I don't know if you have seen the Jim Carrey movie called Eternal Sunshine of the Spotless Mind.  It is supposed to be a comedy according to the movie poster, but is really pretty sad and has some interesting science fiction in it. There is a procedure people can undergo to erase their memories when their relationships turn sour. A similar feat is seen in Total Recall with Arnold Schwarzenegger.  In this movie, one of the neat things is that if you want to take a vacation to Mars, and you don't have the money to go, they can implant you with the memories so you will feel like you have been there (they can even provide someone for you to meet or put you in the role of a spy, etc).

At any rate, we all know that science fiction often ends up becoming reality (after all, we all know our cell phones resemble early Star Trek communicators).  Scientists have long been trying to understand the hippocampus and how memories can be augmented (for example in diseases that affect memory, like Alzheimer's).  Well, they have made a tremendous breakthrough by being able to erase memories in rat brains (now don't get too upset for the rats, the lost memories can be replaced by new memories and short-term memory is not affected). They did this by inhibiting synaptic strengthening in the hippocampus.  For complete understanding, here is the link to the rest of the article.

Now, I ask you, which vacation trip do you want implanted? And what memories do you want erased?