Obviously the brain is very complex and the nuances of its functioning are very mysterious. But I’m having trouble seeing how complexity relates to free will, especially the “free” part. A complex system may be unpredictable and/or incomprehensible, but how does that make it free?

A single atom is very complex. Two interacting atoms are much more complex. Several atoms interacting are so complex that the fastest supercomputers can’t accurately simulate their behavior. A human being is made up of trillions upon trillions of atoms, all interacting in incomprehensibly complex ways. But just because we can’t  adequately describe those interactions doesn’t mean they stop obeying physics at some point.

@ benzyme - The absence of free will doesn’t imply that people aren’t responsible for their actions. Why would it?