Transcranial magnetic stimulation and the challenge of coil placement: A comparison of conventional and stereotaxic neuronavigational strategies

Abstract

The combination of transcranial magnetic stimulation (TMS) with functional neuroimaging has expanded the potential of TMS for human brain mapping. The precise and reliable positioning of the TMS coil is not a simple task, however. Modern frameless stereotaxic systems allow investigators to base navigation either on the subject's structural magnetic resonance imaging (MRI), functional MRI data, or the use of functional neuroimaging data from the literature, so-called ''probabilistic approach.'' The latter assumes consistency across individuals in the location of task-related ''activations'' in standardized stereotaxic space. Conventional nonstereotaxic localization of brain areas is also a common method for defining the coil position. Our aim was to evaluate the accuracy of five different localization strategies in one single study. The left primary motor cortex (left M1-Hand) was used as target region. Three approaches were based on real-time frameless stereotaxy using information based on either anatomical or functional MRI. The remaining two strategies relied either on standard cranial landmarks (i.e., the International 10-20 EEG system) or a standardized function-guided procedure (i.e., the spatial relationship between the left and right M1-Hand). The results were compared to a TMS-based mapping of the primary motor cortex; center of gravity of motor-evoked potentials (MEP-CoG) was calculated for each subject (n ¼ 10). Our findings suggest that highest precision can be achieved with fMRI-guided stimulation, which was accurate within the range of millimeters. Very consistent results were also obtained with the ''probabilistic'' approach. In view of these findings, we discuss the methods and special characteristics of each localization strategy.

HF-rTMS treatment decreases psychomotor retardation in medication-resistant melancholic depression

“…Other important differences between our and the Hoeppner study (in press) which could explain the divergent results could be that instead the use of infrathreshold stimulation, we used suprathreshold HF-rTMS thought to increase clinical outcome (Gershon, 2003). Furthermore, the imprecise TMS-coil positioning method to target the left DLPFC (Sparing et al, 2008;Peleman et al, in press), the more heterogeneous sampling of depressed patients (not all treatment-resistant), and the concomitant pharmacological antidepressant therapy on the start of their HF-rTMS study might have biased their results (Martin et al, 2003;Herwig et al, 2007).…”

Dynamic changes in prefrontal cortex involvement during verbal episodic memory formation

“…The use of non-stereotaxically navigated brain areas is very common in TMS studies (Sparing et al, 2008;Beam et al, 2009). Although MRI-guided stereotaxic coil positioning is more accurate, studies have found that the International 10-20 EEG system is an acceptable and reliable method to localize brain regions, especially with large cortical areas such as the DLPFC or the VLPFC (Herwig, Satrap & Schönfeldt-Lecuona, 2003;Sparing et al, 2008;Beam et al, 2009). For instance, Herwig et al (2003) investigated the underlying anatomy of F3 and found that in the vast majority of participants the location of F3 determined with the 10-20 system was within the DLPFC.…”

“…In both groups, the coil was positioned according to the standard cranial landmarks of the International 10-20 EEG system, a common approach used in our and other laboratories (Rossi et al, 2001(Rossi et al, , 2004(Rossi et al, , 2006(Rossi et al, , 2011Sparing, Buelte, Meister, Paus & Fink, 2008;Beam, Borckardt, Reeves & George, 2009). In the DLPFC group, the stimulation was delivered by placing the wings junction of the coil on the scalp region corresponding to F3 of the international EEG 10-20 system.…”

How Does Learning to Read Affect Speech Perception?

“…In both cases, stimulation for the test site was individually targeted to a region where TMS disrupted either phonological or orthographic processing, as demonstrated in an independent dataset. Importantly, functional localization of this type reduces the intersubject variance present for other (more heuristic) targeting procedures, optimizing the number of participants needed (Sparing et al, 2008;Sack et al, 2009).…”