[Paleopsych] SW: Gender and Brain Dysfunction

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Neuroscience: Gender and Brain Dysfunction

    The following points are made by Constance Holden (Science 2005
    1) Researchers are seeking biological reasons for the widespread
    gender differences in the prevalence and symptomatology of mental
    disorders. There is little debate that patterns of mental illness and
    disorders vary between the sexes. Women, for example, are more likely
    to get depressed. Men are more severely afflicted by schizophrenia.
    Females have more anxiety. Males exhibit more antisocial behavior.
    Most alcoholics and drug addicts are male; females have more eating
    disorders. Even suicide has a gender bias. Females make more attempts;
    males are more successful. Although culture helps shape how the two
    sexes express mental problems, some differences persist across
    cultures and across time. It's difficult to find any single factor
    more predictive for some of these disorders than gender.
    2) Talking about sex differences has long been taboo in some quarters
    -- people hear "sex differences" and think you're talking about
    individuals, not populations. There is a huge amount of variation
    within a population and overlap between populations. But neuroscience
    research, especially the explosion in brain imaging, has produced data
    that are hard to ignore. "Every time you do a functional MRI on any
    test, different parts of the brain light up in men and women," says
    Florence Haseltine, a reproductive endocrinologist at the National
    Institute of Child Health and Human Development (NICHD) in Bethesda,
    Maryland. "It's clear there are big differences." Understanding these
    differences will have implications for treatments of brain diseases
    and brain injuries.
    3) Most mental disorders are complex and resist the hunt for specific
    genes, yet family and twin studies have demonstrated significant
    heritability for them. These disorders interact with brain differences
    between the sexes that arise from genes on the X and Y chromosomes and
    from the bath of gonadal hormones that soak fetal brains early in
    gestation. Sex hormones are far-reaching in their powers. They are
    master transcription regulators; they affect hundreds of downstream
    genes. There is no question these are big players in mental disorders.
    These sex-related changes are sort of early filters, influencing the
    expression of underlying disorders in different ways.
    4) No one has managed to draw an unbroken line from prenatal
    development to adult behavior. But some researchers are now trying to
    tease apart just what aspects of brain anatomy and chemistry can help
    account for the gender skewing in mental disorders. Some studies are
    contradictory, and there is still more known about animals than about
    Science http://www.sciencemag.org
    Related Material:
    The following points are made by M. Rutter et al (J. Am. Med. Assoc.
    2004 291:2007):
    1) Are boys more likely than girls to have reading disability? The
    answer to this question has both theoretical implications (with
    respect to possible causal mechanisms) and practical implications
    (with respect to service provision). If boys are truly more likely to
    have reading disability, this would direct research attention to
    uncovering the possible source of the sex difference. Also, the sex
    difference would offer a window into the understanding of the causal
    processes involved in the origins of developmental reading
    disability.(1) In addition, if boys are more prone to have reading
    disability, this should motivate educational programs to address boys'
    early emerging disability. Given that reading disability in childhood
    is associated with adjustment problems and long-term adverse outcomes
    in multiple life domains,(2) the elucidation of this disability should
    constitute a high priority.
    2) Thirty years ago, epidemiological studies drew attention to the
    preponderance of male children with reading disability. Surveys both
    on the Isle of Wight and in an inner London borough(3) were consistent
    in showing that reading disability, whether assessed through group or
    individual tests, was substantially more frequent in boys than in
    girls. Moreover, the sex difference was evident whether reading
    disability was considered in terms of IQ-referenced (adjusted)
    specific reading retardation (in which reading was markedly lower than
    that predicted on the basis of age and IQ) or non-IQ-referenced
    general low achievement in reading. Thus, in the inner London sample
    of 10-year-olds, the rates of specific reading retardation on group
    tests were 16.9% in boys compared with 7.2% in girls. Using individual
    testing in those with positive screens on the group reading test, the
    rates were 4.6% vs 2.0%. The comparable data for Isle of Wight
    10-year-old boys and girls were 8.6% vs 3.7% on group tests and 5.6%
    vs 2.9% on individual tests.3
    3) When non-IQ-referenced reading disability was defined as
    performance at least 28 months behind population norms on either
    reading accuracy or reading comprehension, the male-female difference
    on group tests was 15.9% vs 7.2% in inner London, with 22.2% vs 15.6%
    on the basis of individual testing of those who had positive screens.
