Is there a "female brain"?

However, when she delved into the scientific literature, she came across an article that contradicted this opinion. The study, which they published Tracy Shores and her colleagues at Rutgers University in 2001, examined a particular detail in the rat brain: tiny bumps on top of brain cells, called Dendritic spines, and which regulate the transmission of electrical signals. The researchers showed that when cheating the estrogen Olat, female rats had more dendritic spines than males. Schorz also discovered that when male and female rats were exposed to a state of acute stress, after electric shocks to their tails, their brains reacted in opposite ways: in the males, more stings grew, while in the females, they decreased.

Based on this unexpected finding, Yoel developed a hypothesis about differences between the sexes in the brain, a hypothesis that is sparking a new controversy in the turbulent field. Instead of thinking of different brain regions between females and males, she suggested thinking of the brain as a "mosaic" (a new use of a term already used by others), made up of a variety of male and female characteristics that can change and alternate. The diversity itself and the behavioral overlap between the sexes - belligerent females and empathetic males and even men and women with both traits - indicate that it is impossible to associate different brains into one of two well-differentiated categories. The organ weighing about 1.4 kilograms, located under the skull, is neither male nor female, Yoel says. With her colleagues in Tel Aviv, at the Max Planck Institute for Human Cognition and Neuroscience in Leipzig, Germany, and at the University of Zurich, Yoel tested the idea by analyzing magnetic resonance imaging (MRI) brain scans of more than 1,400 brains and showed that most of them indeed contained both male and female characteristics. "We all belong to one very diverse population," she says.

When Yoel's research was published in 2015 in the journal PNAS, like-minded scientists considered it a breakthrough. "The result poses a serious challenge to the entrenched misconception," wrote Gina Ripon, a professor of brain imaging of cognitive processes at Aston University in England. "My hope is that this will change the rules of the game in brain research in the 21st century."

But veteran scholars of gender differences vigorously oppose this approach, disputing Joel's methods and conclusions, as well as her overt feminism. "The article is basically ideology disguised as research," says the neurobiologist Larry Kahill from the University of California, Irvine, and claims that Joel's statistical methods are "biased" (albeit not consciously) to support her hypothesis. Other reviews were more measured. "There is variation in the brains of the subjects, and it shows it in a very beautiful way, but that doesn't mean that there aren't areas of the brain that, on average, will be different in men compared to women," says the neurobiologist Margaret M. McCarthy from the University of Maryland School of Medicine, who studies sex differences in rats.

Yoel, for her part, agrees that genetics, hormones and environment do produce gender differences in the brain. She even agrees that when there is enough information about specific characteristics of any brain, it is possible to guess, with a high degree of accuracy, whether the brain belongs to a woman or a man. But what you can't do, she emphasizes, is the reverse process: looking at a man or woman and predicting the topography and molecular landscape of their mind or personality just because you know their gender.

Although her research is controversial, Yoel's main message is true, she says Catherine is on, a researcher in the field of molecular biology at Harvard University whose studies in mice support Yoel's findings: "There is enormous variation between individuals." Recognition of this fact opened a new direction in the discussion about the meaning of being male or female. In the eyes of neurobiologists, it is no longer enough to look for sex differences in the brain. The discussion now focuses on the source, rate and significance of the differences. This may have a considerable effect on the way we look at sex and gender in the laboratory and outside, as well as on the question of whether it is necessary to adjust drug treatments for women and men separately. "Our entire society is built on the assumption that our genitals divide us into two groups, not only in terms of reproductive ability or possibility, but also in terms of the characteristics of our brain, behavior and psychology," says Yoel. "People assume that the differences accumulate. That if you are feminine in one characteristic, you will be feminine in other characteristics. But this is not true. Most people have a gender mosaic."

Contradictory claims and claims

In the late 19th century, long before anyone even thought of MRI, the main measurable difference between male and female brains was brain mass (measured, presumably, after death). Because women's brains were 150 grams lighter, on average, than men's brains, scientists reasoned that women must therefore be less intelligent. the journalist Angela Saini describes in her book "Inferiority: how science was wrong about women - and the new studies that rewrite the story" How the human rights activist confrontedHelen Hamilton Gardner (literary nickname) with the experts of the time and claim that the weight of the brain in relation to the weight of the body, or the size of the brain in relation to the size of the body, should be more relevant as a measure of intelligence, otherwise "an elephant should be smarter than all of us." Appropriately enough, Gardner turned her mind to science. It was 150 grams lighter than the brain of an average man, but weighed the same as the distinguished male scientist who founded the brain collection at Cornell University, where her brain was housed. (FYI, Gardner was onto something. "Once you take body size into account, most of the differences between the sexes disappear or become very small," she says Lisa Elliott, a neurobiologist at the Chicago School of Medicine at Rosalind Franklin University of Medicine and Science.)

