How does the human brain create and retrieve memories? Scientists figured it out

Scientists have long wondered how the brain updates itself with new information and memories. Some ideas revolve around chemical changes in specific neurons, while others focus on structural shifts among brain cells.

Dr. Tomás Ryan from Trinity College Dublin is among the neuroscientists who have explored these questions by tracking cells involved in learning.

New findings suggest memory formation hinges on connections between groups of engram cells, which are neurons thought to capture and store distinct experiences.

How memories become linked

Researchers believe each experience leaves a pattern of brain cell activation that can be switched on later. To see this process in action, neuroscientists tracked two sets of engram cells, each tied to a different memory.

They discovered that when one set of cells was reactivated, the other set sometimes lit up too, as if the memories had become linked.

This idea runs counter to the old notion that an individual neuron stores an entire memory. Instead, the memory might be in the connections these cells build and reshape over time.

Such structural rearrangements help us handle new information without losing old experiences.

Which brain cells store memories?

“Memory engram cells are groups of brain cells that, activated by specific experiences, change themselves to incorporate and thereby hold information in our brain,” said Dr. Clara Ortega-de San Luis, Postdoctoral Research Fellow and lead author on the study.

She and her colleagues monitored how similar or related memories were stored across different brain areas.

They used genetic techniques to label neurons that fired for one event, then watched how those same neurons responded to a second event that felt related.

One major clue came from measuring how well these labeled neurons made new links with cells that were tied to older, separate experiences.

Optogenetics, a method that turns cells on or off with light, let them test whether blocking these newly formed links disrupted the memory.

How one protein shapes memory

A specific protein, PSD-95, emerged as a gatekeeper of these engram cell connections. This protein sits at nerve cell junctions called synapses and helps anchor receptor molecules. 

When the team lowered the amount of PSD-95 in the neurons storing a given memory, these connections behaved differently. Under certain conditions, the memory seemed to linger even when researchers tried to dampen it.

That persistence hints at how the brain can hang on to memories that we might assume should fade. It also hints at why a shortage or disruption of PSD-95 could derail normal learning patterns.

Brain cells build on old memories

This work taps into a broader shift in neuroscience. Rather than focusing on single cells, many researchers now examine how multiple cells form networks that hold our daily experiences.

By using cutting-edge genetic tagging, scientists can identify where new links are happening and whether these connections are essential for recalling the memory later.

Many of the previous studies mapped separate steps: encoding a memory, storing it, then reactivating it.

This project took it one step further by showing how the brain might slot fresh information into an existing network, so the old memory is updated instead of replaced.

Why these findings matter

Experts have debated how new learning manages not to overwrite older memories in the same region of the brain. According to Dr. Ryan, “we should search for information ‘between’ cells.” 

This view suggests memories are not locked inside one specific location but scattered as connections that can be modified. If true, it may explain how we learn quickly from everyday life without dismantling what we already know.

Therapies could one day target the proteins that enable these shifting connections. If molecules like PSD-95 shape synapses to store a memory, then changing them might help reframe harmful memories tied to fear or trauma, though more studies are needed.

How brain cells shape daily memory

Memory isn’t purely academic. Our daily routines demand constant learning, whether it’s recalling names, navigating busy streets, or picking up a new hobby.

Understanding how the brain cells keep all that information flexible, yet stable, offers hope for tackling age-related memory issues or conditions that affect learning.

Additional work in the field has shown that certain neurons can take on multiple roles depending on the situation.

Those roles often shift over time, especially when new experiences pile up. By homing in on the connections, scientists add a piece to the puzzle of how these cells adapt.

Where this research could lead

Unraveling the complicated dance among engram cells might eventually guide how we teach, treat memory disorders, or support mental health.

If wiring changes are at the core of learning, there might be clever ways to prompt healthy rearrangements in people struggling with conditions like post-traumatic stress or depression.

This study gives a peek into that process. It reveals a fragile, but critical, balance at the heart of learning: strengthen certain neural links for new knowledge, but keep enough structure so older skills and memories remain intact.

The study is published in Current Biology.

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