Reasons for Doubting Thought Comes from the Frontal Lobes or Prefrontal Cortex

Scientists lack any coherent explanation for how a brain could generate thought or intellect. Thoughts are immaterial things, so how could they possibly be generated by material things such as neurons? We know how physical things can generate other physical things (such as continental plates generating earthquakes), and we know how mental things can generate other mental things (such as one idea leading to a related idea). But nobody can give a coherent explanation as to how a physical thing such as a brain could produce a mental thing such as a thought or idea.

Scientists often fall back on localization claims to try to hide this shortfall. A scientist who cannot explain the how of a brain making an idea or a decision will often try to use a where as a substitute, by suggesting that specific mental capabilities come from particular parts of the brain. A common claim is that higher thought comes from the frontal lobe of the brain. More specifically, someone may claim that higher thought comes from the front-most part of the frontal lobe, what is called the prefrontal cortex. But the evidence fails to strongly support such claims, and the evidence often conflicts with such claims.

We certainly do not know from brain scans that higher thought comes from the frontal lobe or the prefrontal cortex. With the exception of the auditory and visual cortex, which show clear signs of “lighting up” during visual or auditory perception, there is no part of the brain that shows more than about a 1 percent increase in activity when humans think, decide, or remember. As a technical paper states, “cognitive effects give signal changes on the order of 1%.”

Those visuals showing “activating regions” of the brain in red are typically making use of a deceptive data presentation technique in which mere 1 percent differences in activity (or less) are represented in red, making them looking like big differences when they're really tiny differences. When you run, your heart gives a very clear signal of being involved in such a thing – for your heart rate may increase by 50 percent. But when you think, decide, or remember an old memory, there is no part of your brain that gives any clear sign of shifting into high gear or being crucially involved in such a thing.

Interestingly, a recent scientific paper notes that "neuroimaging studies have shown that intelligent individuals, despite their larger brains, tend to exhibit lower rates of brain activity during reasoning." So here we have an inverse correlation between brain activity and thinking. 

Let us look at general intelligence and the frontal lobe. It is part of the dubious folklore of neuroscientists that the prefrontal cortex is some center of higher reasoning. But the scientific paper here tells us that patients with prefrontal damage "often have a remarkable absence of intellectual impairment, as measured by conventional IQ tests." The authors of the scientific paper tried an alternate approach, using a test of so-called "fluid" intelligence on 80 patients with prefrontal damage. They concluded "our findings do not support a connection between fluid intelligence and the frontal lobes." Table 7 of this study reveals that the average intelligence of the 80 patients with prefrontal cortex damage was 99.5 – only a tiny bit lower than the average IQ of 100. Table 8 tells us that two of the  patients with prefrontal cortex damage had genius IQs of higher than 140.

In a similar vein, the paper here tested IQ for 156 Vietnam veterans who had undergone frontal lobe brain injury during combat. If you do the math using Figure 5 in this paper, you get an average IQ of 98, only two points lower than average. You could plausibly explain that 2 point difference purely by assuming that those who got injured had a very slightly lower average intelligence (a plausible assumption given that smarter people would be more likely to have smart behavior reducing their chance of injury). Similarly, this study checked the IQ of 7 patients with prefrontal cortex damage, and found that they had an average IQ of 101.

It also should be remembered that brain-damaged patients taking standard IQ tests may have higher intelligence than the test score suggests.  A standard IQ test requires visual perception skill (to read the test book) and finger coordination (to fill in the right answers using a pencil). Brain damage might cause reduced finger coordination and reduced visual perception unrelated to intelligence; and such things might cause a subject to do below-average on a standard IQ test even if his intelligence is normal.  

The 1966 study here states, "Taken as a whole, the mean I.Q. of 95.55 for the 31 patients with lateralized frontal tumors suggests that neoplasms in either the right or left frontal lobe result in only slight impairment of intellectual functions as measured by the Wechsler Bellevue test."  In this paper (page 276), scientist Karl Lashley noted that you can remove 50% of the cortex of an animal without having any effect on the retention of mazes learned by the animal.  Lashley noted on page 270 of this paper something astonishing, that the smartest animal he had tested was one in which the fibers of the cortex had been severed:

"The most capable animal that I have studied was one in which the cortex and underlying association fibers had been divided throughout the length of each hemisphere. His I.Q., based on ten tests, was 309."

It is sometimes claimed that the dorsolateral prefrontal cortex is the "CEO" of the brain. This study examined six patients with damage to the dorsolateral prefrontal cortex, and found that they had an average IQ of 104, above the average of 100. The study here tells us that 37 patients with damage to the dorsolateral prefrontal cortex had an average IQ of 97.4, only slightly below average (Table 1 and Table 2).  The same study tells us that 25 patients with damage to the ventromedial prefrontal cortex had an average IQ of 105.7 (Table 3 and 4).   This study says, “We have studied numerous patients with bilateral lesions of the ventromedial prefrontal (VM) cortex” and that “most of these patients retain normal intellect, memory and problem-solving ability in laboratory settings.” 

In the paper "Neurocognitive outcome after pediatric epilepsy surgery" by Elisabeth M. S. Sherman, we have some discussion of the effects on children of hemispherectomy, surgically removing half of their brains to stop seizures. Such a procedure involves a 50% reduction in the frontal lobe of the brain, and a 50% reduction of the prefrontal cortex. We are told this:

Cognitive levels in many children do not appear to be altered significantly by hemispherectomy. Several researchers have also noted increases in the intellectual functioning of some children following this procedure....Explanations for the lack of decline in intellectual function following hemispherectomy have not been well elucidated. 

Referring to a study by Gilliam, the paper states that of 21 children who had parts of their brains removed to treat epilepsy, including 10 who had surgery to the frontal lobe, none of the 10 patients with frontal lobe surgery had a decline in IQ post-operatively, and that two of the children with frontal lobe resections had "an increase in IQ greater than 10 points following surgery." 

The paper here gives precise before and after IQ scores for more than 50 children who had half of their brains removed in a hemispherectomy operation.  For one set of 31 patients, the IQ went down by an average of only 5 points. For another set of 15 patients, the IQ went down less than 1 point. For another set of 7 patients the IQ went up by 6 points. 

