How hippocampal place cells and synaptic plasticity contribute to the progressive acquisition of memories

The human brain is known to store various memories for long periods of time, progressively learning from new experiences and forming adaptive representations that ultimately guide decision-making and behavior. When people experience new things, their brain creates new memories and mental representations, without overwriting or deleting old ones.

Many past neuroscience studies have tried to uncover the neural processes underpinning this progressive acquisition of new memories over the course of the human lifespan. While the findings collected so far have improved the overall understanding of memory encoding and consolidation, the mechanisms through which the brain stores new memories without overwriting older ones have not yet been fully elucidated.

Researchers at Baylor College of Medicine recently carried out a study aimed at further exploring these neural mechanisms, specifically looking at the activity of place cells in the CA1 region of the hippocampus, neurons that become active when an animal or human is in a specific location.

Their findings, published in Nature Neuroscience, suggest that to retain old memories while also enabling the formation of new ones, the brain progressively modifies connections between neurons via a process known as synaptic plasticity.

“How brain networks connected by labile synapses store new information without catastrophically overwriting previous memories remains poorly understood,” wrote Sachin P. Vaidya, Guanchun Li and their colleagues in their paper. “To examine this, we tracked the same population of hippocampal CA1 place cells (PCs) as mice learned a task for 7 days.”

The researchers carried out an experiment involving adult mice that were trained to complete a behavioral task. This task required them to run on a treadmill to receive water rewards, while learning to interpret light cues and behave accordingly to receive greater rewards.

As the mice learned to complete the task, Vaidya, Li and their colleagues tracked the activity of place cells in the CA1 region of the animals’ hippocampi, using a technique known as calcium imaging. This is a widely used method that allows neuroscientists to detect when neurons are active, using genetic tools that cause cells to light up when calcium enters them, and a tiny microscope implanted in the mouse brain, which can be used to observe neurons and when they light up.

“We found evidence of memory formation as both the number of PCs maintaining a stable place field and the stability of individual PCs progressively increased across the week until most of the representation was composed of long-term stable PCs,” wrote the researchers.

“The stable PCs disproportionately represented task-related learned information, were retrieved earlier within a behavioral session and showed a strong correlation with behavioral performance. Both the initial formation of PCs and their retrieval on subsequent days were accompanied by prominent signs of behavioral timescale synaptic plasticity (BTSP), suggesting that even stable PCs were re-formed by synaptic plasticity each session.”

Essentially, the researchers found that some place cells became more stable and remained active at the same sites while the mice were learning the behavioral task. These “stable” cells appeared to encode information that was important for the completion of the experimental task, as they were activated early each time the mice started a new learning session.

The team’s results suggest that while the activity of some place cells was more stable, the connections between them were not. Instead, they adapted over time as the mice engaged in different behaviors, via a fast process known as BTSP.

“Further experimental evidence supported by a cascade-type state model indicates that CA1 PCs increase their stability each day they are active, eventually forming a highly stable population,” wrote the researchers. “The results suggest that CA1 memory is implemented by an increase in the likelihood of new neuron-specific synaptic plasticity, as opposed to extensive long-term synaptic weight stabilization.”

The experiments carried out by this research team shed some new light on the processes that could allow the brain to learn new information without erasing older memories. The findings they gathered could be validated and explored further in additional experiments involving mice or other species.

Eventually, the team’s efforts could help scientists and physicians to better understand some memory-related diseases, potentially helping to devise new treatments to prevent memory loss. In addition, they could inform the development of machine learning techniques and other computational models designed to emulate how the brain stores memories and learns new information.

© 2025 Science X Network

The human brain is known to store various memories for long periods of time, progressively learning from new experiences and forming adaptive representations that ultimately guide decision-making and behavior. When people experience new things, their brain creates new memories and mental representations, without overwriting or deleting old ones.

Many past neuroscience studies have tried to uncover the neural processes underpinning this progressive acquisition of new memories over the course of the human lifespan. While the findings collected so far have improved the overall understanding of memory encoding and consolidation, the mechanisms through which the brain stores new memories without overwriting older ones have not yet been fully elucidated.

Researchers at Baylor College of Medicine recently carried out a study aimed at further exploring these neural mechanisms, specifically looking at the activity of place cells in the CA1 region of the hippocampus, neurons that become active when an animal or human is in a specific location.

Their findings, published in Nature Neuroscience, suggest that to retain old memories while also enabling the formation of new ones, the brain progressively modifies connections between neurons via a process known as synaptic plasticity.

“How brain networks connected by labile synapses store new information without catastrophically overwriting previous memories remains poorly understood,” wrote Sachin P. Vaidya, Guanchun Li and their colleagues in their paper. “To examine this, we tracked the same population of hippocampal CA1 place cells (PCs) as mice learned a task for 7 days.”

The researchers carried out an experiment involving adult mice that were trained to complete a behavioral task. This task required them to run on a treadmill to receive water rewards, while learning to interpret light cues and behave accordingly to receive greater rewards.

As the mice learned to complete the task, Vaidya, Li and their colleagues tracked the activity of place cells in the CA1 region of the animals’ hippocampi, using a technique known as calcium imaging. This is a widely used method that allows neuroscientists to detect when neurons are active, using genetic tools that cause cells to light up when calcium enters them, and a tiny microscope implanted in the mouse brain, which can be used to observe neurons and when they light up.

“We found evidence of memory formation as both the number of PCs maintaining a stable place field and the stability of individual PCs progressively increased across the week until most of the representation was composed of long-term stable PCs,” wrote the researchers.

“The stable PCs disproportionately represented task-related learned information, were retrieved earlier within a behavioral session and showed a strong correlation with behavioral performance. Both the initial formation of PCs and their retrieval on subsequent days were accompanied by prominent signs of behavioral timescale synaptic plasticity (BTSP), suggesting that even stable PCs were re-formed by synaptic plasticity each session.”

Essentially, the researchers found that some place cells became more stable and remained active at the same sites while the mice were learning the behavioral task. These “stable” cells appeared to encode information that was important for the completion of the experimental task, as they were activated early each time the mice started a new learning session.

The team’s results suggest that while the activity of some place cells was more stable, the connections between them were not. Instead, they adapted over time as the mice engaged in different behaviors, via a fast process known as BTSP.

“Further experimental evidence supported by a cascade-type state model indicates that CA1 PCs increase their stability each day they are active, eventually forming a highly stable population,” wrote the researchers. “The results suggest that CA1 memory is implemented by an increase in the likelihood of new neuron-specific synaptic plasticity, as opposed to extensive long-term synaptic weight stabilization.”

The experiments carried out by this research team shed some new light on the processes that could allow the brain to learn new information without erasing older memories. The findings they gathered could be validated and explored further in additional experiments involving mice or other species.

Eventually, the team’s efforts could help scientists and physicians to better understand some memory-related diseases, potentially helping to devise new treatments to prevent memory loss. In addition, they could inform the development of machine learning techniques and other computational models designed to emulate how the brain stores memories and learns new information.

© 2025 Science X Network