[Anthony]

The standard interaction between a no mana zone and a spell is that the spell is suspended within the zone. I would extrapolate this to say that if a spell is partially in a zone, that portion of the spell that is in the zone gets suspended. If the spell is not something that can reasonably be split (e.g. a Wisdom spell), the GM should define a key location, usually either the vitals or the brain, and use the position of that key location.

For casting spells, I would typically set the key location to the brain; casters with No Brain should define an appropriate location.