For most of the next century, tangible sex differences in the brain were the preserve not of neurobiologists but of endocrinologists, who studied sex hormones and sexual behavior. Sex determination is a complex process that begins when a combination of genes on the X and Y chromosomes act in the womb, flipping the switch in the direction of femininity or masculinity. But apart from the reproductive system and the distinction between boys and girls, there were also reports of psychological and cognitive differences between the sexes. But the psychologist Eleanor McCobefrom Stanford University, who studied the subject from the 60s to the 80s, found fewer differences than expected: girls have better language skills than boys, while boys did better in spatial and mathematical tests. As expected, the criticism was not long in coming. Janet Hyde, a psychologist at the University of Wisconsin-Madison, performed a meta-analysis that combined the results of previous studies, and suggested, as she wrote in a 2016 article, that women do just as well in math as men "and that men and women are quite similar in most, but not all, psychological variables." Based on these results, Hyde developed a hypothesis she calls the "gender similarity hypothesis", which claims that the psychological makeup of men and women are more similar than they are different.

From the moment technology made it possible to peer into the inner workings of the living brain, a long list of sex differences emerged that had nothing to do with reproduction or parenthood. In the article From 2006 in the journal Nature Review Neuroscience, Kahil described "a flood of findings from animals and humans related to the effect of sex on many areas of the brain and on behavior, including emotions, memory, vision, hearing, visual processing of faces, pain perception, navigation, messenger levels nerves, the action of stress hormones on the brain and disease states." In rats, McCarthy measures everything, from the size of clusters of nerve cells that together make up the cell nucleus in the brain, to the number of astrocytes and microglia that form the support system for the nerve cells. "There is irrefutable evidence for the biological basis for brain differences between species ranging from animals to humans," she says. But McCarthy also emphasizes that the origin of sex differences in humans is more complicated than in animals that do not deal with the issue of gender, that is, with the psychological and social characteristics of sex. "In humans, the very thing that educates us to behave according to a certain gender from the moment we are born, has a biological effect on the brain," she says. In her 2009 book, Pink Brain, Blue Brain, Elliott agrees, arguing that this plasticity, the way the brain changes in response to experiences, underlies gender differences in behavior rather than biology.

The jump from the mind to the behavior provokes the most jarring disputes. The most recent high-profile study accused of being guilty of stereotyping (and thus earning the nickname "neurosexist") was reported In the article in 2014 by Ruben Gore, Rachel Gore and Ragini Verma, all from the University of Pennsylvania. The group used the so-called simile method DTI, which shows the strength of connections between nerve cells, to examine nearly 1,000 brains of subjects aged 8 to 22. The researchers found that males had stronger connections within each of the hemispheres (left and right), while females had stronger connections between hemispheres. The researchers concluded "that the results indicate that male brains are structured to facilitate connectivity between sensory perception and coordinated action, while female brains are designed to facilitate communication between analytical and intuitive information processing." (Counterargument: the study did not take brain size into account.)

in search of variety

And into this entanglement came Dafna Yoel. Many previous studies have identified differences in single characteristics of the brain and then used those differences to make claims about entire populations—the averages for women and men. Yoel and her colleagues did the opposite: they used an image of the population-level differences encountered in the group as a whole, to ask what claims can be made about individual minds. "These are two different descriptions of the world," says Yoel. Both show the same differences at the group level. The important question is: which one best describes the human brain: the first description, in which one type of brain characterizes males and another type characterizes females, or the second description in which most human brains are a mosaic of male and female characteristics?

Yoel asked, in fact, two questions: What is the degree of overlap in the brain characteristics in which there are differences between females and males? And do minds show "internal cohesion"? The second question is a measure Yoel developed to determine whether all characteristics in a given brain are male or female. Using four large series of MRI data, the researchers identified in the group in each data series some characteristics that show the greatest differences between males and females, such as the total volume of the nerve cell bodies and their dendritic branches (the gray matter) and of the branches that connect them (the white matter). They discovered a continuum of characteristics. Distinctly feminine or masculine characteristics inhabited the ends of the continuum, and the intermediate zone was characterized by mixed characteristics.

The researchers examined each brain in the data series and coded each characteristic [See box]. The consideration was that if the brains have internal cohesion, then characteristics that show differences between the sexes will be consistently male or female. It follows that very few minds will contain both female and male traits. But between 23% and 53% of brains (depending on the data series) contain characteristics from both ends of the spectrum. Brains that showed internal cohesion were rare, between 0% and 8% of those examined.

Yoel cites arguments in favor of single-sex classes as a realistic example of the importance of diversity. "[Same-sex education] assumes that boys have one set of characteristics - for example, they are more active and have less patience - and construct another set of characteristics. Therefore, they must be separated and each group treated differently. What we show is that although this is true At the group level, this is not true at the individual level. You cannot assign students to a group that is very active, for example in sports, and is not a fan of poetry, or to a group that is the mirror image. There are very few such children."

