INVASIVE PROOF OF CONCEPT. “Malinow believes that he has the potential to do something revolutionary: erase a memory or reactivate it at will. Optogenetics relies on the ability to insert a protein into nerve cells that will make them sensitive to light. Researchers can then activate the cells by exposing them to a light pulse: each time the light hits the cells, the nerve fires.”
http://www.newyorker.com/science/maria-konnikova/can-memories-implanted-removed