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.

Visual evoked potentials (VEPs) are especially useful for evaluating patients with visual pathway involvement but no objective findings on ophthalmic examination. To apply VEPs appropriately in clinical practice, clinicians should be well aware of the standard test techniques and various factors affecting the interpretation of VEPs to detect visual pathway abnormalities. This article summarizes the method for recording VEPs and the technical and physiologic factors associated with VEPs.

Cortico-cortical evoked potential (CCEP) mapping is a rapidly developing method for visualizing the brain network and estimating cortical excitability. The CCEP comprises the early N1 component the occurs at 10-30 ms poststimulation, indicating anatomic connectivity, and the late N2 component that appears at < 200 ms poststimulation, suggesting long-lasting effective connectivity. A later component at 200-1,000 ms poststimulation can also appear as a delayed response in some studied areas. Such delayed responses occur in areas with changed excitability, such as an epileptogenic zone. CCEP mapping has been used to examine the brain connections causally in functional systems such as the language, auditory, and visual systems as well as in anatomic regions including the frontoparietal neocortices and hippocampal limbic areas. Task-based CCEPs can be used to measure behavior. In addition to evaluations of the brain connectome, single-pulse electrical stimulation (SPES) can reflect cortical excitability, and so it could be used to predict a seizure onset zone. CCEP brain mapping and SPES investigations could be applied both extraoperatively and intraoperatively. These underused electrophysiologic tools in basic and clinical neuroscience might be powerful methods for providing insight into measures of brain connectivity and dynamics. Analyses of CCEPs might enable us to identify causal relationships between brain areas during cortical processing, and to develop a new paradigm of effective therapeutic neuromodulation in the future.

Citations

• The impact of radiofrequency thermocoagulation on brain connectivity in drug‐resistant epilepsy: Insights from stereo‐electroencephalography and cortico‐cortical evoked potentials
  Justyna Gula, Rutger J. Slegers, Raf H. M. Van Hoof, Balu Krishnan, Massimo Mischi, Vivianne H. J. M. van Kranen‐Mastenbroek, Ilse E. C. W. Van Straaten, Danny Hilkman, Louis Wagner, Albert Colon, Olaf E. M. G. Schijns, Borbála Hunyadi, Jacobus F. A. Jans
  Epilepsia.2025; 66(4): 1260.     CrossRef
• Recent developments in stereo electroencephalography monitoring for epilepsy surgery
  Debopam Samanta
  Epilepsy & Behavior.2022; 135: 108914.     CrossRef

Transcranial magnetic stimulation is a non-invasive, painless diagnostic tool of nervous propagation as well as of motor cortex excitability in healthy subjects and in patients affected by several neurological disease ie, stroke, epilepsy and multiple sclerosis etc. Motor areas can be reliably mapped and short-and long-term 'plastic' changes of neural connections can be studied and monitored over time. Recent studies suggest a therapeutic role of repetitive magnetic stimulation in neurologic and psychiatric disorders.

Background
and Purpose : Brainstem auditory evoked potentials(BAEPs) are responses of the brainstem by auditory stimulation. Vertebrobasilar transient ischemic attacks is the disease that occurs by insufficient circulation in the region of brainstem. The purpose of this study is to know the factors influencing the changes of BAEPs in vertebrobasilar transient ischemic attacks. Methods : The subject of study was 96 patients diagnosed as vertebrobasilar transient ischemic attacks. Patients were divided into two groups according to the BAEPs findings, age, sex, presence of hypertension, diabetes, hyperlipidemia, heart disease, neurologic findings, previous stroke, previous stroke, previous vertebrobasilar transient ischemic attacks, smoking and alcohol drinking, and time period between symptom onset and testing were compared. Results : There were no significant differences in age, sex, and presence of hypertension, diabetes, hyperlipidemia, heart disease, previous stroke history, previous vertebrobasilar transient ischemic attack, smoking, and alcohol drinking between two groups. The presence of abnormal neurologic findings in the first examination and time period between symptom onset and testing were significantly different between normal BAEPs group and abnormal BAEPs one(P < 005). Conclusions : The factors influencing the changes of BAEPs were presence of abnormal neurologic findings and time period between symptom onset and testing. These finding suggest that BAEPs test should be performed in acute stage of ischemic attack.

Background
It has been proposed that proprioceptive input can modulate neural excitability in both primary motor cortices (M1) simultaneously, although direct evidence for this is still lacking. Previous studies showed that proprioceptive accuracy of one hand is reduced after the application of one-Hz repetitive transcranial magnetic stimulation (rTMS) for 15 minutes over the contralateral somatosensory cortex. The aim of this study was to investigate the effect of rTMSinduced central proprioceptive deafferentation to excitability of both M1 as reflected in ipsilateral and contralateral motor evoked potentials (MEP).
Methods: MEPs of both abductor pollicis bravis (APB) muscles were recorded using single-pulse TMS over right M1 in seven healthy subjects. Immediately after one-Hz rTMS was applied for 15 minutes over the right somatosensory cortex, the MEP measurement was repeated. The proprioceptive function of the left thumb was assessed, before and after rTMS, using a position-matching task.
Results: There was an increase in ipsilateral MEP after the rTMS: whereas no MEPs were recorded on the ipsilateral hand before the rTMS, MEPs were recorded in both ipsilateral and contralateral hand in three of seven subjects. At the same time, the mean log amplitude was reduced and the mean latency was prolonged in the contralateral MEP.
Conclusions: rTMS-induced central proprioceptive deafferentation reduces the MEP generation in the contralateral hand, and fascilitates that in the ipsilateral hand. A further study with a larger sample seems warranted to confirm this finding and to elucidate the neurophysiology underlying it.

We report a case of chiasmal optic neuritis in a patient who had been diagnosed as multiple sclerosis, and was presented with bitemporal hemianopsia. The brain MRI revealed a high signal lesion with focal enhancement in optic chiasm, and the visual evoked potential functionally supported it. This is the first case of chiasmal optic neuritis in multiple sclerosis with temporally and spatially disseminated lesions.

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.