title: Transcallosal inhibition across the menstrual cycle: a TMS study.
abstract: OBJECTIVE
  To determine if there are steroid-dependent changes in transcallosal transfer during the menstrual cycle in normal women.
  
  
  METHODS
  We tested 13 normally cycling women during the menstrual, follicular and midluteal phases. Blood levels of estradiol (E) and progesterone (P) were determined by radioimmunoassay. Ipsilateral tonic voluntary muscle activity suppression, called ipsilateral silent period (iSP), was evoked by applying transcranial magnetic stimulation (TMS) over the left motor cortex and by measuring the EMG of the ipsilateral first dorsal interosseus (FDI) muscle. Both iSP-duration and transcallosal conduction times were measured and related to cycle phase and steroid levels.
  
  
  RESULTS
  Duration of iSPs varied over the cycle with largest differences between follicular and midluteal phases. During the midluteal phase high levels of P were significantly related to short iSPs. This relation also applied to E levels and iSPs during the follicular phase.
  
  
  CONCLUSIONS
  Our study shows for the first time that the transcallosal transfer is modulated by E and P and changes over the menstrual cycle.
  
  
  CONCLUSIONS
  It is suggested that gonadal steroid hormones affect the interhemispheric interaction and change the functional cerebral organization sex dependently via its neuromodulatory properties on GABAergic and glutamatergic neurons.
authors.affiliation: Biopsychology, Institute for Cognitive Neuroscience, Ruhr-University Bochum, GAFO 05/620, 44780 Bochum, Germany. markus.hausmann@ruhr-uni-bochum.de
authors.forename: M
authors.initials: M
authors.lastname: Hausmann
authors.forename: M
authors.initials: M
authors.lastname: Tegenthoff
authors.forename: J
authors.initials: J
authors.lastname: Sänger
authors.forename: F
authors.initials: F
authors.lastname: Janssen
authors.forename: O
authors.initials: O
authors.lastname: Güntürkün
authors.forename: P
authors.initials: P
authors.lastname: Schwenkreis
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D003337:Corpus Callosum / Q000502:physiology / Q000528:radiation effects*; D004576:Electromyography / Q000379:methods; D004958:Estradiol / Q000097:blood; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D007266:Inhibition, Psychological; D016014:Linear Models; D008597:Menstrual Cycle / Q000097:blood / Q000528:radiation effects*; D009044:Motor Cortex / Q000502:physiology / Q000528:radiation effects*; D018482:Muscle, Skeletal / Q000502:physiology / Q000528:radiation effects; D011374:Progesterone / Q000097:blood; D011863:Radioimmunoassay / Q000379:methods; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation
chemical_list: D011374:Progesterone; D004958:Estradiol