As a scientifically minded disbeliever in anything supernatural, I don't usually like magic in my fantasy worlds, but lately I have entertained the idea of a magic system that had a quasi-scientific foundation. This magic would stem not from gods or other mystical forces, but would come from within people, and it would have certain physical limits such as energy costs. Let me explain:
All people possess a region in their brains that allows them to mentally manipulate the laws of physics---in other words, to do magic. This area's initial size varies across individuals, therefore predisposing some to greater magical proficiency than others, but it can expand in anyone with enough training and practice. However, magic costs a lot of energy to use, with the exact amount increasing with spell power; the most devastating or wide-ranging spells can knock out or even kill their casters. As a consequence, magicians must eat frequently to resupply the energy they need for spellcasting.
One thing I wonder is increased magical proficiency could have negative effects on people's other cognitive functions. If their "magic lobe" grew in size, would that crowd out other areas of the brain?