nuanced and less obvious in our daily lives, scientists focused on ‘hard’ and ‘soft’ boundaries for research purposes.
The size of the deviation from the ongoing narrative is the difference between hard and soft boundaries. Is it a new scene from the same story, or is it a completely different story?”
What were the two new cells?
Researchers discovered two types of cells that responded to cognitive boundaries: “boundary cells,” which responded to both soft and hard boundaries, and “event cells,” which only responded to hard boundaries.
“Creating a new folder on your computer is similar to a boundary response,” the researchers explained.
“After that, you can put files in there.” When a new boundary presents itself, you close the first folder and start a new one.”
The peaks of neural activity at these boundaries are used by the brain to find the right folder when it needs to revisit a memory.
“Trying to remember something causes brain cells to fire,” says the researcher.
The findings suggest that boundary and event cells play two roles in episodic memory: they structure memories during encoding and serve as markers for periods that are later reinstated, according to the authors.
Furthermore, participants could better remember the order of images they had seen when the event cells fired in time with one of the brain’s internal rhythms, the theta rhythm – a waveform of neurological activity associated with learning, memory, and navigation.
“Theta rhythms are thought to be the ‘temporal glue’ for episodic memory,” said Jie Zheng, a postdoctoral fellow at Harvard Medical School and the study’s first researcher.
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“We believe that firing event cells in time with the theta rhythm establishes time-based links between memory folders.”
As a result, event cells appear to assist us in establishing the temporal order of our memories, whereas boundary cells appear to be more involved in memory recognition.
Also published on Medium.