On May 6, Sean McDowell released a podcast at YouTube on which he interviewed neurosurgeon Michael Egnor, author, along with me, of The Immortal Mind: (Worthy, June 3, 2025).

After six days, the podcast has reached 225,000 views, attracting nearly 1700 comments to date. One of them stood out:

“The part about split brain procedure seemed really convincing, until I looked up the procedure and there are still three parts of the brain that usually connect the two halves. Some additional transparency on these aspects to rule in or out this having an effect would be appreciated.”

Good question! In the podcast, Dr. Egnor was discussing the “split brain” operation, a radical but sometimes necessary treatment for epilepsy, discussed in the book.

When severe epilepsy cannot be controlled by drugs, a neurosurgery team might split a patient’s brain in half. Splitting the brain — obviously quite a radical step — prevents the seizures from becoming brainwide, thus limiting their worst effects.

The procedure gained status as a treatment because, except for some minor disabilities, post-surgical patients behave normally. The separated halves of the brain appear to co-ordinate quite well:

Image Credit: iconimage - Adobe Stock

Neuroscience pioneer Roger Sperry (1913–1994) won a Nobel Prize for his clever experiments on split-brain subjects, showing what they could and couldn’t do. But, Egnor notes, the big story is the one that receives very little emphasis: “You could cut the brain in half and practically nothing happens.

“That is, split-brain subjects needed to move their heads in order to associate, say, the word “apple” with an apple because the word and the recognition are governed by opposite brain areas. On the other hand, he found nothing like split consciousness or two separate personalities. A simple adjustment was all that was needed:

The only thing that happens takes Nobel laureate level research to detect!”

“What Did Splitting Human Brains in Half Tell Us About the Mind?” August 21, 2024

Is the brain really split?

To go back to the question raised in the podcast’s comment box, Dr. Egnor responded by e-mail, citing the work of researchers:

It’s a red herring. There are multisynaptic pathways through deep brain pathways by which the hemispheres could communicate. But the fact is they don’t communicate with many kinds of perception — everyone agrees that much of perception is split.

A substantial portion of Justine Sergent’s and Yair Pinto’s research was checking for a multi synaptic back door. The evidence for it is weak. Even if there were a back door, the back door would have the peculiar property that it was only active for certain kinds of perceptual thought and responses to perceptions but not for others.

Perceptual thought is mostly split and everyone agrees that there is no back door there. The evidence suggests that subcortical back-door pathways are not adequate to explain the remarkable unity of consciousness, but even if there were an active back door for we would still have to explain why that back door was only used by some kinds of thought and responses and not by other kinds of thought and responses.

Both the experimental evidence and straightforward logic points to the absence of a back door playing any role in these experiments. both Sergent and Pinto were very careful about this. (Slightly edited)

He added,

There are multiple references in the literature to subcortical connections that authors claim may account for the integrated consciousness. But my reading of that is that the hard evidence for that is minimal and it’s basically handwaving. They simply infer that there must be subcortical connections because they can’t account for the integration otherwise. … The substantial dichotomy between perceptual split and conscious unity implies that subcortical connections cannot be an adequate explanation for the unity because it doesn’t explain why perceptual disunity persists if subcortical connections are robust. Sergent and Pinto tested response times with either hand to unilateral input, as I noted above, and my clear recollection is that they did not find dramatic differences.

We are learning new things about the mind–brain complex every day and not everything is what materialists expected to find. The fact that split brain patients show unity of consciousness despite splitting of the brain hemispheres is a huge problem for the materialist theories of consciousness. Immaterial theories of the soul, such as Thomistic dualism, account for it naturally. From that perspective, perception is a material power of the soul, and thus can be split surgically, but intellect and will—the spiritual powers of the human soul—are immaterial and cannot be split by the surgeon’s knife.

The Thomistic view has broad explanatory power and is the one that aligns most closely with modern neuroscience we expected to find.