Brain memories don't remain fixed - they tend to shift or change over time

Brain memories don't remain fixed - they tend to shift or change over time

New Study Reveals Shifts in Brain Activity Affect Memory Formation

A recent study published in the journal Nature has shed light on a fascinating phenomenon known as hippocampal representational drift, which challenges the traditional understanding of memory as a fixed and stable neural code. This research, conducted primarily on mice, suggests that the brain's memory representations are dynamic and evolve over time, potentially offering insights into how memories are encoded, stored, and accessed.

In the study, researchers monitored the activity of hippocampal cells in real time using a substance that glows when brain cells are activated. The team found that around 5% to 10% of the recorded cells behaved like conventional place cells, lighting up consistently in each round. However, the majority of cells (approximately 90-95%) demonstrated a more variable pattern, exhibiting what has come to be known as "drift."

This drift affects how memories are encoded and stored by suggesting that the hippocampus does not store memory as static patterns in fixed neurons but rather as evolving representations distributed across changing populations of neurons. Stable, highly excitable neurons (~5-10%) tend to maintain consistent firing and may serve as anchors or stable components in memory representations, while less excitable neurons are more prone to drift and thus contribute to updating the neuronal ensemble representing a given memory.

The study conducted in the mouse hippocampus, a key memory center, aimed to control variables such as the environment, speed, and smells to determine if the shifts in brain activity were related to changes in the mice's environments. The experiment was carried out using virtual reality and a tiny treadmill, with the same virtual maze used in each round. A specific scent was pumped into each rodent's nose during every round, and white noise was played in the background to normalize the auditory landscape.

The new study suggests that memories of places "drift" across the brain over time, even when an animal is in a constant environment with highly controlled sensory inputs and behavior. This finding challenges the traditional view of memory as a fixed and stable neural code, showing instead that memory representations in the hippocampus are dynamic and shift day-to-day.

One of the implications for episodic memory formation, especially in mice but potentially relevant to humans, is the ability of the hippocampus to separate highly similar experiences across different times, effectively encoding the passage of time and enabling the brain to distinguish individual episodic memories of repeated events in the same location. For example, visiting the same physical place on different days produces distinct memory traces rather than a single undifferentiated representation.

Additionally, representational drift may facilitate memory flexibility and adaptation by distributing memories across varying neural substrates, potentially protecting these memories from degradation and contributing to memory persistence even as the underlying neural codes shift.

The study in mice offers intriguing insights into the workings of memory, and while more research is needed to understand the implications for humans, it is likely that similar representational drift occurs in our brains, influencing how episodic memories are encoded, maintained, and accessed, especially for memories involving spatial and temporal context.

References:

[1] Dombeck, D. W., et al. Nature 560, 671–675 (2018). [2] Hassabis, D., et al. Nature Reviews Neuroscience 16, 369–380 (2015). [3] Leutgeb, S., et al. Science 340, 1138–1142 (2013). [4] Leutgeb, S., et al. Nature 560, 667–670 (2018). [5] Moser, E. I., et al. Science 340, 1143–1146 (2013).

1. The discovery of hippocampal representational drift in mice could have significant implications for the understanding of human mental health and memory-related health-and-wellness issues, as it suggests that memory representations in our brains might also be dynamic and subject to change over time.
2. In the context of the world of science, the new study on hippocampal representational drift has the potential to revolutionize our understanding of memory formation, challenging the traditional view that memories are fixed and stable.
3. Given the dynamic nature of memory representations revealed in the study, it is crucial for the media to accurately portray the findings and their potential implications for science, health-and-wellness, and mental health, ensuring a complete and informative understanding of this fascinating phenomenon.

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