Description:
<jats:title>Summary</jats:title><jats:p><jats:bold>Objective </jats:bold> The pathophysiology of catamenial diseases such as epilepsy is unclear. Therefore, we investigated changes in cortical excitability during anovulatory and ovulatory cycles.</jats:p><jats:p><jats:bold>Patients and methods </jats:bold> Using transcranial magnetic stimulation (TMS), eight healthy women were investigated during anovulatory and 12 during ovulatory cycles. On days 8, −14, −7 and 2 of the cycle, resting motor threshold (RMT), cortical silent period (CSP), intracortical inhibition (ICI) and intracortical facilitation (ICF) were investigated. Repeated‐measures analysis of variance (<jats:sc>anova</jats:sc>) and nonparametric methods were used for statistical analysis.</jats:p><jats:p><jats:bold>Results </jats:bold> A trend was seen for group by phase interaction regarding ICI (<jats:italic>F =</jats:italic> 2·5, <jats:italic>P</jats:italic> = 0·10). ICI varied during anovulatory cycles (median: 51·0% on day 8; 45·3% on day −14, 51·0% on day −7, and 28·6% on day 2; <jats:italic>P</jats:italic> = 0·040), mainly because of an increased inhibition on day 2. ICI was more pronounced in anovulatory cycles on day −14 (<jats:italic>P =</jats:italic> 0·021), −7 (<jats:italic>P =</jats:italic> 0·048) and 2 (<jats:italic>P =</jats:italic> 0·018) compared to ovulatory women who did not show intraindividual changes (<jats:italic>P =</jats:italic> 0·56). RMT, CSP and ICF showed no significant changes during anovulatory or ovulatory cycles.</jats:p><jats:p><jats:bold>Conclusions </jats:bold> The results suggest fluctuations in cortical excitability during anovulatory cycles, possibly due to the withdrawal of ‘excitatory’ oestrogens that initiate menses in anovulatory cycles.</jats:p>