Transcranial Magnetic Stimulation
Transcranial Magnetic Stimulation (TMS) is a noninvasive technique used to induce electric currents in neurons of the brain. In a way, TMS and magnetoencephalography (MEG) are like mirror images of one another: The former induces currents in the brain via magnetic fields while the latter detects magnetic fields generated by neural currents. Both are noninvasive, because magnetic fields pass effortlessly through tissues such as skin and skull.
TMS plays a unique part in understanding how the brain works because it can be used to disengage a brain area for a fraction of a second, thus allowing scientists to understand the area's functional role. This distinguishes it from other noninvasive brain imaging modalities - fMRI, EEG, MEG, and optical imaging, for example - that can only detect brain activations. Clinically, TMS is used to treat depression as well as to localize brain areas important for motor functions and speech, which should be avoided by the surgeon during removal of brain tumors. Several other applications (e.g., migraine, epilepsy, Parkinson's disease, schizophrenia) are being investigated.
At the Martinos Center, researchers use TMS often in conjunction with EEG, MRI, fMRI and optical imaging to obtain maps of brain activity in cognitive neuroscience studies designed to investigate the workings of the normal and damaged brain.