NeuroImage: DTI-Guided TMS Effectively Targets Deep Brain Structures

Transcranial magnetic stimulation (TMS) has emerged as a powerful tool for exploring cortical function and has been demonstrated in the treatment of various psychiatric and neurological disorders
.

Unfortunately, due to the direct effects of TMS, most of the conclusions are limited to an area a few centimeters below the scalp, however, more distant areas may be affected by structurally connected stimulation points

In this study, Bruce Luber et al.
sought to develop a new paradigm for individualized placement of TMS coils to noninvasively activate specific deep-brain targets associated with the treatment of psychiatric disorders
.

In 10 subjects, structural diffusion imaging fiber tracing data were used to identify an accessible cortical target in the right frontal pole that displayed anatomical and functional connectivity to BA25
.

A series of single interleaved TMS pulses were applied to the right frontal pole at four levels of intensity from 80% to 140% of motor threshold

Four regions of interest for functional analysis
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Red: stimulation site; purple: dorsal control site; green: area defined by R-BA25 fiber bundles; blue: area defined by L-BA25 fiber bundles

Four regions of interest for functional analysis

Group fiber bundle results
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BA25 seed point ROIs for fiber bundle analysis are shown in yellow

Group fiber bundle results

Stimulus-dependent differences in fMRI activity
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a) 120%MT vs 80%MT, B) 140%MT vs 80%MT

Stimulus-dependent differences in fMRI activity

Population-level stimulation effects in activation
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Population-level stimulation effects in activation
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Structure-connectivity basis (A) and function-connectivity basis (B) target effectiveness
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Structure-connectivity basis (A) and function-connectivity basis (B) target effectiveness
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Preliminary applications of DTI-guided TMS suggest a new tool that expands the utility of non-invasive stimulation, allowing researchers to target deep areas of the brain that were previously thought to be inaccessible
.

The underlying target here is BA25, which is thought to be a key node in the nervous system in depression
.
BA25 was successfully activated in a dose-dependent manner, indicating that no matter where the target is located in the brain, the use of DTI-guided TMS is the first step in noninvasive therapy,

The robust activation of BA25 in a dose-dependent manner suggests that a combined TMS-fMRI approach can leverage network properties to help overcome depth limitations and enable the possibility of non-invasive brain stimulation affecting deep brain structures
.

The combined TMS-fMRI approach can leverage network properties to help overcome depth limitations and enable the possibility of non-invasive brain stimulation affecting deep brain structures
.
The combined TMS-fMRI approach can leverage network properties to help overcome depth limitations and enable the possibility of non-invasive brain stimulation affecting deep brain structures
.

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Using diffusion tensor imaging to effectively target TMS to deep brain structures

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