Optimal transcranial magnetic stimulation coil placement for targeting the dorsolateral prefrontal cortex using novel magnetic resonance image-guided neuronavigation.

The dorsolateral prefrontal cortex (DLPFC) has been implicated in the pathophysiology of several psychiatric illnesses including major depressive disorder and schizophrenia. In this regard, the DLPFC has been targeted in repetitive transcranial magnetic stimulation (rTMS) studies as a form of treatment to those patients who are resistant to medications. The '5-cm method' and the '10-20 method' for positioning the transcranial magnetic stimulation (TMS) coil over DLPFC have been scrutinised due to poor targeting accuracies attributed to inter-subject variability. We evaluated the accuracy of such methods to localise the DLPFC on the scalp in 15 healthy subjects and compared them with our novel neuronavigational method, which first estimates the DLPFC position in the cortex based on a standard template and then determines the most appropriate position on the scalp in which to place the TMS coil. Our neuronavigational method yielded a scalp position for the left DLPFC between electrodes F3 and F5 in standard space and was closest to electrode F5 in individual space. Further, we found that there was significantly less inter-subject variability using our neuronavigational method for localising the DLPFC on the scalp compared with the '5-cm method' and the '10-20 method'. Our findings also suggest that the '10-20 method' is superior to the '5-cm method' in reducing inter-subject variability and that electrode F5 should be the stimulation location of choice when MRI co-registration is not available.