Wired:

Remember that horrible date you went on a few years ago? The one where you knocked over a candle and doused the flaming tablecloth (and your date) with a bottle of Bordeaux? Horrible! But now the two of you are happily married and the whole thing seems… kind of sweet. Time has a way of shifting the emotions tied to our memories.

Now there’s another way. Neuroscientists have devised a technique for switching the emotional association of a memory from bad to good by directly manipulating the neurons that encode it.

If that sounds like a promising therapy for disorders like PTSD, you’ll have to wait. The experiments were done in mice, and the methods, which include genetically altering neurons and inserting an optical fiber into the brain, won’t be used in people anytime soon (if ever). But this study and others like it are illuminating the neural mechanisms of memory in unprecedented detail, and showing that it’s possible to activate, alter, or even create memories just by tweaking the right neurons.

The work was done in the lab of Nobel Prize-winning immunologist-turned-neuroscientist Susumu Tonegawa at MIT. The team, led by postdoctoral fellow Roger Redondo and graduate student Joshua Kim, first created good and bad memories in mice by giving them either a food reward (good!) or a mild shock (bad) when they wandered into a certain part of their enclosure.