Surprising Studies on Memory Loss or IQ Changes After Brain Surgery or Brain Damage

Neuroscientists typically claim that memories are stored in the brain. There are some very complex ways and very simple ways in which such a hypothesis can be tested. A very complex way would be to use dissection to see whether any sign of human memories can be found. You could do this in two different ways: (1) by dissecting the brains of people who had recently died, looking for learned information such as facts learned in school; (2) by analyzing tissue removed from the brains of living people, to look for  learned information such as facts learned in school. There are plenty of opportunities for the second of these methods, because brain tissue is often removed to treat diseases such as epilepsy. Sometimes an entire half of the brain is removed in an operation called a hemispherectomy, to treat very severe and frequent seizures. Epilepsy is also treated by less severe operations that involve removing much less than half of the brain. 

Examining removed brain tissue has never produced any support for the claim that memories are stored in brains. No one has ever seen any words or letters by looking at brain tissue through a microscope. No one has ever used a microscope to look at brain tissue of some particular person, and seen images corresponding to sights that person  previously saw. No one has ever seen any sign of encoded information by looking at brain tissue through a microscope,  other than genetic information which is not information that anyone learns through school or experience.  

The method described above is a very complex method that might require the use of very sophisticated equipment such as electron microscopes. But there is a very simple way of testing the hypothesis that memories are stored in brains. You can simply do what may be called a  "loss of learned information" test, testing someone both before and after the person had surgery to remove some of their brain tissue. You can look for loss of memories and learned information that had been acquired before the operation. 

Such a test would be different from a typical memory test. A typical memory test might measure how well someone can remember some new information he was asked to memorize. But a "loss of learned information" test would only test whether something learned or remembered before some brain surgery had been lost by the act of surgery itself. 

You would think that scientists eager to prove their claims that memories are stored in brains would often do such a "loss of learned information" test.  But it seems very hard to find examples of such tests in the scientific literature. 

Let us look at some papers that may be relevant to discussions of whether human brains store memories.  We must carefully distinguish between two types of tests:

(1) A "performance on new learning" memory test will test how well some person can still acquire different types of new memories after having lost some brain tissue.

(2) A "loss of old memory" test will test whether a person lost some memory he had acquired, because of some loss of brain tissue.  

The second type of test is more relevant to whether the brain stores memories.  Removal of some brain tissue might damage your senses or perception in a way that might decrease your ability to learn new things and acquire new memories. But that would not show that your previous memories acquired before such a removal were stored in your brain. Similarly, if you make a person blind, that will reduce his ability to learn, but that does nothing to show that brains store memories. 

We must also carefully distinguish between a random pool of brain tissue loss subjects, and a pool of subjects who have been selected because they showed symptoms of memory loss. I have looked at quite a few papers in which we are told that some pool of subjects was selected for both brain tissue loss and also memory problems. Tests of the extent of memory loss in such persons may be giving a very misleading impression, because only subjects having memory loss were selected for the tests. Such studies may merely show that "people with memory problems have memory problems." 

It seems that our medical professionals are usually bad about testing preservation of memories after doing operations that remove half of a brain or a large fraction of the brain. I think this may be because they do not want to do a test that will produce results that contradict their dogma that memories are stored in brains. But here and there in the scientific literature you will be able to find some tests that serve as tests of how well memories were preserved after half of the brain was removed. In some other cases, we will be able to infer that there was  little or no loss of memories acquired before the operation, either because of a lack of mention of any such thing (which would be noteworthy and worthy of mention if it occurred), or because of some general assurance that the operation usually produced "no serious complications," a claim that should only be made if previously acquired memories were well-preserved.  

Let us look at some of the papers that might be relevant. 

