Interhemispheric integration during the menstrual cycle: failure to confirm progesterone-mediated interhemispheric decoupling

A recent theory proposed that high levels of progesterone during the menstrual cycle may lead to functional decoupling of the cerebral hemispheres [Neuropsychologia 38 (2000) 1362]. The present study tested this theory with a well-validated behavioral measure of interhemispheric communication administered to 55 naturally-cycling women at the luteal or menstrual phase of the cycle. Neither between-subjects nor within-subjects analyses found significant differences in interhemispheric communication between the menstrual and luteal phases (F < 1). Correlations between salivary progesterone levels and interhemispheric communication also failed to support the theory. Although negative affect (NA) was associated with decreased effectiveness of interhemispheric communication, mood variables could not account for the lack of relationship between hormonal and interhemispheric variables. In summary, despite a rigorous and valid test, the theory that progesterone leads to interhemispheric decoupling found no support.