This question is inspired by a question I answered on Health.
Can we erase problematic memories to aid recovery from depression?
A depressed person asked how to erase specific unpleasant memories in order to manage his depression. My answer was basically "that's impossible, here is how you deal with these memories instead". And then somebody asked in the comments why it is impossible.
I thought of tackling this question and realized I can't do it well. My best attempt was something like, "First, you have to find out which millions of neurons (out of the billions the person has) light up together to represent 'a memory', and we don't have a method for brain imaging with that resolution. Second, you have to stop them from activating in exactly that combination, while preserving their ability to activate in any other combination, and we have no idea how to achieve that". But this level of explanation does not satisfy me. It is very vague, and I'm not even certain it's correct.
To our best knowledge, what would we have to do if we wanted to erase a specific memory of an event happening to a person? And how far is our technology from achieving each of the steps needed?