    The comparable Isle of Wight data were 8.6% vs 3.7% on group testing
    and 10.5% vs 6.1% on individual testing. The sample sizes in both
    cases were large: 1689 for the inner London 10-year-olds and 1142 for
    the Isle of Wight 10-year-olds.
    4) Some 15 years later, in 1990, Shaywitz et al,(4) reporting on a
    sample of 414 children aged 7 to 8 years, drew attention to their
    finding that the sex ratio in their epidemiological study was very
    much less than that in their sample of children identified on the
    basis of school records. Among the children in second grade, the rates
    were 8.7% in boys vs 6.9% in girls, and 1 year later (at a mean age of
    8.7 years), the comparison was 9.0% vs 6.0%.
    5) The authors summarize the history of research on sex differences in
    reading disability and provide new evidence from four independent
    epidemiological studies about the nature, extent, and significance of
    sex differences in reading disability. In all 4 studies, the rates of
    reading disability were significantly higher in boys. The authors
    conclude: "Reading disabilities are clearly more frequent in boys than
    in girls."(5)
    References (abridged):
    1. Rutter M, Caspi A, Moffitt TE. Using sex differences in
    psychopathology to study causal mechanisms: unifying issues and
    research strategies. J Child Psychol Psychiatry. 2003;44:1092-1115
    2. Snowling MJ. Reading and other learning difficulties. In: Rutter M,
    Taylor E, eds. Child and Adolescent Psychiatry, 4th Edition. Oxford,
    England: Blackwell Science; 2002:682-696
    3. Berger M, Yule W, Rutter M. Attainment and adjustment in two
    geographical areas, II: the prevalence of specific reading
    retardation. Br J Psychiatry. 1975;126:510-519
    4. Shaywitz SE, Shaywitz BA, Fletcher JM, Escobar MD. Prevalence of
    reading disability in boys and girls: results of the Connecticut
    Longitudinal Study. JAMA. 1990;264:998-1002
    5. Flannery KA, Liederman J, Daly L, Schultz J. Male prevalence for
    reading disability is found in a large sample of black and white
    children free from ascertainment bias. J Int Neuropsychol Soc.
    J. Am. Med. Assoc. http://www.jama.com
    Related Material:
    The following points are made by T. Canli et al (Proc. Nat. Acad. Sci.
    2002 99:11802):
    1) Emotionally arousing experiences are more memorable than neutral
    experiences. There is superior memory for traumatic relative to
    mundane events (1) and for emotionally provocative relative to neutral
    words (2) and pictures (3). Memory for emotional stimuli and
    experiences differs between the sexes (4,5). Women recall more
    emotional autobiographical events than men in timed tests, produce
    memories more quickly or with greater emotional intensity in response
    to cues, and report more vivid memories than their spouses for events
    related to their first date, last vacation, and a recent argument (4).
    2) Two explanations for the difference in memory performance have been
    proposed. The "affect-intensity" hypothesis posits that women have
    better memory because they experience life events more intensely than
    men and thus may better encode such events into memory (4).
    Controlling for affect intensity at encoding should therefore
    eliminate women's superior memory performance. The "cognitive-style"
    hypothesis posits that women may differ from men in how they encode,
    rehearse, or think about their affective experiences or in how they
    generate responses in a memory test (5). According to this view,
    controlling for affect intensity at encoding should not remove
    sex-based differences in memory performance.
