Functional equality in RTs is present in luteal women, when progesterone is elevated. A decline in progesterone in early follicular women correlates
with functional inequality visualized by larger latency in RTs in right compared to left hemifield presentation. Thus, at the behavioral level right hemisphere is dominant in attention tasks. Dominance of right hemisphere has been Selleck Z-VAD-FMK identified in several attention tasks (Petersen and Posner, 2012 and Somers and Sheremata, 2013). Mutual inter-hemispheric inhibition at the physiological level is visualized in differences in ERP or alpha-amplitude. Ipsilateral alpha amplitude is larger in right than left visual field presentation. This asymmetry in amplitude is statistically significant in luteal women. Thus, suppression of the dominant right hemisphere requires
synchronization of a larger inhibitory neuronal network than suppression of the subdominant left hemisphere. One interpretation of larger right hemisphere synchronization is that subdominant areas in the left hemisphere may trigger synchronization of a larger inhibitory network in the dominant, right hemisphere when progesterone is elevated. An alternative interpretation is that the dominant right hemisphere suppresses the subdominant left hemisphere more efficiently and, thus, decreases interferences in information processing. In both cases, progesterone find more enhances synchronization in alpha frequency band and therefore leads to suppression of irrelevant information in the ipsilateral hemisphere and minimizes interferences between cerebral hemispheres. Thus, our findings may contribute to elucidate an interesting paradox regarding the impact of sex hormones on functional cerebral asymmetry and physiological hemisphere laterality. On the one hand, the progesterone-mediated interhemispheric decoupling model by Hausmann and Güntürkün predicts that an increase in progesterone decrease hemisphere asymmetry (Hausmann
and Güntürkün, 2000). This model PRKD3 states that hemispheres are coupled when the dominant hemisphere suppresses homotopic areas of the subdominant hemisphere. Glutamatergic neurons, projecting form the dominant to the subdominant hemisphere, synapse on pyramidal neurons, which activate GABAergic neurons. An increase in progesterone decouples cerebral hemispheres and, thus, decreases functional cerebral asymmetry. Accordingly, functional cerebral asymmetry is only detectable in menstrual cycle phases with low progesterone level (Hausmann and Güntürkün, 2000). On the other hand, the Hampson model predicts that an elevation of ovarian sex hormones facilitates left hemisphere processing. Accordingly, hemispheric lateralization is associated with an increase in sex hormones (Hampson, 1990). In conclusion, we suggest that functional cerebral asymmetry at the behavioral level in early follicular women is related to dominance of the task specific hemisphere.