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Prof. Marek Glezerman's comment on Joel et al. paper: Sex Beyond the Genitalia: The Human Brain Mosaic that was published in November 2015 in PNAS.

The Problem of the Definition and Quantification of Reality

Marek Glezerman, MD
President, the International Society for Gender Medicine

In the November issue of the prominent scientific journal PNAS, a group of distinguished researchers from leading academic institutions in Europe and Israel published a study titled: Sex Beyond Genitalia: The Human Brain Mosaic. The authors, led by Prof Daphna Yoel from Tel Aviv University, had set out to establish that the brains of male and females  are not categorically different, that they are not dimorphic as is the categorical difference between the genital systems of the two genders. In order to confirm their hypothesis, the research team examined several large data sets of magnetic resonance imaging  and of behavioral attitudes, comprising   surveys which included  thousands of men and women. The research focused on measuring brain voxels, which are volume values in a three dimensional space, and connectomas, which are a kind of wiring graph of connecting  nerve cells. The overarching objective of the study was,  to produce proof that brains of men and women resemble  more a   mosaic, comprised of specific overlapping functional regions, than distinct organs. The authors conclusion was  that there is no such thing as distinct  male and female brains.  Well,  the general and often cited dictum that “absence of an evidence  is not  evidence of absence.” applies also in  this case. With the means deployed  in their study, the authors did not find morphological differences between brains of men and women. An acceptable conclusion of this study might therefore have been that with the tools they applied, no  morphological categorical differences between brains of men and women could be ascertained.  Perhaps different tools, such as  functional MRIs might have yielded  other results.  There are also questions pertaining to the methodology of this paper. The MRI images the researchers examined were comprised of “still images”, that is,  images which by their very nature cannot represent and   demonstrate dynamic functions of distinct parts of the brain. Looking at these images is more  akin to examining a  road map and draw conclusions about traffic patterns , without looking at the  actual traffic.  Moreover, the paper makes no mention on  whether MRIs from women and men were matched with any parameters, such as  age, occupation, background diseases, time of the day etc.  To find differences between two organs, organisms, entities and probably for most things in life, it is not enough to examine quantity and morphology, connections and voxels. Reality is not fully revealed from quantities  or distributions of quantities.  At the heart of such evidence must be the functionality of the system. There are functional differences in various activity centers in the brain while performing physical or cognitive tasks or undergoing emotional experiences, but there are no morphological distinctions between brains, that experience happiness or sorrow, love or hate, empathy or compassion. Despite the substantial body of data on  these issues, the subject research  does not relate to this aspect and chose to exhibiting the absence of morphological differences between the brains of men and women.  There was in fact no need  for such an elaborate study that eventually corroborated a rather obvious fact that one cannot morphologically  distinguish between a male and a female brain like one can concerning male and female genitalia. This adds  but very little to scientific understanding of gender related research.  Did  any anatomists or pathologists ever claim that they could determine the sex of a person by mere morphological and quantitative examination of their brain or even  dissection of brains ?  Are slices of male brains supposed to be colored blue and those of women pink? The only areas where such distinctions can be made are relative to the genital systems and perhaps  distinct  parts of the skeleton.   Whenever the terms “female brain” and “male brain” are used, the intention should be functional and not morphological, qualitative and not quantitative,  statistical and not categorical.  This is in fact  true for most  bodily systems and indeed, functionally,  brains of women and men are different. Not better, not worse, neither stronger, nor weaker -  just different.

Moreover,  the very brain cells of course differ chromosomally: The sex chromosomes of women comprise two XX chromosomes while  those of men have an  XY chromosomal pattern. Is it reasonable to assume that this fundamental cellular difference is without consequences. The male brain is exposed to a completely different hormonal environment during intrauterine life than the female brain. Available overwhelming scientific data as to the crucial  effect  of testosterone on the developing male brain cannot seriously be challenged by morphometric imaging studies.

Ovaries and testes function differently, because of differences in hormone secretion by distinct  brain regions ( hypothalamus and pituitary). In the female brain, this secretion is pulsatile and that is the reason for the existence of the female menstrual cycle. In the male, the secretion is almost constant which  is one of the reasons for the continuous process of sperm production. These brain regions look morphologically  exactly the same, the hormones secreted are exactly the same – just the pattern of secretion in the brain  is different, leading to fundamentally different functions of our gonads. The effects of testosterone to which only the male fetus is exposed at a great magnitude  prior to  birth are numerous, including behavioral characteristics after birth, preferences for toys, verbal skills, communication  and many other features. Of course, this is not categorical and overlaps are common. The question is whether distinct features related to bodily functions, including brain functions,  are more common in one sex  or the other,  not whether a certain organ looks morphologically similar or dissimilar.  Consider the human heart: Except for size, the heart in males and in females  are indistinguishable from each other. Yet, more women than men who suffer from a heart attack will have open coronary arteries and atypical symptoms. Consider drugs: Prophylactic aspirin taken by women will more often prevent strokes and if taken by men, will more often prevent a heart attack. Not always, just more often. Consider the gastrointestinal system: Passage time of food and drugs will more often be longer in women than in men, which has consequences for drug absorption and food digestion. More often, not always. An consider the brain: certain features, like spatial imagination, nest memory, multitasking capabilities, communicative strategies and many, many others may be more often present in one sex than in the other. More often, not always. In short, the definition of a male brain as opposed to a female brain should not be based on morphology but on functionality, or even better, on the relative  prevalence of certain functional capabilities. In the Middle Ages , scholars tried to quantify  the soul and to measure its  weight by subtracting  the weight of a dead person from his or her weight  before death. This was my association, while reading the article about the human brain mosaic.

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