Methodological Individualism

I have been thinking about whether or not I am a "methodological individualist", since it has been asked twice in class.  I somewhat wonder whether the term is meant somewhat like the Copernican model or if it's all the way to Newton.  To reject individualism do I have to believe that there really is more to the whole than the sum of its parts, or is it sufficient to believe that for the purpose of modeling the whole it's simpler to render it as though there were something extra?  From an Ockham's razor perspective, is there a difference at this point?  Is it enough that assuming there's something extra makes the model easier and so we can represent a whole without understanding the parts even if at our core we believe the whole thing might come down to neurons?