A writer at Slate.com states the following: 

And victims of prefrontal injuries can still pass most neurological exams with flying colors. Pretty much anything you can measure in the lab—memory, language, motor skills, reasoning, intelligence—seems intact in these people.

Now let us look at whether there is good evidence that decision making is generated by the prefrontal cortex. It should be first noted that the evidence discussed above discredits such an idea, because you can't perform well on an IQ test unless you have a good decision-making ability. Each IQ test question requires you to make a decision; none are tests of learned knowledge. For example, when an IQ test asks which of 5 figures most closely resembles a particular figure, that is something that requires you to make a decision rather than just remember something you have learned.

A 2002 scientific paper was entitled “Decision-making processes following damage to the prefrontal cortex.” The scientists who wrote the paper identified 19 patients with damage to the prefrontal cortex, and had them do various tests. Some of the results are below:

• Patients with local orbitofrontal lesions performed normally (at control levels) on three-decision making tasks.
• There was no statistically significant difference among the four frontal subgroups and controls on letter fluency or category fluency.
• Pattern recognition performance (percentage correct) was not significantly impaired in either the combined frontal group or the five subgroups.
• On spatial recognition (percentage correct), the combined frontal group were unimpaired relative to controls.
• On a gambling test to determine decision making, “The combined frontal group did not show poorer decision making than controls... and there were no significant differences among the five subgroups.”

Based on the results above, you would have to conclude that the idea that the prefrontal cortex generates decisions or thoughts is false. But there's another test that neuroscientists use in cases such as these – a kind of very subtle and sneaky test. We might put this test under a category of “desperately seeking evidence of performance deterioration.

The test is called the “Iowa gambling task.” A person will sit in front of a computer screen that shows four card decks. The person can pick from any of the decks, and is told that when you pick a card, your money can be either increased or decreased. Normally decks A and B give you a much higher money reward, compared to decks C and D. For example, it might be that picking from deck A will normally give you about $100, and picking from decks C and D will normally give you only about $10. But there's a sneaky catch. Occasionally decks A and B will cause you to lose a large amount such as $1200.

So a person doing this test has to recognize a very subtle rule that can be detected only after 40 or 50 trials – that even though decks A and B normally give more money, they can cause big money subtractions, which means that it's really better to keep picking from decks C and D.

As a test of executive ability, the Iowa gambling task is dubious indeed. One reason is that it may be largely testing short-term memory or prolonged concentration rather than executive ability. Another reason is that it is debatable whether the assumption of the people applying this test (that picking from decks C and D is a wiser decision) is correct. It can be argued that the person who picks from decks A and B has made a correct short-term decision. Such a person is like an investor who continues to invest in the stock market because of nice annual gains even though he knows that about every 8 years or so, stock markets have nasty downturns in which investors lose 30% or so of their money. This wikipedia page on the Iowa gambling task gives some scientific papers that argue it is flawed, and should not be used to judge executive ability.  In the paper I referred to above, the patients with prefrontal damage did worse on the Iowa gambling task, although whether that actually was inferior executive ability is debatable. We can summarize the paper by saying its tests provided no clear evidence that decisions are produced by the prefrontal cortex, and no clear evidence that damage to the prefrontal cortex significantly impairs executive ability.

Another dubious test used on some patients with frontal lobe damage is called the Wisconsin Card Sorting Test. Subjects are asked to put a card in one of 4 card stacks. As soon as they make a choice, they are told whether their choice was correct. We are told in 1:34 of this video that “After ten consecutive correct matches, the classification principle changes without warning.” So this test is also a subtle, sneaky type of test, not a straightforward test of executive ability. What it tests is the ability to discard a principle you have already adopted when the evidence no longer supports that principle. One paper says, “These findings strongly suggest that WCST scores cannot be regarded as valid nor specific markers of prefrontal lobe function.” 

The studies above are studies involving small numbers of unusual subjects with damage in the frontal lobes. Perhaps a much better way to consider the issue of how much cognition depends on the frontal lobes (or the prefrontal cortex) is to consider a much larger class of subjects: the many millions of people older than 60.

This scientific paper states this: “General linear model analyses revealed that the greatest age effects occurred in prefrontal cortex gray matter... with an average rate of volumetric decline of 4.9% per decade” after age 18. This should result in a decline in the prefrontal cortex gray matter of more than 20% by the time someone reaches 70. But we see nothing like a 20% decline in intelligence or decision-making ability in those who have reached the age of 70. People older than 70 still serve as presidents, congressmen, senators and CEO's. 

I could cite some statistics comparing the IQ tests of 20-year-olds and 70-year-olds, but then we would run into the confounding factor known as the Flynn Effect. The Flynn Effect is that for many decades, the performance of young people on IQ tests has been improving, with the improvement being about 3 points per decade. The study here states the following:

The Flynn effect was large enough to account for 100% of the variance in performance between age groups for cross-sectional analyses. After accounting for the Flynn effect, IQ was found to be relatively stable across the adult portion of the lifespan. Verbal abilities remain stable and even show gains through a large segment of the lifespan, while abilities measured by the Performance scale show modest declines from younger to older samples.

So the study finds that after we adjust for the Flynn effect, the IQ of people about 70 is about the same as people about 20. This finding is not at all what we should expect if the prefrontal cortex is responsible for intellectual capabilities, given a decline of about 20% that should occur in the prefrontal cortex between the age of 20 and 70.

I may note that the very fact of the Flynn effect is inconsistent with the dogma that our intelligence is a product of our brain. The Flynn effect, which involved an increase in IQ scores of about 3 percent per decade, went on for at least seven decades (although some think it is wearing off). During this time there was no change in human brains that could account for such a change.

Another relevant point is that the human brain is currently much smaller than it was previously. A science article in the mainstream Discover magazine tells us this: “Over the past 20,000 years, the average volume of the human male brain has decreased from 1,500 cubic centimeters to 1,350 cc, losing a chunk the size of a tennis ball.” But most people would guess that humans are smarter, or as least as smart, as those who lived 20,000 years ago.

