Once again, we have an article in which a neuroscientist misinforms us very badly on the very important topic of split-brain patients. This time it is an article I read recently at the MIT Press Reader. The article is entitled "What Split-Brain Patients Reveal About Consciousness." After discussing facts that contradict his claim, the author (neuroscientist Christof Koch) senselessly refers without any warrant to "two conscious minds in one brain."
A split-brain patient is typically a patient who underwent an operation severing the corpus callosum, a mass of fiber-like nerves that connect the left hemisphere of the brain and the right hemisphere of the brain . Each of these hemispheres makes up half of the brain. Such an operation is typically done to treat very severe and frequent seizures. Below is a Google Gemini infographic on the topic of this operation, called a corpus callosotomy.
After this operation is performed, a person is left with two disconnected brain halves. If it were true that your brain makes your mind, such an operation should produce two minds in the same individual. But no such thing happens.
In 2014 the wikipedia.org article on split-brain patients stated the following:
"In general, split-brained patients behave in a coordinated, purposeful and consistent manner, despite the independent, parallel, usually different and occasionally conflicting processing of the same information from the environment by the two disconnected hemispheres...Often, split-brained patients are indistinguishable from normal adults."
Neuroscientist Koch tells us something similar in the middle of his article. He states this:
"Remarkably, once these 'split-brain' patients recover from the surgery, they are inconspicuous in everyday life. They see, hear, and smell as before; they move about, talk, and interact appropriately with others, and their IQ remains unchanged. They have their usual sense of self and report no obvious alteration in their perception of the world — no shrinkage of their visual field, for example. The surgeons who pioneered this operation, including Joseph Bogen at Loma Linda University in Southern California, were puzzled by this lack of clear symptoms."
Koch then goes into an account claiming that certain things were observed in split-brain patients. It is the kind of account that typically goes on when authors will be making false "two minds in one skull" claims: an account that has no link to particular papers. What we have is flimsy anecdotal evidence making claims about what supposedly happened in a handful of patients. We don't have straightforward accounts of what was observed, but accounts that are littered with dubious or unbelievable interpretations. And we don't have specific mentions of what exactly one particular identified person did. Koch states this:
"If specific data are given to one hemisphere, that information is not shared with its twin on the other side. Furthermore, only one hemisphere, typically the left one, speaks. That is, if the right hemisphere is lost or silenced by anesthesia, the patient can still talk, which is why the left hemisphere is called the dominant hemisphere. The right hemisphere by itself has only limited language comprehension and is mute, though it can grunt and sing. So, when engaged in conversation with a split-brain patient, it is the person’s left hemisphere that is doing all the talking."
Data is given to persons, not to single hemispheres in the brain. And there is never any evidence that learned information is stored in a brain. The microscopic examination of brain tissue has never revealed the slightest trace of anything anyone learned, nor have any brain scans. It is not a hemisphere of the brain that speaks or comprehends or sings, but a person who speaks and comprehends and sings. So Koch is writing erroneously when he states "only one hemisphere, typically the left one, speaks"; and he is speaking just as erroneously when he says that the right hemisphere sings; and he is speaking just as erroneously when he claims that the right hemisphere comprehends something. Both hemispheres of the brain are equally active in normal people and split-brain patients, so it is ridiculous to say of anyone "only one hemisphere, typically the left one, speaks." Brain hemispheres don't speak or sing or comprehend; people speak and sing and comprehend.
In the paragraph quoted above and his next paragraph, Koch fails to link to any scientific papers, and fails to mention any specific persons who were observed. He mentions some alleged perceptual difficulties in split-brain patients. Using the phrase "the patient" in an ambiguous way, he claims that "The patient can’t name an object presented in the left visual field because that image is processed by his mute right visual cortex." We can't tell whether he is referring to only one patient or to split-patients in general. Koch also makes this claim:
"If a key is placed in the patient’s right hand, with the hand under the table and out of sight, they will quickly name it. Touch information from their right hand is transmitted to their left hemisphere, where the object is identified, and its label is relayed to the language center. If the key is placed in the person’s left hand, however, the patient is unable to identify it and rambles on."
