I'm signed up to receive PubMed updates on spinal cord injury papers, but a few things are bugging me...

Pubmed lets you search by First Author and Last Author (Source), but there's no way to search by lead author. What is the significance of the first and last authors? (I read somewhere that one of them is the contact for the paper, but they may not be the lead author.)

Is there a fool-proof way to determine the lead author from the author list of a PubMed abstract?

Thanks in advance to anyone who can help.