[Paleopsych] SW: Gender and Brain Dysfunction
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Neuroscience: Gender and Brain Dysfunction
http://scienceweek.com/2005/sw050819-1.htm
The following points are made by Constance Holden (Science 2005
308:5728):
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
humans.
Science http://www.sciencemag.org
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Related Material:
MEDICAL BIOLOGY: SEX DIFFERENCES READING DISABILITY
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.
2000;6:433-442
J. Am. Med. Assoc. http://www.jama.com
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Related Material:
SEX DIFFERENCES IN THE NEURAL BASIS OF EMOTIONAL MEMORIES.
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,
225-239.
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
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Related Material:
COGNITIVE SCIENCE: SEX DIFFERENCES IN CHIMPANZEE LEARNING
The following points are made by E.V. Lonsdorf et al (Nature 2004
428:715):
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
humans.(3,4)
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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