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WIREs Cogn Sci
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Hormonal effects on the plasticity of cognitive brain functions

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Abstract Sex hormones have powerful neuronal actions in the brain and affect the interaction between functionally linked cortical areas within and across cerebral hemispheres, probably via their neuromodulatory properties on gamma‐aminobutyric acid and glutamate receptors. Menstrual cycle‐related dynamic fluctuations in functional cerebral asymmetries and interhemispheric crosstalk have been shown to be a useful experimental model to investigate the activating effects of sex hormones on cognitive brain functions, particularly those of estradiol and progesterone. Besides a better understanding of sex hormonal effects on cognitive brain functions, this research may significantly contribute to addressing the question of whether sex differences in cognitive brain functioning truly exist and where they originate from. Copyright © 2010 John Wiley & Sons, Ltd. This article is categorized under: Psychology > Brain Function and Dysfunction Neuroscience > Cognition

The menstrual cycle. Schematic illustration of fluctuations in sex hormone (E, estradiol; P, progesterone) and gonadotropin levels (LH, luteinizing hormone; FSH, follicle‐stimulated hormones) during an average 28‐day menstrual cycle. LH and FSH secretion by the pituitary gland determines the menstrual cycle. Cycle day 1 is defined by the discharge of blood from the nonpregnant uterus. During the menstrual phase (1), cycle day 1–5, the concentrations of E and P are lowest. Beginning with cycle day 6, E level continuously increases, approaching its maximum about 1 day before ovulation (follicular phase; 2). P level remains low during the follicular phase. About 14 days after menstruation begins, LH secretion initiates ovulation (3). E level drops slightly. After ovulation, the small cells that surround the egg undergo chemical changes (luteinization). During this luteal phase, E and P are secreted by the luteinized cells. About 7–8 days postovulation, E level approaches its second maximum, this time together with P. P level reaches its peak at around cycle day 22 (midluteal phase, 4). Levels of E and P fall rapidly between cycle day 24–28 (premenstrual phase, 5) and a new cycle begins.7.

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Functional imaging and connectivity analysis (adapted from Ref 20). The most significant activation during word‐matching as compared to rest across cycle phases in 14 normally cycling women was located in left inferior frontal gyrus (IFG) (a). A seed region was defined in each female participant as a sphere around the individual local maximum located closest to the maximum of the group activation. Then, a psychophysiological interaction (PPI) analysis was used to identify those brain regions on which the seed region exerts a significantly stronger inhibitory influence for word matching during the menstrual phase as compared to the follicular phase. The only such region was located in right IFG (b). The activation maps [conjunction analysis at p < 0.01, corrected for multiple comparisons in (a), PPI analysis at p < 0.01, corrected for multiple comparisons in (b)] are shown overlaid onto a canonical brain rendered in three dimensions. The anatomical location of the most significant activation in left IFG (shown in black) and the area in right IFG which is inhibited more significantly during the follicular phase (shown in white) are shown overlaid onto the mean high‐resolution T1 scan of the female group at the maximum of the left IFG activation (c) and the maximum of the inhibited area (c). Reproduced by permission of The Journal of Neuroscience.

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Schematic illustration of the hypothesis of progesterone‐modulated interhemispheric inhibition. (a) The process of interhemispheric inhibition. Although the corticocortical transmission is mainly excitatory, the main and longer lasting effect in the contralateral hemisphere appears to be inhibitory, probably because most excitatory callosal fibers terminate on pyramidal neurons which then activate inhibitory interneurons. These activated inhibitory cells could then induce a widespread inhibition in homotopic regions of the contralateral hemisphere. According to Hausmann and Güntürkün,11,12 progesterone reduces corticocortical transmission during the midluteal phase by suppressing the excitatory responses of neurons to glutamate and by enhancing their inhibitory responses to GABA. The combined effect would result in the functional hemispheric decoupling and thus to a temporal reduction in functional asymmetry (b).

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Psychology > Brain Function and Dysfunction

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