10/22/2012. Nature versus nurture Are boys and girls really different? Are differences age dependent? Are there cognitive and behavioral differences?

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1 Is anything new in the age-old battle between the sexes? DOES GENDER MATTER? The Neurobiology of Gender differences in Learning and Learning Disabilities Dr. Susan R. Grant Lutherville, Maryland,21093 USA Nature versus nurture Are boys and girls really different? Are differences age dependent? Are there cognitive and behavioral differences? Recent Neuroscientific Investigations into Sex- Brain Differences (Scientific American 2012) Neuroscience is better identifying and uncovering anatomical, chemical and functional differences in male and female brains. Variations occur throughout the brain in regions involved in memory, language, emotion, vision, hearing and navigation that are temporo-spatially different. Researchers are working to determine how these sex based variations relate to differences in male/female cognition and behavior. 1

2 Refining Definitions Biological sex: determined by sex chromosomes XX-female and XY-male. Includes genetic disorders in which sex chromosomes are missing or duplicated. Gender identity: subjective feelings of maleness and femaleness. (eg. Transsexuals, have normal chromosomes) Sexual orientation: supported by the wide spectrum of homosexual individuals. FOODFORTHOUGHT: Can Innate biological differences account for these statistics? Boys academic performance has dropped in the last 20 yrs. in American schools. According to the US Dept. of Education the average 11 th grade boy writes at the same level as the average 8 th grade girl. US Dept of Education projects that by 2011 there will be 140 female college graduates for every 100 male graduates. Casual or Co-Occurring? With the onset of puberty there is: rapid and disproportional increase in accidental deaths, suicide, substance abuse and violent offenses in males. disproportional increase in mood, anxiety and eating disorders in females. Sizable Brain Variations Parts of frontal cortex, the area of higher cognitive functions and limbic cortex, involved in emotional responses, are bulkier in women than men. Parietal cortex, which is involves in space perception and the amygdalainvolved in heart pumping/ adrenaline flowing emotionally arousing information, are bigger in men. 2

3 What accounts for sexual diversity? Some of the sexual anatomical diversity (evident in fetal development) may reflect the activity of the sex hormones that bathe the fetal brain. These steroids help to direct the organization and wiring of the brain during development. Correlations between brain region size in adults and sex steroid action in utero that are present at birth- suggest that some sex differences in cognitive function do NOT result from cultural influences or hormonal changes associated with puberty. Areas in the brain found to be different between men and women are the ones that in animal studies contain the highest number of sex hormone receptors during development. ( Jill Goldstein, Harvard Medical School) The Newest Neuroscientific Evidence: from the NIH (Raznaham, Lee, Stidd, etal.) We are now seeing the results of the first spatially detailed longitudinal MRI studies describing how the brains of human males and females grow differently. (We have known these differences in animals.) How do our brains differ? Let me count the ways! Chemical differences Hormonal differences Functional differences Structural differences Sex and sex steroids (hormones) shape brain development in a spatiotemporally specific manner. These changes in brain development change neural systems known to under underpin sexually different behaviors. 3

4 Sex differences in the brain diminish over time Brains of 9 year olds are remarkably different. Sex differences in the brain decrease after the onset of puberty when girls start making estradiol and other female hormones and boys start producing testosterone and other male hormones. By age 22 more than half the brain, including the frontal cortex shows no significant sex differences. (white areas on slide) If sex differences are negligible at birth and resulted from a sexist society then the neuroscience should find that sex differences in the brain would increase as a function of age, especially after the onset of puberty. (NIH findings suggest the opposite) Still-frame images from Movies S1 and S2 show how group differences in estimated mean cortical thickness between male and female subjects change between 9 and 22 y. Neural changes = Behavioral changes Delay of frontal maturation in males in subregions critical for self regulation may partially account for why males show more impulsive and risk taking behavior in adolescence than females. Prolonged cortical maturation in these critical frontal and prefrontal areas in males may lead to a longer window of opportunity for other genetic and environmental influences to accrue. In contrast to female advantage in prefrontal domains of cognition and behavior, male advantage is seen for parietal domain of visuospatial tasks (mental rotation skills) with male advantage increasing through puberty. Raznahan A et al. PNAS 2010;107: by National Academy of Sciences Biochemical and Anatomical Differences Sex differences in the brains chemistry influence stressreactions and how males and female respond to the environment, react to and remember events. Amygdala: larger in males and in animal studies see more serotonin receptors in males. (neurotransmitter that mediates emotion) Hippocampus: larger in females. In animal studies, a enriched environment increased dendritic tree cells in female with no change or slight pruning in males. The more we discover about how brain mechanisms of learning differ between the sexes, the more we will need to consider how optimal learning environments differ for boys and girls. ANIMAL STUDIES: Hippocampus of female shows a decrement in response to acute stress, but appears to be more resilient than male with chronic stress. Males rodents learn better in the face of stress. One second tail shocks increased density of dendritic connections but impaired performance and decreased connection density in female rodents. 4

