OPTICAL LASERS. “The rats soon learned to associate the optical nerve stimulation with pain and displayed fear when the nerves were stimulated. The scientists then used a series of low-frequency optical lasers to stimulate the same nerves in a different way, erasing the memories.”
http://www.dailymail.co.uk/health/article-2645740/How-flash-light-delete-bad-memories-Breakthrough-help-dementia-patients.html