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Abstract:
We previously reported sex differences in the
neurocognition of language. Converging evidence from
psycholinguistic, neuropsychological and electrophysiological
studies indicated that women tend to memorize at least certain
complex linguistic representations (e.g., walked) in a
temporal-lobe based lexical/declarative memory system, whereas
men generally compute them compositionally (walk + -ed) in
real-time with a frontal/basal-ganglia grammatical/procedural
system (1, 2).
We predicted these findings on the basis of a
previously-demonstrated female advantage at remembering words
(3). This advantage depends on declarative memory,
especially the hippocampus (4, 5). Word-learning and
hippocampal sex differences are linked to estrogen.
Estrogen improves word memory in women (6, 7) and men (8), and
strengthens hemodynamic, physiological and biochemical correlates
of hippocampal learning (9, 10). Testosterone, which is the
main source of estrogen in men, improves their word memory
(11).
Estrogen levels in males are lower than in
females, prior to menopause (3). Thus our findings could be
explained by organizational sex differences in utero or by
differences in circulating estrogen levels during childhood,
resulting in a greater tendency of girls than boys to memorize
complex forms. Additionally, perhaps both sexes memorize
complex forms, but females have superior lexical retrieval
abilities, possibly due to higher levels of estrogen.
To examine these issues, we carried out a
randomized, double-blind, placebo-controlled study in which 12
elderly men and 10 age-matched post-menopausal women were given
hormone replacement therapy (women: estrogen; men: testosterone)
and placebo, each for three months. They were tested on
past-tense production after each three-month period.
Hormone therapy in both sexes led to an increase
in the production rate of real and novel irregular forms
(break-broke, spling-splung), p<.05, with no interaction
between treatment (placebo/hormone) and sex (male/female).
This suggests that estrogen in women and testosterone in men
improve memory retrieval or processing. The absence of a
treatment-by-sex interaction indicates that the two hormones have
similar effects, suggesting the same mechanism --- presumably
estrogen-modulated --- in the two cases. Performance at
novel regulars (plagged) decreased with hormone therapy
(p<.05; no interaction with sex), likely due to increased
irregularizations (plag-plog). Thus the sex hormones do not
ameliorate grammatical/procedural functions. Importantly,
accuracy at real regulars (swayed) increased in women but
decreased in men as a result of hormone therapy (treatment-by-sex
interaction, p=.057) --- supporting the view that women but not
men memorize complex forms. In summary, estrogen in women
and testosterone in men improve lexical retrieval/processing but
not rule-based computations.
References
[1] M. T. Ullman (2001). Nature
Reviews Neuroscience, 2, 717-726.
[2] M. T. Ullman et al., (submitted).
[3] D. Kimura (1999). Sex and
Cognition. The MIT Press, Cambridge.
[4] L. R. Squire, B. J. Knowlton
(2000). In The New Cognitive Neurosciences, M. S. Gazzaniga
(Ed.), pp. 765-780. The MIT Press, Cambridge, MA.
[5] T. Pfluger et al. (1999).
Epilepsia, 40, 414-423 (1999).
[6] P. M. Maki, A. B. Zonderman, S. M.
Resnick (2001). American Journal of Psychiatry, 158,
227-233.
[7] B. B. Sherwin (1996). Proceedings
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[8] C. Miles, R. Green, G. Sanders, M. Hines
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[9] C. S. Woolley, P. A. Schwartzkroin
(1998). Epilepsia, 39, S2-8.
[10] P. M. Maki, S. M. Resnick (2000).
Neurobiology of Aging, 21, 373-383.
[11] M. M. Cherrier et al. (2001).
Neurology, 57, 80-88.
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