Assessment of standard coil positioning in transcranial magnetic stimulation in depression
Introduction
Transcranial magnetic stimulation (TMS) is a tool used in neurosciences to investigate neuronal connections (Paus et al., 1997) and cognitive functions such as working memory by creating temporary “virtual lesions”. TMS is also used as a therapeutic tool in neurology and psychiatry. It is increasingly used for the treatment of major depression. The antidepressant properties of TMS were discovered in 1995 (George et al., 1995) and repetitive transcranial magnetic stimulation (rTMS) has been used in many studies, including randomized sham-controlled ones. These studies have demonstrated the efficacy of real rTMS compared with sham rTMS (George et al., 1997, Avery et al., 1999, Eschweiler et al., 2000, Fitzgerald et al., 2003, Avery et al., 2006). Several meta-analyses (Gershon et al., 2003, Couturier, 2005, Loo and Mitchell, 2005) have also noted a degree of efficacy, though not as great as that expected by clinicians using this tool. These disappointing results can be explained by a number of different factors: firstly, the heterogeneity of the patients; secondly, the parameters used, such as the intensity and frequency of stimulation; and thirdly, the location of the cortical area being stimulated, which is the focus of this article.
In most of the published studies, the dorsolateral prefrontal cortex (DLPFC) was chosen as the stimulated target. This area is large: a broader definition defines the DLPFC as the lateral portions of Brodmann areas 9, 10, 11, 12, of areas 45, 46 and the superior part of the area 47. (Procyk and Goldman-Rakic, 2006). As others (Petrides and Pandya, 1999; Mayberg et al., 1999, Drevets, 2000, Rogers et al., 2004), we defined the DLPFC as part of the rostral frontal lobe roughly equivalent to Brodmann areas 9 and 46. The interface between these both areas roughly corresponds to the second third, i.e. middle part, of the middle frontal gyrus along an anteroposterior axis. As neuroimaging studies have revealed hypometabolism of the left prefrontal cortex in depressive patients (Mayberg et al., 1999, Drevets, 2000, Rogers et al., 2004) and George et al. (1996) have shown that stimulation of this target area has an antidepressant effect, this is the target we chose for our study.
The left DLPFC is localized following a “standard procedure” devised by George et al., 1995, Pascual-Leone et al., 1996. The primary motor cortex is first located by looking for the response of the controlateral abductor pollicis brevis muscle. The coil is moved 5 cm rostrally in a parasagittal plane. The stimulation point is then drawn on a cap previously placed on the patient's head, on which anatomical landmarks are drawn in order to be able to reposition it correctly for each stimulation session.
Although this method is easy to use in clinical routine, we identified three main sources of error: cap repositioning between stimulation sessions (only for groups using a cap), variability in locating the left DLPFC between the different clinicians practicing TMS (interexpert variability) and the discrepancy between the stimulation locus and the reference stimulation target recorded in the magnetic resonance imaging (MRI) coordinate system (interindividual anatomical variability). The latter is different from the operator-dependent bias and remains present even if the localization procedure is perfectly performed. Herwig et al. (2001) tested the reliability of the standard coil positioning method on 22 subjects using neuronavigation and showed that only 7 out of 22 were correctly targeted. As this is the method used to locate the left DLPFC in most previous studies, the high degree of variability in the stimulated target must surely have affected their clinical results.
The ability to stimulate the right target accurately is also a requirement in neurosurgery. Neuronavigation systems have therefore been developed for use in computer-assisted procedures and can be adapted to TMS. These systems make it possible to determine the position of the left DLPFC more accurately by finding the middle part of the middle frontal gyrus. A neuronavigation system limits localization errors, obviates the need for cap repositioning and takes account of interindividual anatomical variability. However, in order to assess the need for a neuronavigation system, we first needed to quantify the inaccuracy of the standard method arising from the three sources of error which are cap repositioning, interexpert variability in coil positioning and distance between the actual “reference” DLPFC located on the MRI and its standard determination.
Section snippets
Subjects
We recruited one healthy subject for Studies 1 (assessment of cap repositioning) and 2 (assessment of interexpert variability in coil positioning) and 10 right-handed depressed patients (4 men, 6 women) (mean age: 54 years, standard deviation: 9.77) for Study 3 (quantification of distance between actual DLPFC and its standard determination).
Patients were interviewed with the MINI (Sheehan et al., 1998) in order to diagnose current major depressive disorders and rule out other psychiatric
Study 1: Cap repositioning
The prefrontal cortex was chosen as the target, in order to reproduce the usual coil positioning situation. Standard deviations (SD) for the target along the three axes were 3.18 mm (left/right axis), 1.74 mm (head/foot axis) and 2.32 mm (anteroposterior axis) when the cap was repositioned 30 times by the same expert (Fig. 2). When the cap was repositioned by different experts, the standard deviations were 3.80 mm, 2.52 mm and 2.89 mm (20 successive cap repositioning). To analyze the variance in the
Discussion
In our study, we sought to provide a more accurate measurement of the three main sources of inaccuracy in the standard location of the DLPFC: cap repositioning, inter-expert variability in coil positioning and the intrinsic error of the standard location method.
