Intra- and interobserver variability of language mapping by navigated transcranial magnetic brain stimulation

Background: Repetitive navigated transcranial magnetic stimulation (rTMS) has been used for studying language organization in healthy volunteers and patients, and to detect cortical areas involved in language processing. However, little is known about the reliability of this method. To determine the reliability of rTMS language mapping, we conducted both an interobserver and an intraobserver investigation. Methods: Ten right-handed healthy subjects underwent language mapping by rTMS and the same object-naming task three times. Intraobserver and interobserver reliability of seven different error types were tested by two investigators. Analysis was performed blinded to the previous results and stimulated cortical sites. Results: Overall, the results of both the interobserver and the intraobserver investigations show variable accordance. This is demonstrated by comparing the error rates of all different error types of the three examinations. Considering the most important error type, no response, there is only small variability in inter-and intraobserver mapping. Conclusions: With our current protocol, interobserver and intraobserver comparisons only corresponded partially. Thus, although rTMS seems a promising method for preoperative planning as well as neuropsychological research, the current protocol needs further improvement.