Sex on the brain
Sex on the brain
WHAT do you think would happen if someone were to discover, god forbid, that either of the 2 Homo sapiens sexes is biologically more gifted than other?
Ever since Mary Wollstonecraft laid the foundation of feminism -- as we know it today -- late last century and right through suffragetism to the "60s women"s liberation movement to present day womanism, the debate on male-centric inequality has been swinging between militancy and quiet despair. And still we are no nearer an answer to the question of whether women and men are so radically different that no compromise will ever be possible.
It is a rare and certainly crazy scientist who would argue that there is physiologically no difference between the sexes (although this view had some currency a decade ago, based on foetal development). What is in dispute is the exact nature and magnitude of the differences.
It was almost pre-ordained that after knocking about the dispute had to finally come to rest in an area about which very little is known: the brain. This 2-decade-old complex and taxing discipline has been trying to find out whether there are intrinsic gender differences in the functioning of the human male and female brains. Today, the issue has become a mess of individual opinions, disputable findings and prejudices.
Indeed, in the opinion of one researcher, psychologist Diane Halpern of the University of Southern California, "The hostile and politically charged climate surrounding sex difference research has called into question the possibility of ever obtaining bias-free research."
The most striking, widely publicised and controversial study on sexual differences in the functioning of the human brain has come from a group of American researchers who say that men and women not only think differently but also use different portions of their brain to do the same things.
In order to track where specific language-related tasks were carried out, Sally Shaywitz and Bennit A Shaywitz of the Department of Neurology, Yale University School of Medicine, New Haven, Connecticut, and their colleagues scanned the brains of volunteers as they went about a variety of tasks.
They used functional magnetic resonance imaging (functional MRI) -- for detailed 3-dimensional pictures of the brain"s structures -- to watch grey matter in action, as 19 male and 19 female volunteers read pairs of nonsense words -- "lete and jete, loke and joke" -- flashed on a screen and determined whether they rhymed.
The Shaywitzes observed that in all the 19 men, a particular region behind the left eyebrow -- the left interior or frontal gyrus -- showed increased activity. This is close to "Broca"s area", which has long been thought to be associated with speech; 11 of the 19 women, however, used both this area and an area just behind the right eyebrow.
The Shaywitzes" findings, published in the recent issue of Nature***(when?), bolsters the notion that the brain concentrates language-related jobs on its left side more in men than in women. "We have demonstrated remarkable differences in functional organisation of a specific component of language that is phonological(eh?) processing between males and females," say Bennet and Sally Shaywitz.
The implications of this observation are both serious and curious: it could mean that in case of males, the brain is a house divided -- that is, the right portion does not know what the left is up to -- while in women, both sides function in close tandem with each other. The right side of the brain is supposed to be the seat of emotion. Perhaps women are very good at language -- since they draw on emotions (right brain) and reason (left brain) when articulating words. The language capabilities of a woman have a better chance of surviving a left brain stroke -- perhaps they can tap the language capacity of their right brain -- compared to men.
Interestingly, the findings of the Yale University team contradict an equally vociferous claim made from a similar study by the researchers from the Washington University School of Medicine in St Louis. The latter had presented their results at the Society of Neuroscience annual meeting in Miami in November 1994 -- 3 months before the Shaywitzes.
The Washington University team argued that that men and women may have different conversational styles, but they use the same parts of the brain to produce words. However, women may perform language-related tasks with much less effort than men, the study suggests.
"Our results argue against the idea that men and women use fundamentally different areas of brain in speech production," says Steven E Petersen, one of the study"s co-authors and associate professor at the Washington School.
He and his doctoral student Randy L Buckner examined positron emission tomography (PET) scans -- the latest in hi-tech imaging that allows researchers to study the brain in realtime action -- of 61 volunteers, as part of an ongoing effort to map the portions of the brain that produce language.
They found that the language task activates the same areas of the left prefrontal cortex in both males and females. "Little, if any, activity was seen in the right prefrontal cortex in either sex. And these findings apply only to language production. It is not yet known if male and female brains differ in the way they handle language comprehension," they say.