But what confidence can we have in such claims, as Koch does not mention any source for such generalizations? If there were actually good evidence for such claims, why would Koch have failed to link to the relevant paper reporting this claim? And if a single paper reported seeing such a thing in one person, why should we assume that such a thing is generally true of split-brain patients, without substantial replication of such a result?
We then have this extremely weak piece of evidence, which consists of an anecdote involving one person, and a dubious self-report provided by that person:
"Victor Mark, a neurologist at the University of North Dakota, videotaped an interview with a split-brain patient. When asked how many seizures she had following her operation, her right hand held up two fingers. Her left hand then reached over and forced the fingers on her right hand down. After trying several times to tally her seizures, she paused, then simultaneously raised three fingers with her right hand and one with her left. When Mark pointed out this discrepancy, the patient commented that her left hand frequently did things on its own. A fight ensued between the two, looking like slapstick comedy. Only when the patient grew so frustrated that she burst into tears was I reminded of her sad situation."
As evidence of anything, this is extremely weak. We have no link to the original account. We do not have a link to this video, or a transcript of what the patient said. Someone (maybe Victor Mark) has claimed that the "patient commented that her left hand frequently did things on its own." But we don't know exactly what the exact words of the patient were, and we don't know whether that was a response to some "leading question" suggesting such a thing. What we have is a second-hand account of someone claiming that a brain-damaged person said a particular thing. That is extremely flimsy as evidence. We don't know what exactly the patient might have meant by saying such a thing; and we can't be sure that any such thing was said as Koch suggests.
Koch then states this, making an outrageous misstatement that has no warrant in the few anecdotes he has presented:
"Studies with split-brain patients, work for which Sperry was awarded the Nobel Prize in 1981, teach us that cutting the corpus callosum cleaves the cortico-thalamic complex in two but leaves consciousness intact. Both hemispheres are independently capable of conscious experience, one being much more verbal than the other. Whatever the neural correlates of consciousness are, they must exist independently in both hemispheres of the cerebral cortex. Two conscious minds in one skull. "
Two conscious minds in one skull? Nothing that Koch has discussed provides any warrant for such a claim. To the contrary, Koch's previous statement contradicts such a claim. As I previously mentioned, Koch stated this:
"Remarkably, once these 'split-brain' patients recover from the surgery, they are inconspicuous in everyday life. They see, hear, and smell as before; they move about, talk, and interact appropriately with others, and their IQ remains unchanged. They have their usual sense of self and report no obvious alteration in their perception of the world — no shrinkage of their visual field, for example."
Split-brain patients do not have two conscious minds, but a single unified conscious mind. The result of split-brain operations dividing a brain into two separated halves is a result the opposite of what we would expect under claims that brains make minds.
It is almost always the same when neuroscientists or layman materialists tell this outrageous falsehood that split-brain patients have two minds. Almost always, they do not link to any relevant papers. Almost always, all that is offered is a few crummy anecdotes, which usually take the form of second-hand evidence or third-hand evidence. Basically what is going on is a tactic of "give them an inch, and hope they take a mile." Don't fall for such silliness, which is not following decent standards for evidence.
In Chapter 7 of the book you can read here, we have on page 111 a paper from 1944:
We have a report on two split-brain patients who had their corpus callosum severed, leaving them with two separated brain hemispheres. The first one (called Case 1) was a married farmer. On page 113 we read that his "corpus callosum was sectioned completely" to treat seizures. This means the fibers connecting his two brain hemispheres were completely severed.
Here is the page discussing the patient's split-brain operation severing his corpus callosum, and the patient's status after the operation:
We have no report of anything very unusual. There is nothing to justify any claim of "two conscious minds in one skull." Contrary to Koch's claim about dysfunction in the left hand of people with split brain operations removing the corpus callosum connecting the two brain hemispheres, we are told on the page shown above that this Case 1 split-brain patient with a severed corpus callosum "was able to write with either hand with eyes open or when blindfolded."
Page 115 suggests that a later examination indicated there were no big problems detected with this split-brain patient:
The scientific paper "Functional outcomes in adults following corpus callosotomy: A systematic review" (which you can read here) summarizes case studies of split-brain patients who had their corpus callosum severed. We have a systematic methodology that approaches this topic in a scientific way, unlike Koch's palm-full-of-wobbly-anecdotes affair. The paper summarized 15 different studies reviewing 73 different subjects having the split-brain operation. 18 of these subjects are identified as "Total CC," by which the paper means a total corpus callosotomy completely severing the corpus callosum, leaving two disconnected brain hemispheres.
