Verbal and music dichotic listening tasks reveal variations in functional cerebral asymmetry across the menstrual cycle that are phase and task dependent.

Two dichotic listening tests, one a verbal consonant-vowel identification task, the other a musical chord recognition task, were administered to 32 women at two points during the menstrual cycle, menses (when oestrogen is low) and the midluteal phase (when oestrogen is high), in a counterbalanced repeated measures design. The degree of asymmetry changed across the cycle for both syllables and music. The right ear advantage recorded for the verbal task was greater during the midluteal phase than during menses. The left ear advantage recorded for the music task was greater during menses than during the midluteal phase. These reciprocal changes in asymmetry were the result of consistent changes in ear performance. From menses to the midluteal phase, left ear (right hemisphere) performance fell significantly for both tasks whereas right ear (left hemisphere) performance showed a small, but non-significant, increase. The findings are discussed in the light of evidence for phasic activational effects of gonadal steroids on both asymmetry and cognition which provide an explanation for the sometimes elusive nature and small effect size of sex differences in these characteristics. The relationships between sex differences in asymmetry and cognition are re-examined.