Jason Castro, assistant professor of psychology and neuroscience.

The first question is whether the brains of introverts and extraverts differ. Yes, says Castro, but “we don’t have experiments that really address whether those brain differences play a causal role.”

The second is what neuroscience tells us about free will. In fact, we may have free will and not even know it. “There is brain activity that registers our intent to make a decision — a spontaneous decision — well before we’ve consciously decided to make a decision,” Castro says.

• View story from The Daily Circuit, Minnesota Public Radio, Oct. 16, 2012.