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
This study aimed to determine the effects of perampanel on the nervous system using commonly performed neurophysiological tests.
Methods
Twelve healthy adult males underwent electroencephalogram and measurements of median nerve somatosensory evoked potentials (SSEPs), visual evoked potentials (VEPs), and brainstem auditory evoked potentials before and after ingesting 6 mg of perampanel. The pre- and postadministration data were cross-compared and then correlated with serum perampanel levels and reported side effects.
Results
After ingesting 6 mg of perampanel there was a statistically significant increase in the P100 latency of VEPs elicited using a 64 × 64 checkerboard pattern (p = 0.027) and a decrease in the N20 latency of median nerve SSEPs (p = 0.033). Reported side effects were not correlated with the serum perampanel level or statistically significant latency changes.
Conclusions
This study is the first to explore the effects of perampanel on results obtained in neurophysiological tests. Our findings indicate that perampanel increases sensory conduction, as evidenced by a decrease in N20 latency. Perampanel may additionally interfere with visual processing, in part by prolonging P100. Further studies with larger samples and various doses are needed to clarify these findings.

The newly identified frontal aslant tract (FAT) that connects the posterior Broca’s area to the supplementary motor area is known to be involved in speech and language functions. We successfully intraoperatively monitored FAT using cortico-cortical evoked potentials generated by single-pulse electrical cortical stimulation in a patient with oligodendroglioma.

Citations

• Developmental trajectory of transmission speed in the human brain
  Dorien van Blooijs, Max A. van den Boom, Jaap F. van der Aar, Geertjan M. Huiskamp, Giulio Castegnaro, Matteo Demuru, Willemiek J. E. M. Zweiphenning, Pieter van Eijsden, Kai J. Miller, Frans S. S. Leijten, Dora Hermes
  Nature Neuroscience.2023; 26(4): 537.     CrossRef

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

Background
Neuromodulation therapy has been used to an adjunctive treatment promoting motor recovery in stroke patients. The objective of the study was to determine the effect of repetitive transcranial magnetic stimulation (rTMS) on neurobehavioral recovery and evoked potentials in rats with middle cerebral artery occlusion. Methods: Seventy Sprague-Daley rats were induced permanent middle cerebral artery occlusion (MCAO) stroke model and successful stroke rats (n=56) assigned to the rTMS (n=28) and sham (n=28) group. The 10 Hz, high frequency rTMS gave on ipsilesional forepaw motor cortex during 2 weeks in rTMS group. The somatosensory evoked potential (SSEP) and motor evoked potential (MEP) were used to evaluate the electrophysiological changes. Behavioral function of the stroke rat was evaluated by the Rota rod and Garcia test. Results: Forty rats (NrTMS=20; Nsham=20) completed all experimental course. The rTMS group showed better performance than sham group in Rota rod test and Garcia test at day 11 (p<0.05) but not day 18 (p>0.05). The amplitude of MEP and SSEP in rTMS group was larger than sham group at day 18 (p<0.05). Conclusions: These data confirm that the high frequency rTMS on ipsilesional cerebral motor cortex can help the early recovery of motor performance in permanent middle cerebral artery stroke model and it may simultaneously associate with changes in neurophysiological activity in brain.

Citations

• A C-shaped miniaturized coil for transcranial magnetic stimulation in rodents
  Wenxuan Jiang, Robert Isenhart, Charles Y Liu, Dong Song
  Journal of Neural Engineering.2023; 20(2): 026022.     CrossRef
• Effects of high‐frequency repetitive transcranial magnetic stimulation (rTMS) on spontaneously hypertensive rats, an animal model of attention‐deficit/hyperactivity disorder
  Jungyun Kim, Heamen Park, Seong‐lan Yu, Sungju Jee, Keun‐Ah Cheon, Dong Ho Song, Seung Jun Kim, Woo‐Young Im, Jaeku Kang
  International Journal of Developmental Neuroscienc.2016; 53(1): 83.     CrossRef

Background
Transcranial magnetic stimulation (TMS) is a non-invasive diagnostic method particularly suited to investigation the long motor tracts. The clinical value of TMS in most spinal cord diseases has still to be made. Diagnostic value of magnetic motor evoked potential (MEP) parameters in intramedullary spinal cord lesions was investigated.
Methods
MEP elicited by TMS was recorded in 57 patients with clinically and radiologically defined intramedullary myelopathy. Twenty five patients with cervical myelopathy (CM) and 32 thoracic myelopathy (TM) were included. Recordings were performed during resting and minimal voluntary contraction at both abductor pollicis brevis (APB) and tibialis anterior (TA) muscles. Stimulation threshold(ST), amplitude, and central motor conduction time (CCT) were measured at resting and facilitated conditions. CCT was calculated by two means; central motor latency (CML)-M using magnetic transcranial and root stimulation, and CML-F using electrical F-wave study. The results were compared between patient groups and 10 normal control group.
Results
Facilitated mean ST recorded at TA was elevated in both CM and TM compared with control group. Resting mean CML-M at TA was significantly prolonged in both CM and TM, and CML-M was absent or delayed in 37.1% of CM and 8% of TM at APB with facilitation. Facilitated mean MEP amplitude at ABP was lower in CM than in TM, while MEP/M ratios were not different significantly between groups.
Conclusions
Magnetic motor evoked potential has diagnostic value in intramedullary myelopathy and localizing value in differentiating between CM and TM by recording at APB and TA. It is a noninvasive way to investigate the functional status of motor tracts of spinal cord.

