Poster No:
49
Submission Type:
Abstract Submission
Authors:
Larissa Behnke1,2, Yuki Mizutani-Tiebel2, Kai-Yen Chang2, Frank Padberg2, Daniel Keeser2
Institutions:
1University of Zurich, Department of Psychology, Zürich, Switzerland, 2Department of Psychiatry and Psychotherapy, University Hospital LMU, Munich, Germany
First Author:
Larissa Behnke
University of Zurich, Department of Psychology|Department of Psychiatry and Psychotherapy, University Hospital LMU
Zürich, Switzerland|Munich, Germany
Co-Author(s):
Yuki Mizutani-Tiebel
Department of Psychiatry and Psychotherapy, University Hospital LMU
Munich, Germany
Kai-Yen Chang
Department of Psychiatry and Psychotherapy, University Hospital LMU
Munich, Germany
Frank Padberg
Department of Psychiatry and Psychotherapy, University Hospital LMU
Munich, Germany
Daniel Keeser
Department of Psychiatry and Psychotherapy, University Hospital LMU
Munich, Germany
Introduction:
The treatment of psychiatric disorders is challenging and not all patients respond well to primary indicated medications and/or psychotherapy. One promising method investigated for treatment-resistant psychiatric patients is non-invasive neuromodulation. Therefore, repetitive transcranial magnetic stimulation (rTMS) offers a treatment alternative for psychiatric disorders (Kan et al., 2023). Many rTMS treatment protocols target the left dorsolateral prefrontal cortex (lDLPFC) and stimulation intensity is determined by the participants individual resting motor threshold (rMT) of the left primary motor cortex (lM1). Using the rMT is a reliable measure of cortical excitability with a peripheral response, but it is unknown if the stimulation intensity determined by the individual's lM1 results in comparable cortical activation when stimulation is applied at the lDLPFC. Therefore, we investigated the intensity and spread of an electric-field simulation targeting lDLPFC and lM1 using the simulation software SimNIBS 4.0.
Methods:
We simulated electric-field distributions (n=17, 8 female, age: M=26.29, SD =3,39, range: 21-36 years) from T1 and T2 structural MRI scans of healthy participants recorded as part of a simultaneous TMS-fMRI setup (Mizutani-Tiebel et al., 2022). The baseline scans we used for this simulation were aquired with a 64-channel coil in a 3T Siemens Prisma Magnetom scanner. Coordinates for each lDLPFC target were located by conducting a reverse co-registration from MNI152 stereotaxic coordinates x=–38, y=+44, z=+26 to the subject space of each scan. The initially recorded stimulation marker (pulse) was used as the stimulation target for each simulation. The coil handle direction was manually adjusted to a 45° angle with the line between hemispheres and stimulation points were projected onto the scalp. Stimulation targets for lM1 and rMT were defined by using electromyography on the right abductor pollicis brevis. The rMT was defined with the di/dt value which induced motor evoked potentials (MEPs) greater than 50μV in 5 out of 10 pulses. For the simulation of DLPFC/M1, we specified the MRi-B91 TMS coil file and set the stimulation intensity to the di/dt value recorded from the TMS stimulator during the actual rTMS protocol. The stimulation intensity was defined as 80% of each participants rMT.
Results:
Surprisingly, the 99th percentile electric-field strength was higher for lDLPFC than for lM1 targets. However, at higher (99.9th) and lower (50th, 75th and 90th) percentiles, electric-fields intensity did not show significant difference between lDLPFC and lM1. The field-focality, a measure of gray matter area with a field 75 and 50% of the 99.9th percentile electric-field intensity, significantly differed between stimulation locations. Calculated field-focality at lDLPFC was higher than at lM1, indicating a higher spread of the stimulation at prefrontal areas.
Conclusions:
Here we show that TMS stimulation with the same intensity, but different targets do not result in the same activation in the underlying structures. Our simulation shows that electric-field strength and field-focality can differ between stimulation sites. The primary motor cortex (M1) is more specialized for motor control and has less functional diversity than the frontal brain regions. Frontal brain areas are involved in higher-order cognitive functions such as decision making, working memory and executive functions, which require a more complex and variable cytoarchitecture. Stimulation of these diverse and interconnected regions may lead to a wider range of effects, contributing to greater variability (Mueller et al., 2013). Future investigations should delve into these factors and treatment protocols should consider variations in TMS effects across different stimulation targets.
Brain Stimulation:
Non-invasive Magnetic/TMS 1
TMS
Disorders of the Nervous System:
Psychiatric (eg. Depression, Anxiety, Schizophrenia)
Novel Imaging Acquisition Methods:
Anatomical MRI 2
Keywords:
MRI
STRUCTURAL MRI
Transcranial Magnetic Stimulation (TMS)
Other - electric-field
1|2Indicates the priority used for review
Provide references using author date format
Kan, R. L. D. et al. (2023), "Effects of repetitive transcranial magnetic stimulation of the left dorsolateral prefrontal cortex on symptom domains in neuropsychiatric disorders: a systematic review and cross-diagnostic meta-analysis", The Lancet, Psychiatry, 10(4), 252–259. https://doi.org/10.1016/S2215-0366(23)00026-3
Mizutani-Tiebel, Y. et al. (2022), "Concurrent TMS-fMRI: Technical Challenges, Developments, and Overview of Previous Studies. Frontiers in psychiatry", 13, 825205, https://doi.org/10.3389/fpsyt.2022.825205
Mueller, S. et al. (2013), "Individual variability in functional connectivity architecture of the human brain", Neuron, 77(3), 586–595. https://doi.org/10.1016/j.neuron.2012.12.028