Single-source multi-coil transcranial magnetic stimulators for deep and focused stimulation of the human brain

摘要

Transcranial magnetic stimulation (TMS) is a tool for non-invasive stimulation of neuronal tissue for research in cognitive neuroscience and treating neurological disorders. In TMS, one or more coils located near the scalp produce magnetic fields that induce electric fields and eddy-currents in the conductive brain tissue. When the spatial gradient of the electric field aligns with a nerve fiber, an action potential is generated. Many TMS applications require excitation of specific target regions in the brain while minimizing stimulation elsewhere. Unfortunately, electric fields generated by present TMS coils diffuse rapidly as they penetrate into the brain and stimulate relatively large regions of tissue near the brain surface. This is especially true for the two most commonly used single-source systems, viz. the ‘figure-8’ and ‘Hessed’ coils (Cohen L. et al., Electroencephalogr Clin Neurophysiol, vol.7, no.75, pp.1–4, 350–7; Roth Y. et al., J Clin Neurophysiol, vol.19, no.4, pp. 361–370. Aug. 2002). To broaden the scope of present TMS applications, new coils that focus fields deeper into the brain while limiting the volume of excited tissue are called for.