Neuroimaging studies of major depressive disorder (MDD) indicate interhemispheric differences in prefrontal cortical activity (right greater
than left). AIMS: To investigate whether there are any interhemispheric differences of motor cortical excitability in MDD. METHOD: Eight patients with
treatment-refractory MDD off medication were assessed for the severity of their depression, and transcranial magnetic stimulation studies (bilateral motor threshold and paired-pulse studies) were conducted. Eight normal controls were also studied. RESULTS: MDD patients showed significant interhemispheric differences in motor threshold and paired-pulse curves, both of which showed lower excitability on the left hemisphere. Such differences were absent in controls. CONCLUSIONS: Our findings may aid the further understanding of the
neurophysiology underlying MDD.