Interhemispheric transfer in alexithymia: a transcallosal inhibition study.

OBJECTIVE

This study investigates the hypothesis that alexithymia is associated with an interhemispheric transfer deficit via the corpus callosum (CC).

METHOD

The transcallosal inhibition paradigm was used to assess interhemispheric transfer. Transcranial magnetic stimulation (TMS) and peripheral electromyographic recordings were performed in 10 right-handed male and 10 female students with Toronto Alexithymia Scale (TAS-20) scores of > or = 61 and controls (TAS-20 scores of < 61). The transcallosal conduction time (TCT) reflects the TMS-induced inhibitory cortical activity that is mediated via the CC.

RESULTS

There was a significant interaction between gender and alexithymia (Wilks lambda = 0.89; F = 3.4; d.f. = 2, 57; p = 0.04) indicating that alexithymic males had shorter bidirectional TCTs than controls and a significantly shorter left to right TCT than controls (p = 0.002). However, the left to right TCT was not significantly different from the right to left TCT in alexithymic males (p = 0.39). Alexithymic females were not different from controls.

CONCLUSION

Our results clearly stand in contrast to the hypothesis of a transfer deficit due to a dysfunction of the CC in alexithymia. Facilitated, bidirectional transcallosal inhibition of the contralateral motor activity is associated with alexithymia in males. Facilitated cortical inhibition may be a neurobiological correlate of alexithymia.