Brain Sex Differences
Your
gender, whether you are a boy or girl, man or woman, is one of the most
salient and enduring identifying features one possesses. The term
gender is unique to humans as it incorporates both self and societal
perceptions of one’s sex, which is either male or female. Thus, studies
of animals address sex differences, whereas studies of humans may
involve either or both gender and sex. One’s sex is determined on
several levels that can be summarized as ‘the three Gs’ – genes, gonads,
and genitalia (Joel, 2012).In the overwhelming majority of cases, these three variables align such that an XX individual will develop ovaries and female genitalia whereas an XY individual will develop testis and male genitalia and this will in turn inform gender. Thus, sex and gender are internally consistent. But is this also true for the sex/gender of the brain? That boys and girls, men and women, behave differently is so self-evident as to be hardly worth stating. But this easy generality is in reality highly nuanced and complex in both its origins and manifestations. In what ways are men and women’s brains really different? And why are they different? Is it biology? Culture? Society? Experience? Or some combination thereof?
Only in animals can we hope to tease out truly biological sources of variation in male and female brains and the first experimental evidence of this comes from the publication of the now iconic paper of Phoenix, Goy, Gerall, and Young (1959). This study of guinea pigs established that the sensitivity of adult animals to either male (testosterone) or female (estradiol and progesterone) hormones and the induction of sexual behavior were dependent upon the hormonal milieu experienced early in life, with the authors asserting that the neural substrate controlling behavior had been ‘organized’ (Figure 1).
This was a heretical idea at the time but in hindsight is entirely consistent with other sensitive periods in brain development that alter adult neural function, as well as newly emerging ideas about early life programming that impacts all manners of adult responding including energy utilization, stress responding, and immune system activation (Bale et al., 2010). The authors made the even further heretical assertion that testosterone and its metabolites alter the structure or function of the neural correlates of sexual behavior. Today, we fully embrace the notion that steroids act on the brain to modify neural structure and function, regardless of whether one accepts this contributes to sex differences in behavior. In fact, the more we look, the more we find. But not all sex differences are made equal, and some may have evolved in order to appear only in response to challenge or to compensate for the costs of reproduction that differ in males and females (McCarthy et al., 2012 and McCarthy and Konkle, 2005).
Brain Mapping: An Encyclopedic Reference offers foundational knowledge for students and researchers across neuroscience. With over 300 articles and a media rich environment, this resource provides exhaustive coverage of the methods and systems involved in brain mapping. Brain Mapping fully links the data to disease (presenting side by side maps of healthy and diseased brains for direct comparisons), and offers data sets and fully annotated color images. Each entry is built on a layered approach of the content – basic information for those new to the area and more detailed material for experienced readers. Edited and authored by the leading experts in the field, this work offers the most reputable, easily searchable content with cross referencing across articles, a one-stop reference for students, researchers and teaching faculty.
Brain Sex Differences
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Abstract Read the full article on Brain Sex Differences by M.M. McCarthy here.
Once
thought of as narrowly limited to reproduction, sex differences in the
brain are now emerging as fundamental to a wide swath of neural
functioning. Elucidating the cellular mechanisms of how sex differences
are established during development provides novel insights into the
brain of both sexes. Critical variables include cell death and cell
survival pathways, neuroimmune and inflammatory mediators,
endocannabinoids, and epigenetics. Gender biases in the risk of
neuropsychiatric and neurodegenerative disorders highlight the intrinsic
value of elucidating the biological origins of sex differences in the
brain.
Keywords
- Amygdala;
- Androgens;
- Astrocytes;
- Chromosome compliment;
- Estrogens;
- GABA;
- Hippocampus;
- Hypothalamus;
- Microglia;
- Prostaglandins
Vitae
Margaret McCarthy
received a BA and MA in biology from the University of Missouri -
Columbia and a PhD from the Institute of Animal Behavior at Rutgers
University, Newark NJ. She received postdoctoral training at Rockefeller
University from 1989 to 1992 and spent one year at NIH as a National
Research Council Fellow. McCarthy joined the faculty of the University
of Maryland School of Medicine in 1993 and was a professor in the
Department of Physiology for 18 years before becoming the Chair of the
Department of Pharmacology in 2011. She continues to hold secondary
appointments in the Departments of Physiology and Psychiatry. McCarthy
was the Director of Graduate Education for the Program in Neuroscience
from 2002 – 2005 after which she served as an associate dean with
responsibility for the Graduate Program in Life Sciences which oversees
the training of 400 MS and PhD students and 350 postdoctoral fellows.
She has received numerous awards and recognition for her mentoring of
graduate students.
McCarthy has a long standing interest in
the cellular mechanisms establishing sex differences in the brain. She
uses a combined behavioral and mechanistic approach in the laboratory
rat to understand both normal brain development and how these processes
might go selectively awry in males versus females. She has published
over 170 peer-reviewed manuscripts on these topics. Her research has
been continuously funded by the NIH since 1994 and that same year she
received the Frank A. Beach Award in Behavioral Neuroendocrinology. She
is a past editor of Endocrinology and is currently an associate
editor of the Journal of Neuroscience and is on the Advisory Board for
eNEURO. She is also a former associate editor of Hormones and Behavior,
past secretary of the Society for Behavioral Neuroendocrinology, and
president-elect of the Organization for the Study of Sex Differences and
named one of Maryland's Top 100 Women in 2009.
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