• The paper here ("Unexpected amnesia: are there lessons to be learned from cases of amnesia following unilateral temporal lobe surgery?") tells us that "Cases of amnesia following unilateral temporal lobe surgery are rare." It tells us that "Davies and Weeks (1993) did report one case of postoperative amnesia in a series of 58 cases of unilateral temporal lobectomy, whereas Walczak et al. (1990) found one case of marked deterioration in memory from a preoperative normal state in their series of 100 patients who underwent such surgery." The authors state, "We were able to locate nine definite cases of amnesia following unilateral temporal lobe surgery in the English language literature." But the paper gives us no interesting accounts describing amnesia in any of these cases. We do have a Table 3 that has "before" and "after" columns for seven of the nine cases. The table fails to mention much of anything backing up claims that the patients had amnesia in the sense of loss of memories or learning they had acquired before the surgery. We have "before and after" IQ scores for the first five subjects, which show no significant difference (there sometimes being an increase).  For patient 6 there is no data, and for patient 7 we read "postoperative scores on executive and language function similar to preoperative scores." In the column labeled "Post-surgery memory functioning" we hear of some declines in memory performance tests for some of the subjects, but we hear nothing about a loss of memories that they had acquired before the operation.  And some of the results in that column involve tests taken years after the surgery, so we don't know whether any declines reported were the result of the surgery. In short, the paper fails to provide any good evidence that memories or learned information can be lost by temporal lobe surgery for epilepsy. 
• The paper "Memory outcome after temporal lobe epilepsy surgery: corticoamygdalohippocampectomy versus selective amygdalohippocampectomy" fails to discuss any measurements or observations about how acquired memories or learned knowledge declined after brain surgery that removed substantial tissue. It does tell us that for 63 patients IQ went up by about five points after such surgery, and that for another 60 patients IQ increased by nearly five points. The paper tells us that "General intelligence increases after epilepsy surgery." 
• Almost the same claim is made by the paper here ("Psychiatric and Neuropsychological Problems in Epilepsy Surgery: Analysis of 100 Cases That Underwent Surgery"), which tells us, "The full IQ score of the Wechsler Adult Intelligence Scale–Revised (WAIS-R) was increased after temporal lobectomy in 75% of the cases (p < 0.01; n 4 44)." 
• The paper "Retrograde amnesia in patients with diencephalic temporal lobe or frontal lesions" has some interesting graphs showing memory tests in a group of subjects that included "15 patients with dicephalic lesions, 15 patients with temporal lobe lesions, 15 with frontal lobe lesions and 20 healthy control subjects." We have graphs showing performance on tests that include tests of autobiographical incidents, news recall and famous faces. All of the patients with lesions are able to produce scores ranging from about 70% to 30% of the scores produced by control subjects.  This is not a very impressive result, considering that the paper says, "The patients were selected in all cases on the basis of their having significant anterograde memory impairment in association with clinical and CT scan evidence of pre- dominantly focal lesions in either the temporal or frontal lobes or the diencephalon."  Since both having brains lesions and being not good at remembering the past was a requirement for being chosen in the study, the paper fails to show a link between the lesions and the memory performance. Similarly, if you did a study that only accepted subjects who were both gay and alcoholic, that would do nothing to show that being alcoholic tends to make people gay. 
• The paper "Retrograde amnesia in patients with hippocampal, medial temporal, temporal lobe, or frontal pathology" suffers from the same shortcoming.  We have some graphs showing inferior memory performance on five patients, on tasks of autobiographical recall, recalling famous news events, and recalling famous faces. But the paper eventually tells us that these patients "were selected on the basis of significant anterograde memory loss and MRI evidence that regional brain atrophy was restricted to the medial temporal lobe structures."  So the result merely tells us that people who have trouble remembering what they learned have trouble remembering what they learned. A random sample of five subjects with the same brain tissue loss might tell a very different tale. 
• The paper "Clinical outcomes of hemispherectomy for epilepsy in childhood and adolescence" (about surgeries removing half of a brain) tells us that "the overall developmental/cognitive category was unchanged following surgery in 23 out of 27 children," and that "two children showed a >15 point improvement in DQ/IQ following surgery,"  referring to a substantial increase in intelligence as measured by IQ tests. 
• The paper here "Seizure control and developmental trajectories after hemispherotomy for refractory epilepsy in childhood and adolescence" (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 "With childhood hemispherectomy, one hemisphere can support—but is suboptimal for—word and face recognition" involved tests on 15 left hemispherectomy patients, 24 right hemispherectomy patients, and 58 age-matched control subjects. A hemispherectomy typically involves removal of one-half of the brain to stop very frequent epileptic seizures. According to Figure 5, most of the patients who had a hemispherectomy were only "mildly impaired" in their ability to recognize words and faces, with a few being "moderately impaired," a few others having "average" performance, and one having "above average" performance.  The tests performed seemed to have been purely "performance on new learning" tests. We read that "Childhood hemispherectomy patients showed above 80% accuracy on tasks of face and word recognition," and the paper calls this "surprisingly good performance."
• A 2015 scientific paper ("Brain abscess: surgical experiences of 162 cases") looked at 162 cases of surgery to treat brain abscess, in which parts of the brain undergo the cell death known as necrosis, often being replaced with a yellowish pus. The article contains quite a few photos of people with holes in their brains caused by the abscesses, holes in their brains of various sizes. The paper says that “complete resolution of abscess with complete recovery of preoperative neuro-deficit was seen in 80.86%” of the patients, and that only about 6% of the patients suffered a major functional deficit, even though 22% of the patients had multiple brain abscesses, and 30% of the abscesses occurred in the frontal lobe (claimed to be the center of higher thought). Interestingly, the long review article on 162 brain abscesses treated by brain surgery make no mention at all of amnesia or any memory effects, other than to tell us that “there was short-term memory loss in 5 cases.” If our memories really are stored in our brain, how come none of these 162 cases of brain abscesses seem to have shown an effect at all on permanent memories?
• Similarly, a scientific paper ("Brain abscess: clinical aspects of 100 patients") about 100 brain abscess cases (in which one fourth of the patients had multiple brain abscesses) makes no mention of any specific memory effect or thinking effect. It tells us that most of the patients had “neurological focal deficits,” but that's a vague term that doesn't tell us whether intellect or memory was affected. (A wikiepdia.org article says that such a term refers to "impairments of nerve, spinal cord, or brain function that affects a specific region of the body, e.g. weakness in the left arm, the right leg, paresis, or plegia.")   The paper tells us that after treatment “80 (83.3%) were cured, eight (8.3%) died (five of them were in coma at admission), seven had a relapse of the abscess,” without mentioning any permanent loss of memory or mental function in anyone.
• Another paper ("Epidemiology of brain abscess in Taiwan: A 14-year population-based cohort study") discusses thousands of cases of brain abscesses, without mentioning any specific thinking effects or memory effects. 
•  Another paper ("Retrospective analysis of 49 cases of brain abscess and review of the literature") refers to 49 brain abscess patients, and tells us that "the frontal lobe was the most common site," referring to the place that is claimed to be a "seat of thought" in the brain. But rather than mentioning any great intellectual damage caused by these brain holes, the paper says that 39 of the patients “recovered fully or had minimal incapacity,” and that five died.
• A paper tested the ability to recognize faces and words in a group of control subjects and about 39 subjects who had undergone hemispherectomy, typically to remove half of their brains. Most of those who had the hemispherectomy operation performed almost as well as the normal controls.  We read, "This performance level is perhaps surprisingly high, relative to the brain volume resected  [removed] (often close to 50%), hinting at a nonlinear degradation of function with resection. Second, the patients' accuracy was not dependent on the hemisphere removed. That is, the single LH or RH of patients showed comparable performance on face and word recognition."
• The paper "Memory outcomes following hemispherectomy in children" fails to mention in its abstract any loss of episodic or conceptual memories after hemispherectomy operations typically involving removal of half a brain. It says, "Undergoing hemispherectomy was not necessarily associated with declined memory performance, with the majority of patients showing stable scores."
• The paper "The Cognitive Outcome of Hemispherectomy in 71 Children" describes outcomes of operations typically removing half of a brain to stop very frequent seizures. The paper gives us in Table 7 the pre-operation and post-operation IQ scores for 31 different children. The decline in IQ is only small. The children went from an average IQ of  80.5 to an average IQ of 75.7. 26 of these children were given a test called the Peabody Picture Vocabulary Test. For these 26 children the average score increased from 79.0 to 82.1. This test is very important because it is effectively a test of previously acquired knowledge. In the test a person is shown a series of four pictures, and is asked a question such as "Which picture shows laughing?" The test therefore measures previously acquired knowledge. The increase in the score on this test is most remarkable. It is not at all what we would expect if the human brain stores memories. Under the hypothesis that the brain stores memories, removal of half of a brain should cause a sharp decline in performance on this test. Similar results are shown in Table 9. We have pre-operation and post-operation IQ scores for 15 different children (not the ones described in Table 7). The decline in measured IQ is less than a single point. Scores on the Peabody Picture Vocabulary Test rose from an average of 43.0 to an average of 51.7. Another paper summarizes these results by saying, " Pulsifer et al. ... reported cognitive outcomes in 71 children who underwent hemispherectomies and found little changes in cognitive performance pre- and post-surgery."
• The paper "Long-term functional outcomes and their predictors after hemispherectomy in 115 children" did not test for IQ or memory, but reports on things such as speech ability, walking ability and reading ability. We read this: "In this cohort of 115 children, at a mean follow-up of 6.05 years after hemispherectomy, 83% patients walked independently, 73% had minimal or no behavioral problems, 69.5% had satisfactory spoken language skills, and 42% had good reading skills."
