Interhemispheric asymmetry of motor cortical excitability in major depression as measured by transcranial magnetic stimulation

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Abstract
Background 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.