A recent article on Aeon mentions how there is little correlation between brain size and intelligence, or a correlation between intelligence and the size of a frontal cortex. The article states the following:

Some of the most perspicacious animals are the corvids – crows, ravens, and rooks – which have brains less than 1 per cent the size of a human brain, but still perform feats of cognition comparable to chimpanzees and gorillas. Behavioural studies have shown that these birds can make and use tools, and recognise people on the street, feats that even many primates are not known to achieve. ….Among rodents, for instance, we can find the 80-gram capybara brain with 1.6 billion neurons and the 0.3-gram pygmy mouse brain with probably fewer than 60 million neurons. Despite a greater than 100-fold difference in brain size, these species live in similar habitats, display similarly social lifestyles, and do not display obvious differences in intelligence.

Consider the growth of intelligence in a child. A child is born with about as many neurons as it will ever have. During the period from birth to age 18, the child's intelligence seems to grow by perhaps 300%. But there is no corresponding brain growth.

There are, however, many new connections formed between brain cells. But an article at Neurosciencenews.com tells us the following:

The more intelligent a person, the fewer connections there are between the neurons in his cerebral cortex. This is the result of a study conducted by neuroscientists working with Dr Erhan Genç and Christoph Fraenz at Ruhr-Universität Bochum; the study was performed using a specific neuroimaging technique that provides insights into the wiring of the brain on a microstructural level.…. The researchers associated the gathered data with each other and found out: the more intelligent a person, the fewer dendrites there are in their cerebral cortex.

Let's put some of these facts into a table listing predictions of the theory that your intelligence comes from your brain, comparing such predictions to reality.

Prediction of theory that intelligence comes from brain, specifically the frontal lobe or prefrontal cortex	Reality
Injury to prefrontal cortex or frontal lobes should cause sharp drop in intelligence, as should hemispherectomy	This does not generally occur
Human intelligence should not have increased since 1900, because there has been no change in brain size or structure .	Since about 1930, IQ scores have risen by about 3 percent per decade (the Flynn Effect).
People about 70 should be much less intelligent than 20-year-olds, because of 5% volume decline in prefrontal cortex per decade.	Adjusting for Flynn Effect, no such drop in intelligence occurs.
Humans today should be much more stupid than humans 20,000 years ago, because our brains are smaller by about the size of a tennis ball.	Most people today would guess that humans are smarter, or at least as smart, as humans 20,000 years ago.
Elephants should be much smarter than humans, because their brains are three or four times heavier.	Humans are actually smarter than elephants.
Crows should be very stupid, because their brains are tiny, and have no neocortex.	Crows are astonishingly smart.
Greater number of connections in the brain should increase effective intelligence.	"The more intelligent a person, the fewer connections there are between the neurons in his cerebral cortex." -- neuroscience news cited above.
Men should be about nine percent smarter than women, because their brains are about nine percent bigger.	It is generally recognized that on average men are not significantly smarter than women.
Adults should not be much smarter than babies or toddlers, because they have no more brain cells than babies or toddlers.	Adults seem to be much smarter than babies and toddlers.

We see from this table that the claim that intelligence comes from the brain (specifically the frontal lobe or prefrontal cortex) massively fails to predict reality correctly.

The evidence discussed here argues against the claim that the prefrontal cortex or the frontal lobe can be identified as the source of decision making or the center of higher thought in the brain. The evidence discussed here is consistent with the claim that human higher thought capability does not come from the brain but from some unknown other source. Such a claim is also supported by many other considerations discussed at this site, including (1) convincing and well-replicated laboratory evidence (discussed here and here) for psychic phenomena such as ESP, evidence suggesting that the mind has powers that cannot be explained by brain activity; (2) evidence for near-death experiences indicating minds can continue to function even when brains have shut down because the heart has stopped.

Postscript: In 1930 a patient listed as Joe A. in the medical literature underwent a bilateral frontal lobectomy performed by Dr. Walter Dandy, who removed almost all of his frontal lobes. An autopsy in 1949 confirmed that "both frontal lobes had been removed." The paper describing the autopsy said that from 1930 to 1944 Joe A.'s behavior was "virtually unchanged." On page 236 of this source, we read that Dandy said this of three patients including Joe A.: "These three patients with the extirpation of such vast areas of brain tissue without the disclosure of any resulting defect is most disappointing." I could see how it would be disappointing for someone hoping to prove a connection between some brain area and intellectual function. Page 237 of the same source tells us that on casual meeting Joe A. appeared to be mentally normal.  Page 239 of this source states this about Joe A, summarizing the findings of Brickner.:

Nor was intellectual disturbance primary. The frontal lobes played no essential role in intellectual function; they merely added to intellectual intricacy, and "were not intellectual centers in any sense except, perhaps, a quantitative one." 

A 1939 paper you can read here was entitled "A Study of the Effect of Right Frontal Lobectomy on Intelligence and Temperament." A patient C.J was tested for IQ before and after an operation removing his right frontal lobe. He had the same IQ of 139 before and after the operation. Page 9 says the lobectomy "produced no modification of intellectual or personality functions."  On page 10 we are told this about patients having one of their frontal lobes removed:

Jefferson (1937) reported a series of eight frontal lobectomies in which the patients were observed for intellectual and emotional deficits following operation. There were five cases of right frontal lobectomy, three of whom were living and well when the article was written. It could be stated definitely that in two of the three cases there were no abnormalities which could be noted by the surgeon, patient, or family, and while the third case showed a mild memory defect, the operation had been too recently performed to judge whether or not the loss would be permanent. The three cases of left frontal excision likewise showed no significant changes, but comment was made that one patient was slightly lacking in reserve, another remained slightly facetious, and the third, who suffered a transient post-operative aphasia, appeared a trifle slow and diffident.

If the frontal cortex is some kind of "seat of reason," we might expect the human frontal cortex to be unusually large for a primate. But the paper here states, "The consistency of our results across independent data sets supports the view...that human frontal cortex, and regions and tissue subtypes within it, are no larger than expected for a nonhuman primate of our overall cortex or brain size." 

The following excerpt from a scientific paper tells us of additional cases of people who did not seem to suffer much mind damage after massive damage to the frontal lobes or prefrontal cortex. Resection is defined as "the process of cutting out tissue or part of an organ."

