development of the amygdala. The amygdala is larger, relative to total gray matter, in
boys by age 9 than its adult size but is similar to its adult size, relative to total gray
matter, by age 9 in girls. In contrast, in adulthood, the amygdala in women comprises
a greater percentage of the volume of total gray matter than it does in men. In
addition, other brain regions show different developmental patterns in boys and girls
(e.g., the hippocampus, caudate, pallidum, dorsolateral and orbital frontal cortices,
and parahippocampal white matter). This may result in differential consequences for
men and women in the prevalence and expression of psychiatric disorders with
neurodevelopmental origins, depending on the timing of the putative insults to these
brain regions.”
JILL M. GOLDSTEIN, PH.D., DAVID N. KENNEDY, PH.D., VERNE S. CAVINESS, JR., M.D.,
D.PHIL. Boston, Mass. Am J Psychiatry 156:3, March 1999
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The striking quantity and diversity of sex-related influences on brain function
indicate that the still widespread assumption that sex influences are negligible cannot
be justified, and probably retards progress in our field.
Functional and structural dimorphisms Sex differences exist in every brain lobe,
including in many ‘cognitive’ regions such as the hippocampus, amygdale and
neocortex. Sex differences can also be relatively global in nature. For example,
widespread areas of the cortical mantle are significantly thicker in women than in
men. Ratios of grey to white matter also differ significantly between the sexes in
diverse regions of the human cortex. In many cases, the differences are not evident in
overt anatomical structure, but in some type of functional dimension (hence the
distinction above between ‘functional’ and ‘structural’ dimorphisms). For example, a
region may differ between the sexes in aspects of its neurotransmitter function, or in
its genetic or metabolic response to experience. Furthermore, new methodological
approaches — from gene modification in mice to voxel-based morphometry analyses
of human imaging data — are revealing previously undetected sexual dimorphisms1.
It seems that the sexual dimorphisms uncovered so far, abundant as they may be,
represent only a fraction of the sexual dimorphisms that are likely to exist in the
brain.
Neurochemical sexual dimorphisms Sexual dimorphisms occur in a wide array of
neurotransmitter systems, including serotonin, GABA (γ-aminobutyric acid),
acetylcholine, vasopressin, opioids and monoamines. Again, as a full treatment of this
topic is outside the scope of this review, I briefly highlight a few salient findings ... sex
differences in brain neurochemistry are proving to be much more pervasive than has
been assumed by many. The implications of sex influences for understanding and
treating disease states are considerable. Many CNS related disorders show sex
differences in their incidence and/or nature. These diseases include, but are not