In another study, scientists led by Ruben Gur, director of the brain behaviour laboratory at the University of Pennsylvania School of Medicine, used PET scans to examine brain metabolism in 37 men and 24 women. "In our case, beyond the intrinsic interest in sex-related differences, a major motivation for looking into sex differences in brain function and behaviour comes from the substantial yet poorly understood sex differences in the manifestation of several brain disorders -- such as schizophrenia," Gur told Down to Earth.
Men, on an average, had higher brain activity in the more ancient and primitive regions of the limbic system that stresses physical action; women, on an average, had more activity in the newer and more complex parts of the limbic system -- the cingulate gyrus -- believed to be involved in symbolic forms of processing emotions, such as gestures and communication.
"These findings support the possibility that men are biologically more inclined to instrumental means of expression, such as physical aggression, while women are biologically more inclined to...refined, symbolic means of emotional expression," says Gur.
With the exception of the Shaywitzes, all other findings of differences in the brains or mental abilities of men and women have found that there is an amazing degree of overlap. How have similar studies, employing the latest brain imaging techniques, come up with totally divergent results?
P N Tandon, professor-emeritus, department of neurosurgery, All India Institute of Medical Sciences (AIIMS), New Delhi, explains, "The methodology of interpreting the similar data could give different results, depending upon the predilections of the researchers."
In brain research, there is no single, absolutely correct interpretation of a scan. Several brain states could give much the same results and the researcher may have to chose one that seems more likely. In the opinion of H S Gill, senior advisor, neurosurgery, Army Hospital, New Delhi, "Techniques such as PET scans and functional MRI are very sensitive -- even a small body movement can sometimes give a flurry of false readings."
Gender research on mice & men
The first-ever scientifically researched difference in the mammalian brain was discovered in 1972 by Oxford anatomists Geoffery Raisman and Pauline Field. They reported in Science that male rats had fewer connections linking the 2 halves of the hypothalamus -- seated deep inside the brain and controlling basic behavioural drives such as hunger and sex -- than females. Two years later, they found that rodent brain structures could be changed by changing sex hormone levels, writes Vithal C Nadkarni in his book, The Serpent Within. The recent studies, which scanned the brains of adults whose brains are the product of years of conditioning, are silent on the issue. Some researchers have argued that differing patterns of abilities between the 2 sexes reflect different hormonal influences over their developing brains. In mammals, including humans, an embryo has the potential to be either a male or a female. Early in life, the sex hormones -- estrogens, in case of females, androgens, in case of males -- help in establishing the sexual differentiation.
Scientists believe that not only do sex hormones achieve transformation of the genitals, they also organise male and female behaviourisms early in life. To test this hypothesis, Roger Gorsky, professor of anatomy and cell biology at the University of California in Los Angeles, carried out an experiment: he cut off the supply of androgens to newborn rats at birth. He found that in the first 24 hours, the castrated offsprings lost half the neurons in a region of hypothalamus called the sexual dimorphic nucleus, or SDN. The SDN of male rats is 5 times larger than those in females. This structural difference was absent in castrated infant rats, which had brains similar to the females.
Gorski also discovered that a single injection of the male sex hormone testosterone could restore the splayed rodents into fullblown maleness when administered immediately after birth. But the injection is ineffective if given after first 5 days of birth, he says.
It would be specious to directly extrapolate the research findings from mice to humans. And ethics prevents scientists from researching into how a human foetus brain would react if its hormone exposure was changed.
Fortunately, says Gorski, the potential existence of structural sex differences in the human brain is virtually predicted from work in other animals: "I think it"s a really fundamental concept, and I am sure, without proof, that it applies to our brains."
Nature Vs nurture
Psychological and behavioural studies have indicated that men and women have different intellectual capabilities. For instance, women have been found to outperform men in verbal tasks, arithmatic calculations and in recalling major landmarks in a route; while men, on an average, excel in certain spatial tasks, mathematical reasoning and navigating their way through a route. How do we know whether these are inborn traits or they are acquired by the child when he or she is raised?