Several well-documented patients have been described with a normal level of consciousness after extensive frontal damage. For example, Patient A (Brickner, 1952) (Fig. 2A), after extensive surgical removal of the frontal lobes bilaterally, including Brodmann areas 8–12, 16, 24, 32, 33, and 45–47, sparing only area 6 and Broca's area (Brickner, 1936), “toured the Neurological Institute in a party of five, two of whom were distinguished neurologists, and none of them noticed anything unusual until their attention was especially called to A after the passage of more than an hour.” Patient KM (Hebb and Penfield, 1940) had a near-complete bilateral prefrontal resection for epilepsy surgery (including bilateral Brodmann areas 9–12, 32, and 45–47), after which his IQ improved. Patients undergoing bilateral resection of prefrontal cortical areas for psychosurgery (Mettler et al., 1949), including Brodmann areas 10, 11, 45, 46, 47, or 8, 9, 10, or 44, 45, 46, 10, or area 24 (ventral anterior cingulate), remained fully conscious (see also Penfield and Jasper, 1954; Kozuch, 2014; Tononi et al., 2016b). A young man who had fallen on an iron spike that completely penetrated both frontal lobes, affecting bilateral Brodmann areas 10, 11, 24, 25, 32, and 45–47, and areas 44 and 6 on the right side, went on to marry, raise two children, have a professional life, and never complained of perceptual or other deficits (Mataró et al., 2001).

Apparently patient KM got smarter after they took out most of his prefrontal cortex. That's a case helping to show that brains don't make minds. The book here discusses intelligence tests done on patients who underwent surgery on the frontal lobes:

"It was natural that the effect of an injury on the frontal lobes, said to be concerned with the higher functions of men, should be measured by these tests of intelligence. The absence of marked effects on mental ability, as measured by these intelligence tests, was, not surprisingly, felt to be puzzling." 

This paper here describes a case of a "modern Phineas Gage": a patient C.D. who suffered massive prefrontal  damage after a penetrating head injury. But C.D's IQ after the injury was measured at 113, well above average.  His verbal IQ after the injury was 119, in the 90th percentile. We read:

C.D. reported that he did not have any cognitive or emotional problems following the accident. In describing how his thinking skills were completely unaffected, C.D. stated that, "all the shattered bone was caught in the gray matter in front of the brain." 

The paper also tells us, "C.D.’s performances on memory tests were all in the average to above-average ranges in terms of the traditional measure of level of correct responses." 

A 2021 paper is entitled "Reduced decision bias and more rational decision making following ventromedial prefrontal cortex damage."  So you make more rational decisions if your front brain is damaged? That's a result incompatible with claims that your brain makes decisions. 

Using the term "decorticate" to refer to animals that had their cortex surgically removed, the scientific paper here tells us that rats and cats seem to show relatively little behavioral effects when you remove their cortex:

"All of the behaviors just mentioned are also exhibited by experimental animals after their cerebral cortex is removed surgically, either in adulthood or neonatally. Best studied in this regard are rodents (Woods 1964; Wishaw 1990). After recovery, decorticate rats show no gross abnormalities in behavior that would allow a casual observer to identify them as impaired in an ordinary captive housing situation, though an experienced observer would be able to do so on the basis of cues in posture, movement and appearance (Whishaw 1990, on which what follows relies, supplemented by additional sources as indicated). They stand, rear, climb, hang from bars and sleep with normal postures (Vanderwolf et al. 1978). They groom, play (Pellis et al. 1992; Panksepp et al. 1994), swim, eat, and defend themselves (Vanderwolf et al. 1978) in ways that differ in some details from those of intact animals, but not in outline. Either sex is capable of mating successfully when paired with normal cage mates (Carter et al. 1982; Whishaw & Kolb 1985), though some behavioral components of normal mating are missing and some are abnormally executed. Neonatally decorticated rats as adults show the essentials of maternal behavior which, though deficient in some respects, allows them to raise pups to maturity. Some, but not all, aspects of skilled movements survive decortication (Whishaw and Kolb 1988), and decorticate rats perform as readily as controls on a number of learning tests (Oakley 1983). Much of what is observed in rats (including mating and maternal behavior) is also true of cats with cortical removal in infancy: they move purposefully, orient themselves to their surroundings by vision and touch (as do the rodents), and are capable of solving a visual discrimination task in a T-maze (Bjursten et al. 1976; see also Bard & Rioch 1937)." 

The paper "Neuropsychological outcome following frontal lobectomy for pharmacoresistant epilepsy in adults" here deals specifically with the surgical removal of the frontal lobe to treat epilepsy. Neuroscientists have made more claims about the frontal lobe than any other part of the brain. We have been told that the frontal lobe is some kind of center of judgment and memory.  The paper states the following:

"Forty-eight percent of the sample did not show decline on any of the 16 cognitive measures examined in this study. Forty-two showed decline on measures in 1 or 2 cognitive domains. In contrast, 10% of the sample showed declines in 3 or more cognitive domains." 

Elsewhere the paper states, "The vast majority of patients who undergo frontal lobectomy for treatment of pharmacoresistant epilepsy demonstrate good cognitive and motor outcomes." Using the term "frontal lobectomy" for the removal of the front part of the brain, the paper also states, "Interestingly, there was a subset of patients who demonstrated clinically meaningful improvements in confrontation naming (15% of sample), verbal intellectual function (11%), or memory (10%–17%) following frontal lobectomy."  The paper says, "Existing studies that have examined change in intellectual functioning following frontal lobe surgery have had mixed results, with some studies reporting no change on intelligence measures and others reporting apparent improvements."

A neuroscience paper says, "A series of clinical observations reports the facilitation of artistic abilities in some patients with neurodegenerative disease affecting the frontal lobes, raising the question of a possible increased creativity following frontal damage (Palmiero et al., 2012; Schott, 2012; Gretton and ffytche, 2014)."

