Brain flexibility increases during the peri-ovulatory phase of the menstrual cycle

The brain operates in a flexible dynamic regime, generating complex patterns of activity (i.e neuronal avalanches). This study aimed to describe how brain dynamics change according to menstrual cycle (MC) phases. Brain activation patterns were estimated from resting state magnetoencephalography (MEG) scans, acquired women at early follicular (T1), peri-ovulatory (T2) and mid-luteal (T3) phases of MC. We investigated the functional repertoire (number of ways in which large bursts of activity spread through the brain) and the region-specific influence on large-scale dynamics across MC. Finally, we assessed the relationship between sex hormones and changes in brain dynamics. A significantly larger number of visited configuration patterns, in T2 than in T1, in the beta frequency band was observed. No relationship between changes in brain dynamics and sex hormones was showed. Finally, we showed that, in the beta band, the left posterior cingulate gyrus and the right insula were more present in the functional repertoire in T2 than in T1, while the right pallidum was more present in T1 than in T2. In summary, we showed a hormone independent increase of brain dynamics during the ovulatory phase. Moreover, we demonstrated that several specific brain regions play a key role in determining this change. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement Ministero Sviluppo Economico; Contratto di sviluppo industriale Farmaceutica e Diagnostica (CDS 000606); European Union NextGenerationEU, (Investimento 3.1.M4. C2) of PNRR ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Local Ethics Committee of University of Naples Federico II (protocol n. 223/20) I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The data that support the findings of this study are available from the corresponding author, PS, upon reasonable request.