Examples of Sex Differences Flashcards
Cognition: Why is it unsurprising that studies demonstrating a neural level difference in verbal abilities have failed to replicate?
Verbal abilities differ between men and women by just 0.1 standard deviation, so it is not surprising that findings of sex-related differences in neural activation have failed to hold up to replication.
Cognition: IQ differences
Males show greater variability than females. Males and females have the same mean.
How do brain structures differ: sex-specific areas, volumes (2 weeks), cortical neurons, neuropil, maturation, Wernicke’s, OFC, HPC, amygdalae FMC. Grey /white matter and CSF (Gur et al., 1999); women = higher cerebral blood flow.
Sexually dimorphic regions regulate sex specific physiology/behaviour.
Average brain volumes significantly larger in men than in women (though proportionally similar in terms of most major subdivisions) from about 2 weeks of age. Men have more cortical neurons, while females have more developed neuropil (i.e. synaptically dense regions composed mostly of unmyelinated axons, dendrites, and cell processes). Female brains mature more rapidly. Women have a larger Wernicke’s area, orbitofrontal cortex, hippocampus. Male brains have larger amygdalae and frontomedial cortex.
Women have a higher percentage of grey matter, while men have a higher percentage of white matter and CSF (Gur et al., 1999).
Age-related volume: Young girl HPC (oestrogen synthesis/receptor mRNA; Hojo et al., 2004; Osterlund & Overstreet, 1999). Young male amygdalae (Giedd et al., 1997) androgen receptors in amygdalae (Clark, MacLusky, 7 Goldman-Rakic, 1988)
Age-related volume loss differs too. Young girls have larger hippocampal volume (interestingly where enzymes for oestrogen synthesis and oestrogen receptor mRNA have been localised; Hojo et al., 2004; Osterlund & Overstreet, 1999), whereas young males have larger amygdalae (Giedd et al., 1997). Androgen receptors appear to be more prevalent in the amygdala (Clark, MacLusky, & Goldman-Rakic, 1988).
• Hypothalamus also regulates sexual attraction, ovulation, pregnancy, milk let-down, vaginal contraction during birth, mother-offspring bonding, social/affiliative behaviours, reactivity to stress.
Age-related volume loss: Fronto/temporal (adult men), HPC & parietal lobe (adult women), female sex steroids?
Volume loss in whole brain, frontal, and temporal lobes increases with age in adult men, whereas volume loss in HPC and parietal lobes in women increases with age. This may be related to female sex steroids.
Key issues: exploitation of findings by non-scientists, e.g. Gurian & Annis (2008) justifies discrimination, 6x grey matter, 18% heavier, 9% taller.
o Research findings about sex differences have been distorted and exploited by non-scientists to an extraordinary degree, from education, parenting, to corporate leadership, and marital harmony- these “findings” have been used to validate various stereotypical practices that are discriminatory to both sexes. For example, claims about men having “approximately six and a half times more gray matter related to cognition and intelligence than women have” (Gurian & Annis, 2008) simply reflects overall sexual dimorphism- adult men are 18% heavier and 9% taller than women, and so their brains are larger, as are other organs like the heart and liver.
Key issues: corpus callosum, DeLacoste-Utamsing & Holloway (1982) –> then 49 studies (Bishop & Wahlsten, 1997)
o Beyond global differences in size and proportion, sex differences in specific brain structures have become more difficult to verify. For example, the widely-publicised notion that the corpus callosum is proportionately larger in females, arose from a small post-mortem study displaying a statistically marginal effect size (DeLacoste-Utamsing & Holloway, 1982). Though thoroughly challenged by a meta-analysis of 49 studies collectively showing no significant sex differences in volume or shape, the claim lives on as an explanation for female’s mythically superior multitasking abilities.
Issues: fear of controversial. small effect sizes. temporal specificity. Brain structure differences don’t necessarily predict behavioural differences. Differences are not deficiencies (Halpern). WEIRD samples.
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Issue: model organism studies typically use males (Neuroscience, 5.5:1, pharmacology, 5:1, physiology:, 3.7:1). Real effects: Anxiety in women (2.25X, Bekker et al., 2007), but animal studies on anxiety and anxiolytic drugs on rats (Palanza, 2001). Is there a reason to exclude females/
In the past half-century, male bias in non-human studies has increased while declining in human studies. Studies of both sexes frequently fail to analyse results by sex. Compromised understanding of female biology. The ratio of males to females is mostly skewed in neuroscience (5.5:1), pharmacology (5:1), and physiology (3.7:1).
Real effects: Women are diagnosed with anxiety disorders 2.25x more often than men (Bekker et al., 2007), but the majority of animal studies on anxiety and anxiolytic drugs focus on male rats (Palanza, 2001).
No reason to explicitly exclude females. If there is no convincing evidence of absence of sex differences in a particular trait, can combine into a single analysis group. When the status of sex differences is unknown, should explicitly compare groups side-by-side.
Psychiatric disorders: Female anxiety (GPD, PTSD etc.), why/
o Also in anxiety disorders including GPD, PTSD, etc. PTSD (women more likely to be subject to sexual trauma?).
Males: addiction, developmental disorders, why? Genetic predisposition/biology, ascertainment???
E.g. males perhaps more diagnosed with ASDs because they tend to display more overt and disruptive behaviours, closer conformation to the diagnostic “norm” (designed with males in mind, more male-biased autism research)? Males also tend to have more abstract (i.e. noteworthy) obsessions, females tend to have more “socially-acceptable” obsessions that are less likely to come to clinical attention. Gender difference in autism prevalence less pronounced than previously often thought: females buffered because they tend to display less language problems, and are better able to mirror the behaviour of healthy peers.
Sex-differences in psychiatric comorbidities- e.g. ADHD (inattentive subtype; externaising vs. internalising co-disorder).
Cohort of males with ADHD, low proportion will have inattentive. Much higher proportion of females with inattentive subtype.
Comorbidities in males with ADHD tend to be oppositional defiant disorders, behavioural problems, externalising disorders, whereas in females with ADHD they tend to be internalising disorders such as anxiety and depressive disorders.
Sex differences in neurobiology of bipolar (size; asymmetry; exaggeration)
In bipolar disorder, compare males with to those without, they tend to have larger brains with less asymmetry. Females with bipolar to those without, females with will have smaller brains with higher asymmetry. Effect of bipolar is to exaggerate sex effects of brain size, and diminish effects of brain asymmetry.
Sex difference in pharmaceutical response.
May be due to differing gastric emptying times, different stomach pH, different adipose levels, different expression of enzymes that metabolise drugs in the liver (common to many antidepressants such as citalopram, which have different effects in men and women).
