Researchers have successfully changed the emotional content of memory in mice by forging new neuron associations (between fear and pleasure). While this technology is a long way from being applied in humans, it may eventually lead to a new treatment path for depression and PTSD. Additionally, it demonstrates that cognitive and behavioural therapy to change the emotional content of memory does, indeed, have sound neurological justification: emotional associations with memory are not permanently fixed!

In this study, mice were genetically engineered with a light-sensitive protein, so that researchers could activate neurons by beaming a laser at the desired spot in their brain. First, the mice underwent emotional conditioning, to learn that one situation was scary (small electric shocks) and another pleasurable (interacting with a female). Next, the researchers exposed the mice to the opposite situation, but reactivated the neurons previously activated in the original situation. So a mouse that learned to fear shocks was allowed to spend time with a female while the researchers reactivated the "fear" neurons. Sure enough, the researchers forced the "fear" neurons to link up with the new pleasure neurons, changing the emotional content of the memory. A mouse that was retrained to remember electric shocks positively no longer feared hanging out in the area that it associated with shocks.

Could this research be applied to humans? It is a very new (and invasive) procedure, so the road to human testing is long and uncertain. But the discovery that the emotional content of memory is not permanently fixed may also open the door to other, related treatment options.

For another new and fascinating potential treatment or PTSD, see here: a beta-blocking drug called Propranolol, designed to treat high blood pressure, has an intriguing side effect: in can dampen the emotional content of memories.