Most scientists believe that Yoel's study, which shows variation, is convincing. "Yuel's contribution was to show, for each individual, the diversity within gender," says Elliott. "No one has published [such] data before." But many believe that the measurements of internal cohesion are problematic. One response to Joel's article in PNAS was From Marco del Giudicefrom the University of New Mexico and colleagues. According to them, the definition used by Yoel and her colleagues for internal cohesion is so extreme that it is biologically improbable and perhaps even impossible. To prove this, they re-ran Yoel's data analysis, but used completely different sets of biological variables, and compared, for example, variation in facial features of three very different species of monkeys. If Yoel's method is correct, Del Giudice argued, then the facial features of the monkeys will show clear differences ("internal cohesion") between the strains.

Despite the clearly different appearance of the three strains, the characteristic facial features of each individual monkey often did not show internal cohesion, as defined by Yoel, and therefore in the opinion of the research community "biased". (In response, Yoel claims that while the internal cohesion in monkeys was low, the variation was zero when each species was examined separately, whereas in her own study, the variation, i.e. the mosaic, was more widespread than internal cohesion, "which supports our conclusions that the brains of women and men do not constitute separate populations in a way distinct.")

Her Mind His Mind: The notion that there are "female" and "male" brains is more entrenched in popular culture than in the scientific literature.

The debate focuses on the question of what is more important: the average or the details within the studied population. The answer often depends on the question being asked. But researchers can examine the same evidence and come to different conclusions. "The human brain may be a mosaic, but it is a mosaic with predictable patterns," they wrote Abram Holmes from Yale University and his colleagues in response to Joel in 2015, and they believe that these patterns warrant statistical consideration. to the biological Ann Fausto-Sterling, a retired professor of gender biology and development at Brown University, who is critical of research on gender differences, has a different point of view. "Regarding mean differences is misleading if that's all we're doing," she says. "The brain is not a uniform entity that behaves like something male or something female, and it does not behave the same way in all contexts. Yoel tries to explore the complexity of how the brain works."

This controversy has considerable consequences in science, especially in clinical research aimed at treating diseases. Between 1997 and 2000, ten drugs were withdrawn from the American market because of dangerous and even fatal side effects. Eight of the ten were more dangerous for women than for men. In 2013, the US Food and Drug Administration (FDA) halved the recommended dose for women of zolpidem, the generic name for Ambien, after female patients complained of drowsy morning commutes. Researchers discovered that in the morning the drug was still in the body of some of the women. Here, too, counterclaims appeared. Elliott and Sarah Richardson, a historian of science and gender at Harvard, argue that a significant part of the differences in zolpidem's side effects can be explained by differences in body weight. But weight is not the whole story, because the higher fat levels in women cause some of the drugs to break down more slowly in the body, but accurate identification of the variables that are really important for determining the dosage of the drugs should be feasible [see: "The medical and pharmaceutical treatment for women is different from that for men".]

As a response to these and other questions, the American Institutes of Health (NIH) demanded as of January 2016 that all pre-clinical studies, i.e. at the stage before testing in humans, must include female animals. Janine Clayton, director of the NIH's Office of Women's Health Research, was careful to say, when explaining the new policy, that the inclusion of both sexes in studies does not mean that we must look for gender differences. Many believe that this directive is an important step. McCarthy points out that some neurological diseases that start at a young age, such as attention and concentration disorder with hyperactivity or syndromes on the autistic spectrum, are more common in males, while neurological diseases that appear at a later age, such as depression or anxiety, are more common in females. "Faced with this situation, we have to look at the brain as a biological organ that has differences between males and females," she says. "Not to do so would be a crime." But Joel, Fausto-Sterling and others fear the pendulum will swing too far. They want to promote studies that include gender as a variable, with the same number of male and female subjects, but who also understand, at the stage of analyzing the results, that the categories "male" or "female" may reflect variables that have nothing to do with gender. In a broader context, if this research does change the way society treats sex and gender, it may be by changing terms. "It's time to throw out the word 'dimorphism,'" says Elliott. "A dimorphic structure is ovaries versus testes. A 2% difference in the ratio of gray matter to white matter is not dimorphic. It is simply a sex-dependent variation."

Dolek argues that there is a need for "a more refined way of defining these differences." In mice, she found that neural pathways that control male mating behavior are also found in females, while maternal behavior circuits are also found in males. "It would be a mistake to conclude from our study that there are no differences between males and females," says Dolek. "But the very interesting question is: how do these differences emerge, and how significant are they?"

McCarthy and Joel joined forces this year to design a more sophisticated work framework for defining the indicators in research on gender differences, and defining their meaning. They offer four possible dimensions: is the feature permanent or transient; Does it depend on the context; Does it have one of only two forms, and is therefore truly dimorphic, or is it on a spectrum of possibilities; And is it a direct or indirect result of the species. This way of describing the world of gender differences is not as catchy as the old Mars versus Venus metaphor, but it is probably much more accurate. In general, complexity reflects the person in a better way. "My mother is a very supportive and inclusive woman, but she is also much better than my father at spatial navigation," says Elliott. "It's a mosaic, isn't it?"