Transcallosal inhibition across the menstrual cycle: a TMS study

Area of Science:

• Neuroscience
• Endocrinology
• Human Physiology

Background:

• The menstrual cycle involves fluctuating hormone levels, including estradiol and progesterone.
• Hormonal changes may impact central nervous system function and interhemispheric communication.

Purpose of the Study:

• To investigate steroid-dependent alterations in transcallosal transfer during the menstrual cycle.
• To determine if estradiol and progesterone levels correlate with changes in brain pathway function.

Main Methods:

• Studied 13 normally cycling women across menstrual, follicular, and midluteal phases.
• Measured blood levels of estradiol and progesterone via radioimmunoassay.
• Assessed transcallosal transfer using the ipsilateral silent period (iSP) evoked by transcranial magnetic stimulation (TMS).

Main Results:

• Ipsilateral silent period (iSP) duration varied significantly across the menstrual cycle.
• High progesterone levels in the midluteal phase correlated with shorter iSPs.
• Estradiol levels in the follicular phase also showed a significant relationship with iSP duration.

Conclusions:

• Transcallosal transfer is modulated by estradiol and progesterone, changing throughout the menstrual cycle.
• Gonadal steroids may influence interhemispheric interaction and functional brain organization.
• These hormonal effects on the brain could be mediated by neuromodulatory actions on GABAergic and glutamatergic neurons.