this is prejudicial. Fielding didn't say anything about "evil spirits" nor was that her reason for performing the procedure. you're speaking from ignorance and displaying your own biases.
do you know for certain that it's irrational? there are some serious medical conditions caused by swelling of the brain (encephalitis, concussions, etc.) so it doesn't seem completely unfounded. her approach to it was unconventional and she failed to persuade other researchers to pursue the project. that doesn't mean she's crazy. her remarks about "feelings of buoyancy" were in response to a question about what kind of qualitative difference she felt. her answer was appropriate to the question as it was asked. what else do you expect from her?
it's very clear from your remarks that you are ideologically committed to this person being wrong because she offends your sensibilities for some reason. maybe do some introspection and think about why she offends your sensibilities. this seems like tribalism to me. you're reacting like "ewww dirty hippy" and dismissing her because of it.
I'm dismissing her because she has made no testable claims, and the medical conditions that do cause swelling of the brain are orthogonal to the brain in its healthy state. It does not follow that what is appropriate treatment for a pathology would have a similar effect on a non-swollen brain. This is, quite literally, one of the most common logical fallacies there is. By definition, that makes it an irrational belief.
In addition, there are a vast number of medical cases involving cranial penetration in otherwise healthy adults. Some of them involve the skull only, with no underlying brain trauma. If trepanation has some sort of unsuspected, detectable benefit aside from placebo, it would have been noticed by now. Head trauma is not that uncommon.
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If she wants to explore the potential benefits of trepanation and get it taken seriously, she needs to make testable claims. As she is going uphill against a mountain of pre-existing evidence that holes in the heads of healthy people are not good, she needs to have exceptional evidence, at that. That's how science and knowledge progression works.
If she wants her opinion to be taken seriously, give us something testable instead of new age woo about feelings of buoyancy.