In an article last year on the site of Forbes magazine, we read the following:

"One more bizarre thing the researchers noticed was the bigger the lesions on the cortex, the better the mice performed. 'It was a strange result…' says Hong, who hesitates before adding: 'I wouldn't say that we're confident that if we [tested] a lot more animals we would see it. It was sort of a trend that we noticed. I guess the answer is, we don't know. Basically, it implied that the less the cortex is active, the better the animal is doing and the cortex was somehow interfering with the animal's ability to learn.' "

A paper in the journal Science refers to "the large number of reports describing 'negative' findings -- that is, the absence of demonstrable 

deficits in test performance, despite the presence of large

cerebral lesions, especially in the frontal lobes." The paper compared IQ tests for 60 armed force members who had their intelligence tested before penetrating brain injuries, and also had their intelligence tested after their brain injuries. Speaking of results on IQ tests, the paper states, "These analyses demonstrated that lesions of the frontal and occipital lobes did not produces a significant decline in score, and that only lesions of parietal or temporal lobes of the left hemisphere showed a significant decrease." The soldiers with lesions in these areas actually performed higher on IQ tests after their penetrating brain injuries, with an average of about a 7% increase:

• The left nonparieto-temporal region
• The right parietal region
• The right temporal lobe
• The right parietotemporal lobe
• The right nonparieto-temporal region

The only decrease in IQ scores occurred with injuries to the left parietotemporal lobe.  Referring to removal of brain tissue (resection), the paper here states that " intellectual or memory decrements are seldom found after frontal resections."

The paper here ("Better without (lateral) frontal cortex? Insight problems solved by frontal patients") tells us this interesting result about a type of math reasoning test in which people with frontal cortex damage did very much better than normal people:

"We derived the counterintuitive prediction that patients with focal damage to the lateral frontal cortex should perform better than a group of healthy participants on this rather difficult task. We administered the matchstick task to 35 patients (aged 26–65 years) with a single focal brain lesion as determined by a CT or an MRI scan, and to 23 healthy participants (aged 34–62 years). The findings seemed in line with theoretical predictions. While only 43% of healthy participants could solve the most difficult matchstick problems (‘type C’), 82% of lateral frontal patients did so (Fisher's exact test, P < 0.05)."

Post-postscript: On page 1 of his main work, the very famous brain expert Donald Hebb asks this: "How can it be possible for a man to have an IQ of 160 or higher, after a prefrontal lobe has been removed (Hebb, 1939), or for a woman (described by Rowe, 1937) to have an IQ of 115, a better score than two-thirds of the normal population could make, after losing the entire right half of the cortex? " On page 286 of his main work, the very famous brain expert Donald Hebb states this: "Although the frontal lobe is the favorite place m which to localize higher functions when one is speculating about these matters, it is still true that there is no proof that any single, higher, function depends on this part of the brain (Hebb, 1945b)."

On page 287 Hebb tells this account of a person whose IQ and mental health increased after the person had his frontal lobes removed:

"The first and most effective piece of evidence is the history of a patient both of whose prefrontal lobes were removed by Dr. Wilder Penfield, with results that radically changed the possibilities of surgical therapy m the frontal area Before this time, it was universally accepted that loss of both frontal poles must be followed by gross deterioration of personality and intellect. Dr. Penfield's patent completely reversed the prediction, by being psychotic before operation (when the damage was relatively small) and quite indistinguishable from a normal person afterward (when the total destruction was increased in size— with the simultaneous removal of a source of physiological disturbance).

The history is that of a boy of sixteen whose skull was fractured, with damage to both frontal lobes, and who ш the following ten years developed severe epilepsy and became (much of the time) an irresponsible and rather dangerous charge. The condition varied, not only with the occurrence of attacks but also between attacks—apparently owing to subclinical seizures: the IQ, on the basis of an uncompleted testing on one day, was estimated to be below 70, next day a completed test gave an IQ of 84. After operation, the IQ was consistently close to 96, no evidence of intellectual loss could be found їп any one test or in the pattern of test scores as a whole, and the psychotic behavior completely disappeared. Clinically and socially he was 'normal' and was able to take full control of his own affairs on the last examination he had been doing so for more than five years. He enlisted m the army and served satisfactorily overseas for ten months until he had another fit—at which time the medical officers caught up with him and he was discharged."

Reflecting on this remarkable case, Hebb showed a very bad inability to put two and two together. Here we have a medical case history that defies dramatically the dogma that the brain is the source of the mind, and also the more specific dogma that the prefrontal lobes play a foremost role in the generation of thought. We have a patient who had his prefrontal lobes surgically removed to treat epilepsy. But instead of this producing a decrease in IQ, the result is an increase in IQ. Also the operation causes the patient's mental health to increase, so that he goes from being psychotic to being normal in a clinical and social sense. If you put two and two together from this case and other cases I have quoted above from Hebb's book, you should conclude that the brain is not the source of the human mind. 

But Hebb just couldn't make so obvious an inference. So on the same page and the next page, he says this: 

"My conclusion is not that the frontal lobes have no function, but either (1) that we have not yet guessed at the real nature of this function—have not asked the proper questions in such investigations, or (2) that once the development of behavior has been completed the prefrontal lobes have no great further importance. Surely it is the first of these, 1, that is the answer, not 2, but there is nothing ın the evidence at present that justifies the idea that the frontal lobes have some special relation to higher functions in human behavior."

On the next page he says, "The evidence that has been supposed to show the importance of the frontal lobes does not withstand scrutiny (it has been reviewed m detail elsewhere—Hebb, 1945b)."

An Analogy Clarifying Why the "Brain Stores All Your Memories" Dogma Is Implausible

Let us imagine a man named Ed who gets a job as a warehouse worker at a warehouse called Warehouse B. Ed reports to work on the first day.

Ed: Reporting for work, sir.

Supervisor: Welcome to Warehouse B. Let me brief you on the job we need you to do.

Ed: I'm all ears.

Supervisor: We want to start storing at this warehouse all the information we get from our television set.

Ed: I see you have lots of empty shelves here. That's good; they'll be lots of storage room. So you do have a video recorder to start recording the shows?

Supervisor: Absolutely not. Such devices are forbidden here.

Ed: So how could you store all the information coming from the TV?

Supervisor: That is something you must figure out, given the rules I set.

Ed: Okay, give me the rules.

Supervisor: Nothing can be written down. We have no pens or pencils here, and you can never bring any. Writing with a pen or pencil or electronic device is forbidden here. If you want to store information, you can only use chemicals or proteins or electricity.

Ed: Chemicals or proteins or electricity?

Supervisor: Yes, we have all kinds of chemicals you can use to store the information from the TV. Plus we have lots of batteries, which you can set to any voltage you want. Plus we have lots of proteins lying around: ham, cheese, you name it. You can any use of these things to store the information from the TV set. But no writing is allowed.

Ed: How on earth could I use chemicals, electricity and proteins to store all that complicated information from the TV set?

