Journal: Brain Stimulation 7:19 (2014)
Authors: A Ginou, Y Roth, A Zangen
Traditionally TMS treatment sessions for MDD were administered over the DLPFC using a focal superficial figure-8 coil. Recently the FDA has cleared deep TMS treatment for MDD using BrainsWay H-coil, following a large double-blind, placebo-controlled,multi-center study. The induced electric field characteristics, stimulated brain structures and clinical outcomes are very disparate between the two methods.
To compare the induced electric field characteristics of a standard figure 8 coil and the dTMS H1-coil.
Electric field characteristics of figure-8 coil and of the H1-coil were measured in a realistic head model filled with physiologic saline concentration, and maps of field distribution were produced. We review several studies discussing brain structures and networks which are relevant for clinical outcome in MDD, and discuss the implications of the spatial characteristics of each TMS coil.
Where using 120% of MT the H1-coil induces supra-threshold fields at depth of 1.8 cm and significant sub-threshold field at depth of 3.2 cm, compared to 0.7 cm and 0.7 cm for the figure-8 coil. Various studies have shown that deeper PFC structures have significantly more connections with other reward system sites compared to superficial PFC. The H1-coil induces also significantly wider stimulation compared to the figure-8 coil. Recent studies suggest that stimulation of PFC structures with extensive connections to the subgenual cingulate may be crucial for the antidepressant action of standard TMS. It was shown that the exact location of these structures varies greatly between individuals.
Since standard TMS coils exert a focal and superficial stimulation, optimal stimulation targets may be easily missed with standard coils. This and the depth differences might contribute to the large efficacy differences found in DBPC multi-center studies with Deep TMS compared to standard TMS.