So Epicurus was "right" in a sense that there is no neutral state. You're either feeling pleasure or pain.
Anytime someone says "So Epicurus was 'right'..... you can expect me to agree, however:
I'm not able to take the time to read Feldman and comment on the analysis other than what you guys are saying.
The reason I am posting this comment is that as to the position that there is no "neutral state," I want to go on record as not being sure whether that position was intended to be something that he was taking on based on observation (such as on observation of babies and kittens and puppies) or whether that is a position he took on some kind of "logical" ground, as he did in the case of the swerve, and of the existence of the void. If it's the latter, that would be another reason to be cautious in drawing parallels with neurological or medical research.
Personally, I doubt that the denial of a neutral state is of as much practical significance as it is of "logical" significance in debating with Plato on the nature of pleasure as the greatest good.