Conceptual illustration of neurons that "map" memories in the human brain. CREDIT Salman Qasim/Columbia Engineering

Discovered: the brain’s map pins

New finding sheds new light on how the brain processes spatial memory.

Think of one of your favourite places: somewhere you’ve been to many times in your life. Now think of all the things you’ve done there. Being able to link together different moments from a particular place is one of the miracles of memory, and now researchers have pinpointed specific neurons that allow us to do this.

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The neurons were discovered in a region of the brain called the ‘entorhinal cortex’ (EC). Previous work has shown that the EC and a nearby region called the ‘hippocampus’ are important for spatial cognition, containing neurons that work as a GPS for the brain, allowing us to understand our position in space.

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Now, researchers directed by neuroscientist Dr Joshua Jacobs at Columbia University, New York City, have discovered neurons in the EC that go one step further, linking memories in the brain to the location in which they were formed.

The scientists created a VR computer game in which participants used handheld controllers to move along a track, learning the positions of four different objects. The researchers then removed the objects, and asked the participants to move along the track again, marking the location of specific objects from memory.

The 19 participants had drug-resistant epilepsy, and so had already had recording electrodes implanted in their brains for their treatment.

This allowed the researchers to measure the activity in individual neurons, and they found ‘memory-trace’ neurons that only fired in locations relevant to the memory the patient was recalling. When the participants switched to remembering the location of a different object, the neurons changed their activity.

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“Our study demonstrates that neurons in the human brain track the experiences we are wilfully recalling, and can change their activity patterns to differentiate between memories,” said Salman E. Qasim, Jacobs’ PhD student and lead author of the study. “They’re just like the pins on your Google map that mark the locations you remember for important events.”

Reader Q&A: What happens in your brain when you make a memory?

Asked by: Keith Walker, Lincoln

Memories are formed by the changing strength of connections between networks of brain cells, particularly in the hippocampus, which is found in each temporal lobe (the part of your brain near your ears). A key memory-related process is ‘long-term potentiation’, which refers to a lasting change in how strongly one neuron influences another.

It’s tempting to think of memory like a recording, etched permanently into patterns of brain cells, but it’s more accurate to see it as a creative process. During recollection, earlier patterns of brain activity are re-enacted – a fragile process that leaves plenty of room for error and editing.

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