Motor cortical excitability and clinical response to rTMS in depression

Background: The relationship between frontal lobe activity in the left and right hemispheres and the pathophysiology of depression remains unclear. In addition, it is uncertain whether levels of frontal or motor cortical excitability relate to clinical response to treatment modalities. We aimed to explore whether motor cortical excitability as assessed with single and paired pulse transcranial magnetic stimulation (TMS) could be used to predict the response to treatment with repetitive TMS (rTMS) applied to the left or right prefrontal cortex. Methods: Motor thresholds, cortical excitability and cortical inhibition (CI) were assessed prior to a trial of rTMS in patients with treatment resistant depression. Results: There was no consistent pattern of differences in hemispheric activity, although there was a relationship between the degree of psychopathology and cortical excitability (right hemisphere) and an inverse relationship between inhibitory activity and clinical response (left hemisphere). Conclusions: The study does not support a simple model of laterality in motor cortical excitability in depression. The TMS measures used in this study appear to be of limited use in the prediction of clinical response to rTMS.