Journal: Brain Stimulation (2017)
Authors: Schmittwilken L, Schuchinsky M, Kedzior KK
Background:
Deep transcranial magnetic stimulation (dTMS) with H-coil is a noninvasive stimulation of presumably deep brain regions.
Objective:
To systematically review the literature on the neurobiological mechanisms of dTMS.
Methods:
Following a systematic literature search of PsycInfo and Medline (until August 2016) and hand search, k=8 open-label studies and k=7 randomized controlled trials with n=155 participants (n=47 healthy, n=10 psychiatric, n=98 neurological patients) were included in the qualitative synthesis. Neurobiological effects of dTMS were indirectly measured using electromyography (k=4), functional magnetic resonance imaging (fMRI; k=2), hormonal assays (k=2), language (k=2) and motor functioning assessments (k=5).
Results:
Compared to repetitive transcranial magnetic stimulation (rTMS) with figure-of-eight coil, dTMS with H-coil reached threshold for motor activation at larger distances from the scalp, produced longer motor evoked potential (MEP) latencies at threshold, and activated larger brain volume (k=4; n=47 healthy participants). fMRI studies (n=1 each with tinnitus or major depression patients) showed activation associated with improvements in episodic and working memory following high-frequency dTMS with H1-coil. Compared with sham conditions, brain-derived neurotrophic factor (BDNF), cortisol, and prolactin levels were lower after high-frequency dTMS with H-coil (k=2; n=13 healthy and n=9 alcohol dependent cases). In addition, language, motor functioning (k=5; n=5 stroke, n=46 Parkinson’s disease, n=11 aphasia cases) and limb pain (k=1; n=23 neuropathy cases) improved after high-frequency dTMS relative to sham or baseline conditions. After low-frequency dTMS, clinical and electrophysiological functioning were ameliorated relative to sham condition in benign essential blepharospasm (k=1; n=12).
Conclusions:
The indirect evidence suggests that compared to rTMS, dTMS might stimulate less focal but possibly deeper regions, beyond the cortical areas. More evidence using homogeneous stimulation paradigms is necessary to determine the depth of stimulation.
