A Neurosurgeon Argues That Mind Functions Are Immaterial. Badly. (Pt. 3)

This is my final post discussing creationist neurosurgeon Michael Egnor’s attempts to demonstrate that certain mental functions cannot be accounted for solely by the brain and, instead, indicate the involvement of some unspecified “immaterial” processes or entities. The first two posts in the series can be found here and here.

As before, I am including the video in which he makes his arguments, but it should not be necessary to watch the entire video in order to understand this post.

I’m going to address a specific argument that Egnor makes, even though he does not mention it in the articles he wrote about me, because I believe it encapsulates a basic error commonly made by those who share Egnor’s views. At 5:00 of the video he describes a surgical procedure known as a corpus callosotomy, and notes that it has a surprisingly limited effect on the cognitive functions and personalities of patients who have undergone the procedure. The corpus callosum (CC) is a large bundle of fibres that connects the left and right hemispheres of the brain. It is essentially the means by which the two hemispheres “communicate” with one another.

It is important to note that the CC does not itself perform any sensory, cognitive or motor functions. It is merely a set of tracts by which some of the areas that do perform such functions pass signals from one to another. Egnor cites the Nobel Prize winning research of Roger W. Sperry, who was pivotal in demonstrating that each hemisphere of the brain performs different functions. His initial work was done on cats and monkeys whose CC had been cut. Ordinarily, of course, one would be unable to perform such experiments on humans. However, as it happens, corpus callosotomy also has therapeutic benefit for some people with severe, intractable epilepsy. By severing the CC, electric impulses that arise from a localized epileptic focus are prevented from spreading to the entire brain, reducing the severity of the seizure.

An unintended benefit of the procedure was the creation of test subjects for a number of important neuroscientific experiments. Egnor just sort of glides over these findings, which is unfortunate because they are quite fascinating (not to mention most inconvenient for Egnor’s entire thesis.) Among Sperry’s findings:

• Images presented to one visual field (left or right) would not be recognized when presented later to the opposite visual field.
• If information was presented to the right visual field, subjects could describe it in spoken words or writing, but not if it was presented to the left field.
• An object placed in the right hand (behind a barrier that prevented the subject from seeing it) could be described in spoken and written language, but not if it was placed in the left hand.

It’s important to remember that sensations perceived by our peripheral sense organs are routed to the opposite brain hemisphere.  In other words, if we feel something with our left hand, that sensory information is conveyed to and processed by the right hemisphere, as are things seen by the left visual field (not the left eye) , and vice versa.  What Sperry’s findings demonstrated is that language is usually processed in the left brain hemisphere.  This why these “split-brain” subjects could not describe in words objects presented to the left hand or left visual field.

Under normal circumstances (i.e. in a person whose corpus callosum is intact), visual or tactile information from the left would be conveyed to the right hemisphere and then communicated thru the CC to the left brain, where the cortical areas involved in language are located.  In a person whose CC has been severed, the second part of that process cannot occur, and therefore no connection can be made between the visual or tactile information received and the language that pertains to this.  (The general term for deficits of this sort is disconnection syndrome, which refers to situations in which brain areas responsible for receiving and processing sensory information are relatively intact, but the tracts that connect these areas to each other are damaged.)

Here’s the point: The deficits experienced by people who have undergone corpus callosotomy are perfectly understandable and predictable once one understands the neurological functions of the structures that are disrupted by the surgery. While it may have been initially surprising that the loss of such a large structure had such limited apparent effect, this is no longer at all surprising once the function of the corpus callosum is better understood. Basically, the brain functions that rely on the CC were affected by the surgery and those that do not (which is by far most of them) were not affected. It’s as simple as that. 

Egnor makes some truly bizarre claims when he tries to argue that this rather straightforward finding is evidence for some mysterious, supernatural, immaterial process behind our thoughts. For instance, he says that if “materialism” was true, then cutting the corpus callosum should result in “two people.” Now, I know that neurosurgeons (and psychiatrists, for that matter), are not expected to know as much about neural function as are neurologists or neuroscientists. But this sounds like something a bad science fiction writer with no understanding of neurology whatsoever would come up with. Exactly how is a callosotomy supposed to produce “two people”? Exactly what is it about the function of the CC that leads Egnor to conclude this? He also refers to the operation as “cutting the brain in half”, which is nothing but hyperbole. As I have explained, the procedure involves interrupting a specific set of tracts in the brain, and its effects are limited to the functions of these tracts. If Egnor truly believes that “cutting the brain in half” should have no significant effects if the mind is immaterial, then I would ask him why neurosurgeons never bisect the brain in the coronal or horizontal plane, as shown in the diagrams below. I don’t think you need to be a neurosurgeon realize that such a procedure would not work out too well for the patient:

In summary, what we observe is that specific lesions inflicted on the brain have specific and predictable effects on our higher cognitive functions. This includes language which, arguably, distinguishes the human species more than any other trait. If such mental functions are truly “immaterial” and not produced by the brain, then how is it that they are affected in this manner by processes that affect the brain?

To be clear: I am not saying that these observations demonstrate conclusively that mind functions arise from brain functions. However, they are fully explicable if this position were true. On the other hand, there is nothing about these findings that are better explained if one takes the position that the functions involved arise from something or somewhere other than the brain. There is simply no logic behind Egnor’s argument.

Egnor keeps referring to those who do not accept his claims as “materialists”, but that is not what I consider myself to be. This is not to say that I share Egnor’s belief in immaterial entities with causal properties. Rather, I simply recognize that the ontological questions regarding the ultimate nature of reality have been debated for centuries by the some of the greatest minds in philosophy, with no resolution reached. So it would be quite presumptuous of me, with my limited background in philosophy, to claim that I have figured it all out. And even if it turns out, as I suspect, that all mental functions end up being accounted for by physical brain processes, that would not mean that materialism is true.

Michael Egnor, however, has a clear motivation for denying that properties of the mind can be causally linked, in their entirety, to physical processes occurring in the brain. As the foundational document of the Intelligent Design movement makes clear, proponents of ID view “materialism” as a pernicious force vitiating society and having “devastating” effects on morality, criminal justice, the social sciences and, uh, “product liability” (?). If Egnor sincerely believes this, of course, then he is fully justified in arguing against “materialism” as forcefully as he can.

This does not, however, relieve him of the obligation to do so using sound arguments and evidence. If he must resort, instead, to using fallacious logic and misrepresenting or misunderstanding the scientific evidence in order to support his position, as he has here, then he needs to seriously consider whether his position is defensible in the first place.