If you have a particularly painful memory, scientists can take advantage of its flimsy nature and neutralize the feelings of sadness, fear, or embarrassment that you associate with it. One method is to block norepinephrine -- the chemical associated with our fight-or-flight response -- while triggering the memory. This changes the way the memory is "put back" after it's been retrieved, a process known as "reconsolidation."
In one successful case, featured in a NOVA special about memory hacking, researchers in the Netherlands exposed arachnophobes to live tarantulas in a cage, triggering intense pangs of fear. Then they administered beta-blockers -- which are typically used to treat high blood pressure, but are also known to restrict norepinephrine levels. It proved pretty damn effective: Those same arachnophobes were able to gradually eradicate their fear from their brains, and even touch the tarantulas during follow-up sessions mere days after the first exposure. Obviously this is just an early trial, but the future potential for this kind of science has big implications.