Hemispherectomy is a surgical procedure in which half of the brain is removed. The procedure can be performed on young children suffering from seizures, with surprisingly little negative impact. And the paper here also tells us on page 3 that “Although most hemispherectomies are performed on young children, adults are also operated on with remarkable success.”
Very interestingly, we are told that when half of their brains are removed in these operations, “most patients, even adults, do not seem to lose their long-term memory such as episodic (autobiographic) memories.” The paper tells us that Dandy, Bell and Karnosh “stated that their patient's memory seemed unimpaired after hemispherectomy,” the removal of half of their brains. We are also told that Vining and others “were surprised by the apparent retention of memory after the removal of the left or the right hemisphere of their patients.”
On page 59 of the book The Biological Mind, the author states the following:
A group of surgeons at Johns Hopkins Medical School performed fifty-eight hemispherectomy operations on children over a thirty-year period. "We were awed," they wrote later of their experiences, "by the apparent retention of memory after removal of half of the brain, either half, and by the retention of the child's personality and sense of humor."
In the paper "Neurocognitive outcome after pediatric epilepsy surgery" by Elisabeth M. S. Sherman, we have some discussion of the effects on children of temporal lobectomy (removal of the temporal lobe of the brain) and hemispherectomy, surgically removing half of their brains to stop seizures. We are told this:
"After temporal lobectomy, children show few changes in verbal or nonverbal intelligence....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 remove part of the frontal lobe, "none of the patients with extra-temporal resections had reductions 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 (in Figure 4) describes IQ outcomes for 41 children who had half of their brains removed in hemispherectomy operations in Freiburg, Germany. For the vast majority of children, the IQ was about the same after the operation. The number of children who had increased IQs after the operation was greater than the number who had decreased IQs.
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 in the United States. 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.
There is a new study relating to the topic of intelligence and removal of half of the brain. Once again, the study reports facts shockingly inconsistent with standard claims that the brain is the source of the human mind. But the press reporting on this study is feeding us a kind of "cover story" trying to explain away the shocking result. Upon close inspection, this "cover story" falls apart.
The study involved brain scans of six patients who had half of their brains removed. Table S3 of the supplemental information of the study reveals that the intelligence quotients (IQ scores) of the six subjects were 84, 95, 91, 99, 96 and 80. So most of the six were fairly smart, even though half of their brains were gone. How could this be when half of their brains were missing?
In stories such as the story in Discover magazine, it is suggested that "brain rewiring" can explain such a thing. The story states the following:
"In a study published Tuesday in Cell Reports, scientists studied six of these patients to see how the human brain rewires itself to adapt after major surgery. After performing brain scans on the patients, the researchers found that the remaining hemisphere formed even stronger connections between different brain networks — regions that control things like walking, talking and memory — than in healthy control subjects. And the researchers suggest that these connections enable the brain, essentially, to function as if it were still whole."
The summary above is not accurate, as it tells a story that is not true for one of the six patients, as I will explain below. This hard-to-swallow story (repeated by the New York Times) is reassuring if you wish to keep believing that the brain is the source of your mind. The person who buys such a story can reassure himself kind of like this:
"How do people stay smart when you take out half of their brain? It's simple: the brain just rewires itself so that the half works as good as a whole. It acts kind of like a computer that reprograms itself to keep functioning like normal when you yank out half of its components."
We know of no machines ever built that have such a capability. All brains engage in some "brain rewiring" every year, so any mental effect can always be attributed to "brain rewiring." We cannot dream of how a brain could possibly be clever enough to rewire itself to perform just as well when half of its matter was removed. When we take a close look at the data in the study, it shows that this "brain rewiring" story does not hold up for the smartest subject in the study.
In Table S4 of the study, we have measurements based on brain scanning, designed to show the level of connectivity in the brains of the six subjects. Some of the six subjects have a slightly higher average connectivity score, but it's not very much higher. The average connectivy scores for the controls with normal brains were .30 and .35. The average connectivity scores for the six patients with half a brain were .43, .45, .35, .30, .43, and .41. So it was merely true that the average brain connectivity score of the patients with half a brain was slightly higher than the normal controls. And when we look at another metric (the "max" score listed at the end of Table S4), we see that all of the half-brain subjects had lower "brain connectivity" scores than the controls. The "max" connectivy scores for the controls with normal brains were .90 and .74, but the "max" connectivity scores for the six patients with half a brain were only .57, .67, .49, .51, .63, and .62. So the evidence for greater brain connectivity or "nicely rewired brains" after removal of half a brain is actually quite thin.
Interestingly, the half-brain patient with the highest intelligence (labeled as HS4, with an IQ of 99) had an average brain connectivity score of only .30, which is the same as one of the group of controls with normal brains, and less than the brain connectivity of the other group of controls with normal brains. So the smartest person with half a brain (who had an IQ of 99) did not at all have any greater brain connectivity that can explain his normal intelligence with only half a brain. How can this subject HS4 have had a normal intelligence with only half a brain? In this case, favorable brain rewiring or greater brain connectivity cannot explain the result. So the "cover story" of "their brains rewired to keep them smart" falls apart.
The half brain of subject HS4, IQ of 99, average brain wiring
The only way we can explain such results is by postulating that the human brain is not actually the source of the human mind. If the human brain is neither the source of the human mind nor the storage place of memories, we should not find any of the results mentioned in this post to be surprising.
Subject HS4 is not by any means the most remarkable case of a patient with half a brain and a good mind. The study here is entitled "Development of above normal language and intelligence 21 years after left hemispherectomy." After they removed the part of the brain claimed to be the "center of language," a subject developed "above normal" language and intelligence.
Then there is the case of Alex who did not start speaking until the left half of his brain was removed. A scientific paper describing the case says that Alex “failed to develop speech throughout early boyhood.” He could apparently say only one word (“mumma”) before his operation to cure epilepsy seizures. But then following a hemispherectomy (also called a hemidecortication) in which half of his brain was removed at age 8.5, “and withdrawal of anticonvulsants when he was more than 9 years old, Alex suddenly began to acquire speech.” We are told, “His most recent scores on tests of receptive and expressive language place him at an age equivalent of 8–10 years,” and that by age 10 he could “converse with copious and appropriate speech, involving some fairly long words.” Astonishingly, the boy who could not speak with a full brain could speak well after half of his brain was removed. The half of the brain removed was the left half – the very half that scientists tell us is the half that has more to do with language than the right half.
What is also interesting in the new study is that when we cross-compare Figure 1 with Table S3 (in the supplemental information) we find that the patient with the largest brain (after the hemispherectomy operation) had the lowest IQ, and that the patient with the smallest brain had the highest IQ. In Figure 1 the brain of the subject with an IQ of 80 (subject HS6) looks much larger than the brain of the subject with an IQ of 99 (subject HS4). Such a result is not suprising under the hypothesis that your brain is not the source of your mind.