We read at the beginning of the paper that "Intellectual quotient is largely preserved post corpus callosotomy of different extents." We later read this: "Three individuals that underwent a total CC [corpus callosotomy] were reported to have maintained their pre-surgical level of intellectual functioning at the time of post-surgical follow-up [[18], [19], [20]], while one individual was reported to show a decline despite a reduction in seizure burden [21] (Table 2)."
Under the "brains make minds" dogma, we should expect that this "total CC" (corpus callosotomy) involving a complete severing of the corpus callosum should have produced radical intellectual disability or total mental incapacity. But the paper says that "intellectual functioning (refer to Section 3.1), whether divided into verbal and performance based abilities, or a general IQ, appeared to be largely preserved following varying extents of ACC as well as complete CC [corpus callosotomy] , with 27/30 cases across all reviewed studies for GIQ reporting a positive outcome (i.e. stable or improved)."
Contrary to what we would expect from "brains make minds" claims, the people left with two divided brain hemispheres mostly maintained their intelligence at the same level, as measured on IQ tests.
We hear no mention at all in the paper of anything like "two conscious minds in one skull" being the result of the corpus callosotomy that splits a brain into two separated hemispheres. The continued repetition of such false claims about split-brain operations by some neuroscientists should cause us to ask: in what other cases do brain experts blatantly misinform us?
A scientific study published in 2017 set the record straight on split-brain patients. The research was done at the University of Amsterdam by Yair Pinto. A press release entitled “Split Brain Does Not Lead to Split Consciousness” stated, “The researchers behind the study, led by UvA psychologist Yair Pinto, have found strong evidence showing that despite being characterised by little to no communication between the right and left brain hemispheres, split brain does not cause two independent conscious perceivers in one brain.”
The press release states the following: “According to Pinto, the results present clear evidence for unity of consciousness in split-brain patients.” The paper states, “These findings suggest that severing the cortical connections between hemispheres splits visual perception, but does not create two independent conscious perceivers within one brain.”
Searching on Google Scholar for the term "corpus callosotomy" which describes the operation cutting the corpus callosum and separating the brain into two halves, I find several other long systematic reviews and meta-analysis papers, none of which say anything about any "two conscious minds in one skull" effect. Another example is the paper here. Should we believe that all those very many pages discussing the effects of this operation would fail to mention it producing a "two conscious minds in one skull" effect so spectacular and important, if it actually occurred? No, we should not. It's far more credible that neuroscientist Christof Koch simply told us a groundless "old wives' tale" to try to prop up some narrative claiming brains make minds.
See my post here for a citation of many other scientific articles and scientific papers debunking the groundless myth that split-brain operations produce "two conscious minds in one skull."
Split-brain patients who underwent surgery to split their brains are not the only people with two separated brain hemispheres. Sometimes split-brain subjects arise when the corpus callosum fails to form during the mother's pregnancy. This is called agenesis of the corpus callosum. Making a generalization about people born without a corpus callosum connecting the two sides of the brain, a scientific paper states this:
"The major anatomic feature of Primary AgCC [agenesis of the corpus callosum] is the absence of the corpus callosum....Primary AgCC has surprisingly limited impact on general cognitive ability. Although the full-scale IQ may be lower than expected based on family history, scores frequently remain within the average range."
We hear no mention of any "two minds in one body" effect. Another paper states this, using the term "agenesis of the corpus callosum" which means a failure of someone's body to ever have the corpus callosum connecting the two halves of the brain:
"In the 37 adult cases of agenesis of the corpus callosum, 19 (51%) had some degree of intellectual impairment, with the remainder being judged to have a normal IQ. Of those with learning difficulties, two thirds had a mild impairment, and one third had a moderate or severe problem."
So roughly half of these 37 split-brain people had a normal IQ. You can find papers on the condition of being born with no corpus callosum by searching on Google Scholar for papers having the phrase "agenesis of the corpus callosum." You will not find any discussion of "two minds in one body" in such papers about split-brain subjects, which helps show that the claim of such an effect is groundless.
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