Here's a brief article surveying some recent discussions about neurobiological basis of personhood and when human and nonhuman animals attain this state. In some views, this provides a criterion for moral status.
This is part of the growing recognition that many traits formerly thought to obtain only in humans are actually shared by a wide range of other animal species. But ultimately, this may really lead us to ask, not just which animals possess the traits comprising personhood which many (all?) humans have; but what is the full scope of admirable and valuable traits that many animals have and which humans share? Must you be a "person" to show love, creative intelligence or play? Or is "person" just a relic category from the anthropocentric and possibly Eurocentric traditions that the developments of modern thought, such a neuroscience, tend to make obsolete?