Next, the team injected the mice with a virus that would enable them to control the activity of their LA neurons using red and blue lights, in order to try and artificially link and unlink memories. To do this, they trained mice to memorize one tone, before waiting 24 hours to introduce them to the second tone. However, during the formation of this second memory, the researchers stimulated the same neurons that had encoded the engram for the first memory, ensuring they outcompeted their surrounding neurons and therefore grabbed this new memory.
When performing further behavioral tests, they discovered that the two memories had indeed become linked, despite occurring 24 hours apart.
The team then attempted to unlink memories by training mice to memorize the two tones six hours apart, but inhibiting the neurons that had encoded the first memory so that they would not be able to grab the second memory. Accordingly, their results showed that the memories were indeed unlinked, as extinguishing one did not automatically erase the other.
Knowing how memories become linked by overlapping groups of LA neurons could have major clinical significance, according to study co-author Paul Frankland, who explained in a statement that “understanding how memories are linked may provide hints as to how they become inappropriately connected in conditions such as schizophrenia.”
Understanding the neural circuitry behind overlapping memories could one day help to produce new treatments for cognitive disorders. deeepblue/Shutterstock