5 Differences start early Boys and girls enter the classroom with different needs, different abilities and different goals and this persists through the school years. Males 2x as many conceptions as births 99% of speech comprehensible by 4yrs Play rough, competitive and aggressive Slower to acquire reading and writing skills More likely to ignore voices, even parents Females 25 % lower mortality rate 99% of speech comprehensible by 3yrs Play quieter more cooperative Reads better and sooner Hears equally well with either ear Do sex differences in brain anatomy mean there are sex differences in brain function Newborn girls hear better then newborn baby boys: An acoustic brain response at 1500Hz played to the right ear was 80% greater in the female newborn. Newborn baby girls have substantially more sensitive hearing at higher frequencies ( Hz). This is essential for speech discrimination. The female-male difference in hearing gets bigger as children get older. Consequences of gender differences in hearing Music therapy was more successful with premature girl babies. (Study does not look at differences in the kind of music used or the volume). Differences in how girls and boys hear or perceive sounds has implication in how you should talk to girls. Girls more likely to perceive an adult male voice as yelling. Preteen girls are more likely to be distracted by noise levels about 10 times softer than noise levels boys find distracting Sex differences in the visual system Visual System Differences The visual systems of boys and girls are biologically different: The male retina is thicker because it has many more M (magnocellular) cells which are wired primarily to rods and are sensitive to motion and direction, black and white. The female retina has predominantly the smaller P (parvocellular) cellswhich are primarily wired to the cones and compile information about texture and color. Predominant wiring to: Best at detecting: Answer question: Projects to: P Cells (more in females) cones Color and texture What is it? Inferior temporal cortex M Cells (more in males) rods Location, direction and speed Where is it going and how fast? Posterior parietal cortex 5

6 Implication of gender differences in the visual system In a study of 102 day old infants, boys were twice as likely to look at a dangling mobile than a female face. Boys are prewired to be more interested in moving objects and girls, in faces. Preschool girls more likely to select colors red, orange, green and boys more likely to draw motion, in colors of black, gray, silver that are sensitive to the M cell wiring. Girls draw nouns ; Boys draw verbs. Males Grade level differences Preschool: Stories action based. More speech problems. Grades 1-3: Better at math and 3 dimensional reasoning. 95% of hyperactive kids. Grades 4-6: Better at chess. Females Stories attend to feelings and human dynamics. Differentiates sound better. Better at verbal tasks, grammar, vocabulary. 5% of hyperactive kids. Better at foreign language. Grade level differences Male Upper School: Concentrates on career considerations. Social hierarchies tend to be stable. IQ scores rise between years. Female Concentrates on personal relationships. Social hierarchies tend to be fluid. Higher than normal estrogen level produces some intellectual disadvantages. The fact that each child is unique and complex should not negate the fact that gender and ageare two significant organizing principles in child development, and directly tied to their neurological development. Gray and White Matter matters Gray matter represents information processing centers and white matter is essential for networking or connections. These differences may help to explain why men tend to excel in tasks requiring more local processing, like mathematics, while women tend to excel at the integrating and assimilating of information as required by language facility. Neuro-anatomical differences in Intelligence (R. Haier) Men and women achieve similar IQ results yet very different brain region involvement. Men have 6.5 times the amount of gray matter related to intelligence. (gray= info processing centers) Women have 10 times the amount of white matter related to intelligence. (white= networking or connections between processing centers) 6

7 Regional differences with intelligence Brain difference in intelligence in males and females 84% of gray matter regions and 86 % of white matter regions involved in intelligence in women were in the frontal lobes. 45% of the gray matter regions and 0% of the white matter regions involved in intelligence in males were in the frontal lobes. Practical implications of gray-white regional differences In males the part of the brain where emotion happens (limbic/amygdala) is not well connected to areas where verbal processing and speech happen (frontal). Most 7 yr. old boys and girls can not tell you in detail why they feel sad, distressed, etc. Most 17 yr. old girls can explain how they feel in excruitiatingdetail, but no significant change associated with maturation in male. Writing assignments about feelings or characters emotions may be more difficult for boys. Brains are organized differently in males and females. The differences in what girls and boys can doand learn is not different. The differences in howthey do it can be very different. 7

8 Boys and girls behave differently because their brains are wired differently Play differently: Studies of 9-18 month olds show gender typical toy preferences long before they understand gender differences. Learn differently: Girls ask for help; boys ask as a last resort after exhausting other options. Hear and see world differently: Girls are prewired to look at the face (color, texture); boys are prewired to look at moving objects. Neurodevelopmental readiness The assumption behind the push to teach reading and writing in Pre-K and K is that earlier exposure will guarantee improved performance. The assumption is valid only if what is taught is neurodevelopmentally appropriate. The neurodevelopmentaltiming and learning receptiveness will be different for boys and girls. This applies to expectations for middle school and high school students to be independent, to self evaluate, reflect and predict and manage their time. Gender brain differences that may influence ADHD differences Female brain generally smaller except larger deep structures like the caudate & hippocampus Male brain has greater overproduction of cells in the frontal lobe that shrink as a result of pruning in adolescence resulting in decrease in hyperactivity behaviors Overproduction of dopamine receptors during prepuberty may account for higher incidence of hyperactivity and Tourettes Hormonal changes and receptor cell sensitivity to estrogen in girls may account for worsening of ADHD symptoms in puberty (mood swings, irritability, disorganization) Gender Differences in ADHD More common in males with 2:1 to 10:1 ratio depending on referral bias Males present with more aggressive and antisocial behavior Males have more associated conduct and opposition disorders Male symptoms of hyperactivity diminish with puberty Girls experience more peer rejection Girls show less hyperactivity Girls have more associated disorders of anxiety and depression which become more pronounced with puberty Emotional processing in the brain related to age and gender 7yr. olds-negative emotional activity to unpleasant visual images shows up in the deep structures of the amygdala. Adolescents-increased brain activity associated with negative emotion moves up to include cerebral cortical structures. MRI findings are similar in boys and girls This change occurs most strongly in girls. In males the part of the brain where emotion is registered is NOT well connected to the part of the brain responsible for verbal processing and speech Neuro-developmental Readiness in the Teen Brain (Giedd et.al.) Longitudinal MRI studies at NIMH reveal a second wave of overproduction of gray matter just prior to puberty, peaking in boys at 12 years and girls at 11 years. Even though the brain is maturing between 11 and 18 years, there is a lossof 1 % of gray matter each, the result of selective pruning. 8

9 Teachers and parents must adapt the environment so that differences don t become limitations. 9