We found that the point cloud determined after the cap had been repositioned 30 times was relatively focused and the standard deviation was lower than 5 mm. In order to avoid a bias due to a single user, different clinicians performed the
Acknowledgements
The authors would like to thank Ms. Wiles Portier for preparing the manuscript.
References (38)
- et al.
A controlled study of repetitive transcranial magnetic stimulation in medication-resistant major depression
Biological Psychiatry
(2006) - et al.
Inter-individual variability in optimal current direction for transcranial magnetic stimulation of the motor cortex
Journal of Neuroscience Methods
(2007) - et al.
SPECT mapping of cerebral activity changes induced by repetitive transcranal magnetic stimulation in depressed patients
A pilot study. Psychiatry Research
(2001) - et al.
Three and six month outcome following courses of either ECT or rTMS in a population of severely depressed individuals
Preliminary Report. Biological Psychiatry
(2002) Neuroimaging studies of mood disorders
Biological Psychiatry
(2000)- et al.
Left prefrontal activation predicts therapeutic effects of repetitive transcranial magnetic stimulation (rTMS) in major depression
Psychiatry Research
(2000) - et al.
Exploring the optimal site for the localization of the dorsolateral prefrontal cortex in brain stimulation experiments
Brain Stimulation
(2009) - et al.
A controlled trial of daily left prefrontal cortex TMS for treating depression
Biological Psychiatry
(2000) - et al.
A review of the efficacy of transcranial magnetic stimulation (TMS) treatment for depression, and current and future strategies to optimize efficacy
Journal of Affective Disorders
(2005) - et al.
Repetitive transcranial magnetic stimulation on the prefrontal cortex in depression
Experimental Neurology
(2009)
Executive and prefrontal dysfunction in unipolar depression: a review of neuropsychological and imaging evidence
Neuroscience Research
Transcranial magnetic stimulation in treatment resistant depressed patients: a double blind placebo-controlled trial
Psychiatry Research
Navigated transcranial magetic stimulation
Clinical neurophysiologie
Neuronavigation for transcranial magnetic stimulation (TMS): Where we are and where we are going?
Cortex
Diagnostic and Statistical Manual of Mental Disorders
Repetitive transcranial magnetic stimulation in the treatment of medication-resistant depression: preliminary data
The Journal of Nervous and Mental Disease
Mechanisms of action underlying the effect of repetitive transcranial magnetic stimulation on mood: behavioural and brain imaging studies
Neuropsychophamacology
Design and construction of a realistic digital brain phantom
IEEE Transactions on Medical Imaging
Efficacy of rapid-rate repetitive transcranial magnetic stimulation in the treatment of depression: a systematic review and meta-analysis
Journal of Psychiatry & Neuroscience
Cited by (35)
Non-invasive and invasive brain stimulation in alcohol use disorders: A critical review of selected human evidence and methodological considerations to guide future research
2021, Comprehensive PsychiatryCitation Excerpt :A crucial issue for a correct use of TMS is the accuracy of coil's placement, which should ensure the shortest path for the magnetic field to cross the skull and attain the targeted hotspot, and at the same time, minimize power loss and unwanted stimulation of adjacent regions. Targeting precision is enhanced by MRI based frameless stereotaxic neuronavigation equipment capable to use individual 3D brain reconstructions and track in real time TMS coil's position on participant's heads and brains [46,47].. Randomized clinical trials using rTMS in recently detoxified AUD patients are summarized in Table 1.
Targeting location relates to treatment response in active but not sham rTMS stimulation
2021, Brain StimulationA direct comparison of neuronavigated and non-neuronavigated intermittent theta burst stimulation in the treatment of depression
2021, Brain StimulationCitation Excerpt :While easy to use in everyday clinical practice, there has been some evidence that all skull surface-based approaches lack precision in identifying the location of the lDLPFC and do not fully account for inter-individual differences in human anatomy. This has been demonstrated (to varying degrees) using MRI - based neuronavigation systems [13–17]. Inter-individual differences may be related to age, sex, handedness or pathological volume abnormalities [18].
A single session of repetitive transcranial magnetic stimulation of the prefrontal cortex reduces cue-induced craving in patients with gambling disorder
2017, European PsychiatryCitation Excerpt :All studies but one in the field of addiction research have used an empirical method to localize this area of the brain [38]; we are the first to employ a neuronavigation system and robot-guided coil method based on the subject's MRI. Neuronavigation is assumed to be superior to the “5-cm rule” and the “10/20” method for targeting the DLPFC [39–41] and seems to have increased the therapeutic effects of rTMS in several diseases, including depression [26,42,43]. Regarding lateralization, we chose to stimulate the left DLPFC.
Repetitive transcranial magnetic stimulation: A potential therapy for cognitive disorders?
2017, Revue de Medecine Interne