While I think the quest for an objective metric of morality is often well intentioned it is extremely misguided. This is particularly the case for quests for scientific metrics of morality. Science is by nature, in the business of figuring out how things work. This helps us hugely in informing our ethical systems, though giving us a better understanding of things like sentience, and its possible implications for other species and so on. What it does not do is provide us with moral imperatives.
Moral imperatives are wholly subjectively derived. I would go so far as to say they are inter-subjectively derived but no further. What I mean by this is that we construct our ethical beliefs based on what subjective effects actions have on other ethical beings (by this I mean being capable of ethical thought). We may be able to detect through brain activity what effect some actions may potentially have, but this does not tell us what is good, only what *IS*. We must then appeal to our ethical construct, which has been inter-subjectively defined. This is what I mean by science informing morality, but not constructing it.
More on this in the future.