How are the Mind and Brain Related?

by Bill Meacham

Copyright © 2007, William Meacham. Permission to reproduce is granted provided the work is reproduced in its entirety, including this notice.

I wrote this in the December, 2007, and submitted it to Philosophy Now, a popular journal of philosophy. The assignment was to write 400 words or fewer on the topic.

Researchers have made much progress in identifying the neural correlates of consciousness, the patterns and groups of nerves that fire when experiences take place. Clearly, neural activity and mental states are tightly correlated. Brain scans reliably show the areas of the brain that "light up" during perceptual tasks. Anti-depressant drugs work by altering the chemistry of the synapse. One can reasonably assume that the state of the brain determines our perceptions, thoughts, feelings and actions.

This seems to make humans nothing but automatons, since all our experiences and actions are causally determined. But this conclusion rests on a concept of causality from classical physics; and in the interstices of the brain, at the tiniest level of neural activity, quantum physics is the more accurate description. Causality in quantum physics is quite different.

Experiments show that it is in principle impossible to predict where a single particle fired at a double slit or through an inhomogenous magnetic field will be detected. One can predict that a great number of particles will end up in various places according to their probability distribution. But there is only a probability, not a certainty, that any single particle will end up in one place or another.

The human brain contains 100 billion neurons and five quadrillion synapses. The firing of each synapse depends on where a calcium ion, entering the nerve terminal from outside it, lands within it. Calcium ions and the channels through which they pass are small enough for quantum indeterminacy. A given calcium ion might or might not hit a given triggering site; hence, a given neurotransmitter might or might not be released; hence the receiving neuron might or might not get excited (or inhibited).

At the most fundamental level, brain functioning is not physically causally determined. What, then, determines it?

Here we move beyond what physics can tell us. With Wittgenstein, we could simply shut up about it. Or we could postulate an incorporeal soul with free will or a God that intervenes in nature or a multitude of deities. Science can neither prove nor disprove such assertions. We must look elsewhere -- in introspective analysis of our own experience of making a choice, or in patterns of coincidence or synchronicity -- for evidence. Such evidence would not hold up in the public court of scientific inquiry, but might well be decisive for how we choose to live our lives.

About the Author: Bill Meacham lives in Austin, Texas, USA and is an independent scholar in philosophy. You can contact him at