Abstract
Somatosensory evoked magnetic fields (SEFs) are the most commonly used clinical testing among various stimulus-evoked or event-related magentoencephalogram (MEG). The standardization of stimulus methods for evoked MEG is one of necessary conditions for determining diagnostic protocols in the future. In this study, we reviewed clinical SEF studies regarding stimulus methods or conditions based on a website bibliographic survey. We searched original clinical papers published in English on SEF before July 2012 using MEDLINE by keywords: (magnetoencephalography OR MEG OR magnetic source imaging) AND (presurgical or pathophysiology). Among many papers retrieved, we further narrowed the search to 49 papers based on medical subject headings such as presurgical or pathophysiology: Stimulus methods comprise electrical stimulation in 30 papers, mechanical stimulation in 17 papers, and both electrical and mechanical stimulation in 2 papers. As to parameters in electrical stimulation, many papers followed the recommendations of somatosensory evoked potentials proposed by the International Federation of Clinical Neurophysiology (2008). With regards to mechanical stimulation, a method to produce indentation of the skin as wide as a 10 mm diameter was commonly used but the latency of the cortical response it evokes is markedly long compared to that evoked by the electrical stimulation. Therefore, it is hoped that a novel mechanical stimulation technique which can be used in a magnetically shielded room is available in the near future to quickly indent the skin area as narrow as a 1–2 mm diameter that enables us to effectively stimulate RA1 and RA2 fibers projecting to area 3b.
