Leibniz was an idealist. He lived in peculiar ideological waters: he was Christian. He had to believe that there's the mind, there's reality, and both never touch. If he ever went out the party line, the inquisition would take care of him.

According to Leibniz, neurons can't exist. Exercise does not improve your mood. Brain surgery is useless. Caffeine does not work. Hormones do nothing. Coma is unexplainable by definition. And so on.

Reality killed Leibniz.