Supervisor: I don't know. It's your job to figure that out.

Ed: Can I use some type of electronics to store the information from the TV shows?

Supervisor: No, electronics are strictly forbidden here.

Ed: I see you have lots of boxes.

Supervisor: Yes. If you figure out how to store information from the TV shows using chemicals, electricity, and proteins, you can put your successful solution in a box, and store it on the shelf.

Ed: How many of these TV shows do you need to store?

Supervisor: We need to store all the programs we get for the next 50 years. And after we've stored that, we need to be able to retrieve the information instantaneously. So if someone wants to know what was in some particular show on some particular date, we have to get that information from the shelves real fast.

Ed: So these boxes on the shelf will have to be carefully sorted and labeled, according to some system allowing rapid retrieval.

Supervisor: But you can't label the outside of any box – no writing allowed here. And once you've put a box on a shelf, you can never sort the boxes. And you can't label any of the shelves or aisles.

Ed: Wait a minute. I'm trying to imagine two years into the future, when thousands of these unmarked boxes are on the shelf. How on earth would anyone be able to instantly find a particular box when somebody asked for the info from one particular show – say, the information from the next Super Bowl or from the last episode of America's Got Talent?

Supervisor: I don't know. That's your job to figure that out. We have lots of wire – you can use as much of that as you want. But you can't bend the wire into letters. No writing allowed. And there's one other big problem.

Ed: What's that.

Supervisor: We have ten employees here who like to steal stuff. So once you start putting things on the shelves, whatever you put will get stolen real frequently.

Ed: Can you fire those employees?

Supervisor: No, they're guaranteed lifetime employees, because they're the warehouse owner's kids. They'll stay working here, no matter how much they steal. And another problem is that we get lots and lots of rats who come out every night, and who eat lots of any proteins or chemicals put on the shelves.

Ed: Can we just use some poison to kill off those rats?

Supervisor: No, that's strictly forbidden.

Ed: So let me see if I have this right. I have to set things up so that all the information that comes from the TV for the next 50 years gets stored on our shelves. But I can't use any electronics or writing to store all that information. All I can use is electricity, wire, chemicals and protein. I can use boxes, but none of the boxes can be labeled, marked or sorted. I've got to set things up so that the information from any requested TV show can be instantly retrieved, even though we'll just have shelves filled with unlabeled boxes. The information has to stay put for 50 years, even though there's ten employees who will be stealing lots of it every night, and lots of rats who will be eating up lots of chemicals or proteins I use to store the information.

Supervisor: That's about it. Can you think of some way to handle this?

Ed: Hell, no! I quit!

As you may have guessed already, Warehouse B is an analogy. Warehouse B represents the difficulty of storing information in a human brain. The stream of information from the television set represents the stream of information that flows through a particular person's senses as he lives. Storing the information from 50 years of TV shows would be about as difficult as storing the information from 50 years of living.

In our analogy, Ed is told that he must store the complicated information from the TV using only chemicals, electricity, and proteins, not by using any kind of electronics or writing. This corresponds to some limitations that would be in a brain if a brain were to store memories. We have no electronics in our brains. And neuroscientists examining brain tissue with electron microscopes have never detected any actual writing in the brain. In other words, even if we were to examine neurons at a magnification of 500,000 times, we would never see any tiny little letters that corresponded to some words in your memory.

Neuroscientists claim that the brain stores the very complex information we remember by using only chemicals, electricity and proteins. No neuroscientist has ever given a credible detailed explanation as to how such a miracle of encoding and translation could be accomplished. How, for example, could there ever be some combination of chemicals, electricity or proteins that represented your concept of your country or your religion or your mother?

In our analogy, Ed is told he must stick to a system of storage that is woefully unsuited for the instantaneous retrieval of specific information. He is told that he must put things in unmarked boxes that must be put on unlabeled shelves. Once lots of information accumulates, this system will not be able to handle instantaneous retrieval of specific information. For example, if someone asks three years from now, “What happened in the last Super Bowl?” or “Who were the winners at the Oscar awards two years ago?” no one at Warehouse B will be able to produce a quick answer. With thousands of unmarked boxes on the shelves, there will be no way to get such information instantaneously.

A brain would suffer from exactly this problem if it stored memories. For the brain has no coordinate system or position notation system by which an exact brain location could be located (such as neuron number 343,363,233), nor any labeling capability by which particular neurons or groups of neurons can be labeled. So an instantaneous recall of a specific memory (such as what a particular famous person looks like) should be impossible if it is stored in the brain. Also, neurons cannot be sorted, given the way they are arranged in a brain, with hundreds or thousands of connections between each neuron and nearby neurons. Given such an arrangement, you can no more sort things than you could sort the trees in a forest.

Suppose someone asks me, “Who was John F. Kennedy.” I instantly am able to recall an image of his face, and various facts about him, such as that he died by assassination on November 22, 1963. But how could I find that information so quickly if it was stored in some very tiny little part of my brain, perhaps from a location near neuron number 825,223,252? There would be no way for my brain to know where that exact location was.

It won't do any good for you to suggest that perhaps my brain scans all of its neurons to find that information. When you are asked some specific question, you do not at all have any type of thought experience similar to what it might be like to scan through all of your memories. You just instantly remember something. And if your brain was scanning through all its neurons to retrieve some information, that would take hours or days. You wouldn't be able to remember something instantly.

There is one other state of affairs in Warehouse B which is analogous to the situation in the brain. It is the fact that in Warehouse B there is a rapid loss of information stored on the shelves. In Warehouse B any information put on the shelves has a large chance of being lost within a few weeks, because of all the thievery by the ten guaranteed lifetime employees who are larcenous and can steal without risk, and because of all the rats that eat things on the shelves. In the brain there would be an equally great loss of any information stored, because of the rapid turnover of proteins. The most popular theory of memory storage in the brain is that memories are stored in synapses. But the proteins in synapses have an average lifetime of only a few weeks. There are other types of turnover going on. Synapses themselves have lifetimes of less than a year, as do the protrusions known as dendritic spines and synaptic boutons. As discussed here, there is no understanding of how the brain could possibly store information long enough so that you could remember things that happened decades ago. 

