The electrical signals that pass through neuronal structures generate electrical currents and magnetic fields that can be measured by different electrography and magnetography modalities. In this article, we briefly review the fundamentals of recording bioelectrical currents and biomagnetic fields. This is followed by an analysis of the neurophysiologic substrates of the brachial plexus, cervical roots, and spinal cord, comparing the electrography-based modality of somatosensory evoked potential with the magnetography-based modality of magnetospinography/magnetoneurography (MSG/MNG). We aim to illustrate that MSG/MNG has the potential to address the shortcomings that currently exist in electrography modalities for direct neurophysiologic assessment of the aforementioned neural structures.

Background
: The generators of N37 and P37 of posterior tibial nerve somatosensory evoked potential(PTSEP) have not been exactly known. Recently, some reports suggested that P37 and N37 might have different generator. We conducted a study to know the generators of P37 and N37 of PTSEP using gating mechanism. Methods : We evaluated subcortical and cortical somatosensory evoked potentials(SEPs) in response to posterior tibial nerve stimulation in 2 experimental conditions of foot movement and compared them with PTSEPs in full relaxation of foot. The experimental conditions were: (a) active flextion-extention of stimulated foot, (b) isometric contraction of the stimulated foot, (c) passive flextion-extention of the stimulate foot. We analyzed the latencies and amplitudes of following potentials;P30, N37, P37, and N50. Results : The amplitude of P30 potential did not change during at any paradigms. Te amplitudes of P37 and N50 were significantly attenuated in all condition. However, the amplitude of N37 showed no significant change during at any paradigms. Conclusions : These results suggest that the generators of P37 and N37 pf PTSEP be different I cortex.

B a c k g r o u n d: Somatosensory evoked potential (SSEP) is valuable for the evaluation of the central pathway.However, peripheral neuropathy sometimes renders the test useless by preventing the conduction from reaching theCNS. We postulated that the peripheral conduction problems could be overcome by proximal stimulation in SSEP andwanted to verify this in the study.Methods: Twenty patients with diabetic sensorimotor polyneuropathy were included. SSEP was elicited by stimulatingthe median and posterior tibial nerves. We compared the effect of distal and proximal stimulations in each SSEP inthe aspect of presence/absence and various latencies of resultant waves.Results: Among the 40 cases, proximal stimulation caused reappearance of subsided waves in 10 cases (25%). In themedian nerve SSEP, proximal stimulation made EN1 and CN2 visible which were not evident when distally stimulated.In the posterior tibial nerve SSEP, there was also improvement of forming waves when proximally stimulated.Conclusions: In the diabetic polyneuropathy, proximal stimulation of SSEP is more effective than the conventionaldistal stimulation in evaluating central pathway.

Intraoperative neuromonitoring (INM) is well known to be useful method to reduce intraoperative complications during the surgery of nervous system lesions. Evoked potentials are most commonly used among the electrophysiological tests. Brainstem auditory evoked potentials are for detecting the problems along the auditory pathways including the eighth cranial nerve and brainstem. Somatosensory evoked potentials are applied for preventing the spinal cord lesions. The INM is affected by many factors. In order to perform an optimal INM, the confounding factors including technical, anesthetical, and individual factors should be kept well under control. INM has frequent electrophysiologic changes during the surgery and it might be helpful to keep one

Various electrophysiological tests have provided a large body of valuable information on neuronal responses to a presentedstimulus. The special and general somatic sensory pathways are main targets of evoked potentials. Two types of evokedpotentials, exogenous and endogenous, are commonly used. Exogenous evoked potentials of general and special somatic sensorysystems will be reviewed. One of general somatic sensory functional pathways, proprioception, can be evaluated by generalsomatosensory evoked potentials with electrical stimulation on nerves. The special somatosensory functional pathways,including vision, and audition, can be evaluated by visual evoked potentials and auditory evoked potentials. Also laser-evokedpotentials are newly developed for pain pathway, including lateral spinothalamic pathway, and vestibular myogenic evokedpotentials for sacculocollic pathways. The evoked potentials of sensory system have maximal clinical utility in evaluatingfunctional deficits along the sensory pathways. They are used for evaluating comatose patients, hysterical patients, prematureinfants, patients with suspected demyelinating diseases or neoplasms, and research. We discuss the neurophysiologic testsof sensory systems in views of practical points. The organized evaluation of sensory electrophysiologic tests can be helpfulin detecting and estimating the abnormalities in neurological diseases.