Menstrual Cycle Modulation of Verbal Performance and Hemispheric Asymmetry

Background/Objectives: It has been postulated that sex differences in certain types of verbal abilities arise from sex-dimorphic patterns of hemispheric activation, and that these patterns might be modulated by circulating levels of sex hormones. The aim of this study was to explore the activational effects of sex hormones (throughout the menstrual cycle) on both verbal performance and functional hemispheric asymmetries (qEEG laterality) in three types of verbal tasks: sex-differentiated (verbal fluency and semantic decision) vs. sex-neutral (verbal reasoning) tasks. Methods: A group (n = 32) of healthy young women was tested twice, once during the mid-luteal (high levels of circulating sex hormones) and once during the early follicular (low levels of sex hormones) phases of the menstrual cycle. A comparable group of healthy young men (n = 32) was tested once. EEG was continuously recorded. The differences in alpha power on homologous sites of the left and right hemispheres were then calculated. Results: We found a clear congruence between performance on a task and laterality score: for sex-differentiated tasks, the activational effects of sex hormones were observed in both performance and laterality scores, while there were neither performance nor laterality scores shifts throughout the menstrual cycle for the sex-neutral task. Interestingly, measures of functional asymmetry were higher in the luteal compared to the menstrual phase. Conclusions: These findings suggest that sex hormones modulate verbal performance through their influence on hemispheric asymmetry.