Brain-Behavior Relations: Transcranial Magnetic Stimulation: A Review

This paper reviewed the transcranial magnetic stimulation (TMS) applications for brain-behavior relations. Along with rapid-rate TMS, coils designed for focal stimulation and image-guided targeting of stimulation to desired cortical structures, neuronal processes can now be disrupted even in relatively well-defined cortical areas. Delivering two sequential pulses to the primary motor cortex(MI) allowed the exploration of inhibition and facilitation within the motor pathways. Function brain imaging was combined with TMS for access of extent and loci of local and remote TMS-induced brain effects. Reflecting changes in cerebral blood flow and oxygenation, 15O-H2O or18F-FDG positron emission tomography, 99 mTc ethylcysteinate dimer single photon emission tomography, blood-oxygenation-level dependent magnetic resonance imaging (MRI), and near infrared spectroscopy showed bilateral cortical activity as well as activation of subcortical structures and the cerebellum. The introduction of TMS-compatible EEG allowed one to measure the instant and direct neuronal effects of TMS (Figure 6); bilateral activation patterns, similar to functional imaging, were exhibited in source images derived from the EEG. Intriguing examples of the use of TMS/EEG technique in studying corticocortical connectivity are already available in the literature. TMS shows a great promise for future clinical applications. Presently, the key topics in TMS research include altered cortical excitability in neurological diseases, functional relevance of cortical areas in cognitive task performance, and treatment of psychiatric diseases. To date, however, there are not enough data to establish TMS studies as part of clinical diagnostics or therapy in any neurological or psychiatric disease. Recently, patterned types of stimulation have been introduced, each still under scrutiny, to define its efficacy in research and clinical settings as well as its potential hazards. The last decade has seen a rapid increase in the applications of TMS to study cognition, brain-behavior relations, and the pathophysiology of various neurologic and psychiatric disorders. In addition, evidence has accumulated that demonstrated that TMS provides a valuable tool for interventional neurophysiology applications, modulating brain activity in a specific, distributed, corticosubcortical network. Finally, recent evidences have shown that multiple muscle recordings allow to probe dynamic properties of the multiple representations at the cortical levels to orchestrate the best movement performance(Figure 7).