How far can TMS coils be optimized? A partial resolution

摘要

A long-standing goal of TMS researchers has been to preserve focality of stimulation while allowing penetration to deep brain regions, and a remarkable variety of innovative coil designs has been directed towards that end. Unfortunately, as economists are fond of telling us, "there's no free lunch." Deng et al. show that, overall, coils inducing Fig. 8 electric field patterns produce more focality relative to depth than coils inducing a circular electric field pattern. But the fundamental tradeoff is inflexible: the ability to directly stimulate deeper brain structures is obtained at the expense of inducing wider electrical field spread, and all coil designs tend to converge at depths of more than a few centimetres. Issues of relative efficiency and safety remain unsettled. But when it comes time to select TMS coils for specific applications, Peterchev and his colleagues have provided a much clearer pathway.