    3) In summary: Psychological studies have found better memory in women
    than men for emotional events, but the neural basis for this
    difference is unknown. The authors report they used event-related
    functional MRI to assess whether sex differences in memory for
    emotional stimuli is associated with activation of different neural
    systems in men and women. Brain activation in 12 men and 12 women was
    recorded while they rated their experience of emotional arousal in
    response to neutral and emotionally negative pictures. In a
    recognition memory test 3 weeks after scanning, highly emotional
    pictures were remembered best, and remembered better by women than by
    men. Men and women activated different neural circuits to encode
    stimuli effectively into memory even when the analysis was restricted
    to pictures rated equally arousing by both groups. Men activated
    significantly more structures than women in a network that included
    the right amygdala, whereas women activated significantly fewer
    structures in a network that included the left amygdala. Women had
    significantly more brain regions where activation correlated with both
    ongoing evaluation of emotional experience and with subsequent memory
    for the most emotionally arousing pictures. Greater overlap in brain
    regions sensitive to current emotion and contributing to subsequent
    memory may be a neural mechanism for emotions to enhance memory more
    powerfully in women than in men.
    References (abridged):
    1. Christianson, S.-A. & Loftus, E. F. (1987) Appl. Cogn. Psychol. 1,
    2. LaBar, K. S. & Phelps, E. A. (1998) Psychol. Sci. 9, 490-493.
    3. Bradley, M. M. , Greenwald, M. K. , Petry, M. C. & Lang, P. J.
    (1992) J. Exp. Psychol. Learn. Mem. Cognit. 18, 379-390.
    4. Fujita, F. , Diener, E. & Sandvik, E. (1991) J. Pers. Soc. Pychol.
    61, 427-434.
    5. Seidlitz, L. & Diener, E. (1998) J. Pers. Soc. Pychol. 74, 262-271.
    Proc. Nat. Acad. Sci. http://www.pnas.org
    Related Material:
    The following points are made by E.V. Lonsdorf et al (Nature 2004
    1) The wild chimpanzees in Gombe National Park, Tanzania, fish for
    termites with flexible tools that they make out of vegetation,
    inserting them into the termite mound and then extracting and eating
    the termites that cling to the tool(1). Tools may be used in different
    ways by different chimpanzee communities according to the local
    chimpanzee culture(2).
    2) Chimpanzees use tools for more purposes than any other non-human
    species(3). The cultural variation in tool-use repertoires among
    chimpanzee communities may be attributable to individuals socially
    learning from other members of their community(2). The authors
    investigated this process in wild chimpanzees in Gombe National Park
    by videotaping 14 animals (who were all under 11 years old) and their
    mothers during termite-fishing sessions.
    3) There were no significant differences between the sexes in the
    frequency of social interaction with the mothers, and mothers did not
    show any difference in tolerance towards male or female offspring.
    Because active demonstration of nut-cracking by a chimpanzee mother in
    the Tai forest has been described(5), the authors looked for evidence
    of such behavior in mothers at Gombe. They saw no cases of active
    teaching, by mothers or any other individuals, which would have been
    indicated, for example, by the offering of tools or modification of
    offspring behavior.
    4) The authors conclude: "Our findings indicate that female
    chimpanzees start to fish for termites at a younger age than males;
    they are more proficient than males once they have acquired the skill;
    and they each use a technique similar to their mother's, although
    males do not. To our knowledge, this is the first systematic evidence
    of a difference between the sexes in the learning or imitation of a
    tool-use technique in wild chimpanzees. A similar disparity in the
    ability of young males and females to learn skills has been
    demonstrated in human children and may be indicative of different
    learning processes. A sex-based learning difference may therefore date
    back at least to the last common ancestor of chimpanzees and
    References (abridged):
    1. Goodall, J. Symp. Zool. Soc. Lond. 10, 39-48 (1963)
    2. Whiten, A. et al. Nature 399, 682-685 (1999)
    3. McGrew, W. C. Chimpanzee Material Culture: Implications for Human
    Evolution (Cambridge Univ. Press, Cambridge, 1992)
    4. McCulloch, C. E. & Searle, S. R. Generalized, Linear, and Mixed
    Models (Wiley, New York, 2000)
    5. Boesch, C. Anim. Behav. 41, 530-532 (1991)
    Nature http://www.nature.com/nature

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