Why memories close in time feel connected

Have you ever noticed how memories from the same day seem to blend together, while events that happened weeks apart feel like they exist in totally separate mental files?

A new study sheds light on why this happens – and it’s not because of what’s happening in the main body of brain cells. Instead, the secret lies in the tiny branches called dendrites.

In a recent study, scientists from The Ohio State University used advanced imaging tools, including miniaturized microscopes, to track how mice formed memories in real time.

The team focused on a lesser-known part of the brain cell – dendrites, the slender projections that stretch out from neurons. These branches are known for receiving information, but they’re much more active than previously thought.

Small branches, big role

The researchers zeroed in on the retrosplenial cortex (RSC), a brain area involved in spatial and contextual memory.

When mice were introduced to two different environments close together in time, something remarkable happened: the memories of those places became linked.

If the mice were later given a small shock in just one of the environments, they reacted with fear in both. Their brains treated the two places as connected – even though only one was associated with the unpleasant experience.

“If you think of a neuron as a computer, dendrites are like tiny computers inside it, each performing its own calculations,” said study lead author Megha Sehgal.

“This discovery shows that our brains can link information arriving close in time to the same dendritic location, expanding our understanding of how memories are organized.”

Communication between neurons

The researchers studied how dendrites change during the process of learning and storing information. On the surface of these branches are small bumps called spines – tiny hubs where communication between neurons happens.

When a new memory was formed, they saw clusters of these spines pop up. Then, if another memory formed shortly after, those same spots were more likely to attract additional spines.

This physical clustering of connections appears to be how the brain binds related experiences together.

“The idea is that we don’t form memories in isolation. You don’t form a single memory. You use that memory, make a framework of memories, and then pull from that framework when you need to make adaptive decisions,” said Sehgal.

Critical role of dendrites

To test whether these dendritic branches were really causing the linking effect, the team used a method called optogenetics. This technique lets scientists control brain activity using light.

The experts reactivated the exact dendritic branches that had been used during one memory and found that doing so could link it to another, unrelated memory.

This confirmed the critical role that dendrites play in how memories are joined together in our brains.

Understanding memory-related disorders

This discovery not only changes how we think about memory – it also opens the door to new ways of understanding memory-related disorders.

If scientists can learn to influence how dendrites work, they may be able to treat conditions where memory formation or linking is impaired.

“Our work not only expands our understanding of how memories are formed but also suggests exciting new possibilities for manipulating higher order memory processes,” said Sehgal. “This could have implications for developing therapies for memory-related conditions such as Alzheimer’s disease.”

The research marks an important step in decoding the physical structure of memory -and it all starts with the tiny, busy branches inside each brain cell.

Rethinking memory storage

This study encourages us to rethink how we view memory storage. Instead of seeing each experience as a separate snapshot, it may be more accurate to picture them as parts of a timeline – physically tied together through shared dendritic changes.

This could explain why certain days feel like a continuous stream of events, while others stand alone.

The findings also suggest that how we mentally group events may depend more on timing than emotional weight.

With a clearer picture of how the brain organizes information, scientists can better understand what happens when that system begins to fail, such as in age-related cognitive decline.

The full study was published in the journal Nature Neuroscience.

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