An efficient and accurate new method for locating the F3 position for prefrontal TMS applications

The International 10-20 system is a method for standardized placement of electroencephalogram (EEG) electrodes. The International 10-20 system correlates external skull locations with the underlying cortical areas. This system accounts for variability in patient skull size by using certain percentages of the circumference and distances between four basic anatomic landmarks. This international 10-20 system has recently been used in transcranial magnetic stimulation (TMS) research for locating specific cortical areas. In the treatment of depression (and some types of pain), the desired placement of the TMS coil is often above the left dorsalateral prefrontal cortex (DLPFC), which corresponds to the F3 location given by the International 10-20 system. However, for an administrator with little experience with the International 10-20 system, the numerous measurements and calculations can be excessively time-consuming. In addition, with more measurements comes more opportunity for human error. For this reason, we have developed a new, simpler, and faster way to find the F3 position using only three skull measurements. In this article, we describe and illustrate the application of the new F3 location system, provide the formulas used in the calculation of the F3 position, and summarize data from 10 healthy adults. After using both the International 10-20 system and this new method, it appears that the new method is sufficiently accurate; however, future investigations may be warranted to conduct more indepth analyses of the method's use and potential limitations. This system requires less time and training to find the optimal position for prefrontal coil placement and it saves considerable time compared with the International 10-20 EEG system.

Keywords: transcranial magnetic stimulation, F3, International 10-20, electroencephalogram, coil positioning