Brain memories don't maintain a fixed state; they naturally shift or alter as time passes.
In a groundbreaking study, researchers have discovered that the brain's internal representation of places can change over time, a phenomenon known as "hippocampal representational drift." This finding sheds light on how memories are formed, distinguished, and potentially decay in mammals, including humans.
The study, conducted using controlled multisensory virtual reality setups, involved mice navigating identical virtual environments repeatedly. The team found that despite the stability of the external environment and sensory inputs, the activity patterns of hippocampal place cells—neurons that encode specific spatial locations by their firing patterns—underwent a gradual shift over time.
Place cells, located in the hippocampus, have historically been thought to encode memories of locations and enable navigation. However, the researchers observed that only a small subset of cells, around 5% to 10%, behaved like conventional place cells, consistently lighting up in each round. The rest of the cells showed a drift in their spatial tuning, changing their patterns over days.
This drift appears to be an adaptive mechanism, enabling the brain to distinguish similar but separate experiences by slowly changing their internal representations, thus supporting the formation of discrete episodic memories — memories associated with specific contexts and times.
In terms of potential impact on episodic memories, representational drift may enhance the brain's ability to differentiate repeated visits to the same place, contributing to the uniqueness of each event in memory. However, as hippocampal neurons lose excitability with age, drift dynamics might also relate to memory decline in aging humans, with potential therapeutic implications for preserving memory by targeting neuronal excitability.
To monitor the activity of the hippocampal cells in real time, the researchers opened a physical window into the brain and introduced a substance that glowed when brain cells were activated. In each round of the experiment, the mice were placed on a treadmill surrounded by screens and explored a virtual maze that was exactly the same every time. White noise was played in the background to normalize the auditory landscape, and a cone was placed over each rodent's nose to pump in the same scent during every round.
A 2013 study first revealed the brain's representation of places wasn't as consistent as once thought, and this phenomenon was called "hippocampal representational drift." The new study aims to control variables that could affect the results, using virtual reality and a tiny treadmill, providing a more accurate understanding of this intriguing brain process.
The study captures only a fraction of the cells in the mouse hippocampus, maybe 1% of its hundreds of thousands of neurons. However, it suggests that the observed drift in the brain's representation of places might be a mechanism to separate highly similar experiences into distinct individual memories, contributing to the formation and uniqueness of episodic memories.
According to the study's lead researcher, Dombeck, if we could maintain the excitability of our neurons over time, we could maintain memory. This fascinating discovery opens up new avenues for research into memory formation, preservation, and potential therapies for memory-related disorders.
- This groundbreaking study on hippocampal representational drift in mice shows that science in health-and-wellness, particularly mental-health and fitness-and-exercise areas, could gain profound insights from understanding the brain's internal representation changes in place memories, which may lead to future therapeutic interventions.
- The researchers' observation that representational drift might be linked to memory decline in aging humans suggests a potential connection between brain fitness and mental-health, implying that maintaining neuronal excitability could support memory preservation, shedding light on health-and-wellness strategies for memory-related disorders.
