Epilepsy is a disease causing seizures. When the seizures are frequent, the disruption to a patient's quality of life can be so great that brain surgery may be recommended. In such surgery, large chunks of the brain may be removed. In other cases, the corpus callosum that connects the two hemispheres of the brain may be severed. The most extreme type of brain surgery is hemispherectomy, in which an entire half of the brain is removed.
I have already written several posts on the surprisingly small effects of hemispherectomy operations. Let us look at some reports of the cognitive effects of lesser types of surgery to treat epilepsy. One such type of surgery is temporal lobe resection. A paper tells us this about removal of the temporal lobe: "cognition remains relatively stable in the years following right temporal resection." Another paper discusses surgery in the posterior cortex of the brain. Using the word "resection" which refers to surgical removal of part of the brain, the paper states the following:
"The results of our study show that posterior cortical resections, either in the dominant or non-dominant hemisphere, do not lead to significant changes in general intelligence....This is in contrast to the outcome after temporal lobe resections. Several authors have shown a significant increase in full scale IQ (FSIQ) after non-dominant temporal lobe resection and only a slight increase or a decrease in FSIQ after dominant temporal lobe resections...PIQ [performance IQ] was almost invariably shown to be improved compared to baseline IQ, regardless of the side of temporal resections. The effect of dominant temporal lobe resections on VIQ [verbal IQ] seems to be somewhat inconsistent, with either decreasing or increasing scores, whereas right temporal lobe resection regularly leads to increasing scores."
This is hardly what we would expect if your brain is what makes your mind. It seems that taking out parts of the brain (called a resection) often is followed by an increase in scores on IQ tests.
Another paper states, "The data do not confirm concerns that patients undergoing temporal lobe epilepsy surgery are likely to develop accelerated memory decline over the longer term." Another paper states the following, suggesting no big cognitive effect from epilepsy surgery:
"Pooled data on IQ, executive functioning, and attention indicated few patients show declines post surgery, but a substantial rate of improvement in verbal fluency with left‐sided temporal surgery (27%) was found. Self‐reported cognitive declines after epilepsy surgery were uncommon, and gains were reported in some domains where losses were found on objective tests (i.e., verbal memory and language). Variations in surgical techniques did not appear to have a large effect on cognitive outcomes, except for naming outcomes, which appeared better with more conservative resections. Sensitivity to postoperative changes differed across visual memory tests, but not verbal memory tests. Few conclusions could be made regarding cognitive risks and benefits of extratemporal epilepsy surgery, or of epilepsy surgery in children."
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, although there are many reasons for rejecting such claims. The paper (which studied 90 patients) 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."
Another relevant paper is the paper "Determinants of IQ outcome after focal epilepsy surgery in childhood: A longitudinal case-control neuroimaging study." We read the following:
"Fifty-two children (28 boys, 24 girls) were evaluated for epilepsy surgery and reassessed on average 7.7 years later...). Pre- and postsurgical assessments included IQ tests and T1-weighted brain images...Applying a ≥10-point change threshold, 39% of the surgically treated children improved, whereas 10% declined."
We are not told in this paper how large was the matter removed from the brains of these children, but it is known that epilepsy surgery typically involves removing large parts of the brain, sometimes as much as 50%. Again, we have a result that is inconsistent with claims that the brain generates the mind.
Another relevant paper is "Neuropsychological outcomes after epilepsy surgery: systematic review and pooled estimates." The paper was a meta-analysis that reviewed 23 other papers on the cognitive effects of epilepsy surgery. Four of the studies dealt with IQ changes. The paper states, " Epilepsy surgery was associated with an average 11% loss and 16% gain in IQ for combined left and right surgical groups." The wording of the paper's summary of findings about verbal memory decline is ambiguous, so I won't quote it. But I will note that the paper reports significant percentages of subjects having an improvement in verbal memory, with many others having a decline. The paper states this:
"For visual memory (six studies), average loss was 21% (95% CI 13 to 31) for left sided surgery and 23% (95% CI 18 to 29) for right sided surgery and average gain was 15% (95% CI 10 to 21) in left sided surgery and 10% (95% CI 7 to 13) in right sided surgery. In one study involving children where side of surgery was not reported, gains in verbal and visual memory were 10% and 25% of children, respectively and risks of loss were 5%."
Summarizing four studies dealing with changes in executive function after epilepsy surgery, the paper states this:
"Left and right sided surgery were associated with a loss of 1% and 0% respectively (one study) and a gain of 9% and 4% (one study) in mental flexibility. Left and right sided surgery were associated with an average loss of 10% (95% CI 4 to 23; 3 studies) and 21% (two studies) respectively and an average gain of 27% (95% CI 10 to 55; 2 studies) and 16% respectively (two studies) in word fluency. In left and right sided surgery, two studies reported an average loss of 6% and 2% respectively and an average gain of 10% and 15% respectively in attention."
Summarizing three studies dealing with "overall subjective change in multiple abilities," the paper finds that "Regardless of side of surgery, average overall loss was 9% and average overall gain was 18%."
Overall, the results reported above are in conflict with dogmas that the brain is the source of the human mind and the storage place of human memories. Epilepsy surgery typically involves removing large chunks of the human brain, as much as 50%. The studies mentioned above do not show the kind of big mental damage we would expect under such a dogma. The studies often mention improvements in mental function that are inexplicable under the dogma that the brain is the source of the human mind.
No comments:
Post a Comment