Transcranial magnetic brain stimulation: therapeutic promises and scientific gaps

Since its commercial advent in 1985, transcranial magnetic stimulation (TMS), a technique for stimulating neurons in the cerebral cortex through the scalp, safely and with minimal discomfort, has captured the imaginations of scientists, clinicians and lay observers. Initially a laboratory tool for neurophysiologists studying the human motor system, TMS now has a growing list of applications in clinical and basic neuroscience. Although we understand many of its effects at the system level, detailed knowledge of its actions, particularly as a modulator of neural activity, has lagged, due mainly to the lack of suitable non-human models. Nevertheless, these gaps have not blocked the therapeutic application of TMS in brain disorders. Moderate success has been achieved in treating disorders such as depression, where the U.S. Food and Drug Administration has cleared a TMS system for therapeutic use. In addition, there are small, but promising, bodies of data on the treatment of schizophrenic auditory hallucinations, tinnitus, anxiety disorders, neurodegenerative diseases, hemiparesis, and pain syndromes. Some other nascent areas of study also exist. While the fate of TMS as a therapeutic modality depends on continued innovation and experimentation, economic and other factors may be decisive.