This paper argues that nonphysical souls would violate fundamental physical laws if they were able to influence brain events. Though we have no idea how nonphysical souls might operate, we know quite a bit about how brains work, so we can consider each of the ways that an external force could interrupt brain processes enough to control one’s body. It concludes that there is no way that a nonphysical soul could interact with the brain—neither by introducing new energy into the (...) physical world, nor by borrowing existing energy from it—without apparently violating one or more basic laws of physics, such as the law of conservation of energy. And despite widespread appeals to quantum mechanics to give interactionism an air of scientific respectability, the essential randomness of quantum processes prohibits the distinctly nonrandom influence that a nonphysical soul must have on brain events in order to control the body, and quantum mechanical uncertainty is not great enough to allow neurons to fire action potentials. -/- 1. Introduction -- 2. How the Brain Works -- 3. Mind-Brain Interaction Mechanisms - 3.1 Opening Sodium Channels - 3.2 Altering Voltage Gradients - 3.3 Synaptic Transmission - 3.3.1 The Presynaptic Neuron - 3.3.2 The Post-Synaptic Neuron - 3.3.3 The Beck and Eccles Models - 3.4 Neuronal Modulation - 3.5 Self-Generation of Action Potentials by Neurons -- 4. Harnessing Energy -- 5. How Many Action Potentials for a Volitional Act? -- 6. Input: From Brain to Nonphysical Mind -- 7. Discussion -- Appendix A: Opening Gates on Membrane Channels - A.1 Directly Opening Gates - A.2 Changing Voltage Across the Membrane -- Appendix B: The Biochemical Approach. (shrink)

We suggest that anecdotes have evidentiary value in interpreting nonhuman primate behavior. We also believe that any outcome from the experiments proposed by Heyes can be interpreted as a product of previous experience with trainers or as associative learning using the experimental cues. No potential outcome is clearcut evidence for or against the theory of mind proposition.