TMS Intensity and Focality Correlation with Coil Orientation at Three Non-Motor Regions

Objective: The aim of this study is to define the best transcranial magnetic stimulation (TMS) coil orientations for three clinically relevant brain areas (pre-supplementary motor area, inferior frontal gyrus, and posterior parietal cortex) by means of simulations in 12 realistic head models of current density. Methods: We computed the current densities generated by TMS in our three volumes of interest (VOI) that were delineated based on published atlases. We then analyzed the maximum intensity and spatial focality for the normal and absolute components of the current density considering different percentile thresholds. Lastly, we correlated these results with the different anatomical properties of our VOIs. Results: Overall, the spatial focality of the current density for the three VOIs varied depending on the coil's orientation. There was major interindividual variability, and there was therefore no specific orientation that produced the best focality for all subjects. Further analysis showed that the differences in individual brain anatomy were related to the amount of focality achieved. In general, a larger percentage of sulci resulted in larger spatial focality. Moreover, larger normal current density intensity was achieved when positioning the coil axis perpendicular to the predominant orientations of the gyri of each 's VOI. Conclusion: For a rough approximation, better coil orientations can be based on the individual's specific brain morphology at the VOI. Moreover, TMS computational models should be employed to obtain better coil orientations in non-motor regions of interest. Significance: Finding better coil orientations in non-motor regions is a challenge in TMS and seeks to reduce interindividual variability. Our individualized TMS simulation pipeline leads to lesser interindividual variability in the focality, likely enhancing the efficacy of the stimulation and reducing the risk of stimulating adjacent, nontargeted areas. @font-face {font-family:Helvetica; panose-1:0 0 0 0 0 0 0 0 0 0; mso-font-charset:0; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:-536870145 1342208091 0 0 415 0;}@font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-536870145 1107305727 0 0 415 0;}@font-face {font-family:Calibri; panose-1:2 15 5 2 2 2 4 3 2 4; mso-font-charset:0; mso-generic-font-family:swiss; mso-font-pitch:variable; mso-font-signature:-1610611985 1073750139 0 0 159 0;}@font-face {font-family:Times; panose-1:0 0 5 0 0 0 0 2 0 0; mso-font-alt:Times; mso-font-charset:0; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:-536870145 1342185562 0 0 415 0;}p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin-top:0cm; margin-right:0cm; margin-bottom:8.0pt; margin-left:0cm; line-height:107%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri",sans-serif; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:Calibri; mso-fareast-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-fareast-language:EN-US;}.MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:11.0pt; mso-ansi-font-size:11.0pt; mso-bidi-font-size:11.0pt; font-family:"Calibri",sans-serif; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:Calibri; mso-fareast-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-fareast-language:EN-US;}.MsoPapDefault {mso-style-type:export-only; margin-bottom:8.0pt; line-height:107%;}div.WordSection1 {page:WordSection1;}