Maria Konnikova examines the work of neuroscientist Roberto Malinow, who appears to have wiped out the memories of rats:
Malinow’s team used Pavlovian conditioning to teach the rats to fear a tone: each time the tone sounded, they would feel an electric shock in their feet. Soon, as predicted, they froze at the tone itself. Then, the U.C.S.D. scientists did away with both the tone and shock. Instead, they stimulated the relevant nerve cells – the route between the hearing centers and the fear centers—by shining a blue light pulse. The rats froze, as though they had heard the tone. Not only had the researchers created a memory but they could trigger it without making any environmental changes.
They then went a step further:
if they could use light to make a rat react as though it were recalling a painful shock, perhaps they could also use it to make the memory of the shock go away. The idea is closely related to the notion of modifying memory – reconsolidation, the process in which we recall a memory and, often, subtly change it as we do. (It’s described in detail in Michael Specter’s recent piece for the magazine.) However, instead of working at the level of the stimulus (desensitizing a rat’s memory by playing a tone repeatedly without a shock), you would do it at the level of the synapse. For fifteen minutes, the researchers stimulated the nerve cells that had been responding to the tone and shock in a pattern that has previously been shown to cause L.T.D., the rough equivalent of playing the tone repeatedly with no ill effect. By the end of those fifteen minutes, the rats had forgotten their fear: they no longer froze. Using light stimulation alone, Malinow’s team had been able to extinguish the memory completely.