• The paper "Hemispherectomy in adults patients with severe unilateral epilepsy and hemiplegia" discusses "25 adults who presented severe unilateral epilepsy and hemiplegia and underwent anatomic or functional hemispherectomy in between 2006 and 2011."  16 of these were "anatomic hemispherectomies" apparently involving removal of half of the brain, and the other nine were "functional hemispherectomies."  Very remarkably, we are told "All of the patients’ postoperative scores of overall QOL, full IQ, verbal IQ and performance IQ improved compared with pretreatment scores."  We don't read anything about before-and-after tests of memory retention, but we read that "Hemispherectomy is a safe operation for epileptic adults with hemiplegia and serious seizures and seldom leads to severe complications."  We may presume that the people having these operations still preserve almost all their memories, seeing that the loss of much of your memories would certainly be a "severe complication." 
• The paper here ("Retrograde amnesia after traumatic injury of the fronto-temporal cortex") tells us of a man who suffered severe brain damage after falling from a horse. He was in a coma for 6 weeks, and his MRI showed very extensive brain damage in multiple areas. The man was given various tests of how good his acquired memories were preserved. He scored 33 out of 60 on the Famous Faces Test, and 70 out of 100 on the Semantic Knowledge Test.  He was able to remember 8 of 16 objects from his past. He scored 100 on an IQ test. Since the test was done four years after the fall, we don't know how much of this decline was caused by the fall. 
• The paper "The Effect of Early and Late Brain Injury upon Test Scores, and the Nature of Normal Adult Intelligence" is behind a paywall. But from the freely available first page we get the interesting information that after searching for IQ scores recorded about brain surgery, the author found 15 subjects, and found that they had an average post-operative IQ of 108.   The author also found another group of 23 brain surgery patients who had an average post-operative IQ of 107. We are told "in none was there postoperative loss" of IQ.
• The paper "When only the right hemisphere is left: Studies in language and communication" reports on the case of a patient BL of "above normal intelligence" who underwent a left hemispherectomy at age five. Despite lacking the left half of his brain, BL "attended regular elementary and high school and graduated from college with a Bachelor's degree with a double major in business and sociology," he "played the baritone horn in a band," and worked "several years as an accountant in international business." The paper reports BL scoring normally on most of the cognitive tests he took.
• The paper "Functional consequences of hemispherectomy" gives us in Table 1 before-and-after IQ scores for 12 children who had half of their brains surgically removed. The worst result was a decline in IQ of 11 points, occurring for only one of the subjects. The best result was an increase in IQ of 8 points, which occurred for three different subjects. Overall, there was more of an increase in IQs than a decrease.  
• The paper "Long-term outcome of hemispheric surgery at different ages in 61 epilepsy patients" examines the IQ effects of removing half of a brain.  Near the bottom of Table 2 we are told that out of 55 patients, only 5 experienced post-surgical "intellectual deterioration," with 50 categorized as "not worse" in regard to "intellectual deterioration." 21 of these 55 patients are called "better" in regard to "intellectual improvement," and 34 are called "not better."  We read, "More than 80% appeared improved or unchanged in intelligence following surgery." We don't hear much specifics on memory, but we get the claim that these "remove half the brain" operations have "low risk of adverse cognitive effects." 
• In 1994 Simon Lewis was in his car when it was struck by a van driving at 75 miles per hour. The crash killed Lewis' wife, and “destroyed a third of his right hemisphere” according to this press account. Lewis remained in coma for 31 days, and then awoke. Now, many years later, according to the press account, “he actually has an IQ as high as the one he had before the crash.” In 1997, according to the press account, Lewis had an IQ of 151, which is 50% higher than the average IQ of 100. How could someone be so smart with such heavy brain damage, if our brains are really the source of our minds?  
• In a scientific paper "Why Would You Remove Half a Brain? The Outcome of 58 Children After Hemispherectomy −−The Johns Hopkins Experience: 1968 to 1996" by Vining and others, we read about how surgeons at Johns Hopkins Medical School performed fifty-eight hemispherectomy operations on children over a thirty-year period. Eleven of these children had the left hemisphere of their brains removed; most of the rest had the right hemisphere of their brains removed.  The paper states this: "Despite removal of one hemisphere  [i.e. one half of the brain], the intellect of all but one of the children seems either unchanged or improved. " We are told "language recovers after removal of the dysfunctional left hemisphere," and the authors speculate about why it is they saw "intellectual improvement in these children after removal of half of the cortex." The authors state, "We are awed 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." The final statement is very important. Although the authors do not give us the results of exact tests documenting a preservation of memory, the statement I just quoted suggests they observed a preservation of episodic and factual/conceptual memory after half of the brain was removed. 
• The paper "Cognitive Impairment 3 Months After Moderate and Severe Traumatic Brain Injury: A Prospective Follow-Up Study" gives us the result of cognitive tests on people who had brain injuries as the result of events such as falls and traffic accidents.  We have some tables that are hard to read. In the Discussion section we read that after moderate Traumatic Brain Injury (TBI), "most patients had a normal neuropsychological assessment," with no more than 1 score much below normal (or, to put it more technically, no more than 1 score below 1.5 standard deviates below the norm).  We read that "even after severe [brain] injury, normal performances were found in one third of patients." The authors say, "This was unexpected." We are told that the average total IQ score of 35 subjects with moderate traumatic brain injury was an above-average score of 109, and the average total IQ score of 26 subjects with severe traumatic brain injury was an above-average score of 103. There is a reason to suspect that some subjects may deliberately perform poorly in such tests. Some of the subjects (such as those injured in a crash) may have pending law suits, and may think that good performance in cognitive tests may reduce their chance of being rewarded lots of money in a law suit. 
• At the page here, we read an account of a girl who had the left half of the brain removed in a hemispherectomy operation, to try to stop severe seizures. We hear of a successful operation. We are told, "In addition to the seizures, Rehab also struggled with being able to remember things before her surgery." In the next sentence we hear one of the girl's parents saying, "Her memory was so poor, but now she remembers everything."  This is the opposite of what you would expect under the "brains make minds" hypothesis. 
• The paper "Neuropsychological functioning during the year following severe traumatic brain injury" studied cognitive functioning in 65 subjects who had severe brain damage, mostly after road traffic crashes. The patients were rated with a level of impairment of "mild" or "severe" on various measures, based on tests 6 months after the injury and 1 year after. Fewer than half of the subjects were rated as having "severe" impairment in memory performance tests taken at the 1-year mark. Only 9% of the subjects were rated as having "severe" impairment in one test of executive function at the 1-year mark, with a minority rated as having "severe" impairment in another test executive function at the 1-year mark. One test of attention at the 1-year mark result showed only 8% with a severe impairment, and another test of attention at the 1-year mark result showed only 28% with a severe impairment. There is a reason to suspect that some subjects may deliberately perform poorly in such tests. Some of the subjects (such as those injured in a traffic accident) may have pending law suits, and may think that good performance in cognitive tests may reduce their chance of being rewarded lots of money in a law suit. Moreover, we must also wonder whether the scientists selecting the subjects had a bias in looking for subjects with particularly bad memory problems. The average IQ of the brain-damaged subjects was 93, and we don't know whether this below-average result was caused by brain injury.  There is reason to suspect that the set of average people suffering from traffic accident brain damage may be slightly below average in IQ, given that higher IQ might tend to avoid such accidents. 
• The paper "Association of Traumatic Brain Injury With Dementia and Memory Decline in Older Adults in the United States" used a very large sample of 9,794 patients who had an assessment of traumatic brain injury.  The study says, "There was no significant relation between history of TBI [traumatic brain injury] with LOC [loss of consciousness] and memory score or memory decline." We read this: "In a nationally representative prospective cohort of older adults free of dementia at baseline, we did not find evidence for any long-term associations between history of TBI [traumatic brain injury] with LOC [loss of consciousness]  (of unknown frequency and severity) and risk of dementia over 14 years of follow-up. " We read that "similarly, decline in memory performance did not differ between participants with or without history of TBI with LOC." The authors state, "our findings showing no association between TBI history with LOC and dementia are consistent with the results of several other recent studies looking at dementia, AD [Alzheimer's Disease], or AD biomarkers or neuropathology." 
• The paper "Working Memory after Traumatic Brain
  Injury in Children" tested working memory in eighty children with mild or severe traumatic brain injury (TBI). The paper has nice easy-to-read graphs comparing the performance of the brain-injured with controls, and the first two of the graphs show no appreciable difference in performance in two working memory tests, even when comparing the severe cases with control (uninjured cases).  
• The paper "Central executive system impairment in traumatic brain injury" is one that does not give us a random sample of patients with traumatic brain injury, because the paper tells us this about its 64 patients: "Patients were selected for participating in the study if they complained of lack of attention, poor
  memory or loss of efficiency in everyday life." Despite such a selection bias, Table III of the paper tells us that the majority of the subjects had "normal performance" in long-term memory acquisition, long-term memory storage, long-term memory delayed recall, sustained attention and short-term memory, with an average of about 60% of the subjects being normal in such areas.  
• At the University of Chicago page here, we read, "Nordli recalled a patient whose IQ rose to 100, a normal intellect, from 80 before hemispherectomy." The patient seemed to get much smarter after they took out half of the brain. 
• The very interesting paper "Preserved Cognition After Right Hemispherectomy" gives us extensive performance tests for a woman who had almost all of her right brain removed after a severe stroke at age 29. We have a very good visual showing that her performance on a wide variety of cognitive tests is average or slightly below average. 