Some scientists have reported that sex differences in problem solving do not appear until puberty, indicating that lifestyle may have a role to play in the shaping of an individual. They also concede that hormonal levels and their effects can be influenced by environment and ways of life such as occupation and stress.
But others argue that genetics -- rather than environment-- has a more pronounced role to play in the shaping of an individual. Gill says, "the genes determine the basic attributes in an individual. Environment polishes them. There is no denying that both are important. But genetics has a much greater role to play".
Diane Lunn, from the University of Western Ontario in London, Canada, found three year old boys to be better at targetting than girls of the same age. Similar findings have reported by Kimberly A Kerns and Shere A Berenbaum of the Chicago University, who found that sex differences in spatial rotation performance are present before puberty.
Bulk of evidence, however, suggest that effects of sex hormones on brain organisation occur so early in life that from the start the environment is acting on differently wired boys and girls. This makes it difficult to evaluate the effects of experience independent of physiological predisposition.
"It is really an issue to which there is no clear answer", says Gur. Though our findings, he explains, supports the neuro-biological basis of some sex differences in males and females, effects of upbringing and environmental factors cannot be ruled out.
"Automatically, when people hear something is `biological", they think it can"t be environmentally influenced", says Gur. "But there is nothing to rule out that this is life time conditioning, versus the way people are born".
Gur points out that much of brain"s structure and function is thought to be inherited, but the organ changes under conditioning. Responding to demands the brain can produce physical changes in the blood flow, energy use and the way cells behave.
Tandon agrees. He says, "the phenomena of human existence and experience are always simultaneously biological and social. Any explanation must involve both".
It is clear that there exist fundamental disagreements among researchers on the degree to which biology and environment, when considered independently, contribute to the making of an individual.
Criticism of sex-based studies
The subject of sex differences in the brain probably attracts almost as much inflammatory rhetoric as the `science" of differences in IQ among the blacks and Whites. Though the brain-imaging techniques currently in vogue are the latest and very sophisticated, yet no matter how `scientific" such studies get, this research holds enough surprises to trigger-off sceptical reactions. (SEE BOX: The brain behind history). The critics complaints about research on this subject fall in four broad categories: misuse of statistical methods, failure to clearly state what the structural differences in male and female brains actually mean, bias in the selection of cases and control, and inadequate sample sizes of volunteers for research.
Moreover, the research findings have very often been smirched and sullied by overinterpretation and unjustifiable interpretation of data, making it a perpetually controversial field of enquiry. For instance, there have been claims that women are less intelligent because their brain size is smaller than those of men.
Neuroscientists say that the average weight of a woman"s brain is about 10 per cent that of a man"s. In modern man, the brain at birth is 350 grams in weight -- as large as that of a full grown orangutan. At maturity, the average weight of man"s brain is 1450 grams. "An elephant has a brain size much greater than the humans. Does it mean that the animal is more intelligent?", enquires Gill.
"There is no reason to think that either sex is inherently more intelligent because of the brain size", says Issac Asimov, a renouned science writer, in his book The Human Brain. Russian novelist, Ivan Turgenev, for instance, had a brain that was just over 2000-gram mark in weight, but Anatole France, also a skilled Russian writer, had one that was just under 1200-gram mark.
The troubles are further exacerbated by the failure of scientists to state the exact implications of their research findings. As scientists grope for more evidence, different groups continue to ask: what are the functional significance of these differences?
While stressing extreme caution in drawing conclusions from the research, the Shaywitzes say, "what it means is that we finally have the tools in hand to begin answering the questions". Like the Shaywitzes, Roger Gorky is also wary of drawing conclusions. "What happens is that people overinterpret these things. Brain is a very complicated thing, and even in animals that we have studied for so many years now, we really don"t know the function of many brain areas", he says.
Third, some critics argue that studies in sex differences in the human brain do not account for the bias of the researchers. Typically, most of these studies have been undertaken in institutions, which are usually teaching hospitals. "Volunteers who are referred there for a particular research are not at random", they argue.
