Navigated transcranial magnetic stimulation (nTMS) enables precise targeting of the induced electric field to selected cortical targets found by alignment of the head with a 3-D model of the subject’s brain. This is particularly important in studies of patients as some diseases, such as brain tumors, may modify the brain anatomy and function so that the external skull landmarks are not any more aligned with the brain structures. Comparison with the preoperative nTMS and intraoperative direct electrical cortical stimulation (DECS) localization of hand muscle cortical representations has given distances of 3-12 mm between the two methods. Preoperative nTMS mapping is associated with smaller craniotomies and more extensive resections of tumors. Mapping of speech areas with nTMS during videoed object naming is less specific but more sensitive than DECS and produces reliable “negative” maps: if speech nTMS does not find an active area from the area to be resected, DECS findings are highly improbable as well. The first study of clinical impact infers that speech nTMS is associated with smaller craniotomies and less postoperative speech dysfunctions. Good understanding of the relation of nTMS activation sites with those obtained by DECS adds attractivity of the use of nTMS also in the basic research of brain functions.

Peer reviewed