A 2020 paper gives us an indication of the appalling failure of neuroscientists and doctors to properly test for losses of pre-surgical episodic memories and pre-surgical learning in people who had hemispherectomy operations. We read this:

"Only four studies have investigated memory functioning prior to and following hemispherectomy surgery. It is worth noting that all used short-term memory tasks, typically involving immediate repetition or recognition and did not test for more challenging aspects of memory involving recall or recognition over longer delays."

The authors of a 2017 paper tell us something similar. Referring to hemispherectomy operations in which half of the brain is removed, it says this:

" Physicians have long wondered about the surprising finding that one can lead a normal life with only one hemisphere....

The discrepancy between cerebral and cognitive functioning in these cases is strikingly highlighted by the fact that most patients, even adults, do not seem to lose their long-term memory such as episodic (autobiographic) memories. Even so, this puzzle, and possible explanatory models for this retention of long-term memory, is only rarely

discussed in the medical literature dealing with hemispherectomy. Although memory features are sometimes assessed by using the Wechsler Memory Scale (e.g., Loddenkemper et al., 2004), we were unable to find a single peer-reviewed publication in which the peculiar retention of the patient's autobiographic memory was explicitly addressed. That said, this remarkable phenomenon was at least casually mentioned by authors such as Dandy (1933) and Bell and Karnosh (1949), who stated that their patient's memory seemed unimpaired after hemispherectomy. Similarly, Vining et al. (1997) were surprised by the apparent retention of memory after the removal of the left or the right hemisphere of their patients. Dorman (1991) described the extraordinary case of a subject who was able to perform brilliant calendar calculations, although his left hemisphere had been removed several years before."

Despite this appalling failure to properly test whether episodic memories and learned information are preserved after removing half of a brain, several of the studies quoted above make statements strongly suggesting that such memories are preserved after removal of half a brain, contrary to the dogma that memories are stored in brains. And when studies such as the ones above tell us that there are usually no major cognitive effects of removing half of a brain, we can regard this as being a rather clear indication that episodic memories and learned information are well-preserved after removal of half of a brain, as any major loss of such  episodic memories and learned information would be a severe cognitive effect that should be reported. 

The quote above refers to Dandy. Here is the basis of the reference. The case of Dandy's patients are reported in the American Journal of Psychology, Vol. 46, No. 3 (Jul., 1934), pages 500-503. We read this: 

"Dandy has completely removed the right cerebral hemisphere from eight patients. He has performed total extirpations of one or more lobes much oftener... There are tabulated below certain generalizations on the effects of removing the right hemisphere.... The operation was the complete extirpation of the right frontal, temporal, parietal, and occipital lobes peripheral to the corpus striatum. The weight of the tissue removed varies, with the pathological conditions involved, from 250 to 584 grm [grams].Coherent conversation began within twenty-four hours after operation, and in one case on the afternoon of the same day. Later examinations showed no observable mental changes. The patients were perfectly oriented in respect of time, place, and person; their memory was unimpaired for immediate and remote events; conversation was always coherent; ability to read, write, compute, and learn new material was unaltered. Current events were followed with normal interest. There were no personality changes apparent; the patients were emotionally stable, without fears, delusions, hallucinations, expansive ideas or obsessions, and with a good sense of humor; they joked frequently. They showed a natural interest in their condition and future. They cooperated intelligently at all times throughout post-operative care and subsequent testing of function." How could the memory of patients be "unimpaired for immediate and remote events" if memories are stored in brains?

The quote above also refers to the Vining paper I quote from above. The quote also refers to Bell and Karnosh, who in 1949 referred to 4 operations they had done, stating, "In all cases the relative freedom from severe physical handicap and gross mental defect after removal of almost half the cerebrum was striking" (pages 285-286). That is not a quote anyone would make if patients had lost their episodic or learned memories. 

All in all, the results discussed above are consistent with the idea that the human brain is not the storage place of human memories and is not the source of the human mind.  The results are not the results we would get if brains stored human memories and brains produced minds. 

