Neuroscientists have discovered a curious aspect of how our memory works. When your brain needs to recall information that's related to a specific location, individual neurons can actually target specific memories.
"A key feature of memory is our ability to selectively recall particular experiences even if they occurred in a setting shared with other events," the researchers explain in a new paper.
"For example, if a person is asked to recommend a tourist itinerary for a city they have visited frequently, they can selectively recall distinct memories of locations from different trips to provide an answer."
Researchers from several universities including Columbia University in New York and Emory University in Atlanta looked at the individual neurons - which they've dubbed 'memory-trace cells' - of 19 patients undergoing brain surgery for epilepsy.
The patients completed a spatial memory task where they were moved along a track in a virtual reality (VR) environment, and asked to press a button when they encountered specific objects (you can watch this process in the video embedded below).
In the recall part of the task, the researchers asked participants to navigate the track and mark the location of an object that had been removed.
Although this is a far cry from remembering what you did on your last holiday, the team did find some interesting results.
While looking at the medial temporal lobe (MTL) and in particular the entorhinal cortex, the researchers found that the memory-trace cells were "spatially tuned" to the location, and could then retrieve the location-specific information the person needed to recall.
"Our study demonstrates that neurons in the human brain track the experiences we are willfully recalling and can change their activity patterns to differentiate between memories. They're just like the pins on your Google map that mark the locations you remember for important events," says Salman E. Qasim, a Columbia University biomedical engineer.
"This discovery might provide a potential mechanism for our ability to selectively call upon different experiences from the past and highlights how these memories may influence our brain's spatial map."
This is all part of our spatial memory, which is responsible for recording information about our environment and how to navigate it.
Past research has already looked into how we can do this, finding that place and grid cells are very important to our spatial memory, working in a similar way to a GPS. Spatial tuning is the idea that individual neurons "activate to represent locations in the environment during navigation".
"Previous work proposed that spatially tuned cells remap their firing patterns across different environments, so events that occur in different environments are associated with different spatial maps," the team explains in their study.
"Building on this work, we proposed that single neurons in the MTL, and particularly in the entorhinal cortex, would exhibit spatial tuning modulated by past experiences."
The paper has been published at Nature Neuroscience.