In a near pairing of neurobiology and positive reinforcement, researchers have induced happy memories of a certain location in mice. The hope is that it can provide a new way of dealing with post-traumatic stress disorder.
In the study, published in Nature, two electrodes were placed on the brains of mice. One was on the hippocampus — responsible for memory — and one was placed on the medial forebrain bundle (MFB) — known to be associated with rewards in mice. The one on the hippocampus was put on a specific "place cell," which are neurons that become active when an animal visits a specific location. Based on this correlation, the researchers could match a place cell to a location in the mice's environment.
As the mice slept, the electrodes detected when a place cell was active and delivered stimulation to the MFB. The stimulation did not wake the rats, so any positive association developed by the mice to the place in their environment was entirely done when they were not active.
Once awake, the mice started showing a preference for the area associated with the place cell. They had "learned," while asleep, to positively associate an area with reward. This happened, despite no actual positive event occurring while they were awake.
The researchers concluded:
This suggests that the pairing protocol used here during sleep induced the creation of an artificial explicit memory that could be used by mice in a goal-directed way and thus goes beyond previous observations showing that certain forms of conditioning relying on a reflex response to a conditioned response to a conditioned stimulus can take place in sleeping or anesthetized brain. Moreover, the fact that pairing spikes of a given place cell with rewarding simulation during sleep, when its activity was decorrelated from the actual animal position, leads to a place preference for toward the related place field demonstrates that place cell activity itself functions in spatial memory and navigation. Finally, our results support the theory of spatial reactivation during sleep by showing that place cells encode the same spatial information during sleep and wakefulness.
As for future applications, lead researcher Karim Benchenane says that the goal was to use these results as a tool for post-traumatic stress disorder. He believes that the study could lead to a "non-invasive tool for memory manipulation," by using functional MRI scans to determine when a human is replaying a specific memory while unawake.
He did warn against doing the exact same thing for PTSD sufferers as they did for the rats:
It might be extremely dangerous to get a reward for something fearful.