Last year, NOVA aired a short video, “Is the Human Brain Actually Two Minds?” (5 min 17s, May 17, 2023). It’s not about the pop-science right brain vs. left brain claims. It is much more speculative than that.

The NOVA special’s claim is, “The split brain phenomenon suggests that there can be two separated minds, if you will, inside of a skull.”

From the transcript, which features neuroscientists Michael Miller and Michael Gazzaniga, both of the University of California, Santa Barbara:

Gazzaniga: The split brain phenomenon suggests that there can be two separated minds, if you will, inside of a skull. The cooperation is on the paper, not inside the head.

It’s an astounding example of cross queuing and management of two mental systems into one unified act. And the idea is maybe that’s going on in us all the time too.

That’s a remarkable claim: two human minds in one brain… in all of us all the time, maybe. Based only on these responses to a test in a lab?

We are entitled to ask for more evidence.

Why split brains?

As noted in the mini-documentary, in cases of intractable epilepsy, neurosurgeons may split the patient’s brain in half. That is, they sever the corpus callosum that joins the right and left brains. That prevents a seizure from raging across the whole brain.

Usually, the patient will recover and go back to a mostly normal life, with fewer destructive seizures. There are not two minds going separate ways.

Completely normal people

Stony Brook University neurosurgeon Michael Egnor, who has done the split brain procedure, says,

“What I have seen with these patients — and I’ve dealt with quite a few of them — and what [Roger] Sperry saw also, is that these are, for all intents and purposes, completely normal people. You meet these people, sit down and talk with them. They’re not two people. They certainly don’t think they’re two people. They have very subtle perceptual disabilities of the sort we talked about. But they don’t even notice them.”

Why doesn’t the split-brain patient usually notice the disability much in everyday life? The patient’s single mind compensates for it easily. As Dr. Egnor notes, people with split brains unconsciously present objects to the correct hemisphere by simple, automatic movements.

The Nobel Prize-winning experiments by Roger Sperry, which first identified the split-brain patients’ perceptual handicap, explicitly prevented his subjects from using their usual fixes. That — not the exotic phenomena that we might expect from two separate minds trapped in a single brain — is how the disability was first discovered.

The unity of the human mind is a reality

Egnor stresses that the persistence of normal behavior even when the brain is split is evidence for the unity of the human mind: “ … material things can always be divided into parts. That is, I can take a loaf of bread and cut it any which way you choose. So with material things, you can always make two out of one. But it’s very difficult to see how immaterial things like spirits or souls can be split in two.”

Unity of the mind implies the actual existence of the mind, a concept that many fashionable neuroscientists would very much like to refute. Hence the preference for exotic explanations like “two separated minds … inside of a skull,” that are based on pretty flimsy evidence.

Neuroscientist Yair Pinto and colleagues, who reviewed decades of split-brain research, concluded in 2017 that split-brain patients have split perception but unified consciousness.

Dr. Egnor and I discuss the split brain phenomenon in more detail in The Immortal Mind (June 3, 2025)

You may also wish to read: The left and the right brain both want pop science media to… chill. Neuroscience is not an especially rewarding field for the pursuit of dogma. The risk with neuroscience that tries to encompass Mozart is not that we will know nothing but that we will know just enough to get it all wrong.

and

Split mind: The strangest theory in neuroscience? The idea that we might all have separate, undetected consciousnesses in each half of our brain supports materialism but there’s little evidence for it. The subtle abnormalities displayed by patients whose brains were split in half revealed an uncomfortable truth: The mind is a unity