Postscript: In the article here, we read of a doctor who has performed hundreds of hemispherectomy operations.  We get this quote: 

" 'I've had hemispherectomy patients go to college, get married, have children, have a family, and be cognitively completely normal with one side of the brain,' Bingaman said. 'How that happens? We don't understand it.' "

Traumatic Brain Injury Results Clashing With Prevailing Dogmas About Brains

I have at this site written quite a bit about the preservation of mind and memory after surgeries that removed large portions of the brain, sometimes half of the brain. Examples were my posts "Preservation of Mind and Memories After Removal of Half a Brain" and "Cases of High Mental Function Despite Large Brain Damage." There is another way to look for evidence of how sensitive the mind is to brain damage: we can look for cases of cognitive effects of traumatic brain injury (often referred to as TBI).  Every year we have many cases of traumatic brain injury or TBI that result from events such as accidental falls, traffic accidents, car crashes or people being shot in the head. 

Before discussing such cases, I will need to discuss how there are several reasons why we should assume that the cognitive effects of traumatic brain injuries are probably not as high as typically reported in scientific studies.

Confounding factor #1: the incentive of many to perform poorly on cognitive tests after a brain injury.  There is strong reason to suspect that in many cases people given cognitive tests after a traumatic brain injury may not be trying as hard as they can on the tests. Some of the subjects (such as those injured in a car accident either inside or outside of a vehicle or those who fell in a work accident) may have pending law suits or pending benefit applications, and may think that good performance in cognitive tests may reduce their chance of being rewarded lots of money in a law suit or through a benefit application.  There are three ways in which a person might receive money after a traumatic brain injury:

(1) The person might engage in a law suit against a car driver that results in a large settlement such as an award of $100,000 or more.

(2) A person might apply for benefits under the Worker's Compensation program that provides monthly payments to workers injured on the job. 

(3) A person might apply for disability benefits that can be provided by the Social Security Administration if a worker has been judged to be disabled. 

Given all of these possibilities for potential financial gain after having a traumatic brain injury, it would not be surprising if many people who have had traumatic brain injury do not try as hard as they can on tests of their cognitive abilities. Many people who have traumatic brain injury may think that getting a high score on a cognitive test might damage their ability to get future benefits or future settlement money. 

Indeed, in the paper "Noncredible Explanations of Noncredible Performance on Symptom Validity Tests" we read quite a bit about reasons for thinking that some of those tested after traumatic brain injury might not have been trying as hard as they could.  Here are some excerpts:

"Invalid test results from poor effort or deliberate underachievement do not occur only in groups where there is an obvious external incentive to appear cognitively impaired, such as those seeking financial compensation for cognitive impairment. Even in groups previously assumed to be highly motivated to do well, effort may be poor, leading to invalid test results....Neuropsychologists now know that, in many different contexts, effort can be low to a degree that is sufficient to invalidate test results, especially if there is an incentive to appear impaired (e.g., Chafetz, 2008; Chafetz, Prentkowski, & Rao, 2011; Flaro, Green, & Robertson, 2007; Sullivan, May, & Galbally, 2007)....For people with an incentive to appear impaired and who fail effort tests, the observed test scores typically underestimate actual ability to a marked degree (Fox, 2011; Green, 2007; Meyers et al., 2011; Stevens et al., 2008). In groups of disability claimants or compensation claimants, including those who were already receiving financial disability benefits, it was found that about 30% of cases were not making enough effort to produce valid test results, and in the MTBI group, the figure was roughly 40% (Green et al., 2001)."

There are techniques that can be used to help weed out "memory malingering" in memory tests of those with traumatic brain injury. One technique is to include some easy tests that almost no one fails, and look for failure in such tests, which might be an indication of lack of effort. Another technique is to take the same tests at different intervals, taking the best result at any interval as being the more reliable indication of memory performance. 

Confounding factor #2: selection bias in picking subjects having traumatic brain injury. We must wonder whether the scientists selecting the subjects for papers on traumatic brain injury have a bias in looking for subjects with particularly bad memory problems, because they are hoping to get a result that fits in with the expectations of their colleagues and peer reviewers of their papers. We should look for any confession by the paper authors that they selected patients who had reported memory problems, rather than selecting random patients with traumatic brain injury, regardless of how good their memory was. Any such confession means that the paper may not be telling us about what percentage of traumatic brain injury patients suffer from similar problems. Similarly, if scientists select for some study only people who are gay alcoholics, they may report a high alcoholism rate among gay people; but we won't learn from such a method what percentage of gay people are alcoholic. 

Confounding factor #3: the group of those with traumatic brain injury may be less intelligent and more forgetful than an average group of non-injured people of the same size. While traumatic brain injury often occurs for reasons beyond any person's control, very often such injury happen because of some causal factor that might have been avoided by someone of excellent intelligence and memory. For example, many traumatic brain injury cases occur to reckless or intoxicated drivers, to people who failed to use seat belts, or people who were walking in some dangerous way, to people who were not wearing helmets while bicycling or riding motorcycles, to people who recklessly jaywalked, and so forth. We therefore have a strong reason to suspect that the group of all people with traumatic brain injuries may have had a below-average intelligence or a below-average memory, or both. Accordingly, showing  a small difference in memory or intelligence between those with traumatic brain injury and those without injury does not necessarily show that brains make minds or that brains store memories. 

Confounding factor #4: traumatic brain injury may degrade perception, muscle skills, eyesight and hearing skills without decreasing core intelligence and memory, in a way that causes lower scores on cognitive tests.  Cognitive tests are rarely pure measures of memory and intelligence. For example, a person with a damaged brain may have a damaged vision ability that degrades his performance on paper-based cognitive tests.  Also, a person with a damaged brain may have a damaged muscular ability that degrades his performance on any test requiring muscle skills such as filling in the right little circles on a test sheet. 

Confounding factor #5: incidents producing traumatic brain injury may increase apathy, depression or pain, resulting in lower scores on memory tests that are not caused by lower cognitive ability.  It is has often been reported that following a traumatic brain injury someone may experience pain, depression or an increased level of apathy. Such factors might tend to cause a person to perform more poorly on cognitive tests, for reasons other than cognitive deficits. 

Confounding factor #6: memory tests often involve subjective scores by analysts who may be biased towards giving negative scores to those with traumatic brain injury.  Some memory tests can be performed without any subjective analysis by an analyst. For example,  with the Famous Faces Test, a person either does or does not name the person shown in a photograph.  But in other widely used memory tests, there is a strong possibility of biased analysis. For example, there is an Autobiographical Memory Interview test in which an analyst rates how well a subject has performed when asked to recall incidents at various parts of his life.   But if an analyst knows that a subject has had traumatic brain injury, the analyst may be more prone to rate the subject's response poorly.  To avoid such a bias, a robust blinding protocol would be needed, so that the analyst cannot tell whether the subject had a brain injury.  But neuroscience experiments typically fail to use blinding protocols, and when they are used they are typically not robust protocols.  A robust blinding protocol for a memory test would be one in which analysts could not even see the people giving answers, as such people would often have physical signs of their injury. 

