Researchers from the University of Oxford have rewritten positive memories associated with cocaine in mice. The achievement could expand our understanding of memory, while demonstrating that it’s possible to neurologically reverse ingrained bad behavior, such as drug addiction.
Neuroscientists Stéphanie Trouche and David Dupret from Oxford’s MRC Brain Network Dynamics Unit trained mice to prefer a particular location using cocaine. Then they altered those positive associations using optogenetics—a genetic technique in which living brain cells can be manipulated or controlled with light (typically via fiber optic cables). The mice lost their preference for the cocaine-associated environment, suggesting their memory had been rewritten. The results of this experiment can now be found in Nature Neuroscience.
Whenever a mammal is in a particular environment, the specialized neurons associated with a particular place in its hippocampus (the part of the brain responsible for long- and short-term memory consolidation and spatial navigation) become active. Place cells enable an animal to build a mental representation of a specific location. These cognitive maps can be tied to an emotional response based on an animal’s prior experience at a particular location. For example, if a mouse encounters a hostile cat in a specific area, its cognitive map will feature a negative association, expressed as fear. Alternately, the discovery of a tasty meal would imprint a positive association with that location.
These associations are stored in the brain in the form of memory engrams. Back in 2013, a research team from MIT learned that it’s possible to implant false engrams in a mouse’s mind, causing it to recall an experience that never occurred. After training a mouse to be fearful of a particular room using electric shocks, the researchers activated a light-sensitive protein in its brain using optogenetics.
When the mouse was placed in a room known to be safe, the light triggered the memory associated with the dangerous room, causing it to freeze in fear. This suggests it had formed a false-memory associated with an entirely different room. The experiment affirmed the longstanding notion that memories are physically resident in the brain, and that they’re subject to manipulation.