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.

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
& Objectives : Motor evoked potentials(MEPs) to magnetic trans cranial stimulation were performed to evaluate upper moror neuron involvement and relationship to lower motor neuron involvement in motor neuron disease patients. Method : MEPs were obtained in the 17 consecutive patients with motor neuron disease. These patients were divided into three group based on clinical evidence of upper and lower motor neuron involvement, bulbar symptom; amyotrophic lateral sclerosis(ALS), progressive muscular atrophy(PMA), Progressive bulbar palsy(PBP), MEPs were recorded from abductor pollicis brevis and abductor hallucis. Abnormal MEPs were defined by delayed central motor conduction time or absent MEP. Results : MEPs were abnormal in 64%(11/17) of patients; 100%(7/7) in ALS, 64%(4/7) in PMA, 0%(0/3) in PBP respectively. In 68 total recording muscles, 34 muscles had evidence of motor weakness and showed abnormal responses in 59%(20/34). Whereas 34 muscles with normal strength, only 3%(1/34) of muscles showed abnormal responses. Conclusion : MEPs are well correlated with upper motor neuron signs in ALS and may detect masking upper motor neuron signs I PMA. The muscles with lower motor neuron sign(weakness) usually relate with abnormal MEPs reponses.

Brain stem auditory evoked potential(BAEP) is a useful study to evaluate the integrity of auditory system particularly from cochlear nerve up to brain stem. This review article will provide the basic protocol settings necessary for collecting routine BAEP procedures for the neurological diseases. Also, basic knowledge necessary for the understanding and interpretation of the BAEP responses will be discussed.

Backgroun & Objectives : Hyperexciability of motor system is a well-established characteristic pathophysiologic finding of mayotrophic lateral sclerosis (ALS). Whereas little is known about the source of excitability according to the progression of the disease. We evaluated the excitability and its source in advanced ALS patients using transcranial magnetic stimulation(TMS). Material & Methods : Motor evoked potentials (MEP) by TMS were recorded for abductor pollicis brevis muscles in 20 patients, 11men and 9 women, with ALS. Mean age was 54.2?2.1 years, and mean disease duration was 13.9?3.4 years. Serial magnetic stimulations were applied to get the parameters; excitability threshold (ET), amplitude and latency of MEP. We also had a facilitated MEP (fMEP). Results : The parameters were analyzed according to the clinical setting. ET was higher in ALS(mean 63.5?8.1) than normal control (mean 46.0?.4 , p<0.01). Amplitudes of MEP were reduced I ALS (2.6?.6 mV ; control 6.5?.1mV, p<0.01). Duration of the disease and ET showed significant inverse correlation (Spearson correlation coefficient = -0.57, p<0.01). Duration of the disease and fMEP/MEP ratio showed less but also significant inverse correlation(Spearson correlation coefficient, r=-0,52, p<0.05). Conclusions : Lower ET in advanced ALS patients, in spite of decreased fMEP/MEP ratio, may indicate the hyperexcitability of lower motor neuron in these patients. This study suggests that lower motor neurons is hyperexciable due to upper motor neuron dysfunction at advanced stage.

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.

Background
and Objectives: The proximal and distal nerve segments are preferentially involved in acquireddemyelinating polyneuropathies (ADP). This study was undertaken in order to assess the usefulness of motor evokedpotential (MEP) and somatosensory evoked potential (SSEP) in the detection of the proximal nerve lesion in ADP.Methods: MEP, SSEP and conventional NCS were performed in 6 consecutive patients with ADP (3 AIDP, 3 CIDP).MEP was recorded from abductor pollicis brevis and abductor hallucis using magnetic stimulation of the cortex and thecervical/lumbar spinal roots. SSEP were elicited by stimulating the median and posterior tibial nerves. Latency fromcortex and cervical/lumbar roots, central motor conduction time (CMCT), EN1-CN2 interpeak latency were measuredfor comparison.Results: MEP was recorded in 24 limbs (12 upper and 12 lower limbs) and SSEP in 24 limbs (12 median nerve, 12posterior tibial nerve). F-wave latency was prolonged in 25 motor nerves (25/34, 73.5%). Prolonged CML and PMLwere found in 41.7% (10/24) and 45.8% (11/24), respectively. Interside difference (ISD) of CMCT was abnormallyincreased in the upper extremity, 66.7% (4/6 pairs) in case of CML-PML. EN1-CN2 interpeak latency was abnormallyprolonged in one median nerve (1/10) and LN1-P1 interpeak latency was normal in all posterior tibial nerves.Conclusions: MEP and SSEP may provide useful information for the proximal nerve and root lesion in ADP. MEPand SSEP is supplemental examination as well as complementary to conventional NCS.

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.