In light of these six confounding factors, under the hypothesis that the brain does not make the mind and does not store memories, we might still expect to see some modest differences in cognitive test scores between those with traumatic brain injuries and those without such differences.  But we should expect that the differences will usually not be terribly dramatic, and that differences might tend to show up sometimes and be absent in other cases.  Let us look at some scientific papers to see whether such an expectation is met. 

• The paper "Cognitive Impairment 3 Months After Moderate and Severe Traumatic Brain Injury: A Prospective Follow-Up Study" gives us the result of cognitive tests on people who had brain injuries as the result of events such as falls and traffic accidents.  In the Discussion section we read that after moderate Traumatic Brain Injury (TBI), "most patients had a normal neuropsychological assessment," with no more than 1 score much below normal (or, to put it more technically, no more than 1 score below 1.5 standard deviations below the norm).  We read that "even after severe [brain] injury, normal performances were found in one third of patients." The authors say, "This was unexpected." We are told that the average total IQ score of 35 subjects with moderate traumatic brain injury was an above-average score of 109, and the average total IQ score of 26 subjects with severe traumatic brain injury was an above-average score of 103. 
• The paper "Neuropsychological functioning during the year
  following severe traumatic brain injury" studied cognitive functioning in 65 subjects who had severe brain damage, mostly after road traffic crashes. The patients were rated with a level of impairment of "mild" or "severe" on various measures, based on tests 6 months after the injury and 1 year after. Fewer than half of the subjects were rated as having "severe" impairment in memory performance tests taken at the 1-year mark. Only 9% of the subjects were rated as having "severe" impairment in one test of executive function at the 1-year mark, with a minority rated as having "severe" impairment in another test executive function at the 1-year mark. One test of attention at the 1-year mark result showed only 8% with a severe impairment, and another test of attention at the 1-year mark result showed only 28% with a severe impairment.  The average IQ of the brain-damaged subjects was 93, and we don't know whether this below-average result was caused by brain injury.  There is reason to suspect that the set of average people suffering from traffic accident brain damage may be slightly below average in IQ, given that those with higher IQ might tend to avoid such accidents. 
• The paper "Association of Traumatic Brain Injury With Dementia and Memory Decline in Older Adults in the United States" used a very large sample of 9,794 patients who had an assessment of traumatic brain injury.  The study says, "There was no significant relation between history of TBI [traumatic brain injury] with LOC [loss of consciousness] and memory score or memory decline." We read this: "In a nationally representative prospective cohort of older adults free of dementia at baseline, we did not find evidence for any long-term associations between history of TBI [traumatic brain injury] with LOC [loss of consciousness]  (of unknown frequency and severity) and risk of dementia over 14 years of follow-up. " We read that "similarly, decline in memory performance did not differ between participants with or without history of TBI with LOC." The authors state, "Our findings showing no association between TBI history with LOC and dementia are consistent with the results of several other recent studies looking at dementia, AD [Alzheimer's Disease], or AD biomarkers or neuropathology." 
•  The paper "Working memory after severe traumatic brain injury" tested 30 subjects who had almost all suffered brain damage due to high-velocity motor vehicle accidents. All of the patients had a post-traumatic amnesia (typically an inability to remember what happened a certain number of days before the accident). We are told that this post-traumatic amnesia lasted for at least seven days in all patients, and thar for 14 of 21 patients the post-traumatic amnesia lasted 30 days or more, "suggesting that the majority of patients sustained an extremely severe TBI [traumatic brain injury]." The paper has nice easy-to-read graphs comparing the difference in performance between these brain-injured patients and control subjects. For a "digit span" working memory test (Figure 1) and a "word span" working memory test (Figure 3), we see no major difference between the brain-damaged patients and control subjects. There is also no difference in a "Brown-Peterson task" test, when conducted with "no interference."  On some other tasks there is a substantial difference.  
• The paper "Working Memory after Traumatic Brain
  Injury in Children" tested working memory in eighty children with mild or severe traumatic brain injury (TBI). The paper has nice easy-to-read graphs comparing the performance of the brain-injured with controls, and the first two of the graphs show no appreciable difference in performance in two working memory tests, even when comparing the severe cases with control (uninjured cases).  
• The paper "Central executive system impairment in traumatic brain injury" is one that does not give us a random sample of patients with traumatic brain injury, because the paper tells us this about its 64 patients: "Patients were selected for participating in the study if they complained of lack of attention, poor
  memory or loss of efficiency in everyday life." Despite such a selection bias, Table III of the paper tells us that the majority of the subjects had "normal performance" in long-term memory acquisition, long-term memory storage, long-term memory delayed recall, sustained attention and short-term memory, with an average of about 60% of the subjects being normal in such areas.  
• The paper "Models of Exceptional Adaptation in
  Recovery After Traumatic Brain Injury: A Case Series" discusses nine cases of people who suffered severe brain injuries causing them to be in comas of between 2 and 17 days. All of them made remarkable recoveries. For example, a computer engineer suffering a 15 day coma after a severe crash injury went back to his high-tech job and "helped to plan a complete reorganization of his division." Another recovered from a 14-day coma after a high-speed crash, earning a 4.0 grade point average. 
• The paper "Working memory outcomes following traumatic
  brain injury in children: A systematic review with
  meta-analysis" presents no new experiments, but reviews existing papers on the topic. Using the acronym CE to mean "central executive," the paper says, "Further analyses revealed significant, moderate effect sizes for studies that utilized verbal CE tasks (k = 19, d = −0.56, 95% CI −0.71, −0.41, p < .001), but non-significant and small effect sizes for studies that utilized visuo-spatial CE tasks (k = 7, d = −0.26, 95% CI −0.60, 0.08, p = .13)." The paper notes that "Several studies, however, did not find deficits in CE [executive functions] in children and adolescents who had sustained TBI [traumatic brain injury]." The paper says, "The results of our meta-analysis, however, indicate that children with TBI do exhibit deficits, albeit small-to-moderate ones, in the PL[phonological loop] relative to controls, but not in the VSSP [visual-spatial sketchpad]." We read that "no relation was found between TBI severity and the two storage components," and that "In contrast to findings relating to the impact of TBI severity and to our expectations based on literature suggesting that the frontal lobes play a critical role in WM [working memory], no relationship was found between frontal injuries and WM [working memory] outcomes." 

These results are consistent with the hypothesis that the brain is not the storage place of memories, and that the mind is not the product of the brain. We see some differences in the cognitive scores of those who had traumatic brain injury and those who did not. But the differences are not very dramatic; they have a kind of "sometimes you see them and sometimes you don't" nature; and the differences seem to be largely absent in a large fraction of the people with traumatic brain injury.  The reported differences can be mostly explained by the six confounding factors listed at the beginning of this post.

