What We Don’t Know: How are Memories Stored and Retrieved in the Brain?

Dear Readers,

A lot of my blog has been dedicated to understanding what neuroscientists have already discovered. However, I think it is equally imperative to understand what is left to find.

So, in this blog post, I aim to tackle one question that has plaguing neuroscientists for decades:

How are memories stored and retrieved in brain?

As of now, we only have a basic understanding of memory storage and retrieval.

In the 1950s and 1960s, Karl Lashley and Wilder Penfield discovered that memories are not stored in one specific brain region. Instead, they are spread throughout the entire neural cortex. In fact, memories are stored as groups of neurons that fire together in the same pattern to create a replica of what you felt during a particular moment. Memory is therefore an ongoing process. So, according to this thesis, forgetting is therefore an inability to retrieve information and recreate a particular neuronal firing.

Photo of Wilder Penfield with a sketch of the brain. We have luckily made a lot of progress since we thought the brain looked like that!

Later on, neuroscientists classified two different kinds of memories: episodic memories (every day events that occurred at a specific time and place) and semantic memories (long-term general knowledge we gain such as math and language rather than personal experiences). We need to better understand how these two kinds of memories differ in the brain. Additionally, we have yet to understand to difference between long and short term memory in the brain.

Cartoon of the difference between memory types

The neuroscience community currently thinks that memory depends on synapses, the tiny spaces between two nerve cells. The synapse allows a neuron to pass an electrical or chemical signal to another neuron for a specific reason. They are like the mailmen of letters. When two cells are both active, the connection between the cells becomes stronger. When two cells are not active at the same time, the connection between them becomes less active. It makes total sense! Think about it this way: if you your friend lives across the world from you, then they will be on a different time zone. Let’s imagine your friend lives in France and you live in Boston. At 2:00am in the morning, you will be sleeping while they are getting ready for school. So, due to the time difference, your friendship will most likely weaken because you will see your friend less. It is the same with neurons. When populations of neurons are activated at the same time, it can cause a cascade of reactions. So, when you smell coffee, it will trigger other parts of the memory: the taste, the texture, the first time you tried coffee, etc too.

However, the scientific community has a long way to go from thinking that mere partnered neuronal connections are how memories are formed; memory is a ton more complicated than that. We have yet to understand the specific details of memory.

Yet, our understanding around memory goes much, much deeper than the mini paragraph above; I would need at least 5 blog posts to fully uncover the magnitude of this discussion, and unpack the various studies conducted about memory. So, I am going to list and speculate about what questions warrant further exploration within this debate. After all, the goal of this blog post is not to understand but to question:

  1. Is there a limited amount of space for memories in the brain?
  2. Why can’t we remember when we were a baby?
  3. How does stress and traumatic experiences impact memory?
  4. How do emotions impact how memories are stored?
  5. What is the best way to learn material and memorize information?
  6. Why do some people have better memories than others?
  7. How do other non-human species store and retrieve memory?


So, you may be wondering, why even understand memory? Well, for one, humans are inherently curious creatures, so the sheer pursuit of knowledge motivates us. However, in addition to curiosity, understanding memory may be the key to curing diseases such as Alzheimer’s and mitigating PTSD.



  1. https://human-memory.net/memory-storage/
  2. https://www.thingswedontknow.com/articles/memory#.XmMRnpNKj-Y
  3. https://blog.simonsays.ai/why-memory-is-still-one-of-sciences-greatest-mysteries-part-1-56ae2615c824

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