The Cortex-based Alignment Approach to TMS Coil Positioning

Abstract

TMS allows noninvasive manipulation of brain activity in healthy participants and patients. The effectiveness of TMS experiments critically depends on precise TMS coil positioning, which is best for most brain areas when a frameless stereotactic system is used to target activation foci based on individual fMRI data. From a purely scientific perspective, individual fMRI-guided TMS is thus the method of choice to ensure optimal TMS efficiency. Yet, from a more practical perspective, such individual functional data are not always available, and therefore alternative TMS coil positioning approaches are often applied, for example, based on functional group data reported in Talairach coordinates. We here propose a novel method for TMS coil positioning that is based on functional group data, yet only requires individual anatomical data. We used cortex-based alignment (CBA) to transform individual anatomical data to an atlas brain that includes probabilistic group maps of two functional regions (FEF and hMT+/V5). Then, these functional group maps were back-transformed to the individual brain anatomy, preserving functional-anatomical correspondence. As a proof of principle, the resulting CBA-based functional targets in individual brain space were compared with individual FEF and hMT+/V5 hotspots as conventionally localized with individual fMRI data and with targets based on Talairach coordinates as commonly done in TMS research in case only individual anatomical data are available. The CBA-based approach significantly improved localization of functional brain areas compared with traditional Talairach-based targeting. Given the widespread availability of CBA schemes and preexisting functional group data, the proposed procedure is easy to implement and at no additional measurement costs. However, the accuracy of individual fMRI-guided TMS remains unparalleled, and the CBA-based approach should only be the method of choice when individual functional data cannot be obtained or experimental factors argue against it.

A probabilistic atlas of the human motion complex built from large‐scale functional localizer data

“…Recent methodological advancements have improved our understanding of the coupling in the hMT+ through in vivo multimodal imaging of the individual brain (Duecker et al, 2014;Dumoulin et al, 2000;Van Essen et al, 2012). This approach provides the most precise way to characterize the structural-functional coupling because all data are acquired in the same individual.…”

“…While ITS-AOS junction is prominently identifiable in every brain, it shows morphological variability from one hemisphere to the next (Dumoulin et al, 2000;Malikovic et al, 2007). Moreover, the exact location of the hMT+ relative to the ITS and AOS varies widely among individuals (Duecker et al, 2014;Dumoulin et al, 2000;Malikovic et al, 2007; Van Essen, Glasser, Dierker, Harwell, & Coalson, 2012). Most brain functional imaging studies have used functional localizers to define the hMT+ in each individual brain and then explore the functional properties of hMT+ across participants.…”

“…Moreover, the exact location of the hMT+ relative to the ITS and AOS varies widely among individuals (Duecker et al, 2014;Dumoulin et al, 2000;Malikovic et al, 2007; Van Essen, Glasser, Dierker, Harwell, & Coalson, 2012). To the best of our knowledge, only recently have three studies attempted to develop functional probabilistic atlases (or maps) of the hMT+ (Duecker et al, 2014;Frost & Goebel, 2012;Wilms et al, 2005). As a result, very little effort has been devoted to building a functional hMT+ atlas that could help characterize the spatial consistency and variability of functional hMT+ among individuals.…”

“…As a result, very little effort has been devoted to building a functional hMT+ atlas that could help characterize the spatial consistency and variability of functional hMT+ among individuals. To the best of our knowledge, only recently have three studies attempted to develop functional probabilistic atlases (or maps) of the hMT+ (Duecker et al, 2014;Frost & Goebel, 2012;Wilms et al, 2005). However, the very small sample size (about 10 participants) used in these studies limited the development of reliable statistical representations of spatial consistency and variability in the hMT+ for whole populations.…”

Relax ! Don’t do it …

“…Unlike Talairach coordinates, the CBA method takes the macroanatomical differences of participants into account by aligning the individual anatomical data with pre-existing functional data in a surface space. Therefore, this method preserves a functional-anatomical correspondence, resulting in a higher spatial stimulation specificity over the region of interest and consequently stronger TMS effects (Duecker, et al, 2014).…”