On Tue, 27 Nov 2001, Jeff Ricker went:
> Yesterday, a therapist I know made the claim that recent research ("in
> the last 3 or 4 years") shows that the amygdala is much larger, on
> average, in males than in females ("about four times larger").
>
> I had never before heard that the amygdala is proportionally larger in
> males compared to females;
In three of the four studies whose abstracts I've appended below, it
_isn't_ larger. In one of those three, it's _smaller_.
> nor had I heard that the amygdala is thought to be important for
> differences in aggressive behavior (or that it is involved in
> aggressive behavior, at all).
It is involved in aggression, or parts of it are. Seizure foci in
parts of the amygdala can produce rage or aggression in humans;
accidental or surgical lesions of the amygdala can reduce aggression
in humans. But--
> He also stated that this size difference has been implicated in
> gender differences in aggressive behavior.
I can't find any studies supporting such a statement.
--David
Tebartz van Elst L. Woermann F. Lemieux L. Trimble MR.
Increased amygdala volumes in female and depressed humans. A
quantitative magnetic resonance imaging study.
Neuroscience Letters. 281(2-3):103-6, 2000 Mar 10.
Abstract
The amygdala is thought to play an important role in emotional
information processing. Studies indicate a link between amygdala
atrophy, fear and aggression and between amygdala hypertrophy and
depression. To investigate a possible relationship between amygdala
volumes, aggression and depression, we measured the amygdala of 62
patients with temporal lobe epilepsy (TLE) with and without
aggressive behavior or depression and 20 healthy volunteers using
quantitative MRI. Amygdala volumes of female patients (n=26) were
significantly larger than those of males (n=36) (left side: P=0.001;
right side P=0.05). Depressed patients displayed significant
enlargement of both amygdala (left side: P=0.008; right side:
P=0.001) There was no significant finding relating to the factor
aggression neither was there any significant interaction between
aggression, dysthymia and gender.
Institution
Epilepsy Research Group, Institute of Neurology, University College
London, Queen Square, London,
UK. [EMAIL PROTECTED]
Pruessner JC. Collins DL. Pruessner M. Evans AC.
Age and gender predict volume decline in the anterior and posterior
hippocampus in early adulthood.
Journal of Neuroscience. 21(1):194-200, 2001 Jan 1.
Abstract
[...] With recently refined MRI acquisition and segmentation
protocols, the hippocampus and amygdala of 80 subjects in early
adulthood (39 men and 41 women, age 18-42 years) were
investigated. Whereas the volume of the amygdala appeared to be
independent of age and gender, a significant negative correlation
with age for both left and right hippocampus was found in men (r =
-0.47 and -0.44, respectively) but not in women (r = 0.01 and 0.02,
respectively). [...]
Institution
McConnell Brain Imaging Center, Montreal Neurological Institute,
McGill University, Montreal, Quebec, Canada H3A
2B4. [EMAIL PROTECTED]
Goldstein JM. Seidman LJ. Horton NJ. Makris N. Kennedy DN.
Caviness VS Jr. Faraone SV. Tsuang MT.
Normal sexual dimorphism of the adult human brain assessed by in
vivo magnetic resonance imaging.
Cerebral Cortex. 11(6):490-7, 2001 Jun.
Abstract
The etiology and consistency of findings on normal sexual
dimorphisms of the adult human brain are unresolved. In this study,
we present a comprehensive evaluation of normal sexual dimorphisms
of cortical and subcortical brain regions, using in vivo magnetic
resonance imaging, in a community sample of 48 normal adults. The
men and women were similar in age, education, ethnicity,
socioeconomic status, general intelligence and
handedness. Forty-five brain regions were assessed based on
T(1)-weighted three-dimensional images acquired from a 1.5 T
magnet. Sexual dimorphisms of adult brain volumes were more evident
in the cortex, with women having larger volumes, relative to
cerebrum size, particularly in frontal and medial paralimbic
cortices. Men had larger volumes, relative to cerebrum size, in
frontomedial cortex, the amygdala and hypothalamus. A permutation
test showed that, compared to other brain areas assessed in this
study, there was greater sexual dimorphism among brain areas that
are homologous with those identified in animal studies showing
greater levels of sex steroid receptors during critical periods of
brain development. These findings have implications for
developmental studies that would directly test hypotheses about
mechanisms relating sex steroid hormones to sexual dimorphisms in
humans.
Institution
Harvard Medical School Department of Psychiatry at Massachusetts
Mental Health Center, Boston, MA 02115,
USA. [EMAIL PROTECTED]
Murphy GM Jr.
Title
The human medial amygdaloid nucleus: no evidence for sex difference
in volume.
Source
Brain Research. 365(2):321-4, 1986 Feb 19.
Abstract
The volume of the medial nucleus of the amygdala was determined in
the right and in the left hemispheres in 17 human brains ranging in
age from 35 weeks of gestation to 94 years of age. An analysis of
covariance which adjusted for differing age and brain size
distributions in the male and female samples showed no significant
sexual dimorphism in medial nucleus volume. This finding is
discussed in relation to evidence for sexual dimorphism in the
medial nucleus of the amygdala in animal brains.
---
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