Just as Ed will never be able to figure out a system by which Warehouse B could actually store decades of TV shows (in a manner allowing instantaneous retrieval) given the limitations that the Supervisor has stated, our neuroscientists will never be able to specify a detailed scenario by which a brain could store memories for 50 years despite rapid protein turnover, and also allow specific memories to be instantly retrieved in the way our minds do, so that someone can name some obscure person, and you instantly recall facts about such a person you haven't thought about in many years. The most reasonable conclusion is that memories involve some mental facility other than the brain. We don't know how such a facility works, just as we don't have any reasonable idea of how a memory like a human's could possibly work using a brain.  But by postulating a non-neural basis for memory, we at least have a hypothesis that is not ruled out by what we know about the brain.

Nature never told us that a brain stores all a person's memories, and your body does nothing to suggest to you that you are retrieving memories from your brain. The idea that brains store memories is simply one that scientists gradually started assuming, without ever having sufficient evidence for such a conclusion. 

In one respect, the brain is even less suitable for storing memories than the Warehouse B described here. I described Warehouse B as having boxes and shelves, which would allow for some type of grouping effect, in which related bits of information can be grouped together. But in a brain, physical grouping should be impossible. The brain is a mass of neurons, and the average neuron is connected to 10,000 other neurons. In such a system there would seem to be no way in which related data items can be physically grouped together like pages in a manila file, nor any way in which data can be arranged in a discrete sequence, with a start point and a stop point.  As discussed here, such a system should not at all be suitable for storing long sequences, such as humans remember when they memorize songs, lists, and theatrical roles. 

Split-Brain Cases Conflict with "Brains Make Minds" Dogma

Certain stories crop up in the scientific literature, and persist year after year despite a lack of solid basis in fact. One such story is that Galileo threw spheres of different weights from the Leaning Tower of Pisa to test whether they would reach the ground at the same time. A wikipedia.org article on the experiment says such an experiment (never reported by Galileo) probably never occurred.

Another such story is the idea that Darwin found evidence for his ideas about evolution in finches he studied at the Galapagos Islands. Page 35 of a long paper on the topic by a Harvard scientist (entitled “Darwin and His Finches: The Evolution of a Legend” ) states Darwin “never actually put finches forward as evidence for the theory of evolution.” Page 39 states this:

In spite of the legend’s manifest contradictions with historical fact, it successfully holds sway today in the major textbooks of biology and ornithology, and is frequently encountered as well in the historical literature on Darwin. It has become, in fact, one of the most widely circulated legends in the history of the life sciences, ranking with famous stories of Newton and the apple and of Galileo’s experiments at the Leaning Tower of Pisa.

On page 134 of his recent biography of Darwin, A.N. Wilson states the following:

Peter and Rosemary Grant, evolutionary biologists from Harvard University, spent twenty-five summers studying these birds....They revealed that the beak changes were reversible -- this is hardly 'evolution.'  Beaks adapted from season to season, depending on whether droughts left large, tough seeds, or heavy rainfall resulted in smaller, softer seeds.

A legend that arose fairly recently is that split-brain patients patients have a splitting of their perception, or maybe something like “split consciousness.” Such an idea was based on research done by Roger Sperry and Michael Gazzaniga. A split-brain patient is a patient who has a severing of the corpus callosum, a mass of fiber-like nerves that connect the left hemisphere of the brain and the right hemisphere of the brain. Such an operation is done in particularly bad cases of epilepsy, to prevent very bad seizures that cannot be stopped by medication.

Even though split-brain patients continued to show a unity of consciousness, and did not by any means show something like a split personality, materialists have tried to make as much hay as possible out of the research of Sperry and Gazzaniga. For example, in 2007 psychologist Steven Pinker claimed that “Surgery that severs the corpus callosum, separating the two hemispheres (a treatment for epilepsy), spawns two consciousnesses within the same skull,” and spoke as if this alleged observation was evidence against a human soul. Such a claim was bogus. None of the experimental results reported that split-brain patients had two consciousnesses.

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.

On page 202 of his recent book "The Consciousness Instinct" neuroscientist Michael Gazzaniga claims  that “a neurosurgeon can disconnect the two hemispheres of the brain and produce two minds in your single head.” The claim is false, and he provides no historical examples of this happening. In fact, on page 203 Gazzaniga refers to split-brain patients, and says, “Oddly, after having their brains cut in half, all those patients said they felt fine, and the only difference they noted was the loss of seizures.” That statement contradicts his statement on page 202. 

In the video here we see a split-brain patient who seems like a pretty normal person, not at all someone with “two minds." And at the beginning of the video here the same patient says that after such a split-brain operation “you don't notice it” and that you don't feel any different than you did before – hardly what someone would say if the operation had produced “two minds” in someone. And the video here about a person with a split brain from birth shows us what is clearly someone with one mind, not two. In the video here we have a long interview with a girl who had a split brain operation (a functional hemispherectomy) that disconnected the two hemispheres of her brain. She is obviously a single unified mind, not two minds in a single body. 

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.” Their paper had the visual below showing their results:

Pinto and his colleagues criticize the research previously done on this topic, saying the following:

Strikingly, although this clinical observation features in many textbooks (Gazzaniga et al., 1998; Gray, 2002) the reported data are never quantitative...Sperry notes: ‘Although the general picture has continued to hold up in the main as described [… .] striking modifications and even outright exceptions can be found among the small group of patients examined to date.’

So apparently the original researchers weren't very numerically precise in measuring things, and got mixed results. Such nuances were ignored by a host of writers eager to use Sperry and Gazzaniga's research as something to prop up conventional dogmas that the brain generates the mind. Now doing things in a proper quantitative way, Pinto and his colleagues have come up with a result conflicting with the result of Sperry and Gazzaniga, a result telling us that split-brain patients have a perceptual unity of consciousness.

Pinto's paper notes that his findings spell trouble for two theories of consciousness, the Global Workspace Theory, and the Integrated Information Theory, which are just flavors of the theory that brains make minds:

This preserved unity of consciousness may be especially challenging for the two currently most dominant theories of consciousness, the Global Workspace theory (Baars, 1988, 2005;Dehaene and Naccache, 2001) and the Integration Information theory (Tononi, 2004, 2005; Tononi and Koch, 2015). A core assumption of the Global Workspace theory is that cortical broadcasting of selected information by the ‘global workspace’ leads to consciousness. Thus severing of the corpus callosum, which prevents broadcasting of information across hemispheres, seems to exclude the emergence of one global workspace for both hemispheres. Rather, it seems that without a corpus callosum either two independent global workspaces emerge, or only one hemisphere will have a global workspace, while the other does not. In either case, an integrated global workspace, and thus preserved conscious unity, seems to be difficult to fit into this framework.

