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Background and Objectives: Transcranial magnetic stimulation (TMS) is a neurostimulation and neuromodulation technique, based on the principle of electromagnetic induction of an electric field in the brain. This field can be of sufficient magnitude and density to depolarize neurons. When TMS pulses are applied repetitively they can modulate cortical excitability, increasing or decreasing it depending on the parameters of stimulation, even beyond the duration of the train of stimulation. This effect has behavioral consequences and therapeutic potential. Due to its easy use and relatively minor side effects, transcranial magnetic stimulation is now widely used in neurosciences and medicine. The main areas of transcranial magnetic stimulation application are:
1) the investigation of cortical and spinal excitability,
2) the investigation of neuronal plasticity,
3) the investigation of neuronal connectivity,
4) functional mapping, and
5) the treatment of some neurological and psychiatric disorders.
Transcranial magnetic stimulation alone or in combination with other noninvasive neuroimaging (PET – positron emission topography, MRI – magnetic resonance imaging) and neurofunctional (EEG – electroencephalography, ERP – event-related potentials, FMRI – functional magnetic resonance imaging) methods allows the conduction of research on brain functions. Thus, transcranial magnetic stimulation is suitable as a diagnostic tool in neurological and neuropsychiatric brain investigations. Method: The method of research in this paper was a review of the literature regarding publications that applied TMS for treatment and investigation goals. A total of 104 relevant papers were identified and reviewed and the results are presented here.
Results: TMS is, through inducement of an electrical field, a useful instrument to visualize regional activities in response to stimulation. The mechanism of effect of TMS is through inducing the depolarization of neurons that in turn activates other neurons and produces behavioral and cognitive outcomes, depending on the stimulated area and its function. For example some of the observable TMS-induced effects are: phosphene by stimulating the occipital cortex, interrupting working memory and speech processes by stimulating the frontal lobe, or improving verbal memory in major depressive disorder through modulating effects on the dopamine system. TMS, unlike electroconvulsive therapy (ECT), does not have any substantial cognitive side effects. TMS has effects on neurochemical and synaptic processes in neurons. There are reports in the literature that depression, mania, schizophrenia, pain disorder, hallucinations, catatonia, post traumatic stress disorder, obsessive compulsive disorder, Parkinson's disease, epilepsy, neuronal plasticity studies, tick disorders, migraine and dystonia are improved by TMS procedures.
Conclusions: Current published studies and meta-analyses have evaluated the efficacy of rTMS, given in treatment paradigms that were almost certainly suboptimal (e.g. duration of two weeks), and found that TMS is a safe and tolerable intervention. These findings raise the possibility of using TMS as a therapeutic device in psychiatric disorders and neuroscience research. This study summarizes the mechanisms of effect, advantages, and side effects of TMS and reviews studies of the efficacy of transcranial magnetic stimulation on psychiatric disorders.