Hmm, I guess 'cartésien' is similar to 'cerebral' in some respects, but not in every respect. While you could probably call someone either 'cartésien' or 'cerebral', the former can also be used to describe things. For example, I've heard the French schooling system being described as 'cartésien', but it wouldn't make sense to describe it as 'cerebral', since this adjective is mainly used to describe people (and perhaps also books/films/works of art). I think that 'cartésien' also conjures up the concept of deductive logic, whereas someone who is cerebral isn't necessarily thinking in terms of deductive logic. Just my impressions though!