Biomedical Engineering Reference
In-Depth Information
Fig. 1.2 Brain mapping with TMS of the ADM muscle before (a) and after (b) tumor resection.
Due to the tumor removal, the precentral gyrus shifted and therefore a shift in the localization of
the muscle occurs. Figures from [ 46 ], with friendly permission of the author
Furthermore, single pulse TMS is also applied to produce virtual lesions to study
the brain's connectivity and functionality [ 58 , 84 ].
Repetitive TMS, on the contrary, can change neuronal behavior for a certain
amount of time. In this case, neuronal behavior connects to the level of cortico-
spinal excitability, the connectivity between the stimulated cortex and other
connected brain areas, and the neuronal activity in the stimulated cortex. These
effects of neuro-modulation motivate the application of rTMS in cognitive brain
research and treatments of different neurological and psychiatric conditions.
Depending on the stimulation frequency, rTMS is used for inhibitory or excitatory
brain stimulation. Low frequency stimulation (\5 Hz) decreases and high fre-
quency stimulation ( [ 5 Hz) increases neuronal excitibility. However, the prin-
ciple and the duration of the effect are yet not fully understood. Interestingly,
clinical trials have proven positive effects, e.g., for depression [ 19 ], chronic tin-
nitus [ 35 ] and chronic pain [ 49 ]. Typically, rTMS is applied for 15-30 min for
each single treatment session.
Theta Burst Stimulation (TBS), as a novel paradigm of rTMS, is able to pro-
duce long-term effects after a relatively short period of stimulation (just a few
minutes) [ 28 ]. It uses very high stimulation frequencies in small intervals with a
short pause and a high number of intervals, e.g. 200 intervals with 3 pulses at
50 Hz with an interval pause of 200 ms. First studies reported positive effects, e.g.,
for treatment of chronic tinnitus [ 13 , 65 ].
1.1.3 TMS Coils
For TMS mainly two coil types are available and frequently used. They vary in
shape and therefore in their magnetic field properties. Circular coils (or round
coils) induce a ringlike electric field below the coil's windings. This way, a large
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