As for evidence of damage of episodic memories or learned information after traumatic brain injury, the evidence for it seems to be scant and anecdotal. In general, school-learned knowledge and knowledge of personal experiences seems to survive well after traumatic brain injury. It is sometimes reported that after a traumatic brain injury a person may forget what happened on the day of the injury or for a few days beforehand. It is often said in the literature that people have difficulty recalling only memories acquired a short time before the injury, not older memories. A 2018 paper ("Retrograde Autobiographical Memory From PTA Emergence to Six-Month Follow-Up in Moderate to Severe Traumatic Brain Injury")

says this::

 "There is evidence to suggest that retrograde autobiographical memory deficits exist after severe TBI, although there have been no prospective studies of autobiographical memory in a representative sample of moderate to severe cases recruited from hospital admissions...The overwhelming focus on memory following TBI [traumatic brain injury] has been on anterograde amnesia, and there has been very little research on retrograde amnesia [people losing memories acquired before the injury]... A deficit in retrograde autobiographical memory performance among individuals with TBI has been found in a handful of studies." 

Judging from such lack of study, and such weak evidence, it would seem that people losing memories or knowledge after traumatic brain injury is not a very big problem.  The study quoted above tries to show evidence of memory difficulties in patients with traumatic brain injury, but finds only minor score differences between such patients and control subjects. The minor differences can easily be explained by referring to the six confounding factors listed at the top of this post. In this case the traumatic brain injury patients studied were all patients who had already been diagnosed as having post-traumatic amnesia of at least seven days, before they were tested. So the study tells us that patients with memory difficulties may have memory difficulties, but it does not tell us about what percentage of people with traumatic brain injuries have serious memory difficulties. Also, the study failed to use a robust blinding protocol. We are told that there were two analysts doing the memory tests (apparently only one blind to whether the subjects had brain injury), and that the scores given were based on a discussion between the two analysts.  That is not a robust blinding protocol, and knowledge of whether the subjects had a brain injury may have affected the ratings given in the memory tests. 

Claims that minds are produced by brains and claims that brains store memories are examples of belief traditions passed on from one generation to the next. The latest generation of college students to adopt such beliefs does not adopt them from a long unbiased independent study of the facts, but as an act of social conformity in which people believe as they are told to believe, like some Sunday school student trustingly accepting whatever belief tenets are taught to him. 

Postscript: The 1915 British Journal of Surgery paper "Gunshot Wounds of the Cranium: With Special Reference to the Brain" gives us short summaries of the outcomes of more than 100 persons who suffered gunshot wounds to the head. 62 of the cases are described as cases of "complete recovery," and most of these involved wounds to the brain. In most of these cases, we are simply given the phrase "complete recovery" as the outcome, with no other description. In some of the cases we are given more explicit statements specifically stating there was a complete mental recovery. For example:

"Case 34 w.-P.b.a. unknown; U,o. 10 weeks. Double frontal injury; Slaphylococcus aureirs ; apparently hopeless ; almost all external parts of both frontals smashed, and a great part removed at operation ; superior longitudinal sinus torn across ; muscle grafted ; tedious but smooth convalescence. Complete recovery, with good mental condition. "

Case 40.-P.b.a. unknown ; U.O. 13 weeks. Right frontal injury ; Siaphylo- coccus aureus ; both upper and lower jaws fractured ; large decompression ; bone and pus removed from brain. This case appeared hopeless, but made complete recovery in respect to his mental condition."

Page 13 of the document "Gunshot Wounds of the Head in 1940" tells us "the cases without initial loss of consciousness include three penetrating frontal lobe injuries."  This is contrary to the dogma that the frontal lobes are some source of consciousness.  The 1979 paper "Long-term outcome after severe head injury" studied hundreds of patients with very bad head injuries. The paper states, "This study was concerned with the severest acceleration head injuries, yet severe physical or mental disability were uncommon."

More Evidence of High Mental Function Despite Large Brain Damage

In another post on this site, I presented many cases showing that people can have very high mental function despite massive brain damage. In this post I will look some additional cases showing such a thing.

First let's look at some results concerning strokes. This article in US News and World Report says, "It’s important to recognize that strokes do not cause a drop in overall intelligence.” This paper refers to “the generally minor effect of stroke on IQ” in children. 

A paper here noted a case of retrograde amnesia (failure to remember previous memories) that went across many domains of knowledge. But the paper noted, "Across all domains tested, LSJ showed losses of knowledge at a level of breadth and depth never before documented in retrograde amnesia."  Note the "never before documented."  If brains are storing our memories, you would think that many such cases would have been previously documented, because of all the people suffering brain jury from disease, cancer, or car accidents. 

The recently published scientific paper here is entitled “A Lesion-Proof Brain? Multidimensional Sensorimotor, Cognitive, and Socio-Affective Preservation Despite Extensive Damage in a Stroke Patient.” Here is an astonishing report from the paper's abstract, describing a patient who seems mentally undamaged despite massive brain injury:

At age 43, patient CG sustained a cerebral hemorrhage and a few months later, she suffered a second (ischemic) stroke. As a result, she exhibited extensive damage of the right hemisphere (including frontal, temporal, parietal, and occipital regions), left Sylvian and striatal areas, bilateral portions of the insula and the amygdala, and the splenium. However, against all probability, she was unimpaired across a host of cognitive domains, including executive functions, attention, memory, language, sensory perception (e.g., taste recognition and intensity discrimination), emotional processing (e.g., experiencing of positive and negative emotions), and social cognition skills (prosody recognition, theory of mind, facial emotion recognition, and emotional evaluation).

Below is the paper's startling discussion of the very well-preserved memory in this patient who had suffered heavy brain damage from two strokes:

Even more striking are her mnemonic skills: her procedural and semantic knowledge is fully preserved, as shown in her smooth execution of various action routines (e.g., handling her cell phone, tying her shoe laces) and her intact naming and classification skills (e.g., she could flawlessly denominate all the objects she had thematically organized in different sections of her purse); furthermore, her declarative memory is extremely detailed for events which happened weeks, months, and even years ago. She could describe scenes from her childhood and adolescence, she meticulously narrated episodes occurring immediately before and after her strokes, she remembered the names, specialties, and suggestions of all her doctors, and she could recount details of dozens of books she had read throughout her life.

We know that Alzheimer’s disease can cause an inability to recall memories, although whether the memories are actually lost is debatable. What is remarkable is the fact that a large fraction of the brain can be ruined by Alzheimer’s disease before a patient can become noticeably poor at remembering things. Here is a quote from an expert on the disease:

One of the big challenges we face with Alzheimer's is that brain cell destruction begins years or even decades before symptoms emerge. A person whose disease process starts at age 50 might have memory loss at 75, but by the time we see the signs, the patient has lost 40 to 50 percent of their brain cells.

