"At a time when the treatments for many serious mental illnesses are lacking, the potential clinical applications of memory modification are enticing. 'This is kind of crazy,' says Josselyn, whose work centers on Alzheimer’s disease and other memory-related disorders, 'but maybe somebody with Alzheimer’s... maybe we can figure out a treatment to just go in and do what these guys did in their papers, and sort of activate these cells artificially, boost the activation and have the memories recalled better.'In another theoretical application, PTSD might be eased by repeatedly reactivating a bad memory to show that the memory itself is not harmful, or by erasing the traumatic components of a specific bad memory, or by replacing it with a positive one. Building on Ramirez and Liu’s work, others in the Tonegawa lab did exactly that in male mice earlier this year, converting a negative memory of a foot shock into a positive memory of an encounter with a female mouse.
Ramirez, who is finishing his PhD at MIT, and Liu, who is headed to Northwestern University to start his own lab, have recently taken on another big memory question: Can we intervene in a depressed state in an animal by reactivating positive memories? The answer appears to be yes. They are studying mouse models of anhedonia, or loss of interest in pleasure, a symptom of depression. Experimental mice subjected to stress until they no longer seek pleasure (such as a sip of sugar water) recover their interest when engrams for pleasant experiences are reactivated. The success rate so far is 80 percent.
Ramirez believes that memory surgery is inevitable, though there are a great many questions to address. How could it be done safely? Noninvasively? Ethically? How would patients be selected? As painful as heartbreak usually is, most of us also recognize that it’s a natural, even healthy, part of life. A high-school boy who just broke up with his girlfriend might not be a good candidate for memory surgery. But people with dementia or severe depression—would it be inhumane not to ease their suffering if an effective, safe memory intervention were possible?"