A. Quick trick for figuring out when "whom" will work - if you can replace "whom" with "him" or "her" it works. If you can't, it doesn't. Here, "him brains' neural connection" doesn't make any sense. We need a possessive pronoun here - the brains belong to these people. So "whom" doesn't work.

We should also recognize that everything from "whom brains'" to "monitored" is set off by commas. This means we should be able to remove it and still have a grammatical sentence:

A groundbreaking neuro-psychological research was conducted on epilepsy patients and have discovered that memories of past events are stored in the same neurons in the brain which were active during the original experience.

This makes it much more clear that both the verbs "was" and "have discovered" go with the subject "research". "Research" is singular, so "have discovered" should also be singular - "has discovered". So we have an agreement error in addition to a pronoun error. Eliminate.

C. Here we have "whose", which is a possessive pronoun and works in the sentence! However, we still have "have discovered", which still doesn't agree with "research". Eliminate.