I aim for center mass.
In truth it would depend on what section(s) of the brain was(were) destroyed by the projectile. Assuming the bullet went through the spinal cord at the base of the brain then it would sever it entirely and disrupt any possible motor function.
If the round only went through the auditory or visual cortex's of the brain then it is possible that a signal to the trigger finger could go off uninterrupted.
I would imagine that any blow to the brain would render the person unconscious so the trigger pull would just be an involuntary muscle movement or the BG's brain sent the signal to pull the trigger right as you fired.