The general prediction of the "minds come from brains" dogma would seem to be that if you split a brain so that the left half is not connected to the right half, this should result in two minds -- perhaps a "left half of the body in conflict with the right half of the body" situation. But no such thing occurs. After the split-brain operation there is still one consciousness and one self that at worst has some minor perceptual issues.  The result of a unified consciousness in split-brain patients is perfectly compatible with the thesis of this website, that the human mind is not produced by the brain.

Postscript: See also this scientific paper "The Myth of Dual Consciousness in the Split Brain." The actual facts about split-brain surgery are related here by a surgeon who has performed such an operation. He states this about split-brain patients:

"After the surgery they are unaffected in everyday life, except for the diminished seizures. They are one person after the surgery, as they were before."

The surgeon states: "In a rational scientific community in which evidence and reason held sway, split-brain surgery would be hailed as compelling evidence for dualism and the immateriality of the intellect and will."

Physician Michael Egnor states the following about Sperry's research:

"The neuroscientist Roger Sperry studied scores of split-brain patients. He found, surprisingly, that in ordinary life the patients showed little effect. Each patient was still one person. The intellect and will – the capacity to have abstract thought and to choose – remained unified. Only by meticulous testing could Sperry find any differences: their perceptions were altered by the surgery. Sensations – elicited by touch or vision – could be presented to one hemisphere of the brain, and not be experienced in the other hemisphere. Speech production is associated with the left hemisphere of the brain; patients could not name an object presented to the right hemisphere (via the left visual field). Yet they could point to the object with their left hand (which is controlled by the right hemisphere). The most remarkable result of Sperry’s Nobel Prize­–winning work was that the person’s intellect and will – what we might call the soul – remained undivided. The brain can be cut in half, but the intellect and will cannot. The intellect and will are metaphysically simple."

The recent article here in Psychology Today describes the bizarre experiment that was used to make the groundless claim that split-brain patients have two minds. It was some experiment based only on visual perception, using some experimental strange setup unlike anyone normally encounters. The article shreds to pieces claims that results from such an experiment shows that split-brain patients have two minds:

"Not so fast. There are several reasons to question the conclusions Sperry, Gazzaniga, and others sought to draw. First, both split-brain patients and people closest to them report that no major changes in the person have occurred after the surgery. When you communicate with the patient, you never get the sense that the there are now different people living in the patient's head.

This would be very puzzling if the mind was really split. Currently, you are the only conscious person in your neocortex. You consciously perceive your entire visual field, and you control your whole body. However, if your mind splits, this would dramatically change. You would become two people: 'lefty' and 'righty.' 'Lefty' would only see what is in the right visual field and control the right side of the body while 'righty' would see what’s in the left visual field and control the left side of the body. Both 'lefty' and 'righty' would be half-blind and half-paralyzed. It would seem to each of them that another person is in charge of half of the body.

Yet, patients never indicate that it feels as though someone else is controlling half of the body. The patients’ loved ones don’t report noticing a dramatic change in the person after the surgery either. Could we all — patients themselves, their family members, and neutral observers — miss the signs that a single person has been replaced by two people? If you suddenly lost control of half of your body, could you fail to notice? Could you fail to notice if the two halves of your spouse’s or child’s body are controlled by two different minds?"

A 2020 paper states this about split-brain patientis: " Apart from a number of anecdotal incidents in the subacute phase following the surgery, these patients seem to behave in a socially ordinary manner and they report feeling unchanged after the operation (Bogen, Fisher, & Vogel, 1965; Pinto et al., 2017a; R. W. Sperry, 1968; R. Sperry, 1984)." 

A very relevant case  reported is that of an 88-year old man (identified as H.W.) who tested very well on a test of mental functioning, getting the maximum possible score of 30. But it was found that the man had no corpus callosum. The corpus callosum is the main part of the brain that links the two brain hemispheres.  A man who has no corpus callosum is equivalent to a split-brain patient. As an article reports:

"Given the importance of the callosum for connecting the bicameral brain, you’d think this would have had profound neuropsychological consequences for H.W. In fact, a detailed clinical interview revealed that he’d led a normal, independent life – first in the military and later as a flower delivery man. Until recently, if H.W.’s testimony is to be believed, he appeared to have suffered no significant psychological or neurological effects of his unusual brain...Brescian and her colleagues conducted comprehensive neuropsych tests on H.W. and on most he excelled or performed normally. This included IQ tests, abstract reasoning, naming tests, visual scanning, motor planning, visual attention and auditory perception."

The article has a very clear title telling us the truth about this matter:

This Elderly Man Was Born With His Brain Hemispheres Disconnected. Did It Affect His Life? Hardly.

But the corresponding scientific paper sounds as if was written to try and make this case as unlikely as possible to be noticed. We have this title: "Case study: A patient with agenesis of the corpus callosum with minimal associated neuropsychological impairment." Agenesis is a word meaning "absence," one that would only be used by someone trying to get as few people as possible to notice an absence. At least this language is not as bad as the outright lies that occur when materialist scientists tell us that splitting a brain into two unconnected hemispheres results in two minds. 

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 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."

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 equivalent patients, which helps show that the claim of such an effect is groundless.   

The paper "Outcomes Associated With Isolated Agenesis of the Corpus Callosum: A Meta-analysis" tells us that for those with complete agenesis of the corpus callosum (complete failure of the corpus callosum to appear) "abnormal cognitive status occurred in 15.16% (95% CI, 6.9–25.9) of cases," which is fewer than 1 case in 6. The same paper tells us that for those with partial agenesis of the corpus callosum (partial failure of the corpus callosum to appear) "cognitive status was affected in 17.25% (95% CI, 3.0–39.7) of cases." fewer than 1 in 5.  This suggests the great majority of people born with split brains and no corpus callosum have normal minds, and nothing like split minds or two minds in one body.