Optimizing Functional Accuracy of TMS in Cognitive Studies: A Comparison of Methods

Abstract

Transcranial magnetic stimulation (TMS) is a tool for inducing transient disruptions of neural activity noninvasively in conscious human volunteers. In recent years, the investigative domain of TMS has expanded and now encompasses causal structure-function relationships across the whole gamut of cognitive functions and associated cortical brain regions. Consequently, the importance of how to determine the target stimulation site has increased and a number of alternative methods have emerged. Comparison across studies is precluded because different studies necessarily use different tasks, sites, TMS conditions, and have different goals. Here, therefore, we systematically compare four commonly used TMS coil positioning approaches by using them to induce behavioral change in a single cognitive study. Specifically, we investigated the behavioral impact of right parietal TMS during a number comparison task, while basing TMS localization either on (i) individual fMRI-guided TMS neuronavigation, (ii) individual MRI-guided TMS neuronavigation, (iii) group functional Talairach coordinates, or (iv) 10-20 EEG position P4. We quantified the exact behavioral effects induced by TMS using each approach, calculated the standardized experimental effect sizes, and conducted a statistical power analysis in order to calculate the optimal sample size required to reveal statistical significance. Our findings revealed a systematic difference between the four approaches, with the individual fMRI-guided TMS neuronavigation yielding the strongest and the P4 stimulation approach yielding the smallest behavioral effect size. Accordingly, power analyses revealed that although in the fMRI-guided neuronavigation approach five participants were sufficient to reveal a significant behavioral effect, the number of necessary participants increased to n = 9 when employing MRI-guided neuronavigation, to n = 13 in case of TMS based on group Talairach coordinates, and to n = 47 when applying TMS over P4. We discuss these graded effect size differences in light of the revealed interindividual variances in the actual target stimulation site within and between approaches.

A causal role of the right inferior frontal cortex in implementing strategies for multi-component behaviour

“…High-resolution three-dimensional T1-weighted anatomical brain images were acquired on a 3-Tesla HDxt wholebody MRI scanner (GE Signa) using an 8-channel head coil (BRAVO 8-channel brain) with magnetization-prepared gradient echo images (TR: 10.36 ms; TE: 4.2 ms; FA: 13°; 160 sagittal slices; matrix size, 512 Â 512; FOV, 240 Â 216 mm; 0.5 Â 0.4 Â 1.2 mm voxels). Structural images were prepared and neuronavigation was performed using the BrainVoyager TMS Neuronavigation System (BrainInnovation, Maastricht, The Netherlands) with established guidelines 31 .…”

Topographic Contribution of Early Visual Cortex to Short-Term Memory Consolidation: A Transcranial Magnetic Stimulation Study

“…Therefore, we used fMRI-based neuronavigation (Sack et al, 2009b) to position the coil over the V1/V2 complex of the upper convex of the calcarine fissure (lower visual field) of the right hemisphere in four participants. Neuronavigation was based on the results of an fMRI localizer of the stimulus position in the lower left visual field (6°eccentricity), which was acquired in a separate, unrelated study (De Weerd et al, in press).…”

Proactive control of sequential saccades in the human supplementary eye field

“…We adopted an fMRI-guided procedure for coil placement that has been tested previously, with robust results (27)(28)(29). Furthermore, fMRI-guided TMS has recently been shown to yield a significant behavioral effect using a smaller number of participants (as small as n = 5) compared with group sizes required when placing the coil purely based on anatomy in an MRI scan or using the 10/20 EEG cap grid (30).…”