Secrets of learning: How our brains make and retrieve memories

Have you ever stopped to wonder how we pick up new skills or remember the details of a cherished moment? Our brains are constantly learning and creating new memories, adapting and changing with each new experience.

A recent study has uncovered new details on the fascinating ways our brains learn and store memories.

By exploring how learning reshapes the connections between our brain cells, scientists are giving us a deeper appreciation of memory and the remarkable organ that is the human brain.

Leading this important research is Dr. Tomás Ryan, a neuroscientist from Trinity College Dublin dedicated to unraveling the mysteries of memory. His team’s latest findings offer a fresh perspective on how our neurons change when we learn something new.

Engram cells explained

At the core of this study are engram cells — special groups of brain cells that hold our memories. When we have new experiences, these cells become active and form stronger connections with each other, effectively encoding the memory.

This process is often summed up by the phrase “neurons that fire together, wire together.”

Later, when we try to recall that experience, the same network of engram cells reactivates, allowing us to retrieve the stored information.

“Memory engram cells are groups of brain cells that, activated by specific experiences, change themselves to incorporate and thereby hold information in our brain,” explained Clara Ortega-de San Luis, a Postdoctoral Research Fellow working with Dr. Ryan.

Understanding how these engram cells work is crucial for scientists as they explore the intricate processes of learning and memory formation.

But how exactly do these engram cells store information that matters to us?

Clara adds, “Reactivation of these ‘building blocks’ of memories triggers the recall of the specific experiences associated with them. The question is, how do engrams store meaningful information about the world?”

Exploring similar yet different contexts

To better answer this question, Dr. Ryan’s team designed experiments where animals learned to recognize environments that were similar but not identical.

By observing how the animals distinguished between these contexts, the researchers could see learning in action.

In their experiments, the team used genetic techniques to label two separate groups of engram cells –each linked to a different memory. This allowed them to trace how these cells interacted as new memories formed.

To understand the connections between these engram cells, the researchers turned to optogenetics. This innovative technique uses light to control brain cell activity. By shining light on specific neurons, they could observe how new connections formed during learning.

Proteins that bridge memories

Their work uncovered a molecular mechanism involving a specific protein in the synapse — the junction where neurons communicate.

This protein plays a crucial role in regulating how engram cells connect, essentially bridging separate memories together.

Dr. Ryan believes these findings offer valuable insights into how memories are stored.

“Understanding the cellular mechanisms that allow learning to occur helps us to comprehend not only how we form new memories or modify those pre-existent ones but also advance our knowledge towards disentangling how the brain works and the mechanisms needed for it to process thoughts and information,” Dr. Ryan explained.

More like a sculpture than a computer

Challenging traditional views, Dr. Ryan suggests we might need to shift our perspective on how memories reside in the brain.

“In 21st-century neuroscience, many of us like to think memories are being stored in engram cells, or their sub-components,” Dr. Ryan continued.

“This study argues that rather than looking for information within or at cells, we should search for information between cells, and that learning may work by altering the wiring diagram of the brain — less like a computer and more like a developing sculpture. In other words, the engram is not in the cell; the cell is in the engram,” he concluded.

This idea emphasizes the significance of the connections between neurons rather than the neurons themselves. It’s like considering not just individual musicians but the harmony they create together.

Each new piece of information we take in can modify existing engram cells or create new ones. This continuous remodeling is what allows us to learn and adapt throughout our lives.

Sensory inputs in learning and memory formation

Our brains have an amazing ability to blend the different senses we experience, like sight and sound, into one smooth perception, even though these inputs arrive at different times.

When we see and hear something happening at the same time, our brain uses a process called temporal binding. This means it synchronizes sensory inputs that happen within a tiny time frame, so events appear simultaneous to us.

For example, when we watch someone clap and hear the sound, our brain aligns these inputs despite the light and sound reaching us at different speeds.

How the brain combines inputs

Different areas of the brain handle different senses — the visual cortex for sight and the auditory cortex for sound. These regions communicate to ensure sensory information is processed together.

Areas called multisensory convergence zones, like the superior colliculus and the posterior parietal cortex, play key roles in integrating these inputs.

Making sense of timing in memory and learning

Our brain operates with a flexible time window to consider inputs as simultaneous. It also uses prior knowledge and context to adjust our perception.

For instance, even if thunder arrives after lightning, we understand they are linked events. The brain can compensate for these delays, so we perceive them as connected.

Once the brain has merged these sensory inputs, it forms a coherent experience. This unified perception is what gets stored in our memory, thanks to the hippocampus. It not only records the sensory details but also the context, helping us recall the entire experience later.

Our brain’s ability to integrate sensory information improves with experience. Through neuroplasticity, repeated events strengthen the neural pathways involved, making the process more efficient over time.

This means that the more we experience something, the better our brain gets at combining those sensory inputs.

Sleep: The unsung hero of memory

While we’re on the topic of learning, it’s worth mentioning the vital role sleep plays. Getting enough rest isn’t just about recharging — it’s essential for solidifying the memories we’ve formed during the day.

During sleep, our brains are busy consolidating new information, transferring it from short-term to long-term memory. Lack of sleep can interfere with this process, making it harder to remember what we’ve learned.

Learning, memory, and future research

So, what does all this mean for us? Understanding how our brains store and retrieve memories can have big implications. It might lead to better strategies for learning or new approaches to treating memory-related conditions.

The discoveries made by Dr. Ryan and his team open exciting new avenues for research. If learning reshapes the connections between neurons, perhaps we can find ways to enhance these processes.

Our brains are incredibly complex, and each study brings us a little closer to understanding how we think, learn, and remember. It’s an ongoing journey, and one that’s full of wonder and possibility.

The full study was published in the journal Current Biology.

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