Finally, even a very carefully conducted study faces a constant criticism of having an inadequate sample size of volunteers. Says Madhuri Behari, addtional professor in the department of neurology, AIIMS, "these studies are not conclusive. The findings may not be equally applicable to all men and women".
Ethics of gender research
There are no dearth of people willing to speculate on the functional significance of the differences -- an area which neuroscientists fear to tread.
"Remember, what happened in the Nazi-Germany; Hitler tried to prove that Jews are an inferior race and attempted to have them exterminated. Such studies can also be used against women", says Urmila Garg, an eminent Delhi-based Hindi novelist.
A volunteer of a women"s welfare organisation, Saheli, is even more sceptical. "They have been doing such research for donkeys-years and have so often come up with ridiculous findings. Once you accord a scientific basis to the claims that one gender is capable of doing a particular job much better than the other, you open up the possibilities of discrimination", she says.
But it is not only women but also men who are equally vulnerable. Madhu Kishwar, editor of a popular women"s magazine Manushi, explains that a phobic respose to these kinds of studies would show a lack of confidence. She believes that it is not necessary that research findings could be misused against only women. Men are equally vulnerable, she says.
"I don"t have the phobia that all research is necessarily a conspiracy against women. We are aware of the external differences between the two sexes. I would love to know more about the internal differences. But the studies should take into account the bias of the researchers", Kishwar adds.
Major sex differences in intellectual functions, explains Doreen Kimura, professor of psychology and honorary lecturer in the department of clinical neurological sciences at the University of Western Ontario, in London, Canada, seem to lie in patterns of ability rather than over all level of intelligence. "We are all aware that people have different intellectual strengths. In the same fashion, two individuals may have same overall intelligence but have varying patterns of ability", she says. Neurologists are very cautious to comment. Gill believes that these studies have immense medical utility and should be encouraged. "All the organs of the human body have been studied thread-bare, with the exception of brain", he argues.
Once sex differences in intellectual abilities gets a scientific basis, won"t it used as an instrument of discrimination? "Not really. we already have the concept of aptitude tests in jobs. Such studies may help in providing a more scientific basis to the aptitude tests", says Gill.
Sandra J Witelson, professor of psychiatry at the McMaster University in Hamilton, Ontario, told the Scientific American, " the sexes are different and it does no good to assume they are not. We are not going to help equal opportunity and equal recognition when we assume both are equally good at all aspects, when it may well be that there are certain things each sex is somewhat better at".
P N Tandon does not discount the possibilities of these studies being misused. "Any scientific study has a very strong risk of being misused, particularly if the interpretation of the research findings are extended to absurd levels. Reductionist interpretation of these studies can cause great harm", he says.
Some neuroscientists believe that a code of ethics could revolve around negating the element of exciement and hence, has to be both philosophical and managerial effort. Through philosophy, scientists would know how to go about such research and the limitations that it entails. It has to be a managerial effort so that there is a compulsory, and stringent peer review of the findings by mix of experts from the scientific community as well as non-expert community, both having adequate representation researchers from either sex.
A characteristic feature of present day research, explains Gill, is the unavoidability of a laboratory work being immune from expert and peer review as well as a feedback of opinions from a variety of non-expert opinion. Any research finding or a body of opinion has never succeeded in gaining a foothold, until it has been examined thoroughly by an epistemic community -- a body of transnational researchers and opinion makers. Such a kind of epistemic community has evolved in feminist sociology and politics -- as has been seen since the onset of the Women"s Liberation Movement.
Despite such sobering opinions, the genie of ethical ueasiness over research on sex differences in the human brain cannot be wished away. Many people fear that attempts to give gender differences, either cultural or behvioural, a mooring in biology may sparkoff an absurd gender-war.
What with the unreliable and interpretative nature of this knowledge of this knowledge and the society"s penchcant for hijacking it as scientific basis for deeply rooted prejudices, the neuroscientists will have to exercise extra-caution while making public their research findings. The main intention is to preserve the objectivity of such research and preventing racists, fascists, chauvnists and feminists from using them to create societal schisms.