Changes in physiological, EEG and psychological parameters in women during the spontaneous menstrual cycle and following oral contraceptives.

In a controlled cross-over design study performed with 14 female subjects, serum hormone levels, the EEG and a number of performance tests were recorded during spontaneous and oral contraceptive-controlled menstrual cycles. The mean alpha-frequency showed cyclic changes, i.e. slower alpha-waves during the follicular phase and faster alpha-waves during the luteal phase. Smaller cycle stage-dependent differences in the power of the theta- and beta-bands also were noted. An increase in several performance task scores was noted during the periovulatory period, whereas lowest performance scores were recorded during the late luteal and early menstrual phases. No such effects were observed in the same subjects while they were taking oral contraceptives. These results demonstrate that the gross electrical activity of the brain changes in a parallel with changed hormone levels. The changes in performance tests coincide with increasing or decreasing alpha activities in the EEG. The common underlying mechanism may be an activation of central nervous system monoaminergic pathways which are known to be involved in steroid feedback.