Electric field measurement of two commercial active/sham coils for transcranial magnetic stimulation.

ABSTRACT: OBJECTIVE:Sham TMS coils isolate the ancillary effects of their active counterparts but typically induce low-strength electric fields (E-fields) in the brain, which could be biologically active. We measured the E-fields induced by two pairs of commonly-used commercial active/sham coils. APPROACH:E-field distributions of the active and sham configurations of the Magstim 70?mm AFC and MagVenture Cool-B65 A/P coils were measured over a 7 cm-radius, hemispherical grid approximating the cortical surface. Peak E-field strength was recorded over a range of pulse amplitudes. MAIN RESULTS:The Magstim and MagVenture shams induce peak E-fields corresponding to 25.3% and 7.72% of their respective active values. The MagVenture sham has an E-field distribution shaped like its active counterpart. The Magstim sham induces nearly zero E-field under the coil's center, and its peak E-field forms a diffuse oval 3-7?cm from the center. Electrical scalp stimulation paired with the MagVenture sham is estimated to increase the sham E-field in the brain up to 10%. SIGNIFICANCE:Different commercial shams induce different E-field strengths and distributions in the brain, which should be considered in interpreting outcomes of sham stimulation.

SUBMITTER: Smith JE 

PROVIDER: S-EPMC6125221 | biostudies-literature | 2018 Oct

REPOSITORIES: biostudies-literature