The same very astonishing thing is said in this article, which quotes an expert saying the following:

In Alzheimer’s, brain cells start to die 10, 15, or 20 years before symptoms appear. By the time we observe memory lapses, 40 percent to 50 percent of brain cells are gone, and it’s too late to make a difference.

These statements are astonishing. If our memories are all stored in our brains, why would you have to lose 40 to 50 percent of your brain cells before people started noticing your memory loss? Again, this suggests merely a low correlation between brain health and mental function.

On this page we have the amazing story of an MIT student who helped doctors find a baseball-sized tumor in his brain. Doctors performed surgery and removed the tumor. Later, the student gave a presentation to cancer researchers. A video of the presentation is included on that page. Amazingly, the young man seems to show no sign whatsoever of a damaged mind. He walks and talks normally, and seems to have slick presentation skills sufficient to land him a job as a host on a morning TV show. The page tells us that this young man is now pursuing a PhD in mechanical engineering. In the presentation, the young man tells us that the doctors removed about 12 billion neurons in his brain.

The paper here studied memory effects in 63 patients who had undergone surgery for brain cancer, in addition to other patients who had undergone both brain surgery and radiotherapy. 91% of these 63 patients experienced “no deterioration” in immediate recall; 80% experienced “no deterioration” in delayed recall; and 77% experienced “no deterioration” in recognition. This is a relatively low correlation between brain damage and memory, particularly considering that about half of the patients had 2 or more brain metastases (areas in which the cancer was growing).

Figure 8 of this paper gives us a graph that compares verbal IQ with brain tumor size in a variety of brain cancer patients. Under materialist assumptions, we would expect that there should be a strong inverse correlation between something like verbal IQ and the size of a brain tumor; the bigger the brain tumor, the lower your verbal intelligence should be. But what we see is only a low correlation – a correlation of only .28. High correlations have values like .75 or .85. Astonishingly, the person with the highest verbal intelligence had the biggest brain tumor, and the person with the second highest intelligence also has a very large brain tumor. We can easily account for the slightly-below-average IQ scores of brain tumor patients by simply assuming that in these brain tumor patients there would often be visual perception problems, muscular coordination problems, psychological distress, and head pain problems, which would tend to slightly decrease scores in pencil-and-paper IQ tests, without there actually being a decrease in intelligence.

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 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 brain damage was 99.5 – only a tiny bit lower than the average IQ of 100. Two of the brain-damage patients had genius IQs of higher than 140. This is not a result consistent with the claim that brains make minds. 

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 for these 156 brain-damaged veterans, 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 before they were injured. 

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.  And if you're a patient with a terminal brain tumor, you may have psychological distress and head pain that may cause a reduced score in your paper-and-pencil IQ test. 

There is a type of surgery called a hemispherectomy, and is sometimes performed on children experiencing severe seizures. The operation involves surgically removing half of the brain. The surgery is described in a Scientific American article entitled Strange but True: When Half a Brain Is Better than a Whole One. The article states: “Unbelievably, the surgery has no apparent effect on personality or memory.”

According to this link, 70% of the children who had half of their brains removed were able to speak well, and 42% older than 6 were able to read well. Given that only about 60% of the American population can read well, this 42% figure is amazingly high.  A paper here tracks the before and after IQ scores of 12 children who had a hemispherectomy operation to remove half of their brain (usually to treat severe seizures). Half of the children had higher IQ scores when tested two years after half of their brains were removed, compared to their scores before the operation. 

When we consider sudden traumatic injury to the brain, we also find some cases where the correlation between brain health and mental function seems to be merely a low correlation. One astonishing case is that of Gabby Giffords, a US congress representative who was shot at point-blank range in the back of the head. Not only did she live, but she has recovered to a remarkable degree, to the point of being able to bike, and speak clearly (although in shorter sentences). A similar case was the famous case of Phineas Gage, a nineteenth century railroad worker who had a thick iron railroad spike accidentally drive through his skull, piercing his frontal lobes. A physician reported after examining Gage that he was “quite recovered in his faculties of body and mind.” Gage seems to have had some personality changes later, which may or may not have been related to his injury. But such changes are trivial compared to what we would have expected from such an injury under materialistic assumptions about the brain. An expert on Gage has stated that the personality change “did not last much longer than about two to three years,” but Gage lived for 12 years after the accident.

A Lancet study involving nearly three million people found only a small relation between traumatic brain injury and the risk of dementia. Those with severe traumatic brain injury were only 35 percent more likely to develop dementia. Since the lifetime risk of dementia is less than 20 percent, this means that 70 percent or more of people who suffer traumatic brain injury do not get dementia.  With a correlation this small, we can't even be sure whether there is a causal relation. By comparison, you are 2300% more likely to develop lung cancer if you smoke. 

It has been estimated that the cerebellum contains between 50 percent and 80 percent of the neurons in the brain.  In China a woman was discovered to have no cerebellum at all. But her defects were relatively minor, such as slurred speech, a need to use something like a cane to walk, and a lack of athletic ability. The woman could understand speech well enough. According to a scientific paper describing her, she had merely "mild mental impairment." This is yet another case showing only a small correlation between brain health and intellectual ability. 

In the paper "Subtotal agenesis of the cerebellum in an adult," we read this: 

"We describe a 58-year-old asymptomatic woman with subtotal developmental absence of the cerebellum. MRI evaluation showed minute remnants of cerebellar tissue corresponding to the anterior quadrangular lobules."

Note the word "asymptomatic." This is a case of a woman who suffered no symptoms despite not having a cerebellum, the part of the brain where most neurons exist. Similarly, in the 1950 link here, on the far right, we read of a man who "was born without a cerebellum and seemed to suffer no noticeable disadvantage from the fact."

These cases all tell us the same thing: that there is merely a low correlation between brain health and mental function, and that people can often have very high mental function even when their brains are greatly damaged. As a scientific paper says, “There does not appear to be a direct relationship between the degree of brain pathology or brain damage and the clinical manifestation of that damage.”

Such cases are not at all compatible with the conventional thinking of neuroscientists that the human mind is merely the product of the brain. But such cases are compatible with the assumption that the human mind is mainly the product of some mysterious reality beyond our understanding: a soul or some cosmic consciousness infrastructure much greater than a human body.

But a mainstream might argue that we should believe our memories are all stored in our brains, on the grounds that brains are active when we are remembering, and very heavy brain damage may be associated with memory loss. The visual below illustrates why such

reasoning is not convincing.

Below is a very notable case of the almost complete destruction of a brain by a brain tumor, but with a high preservation of mental function. It comes from page 71 of the document here (and the newspaper story here repeats the same details).