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Dualism and Materialism in Modern Neuroscience

Image credit: Ars Electronica, via Flickr (cropped).

Editor’s note: This article is an excerpt from a chapter in the newly released book The Comprehensive Guide to Science and Faith: Exploring the Ultimate Questions About Life and the Cosmos

One might think that the logical problems with materialism would insulate 21st-century neuroscience from its influence, but that is not so. Most contemporary neuroscientists work from an implicitly materialist perspective — in part because they’re unreflective, in part because materialism is the metaphysical correlate of the atheistic scientism that infests modern science, and in part because public admission of a dualist perspective is perceived (correctly) to be a career impediment in neuroscience. I recently had a friend (a tenured and accomplished neuroscientist) who is a devout Christian tell me privately that if he ever publicly questioned materialism, he would never get another grant. 

Inference to the Best Explanation 

Materialism is the framework for modern neuroscience for ideological reasons, not logical or scientific ones. Materialism is stipulated, not demonstrated, in neuroscience. The reason this stipulation has, despite logic and evidence, been easy to pull off is that it is rather difficult to test materialistic and dualistic theories with unambiguous rigor. How do we know, experimentally, if a thought is material or immaterial? How do you test this metaphysical question? It can be tested and has been tested. There are here two kinds of inferences we can make (discounting abduction): deductive and inductive. All natural science is inductive because, as Thomas Aquinas observed in the 13th century, deduction cannot prove the existence of a thing because essence (the formal structure of a deductive argument) is absolutely distinct from existence. We cannot deduce neuroscience. We gather evidence, apply explanatory frameworks, and see which inference best fits that evidence and the logic. Neuroscience, like all science, is inductive — it is inference to the best explanation drawn from evidence.

To test materialism and dualism, we need to define them. These are the working definitions I use:

  1. Materialism entails the inference that the brain causes all aspects of the mind, without remainder. 
  2. Dualism entails the inference that the brain causes some aspects of the mind, with remainder. 

All parties agree that the brain causes some aspects of the mind. The materialist claim is radical: The brain causes allaspects of the mind; there are no immaterial thoughts. 

The dualist claim is less radical: There are some aspects of the mind that are not caused by the brain. 

The philosophical issues get subtle here, involving supervenience, epiphenomenalism, etc., which are beyond our scope. But the basic claims of materialism and dualism can be tested with some rigor, as we will see. 

The Immaterial Remainder

As noted, materialist and dualist theories of mind differ on the immaterial remainder. That is, they differ on whether all mental states are caused entirely by brain states, or whether there are some mental states that are not caused by the brain (i.e., are immaterial). The evidence, of course, is incomplete — there are countless mental states that are uncorrelated with brain states because no effort has been made to study them, or (perhaps) because the scientific methods employed are insensitive. With these provisos in mind, we can still make reasonable inferences about materialism and dualism based on this fundamental concept: If all mind states are caused by brain states, then every mind state can be evoked by stimulating the brain in some fashion, every mind state can be suppressed by ablating (damaging) the brain in some fashion, and every mind state can be correlated with a brain state in some fashion. If some mind states are notcaused by brain states, then these mind states will be recalcitrant to evocation, ablation, and correlation.

Most of the seminal experiments in neuroscience that address the mind-brain issue can be categorized as evocative (stimulate the brain), ablative (suppress the brain), or correlative (compare brain states to mind states). It is instructive to review the major experiments in neuroscience that speak to the mind-brain question. 

Evocative Experiments 

Penfield — Intellectual Seizures and Free Will

Wilder Penfield1 was a leading neurosurgeon and neuroscientist in the mid 20th century who pioneered the surgical treatment of epilepsy using stimulation and recording from the surface of the brain in awake patients undergoing brain surgery. This was possible because the brain itself feels no pain, and the scalp can be anesthetized with Novocain-like drugs to render the surgery painless. This surgery is still being done today. 

Penfield was especially interested in the relationship between the brain and the mind. He began his career as a materialist and he ended it as a passionate dualist. He based his dualism on two observations:

  1. There are no intellectual seizures: Seizures are sporadic electrical discharges from the brain and they cause a variety of symptoms, from complete loss of consciousness to focal twitching of muscle groups, sensations on the skin, flashes of lights or noises, smells, and even intense memories or emotional states. Penfield could record these electrical discharges from the surface of the brain. Penfield noted that there are no intellectual seizures. That is, there has never been a seizure in medical history that had specific intellectual content, or abstract thought. There are no mathematics seizures, no logic seizures, no philosophy seizures, and no Shakespeare seizures. If the brain is the source of higher intellectual function, as is widely believed, why in medical history has there never been a seizure that evoked abstract thought? This fascinated Penfield, and he inferred quite reasonably that the reason there are no intellectual seizures is that abstract thought does not originate in the brain. 
  2. Free will cannot be simulated by stimulation of the brain: Part of Penfield’s research was to stimulate the motor areas of the brain, which caused patients’ limbs to move during surgery. He was the first surgeon to map the motor areas of the brain in this fashion. In doing this, he noticed that patients always knew the difference between stimulated movements and movements that they freely caused themselves. Penfield would ask patients to move their limbs freely whenever they chose, and he would (without telling them) stimulate their limbs to move. Patients always knew the difference between movements freely chosen and movements caused by the surgeon. Penfield could never find a region of the brain that simulated free will. He concluded that free will is not in the brain — it is an immaterial power of the mind. 


  1. Wilder Penfield, Mystery of the Mind: A Critical Study of Consciousness and the Human Brain (Princeton, NJ: Princeton Legacy Library, 1975).