Evoked Potential Waveform Research Articles

Visual evoked potentials waveform analysis to measure intracortical damage in a preclinical model of multiple sclerosis.

Visual evoked potentials (VEPs) are a non-invasive technique routinely used in clinical and preclinical practice. Discussion about inclusion of VEPs in McDonald criteria, used for Multiple Sclerosis (MS) diagnosis, increased the importance of VEP in MS preclinical models. While the interpretation of the N1 peak is recognized, less is known about the first and second positive VEP peaks, P1 and P2, and the implicit time of the different segments. Our hypothesis is that P2 latency delay describes intracortical neurophysiological dysfunction from the visual cortex to the other cortical areas. In this work, we analyzed VEP traces that were included in our two recently published papers on Experimental Autoimmune Encephalomyelitis (EAE) mouse model. Compared with these previous publications other VEP peaks, P1 and P2, and the implicit time of components P1-N1, N1-P2 and P1-P2, were analyzed in blind. Latencies of P2, P1-P2, P1-N1 and N1-P2 were increased in all EAE mice, including group without N1 latency change delay at early time points. In particular, at 7 dpi the P2 latency delay change was significantly higher compared with N1 latency change delay. Moreover, new analysis of these VEP components under the influence of neurostimulation revealed a decrease in P2 delay in stimulated animals. P2 latency delay, P1-P2, P1-N1, and N1-P2 latency changes which reflect intracortical dysfunction, were consistently detected across all EAE groups before N1 change. Results underline the importance of analyzing all VEP components for a complete overview of the neurophysiological visual pathway dysfunction and treatment efficacy.

Utility of Brainstem Trigeminal Evoked Potentials in Patients With Primary Trigeminal Neuralgia Treated by Microvascular Decompression.

To investigate the characteristics of brainstem trigeminal evoked potentials (BTEP) waveform in patients with and without trigeminal neuralgia (TN), and to discuss the utility of BTEP in patients with primary TN treated by microvascular decompression (MVD). A retrospective review of 43 patients who underwent BTEP between January 2016 and June 2016, including 33 patients with TN who underwent MVD and 10 patients without TN. Brainstem trigeminal evoked potentials characteristics of TN and non-TN were summarized, in particular to compare the BTEP changes between pre- and post-MVD, and to discover the relationship between BTEP changes and surgical outcome. Brainstem trigeminal evoked potentials can be recorded in patients without trigeminal neuralgia. Abnormal BTEP could be recorded when different branches were stimulated. After decompression, the original W2, W3 disappeared and then replaced by a large wave in most patients, or original wave poorly differentiated improved in some patients, showed as shorter latency and (or) amplitude increased. Brainstem trigeminal evoked potentials waveform of healthy side in patients with trigeminal neuralgia was similar to the waveform of patients without TN. In 3 patients, after decompression the W2, W3 peaks increased, and the latency, duration, IPLD did not change significantly. Until discharge, 87.9% (29/33) of the patients presented complete absence of pain without medication (BNI I) and 93.9% (31/33) had good pain control without medication (BNI I-II). Brainstem trigeminal evoked potentials can reflect the conduction function of the trigeminal nerve to evaluate the functional level of the trigeminal nerve conduction pathway. The improvement and restoration of BTEP waveforms are closely related to the postoperative curative effect.

Cervical sympathetic block prolongs the latency and reduces the amplitude of trigeminal somatosensory evoked potentials on the contralateral side.

The purpose of this study was to investigate the latency and amplitude of trigeminal somatosensory evoked potentials to clarify how nerve function on the contralateral side is affected after cervical sympathetic block (CSB). Subjects comprised 16 volunteers. For CSB, the tip of a needle was contacted with the transverse process of the sixth cervical vertebra on the right side, and lidocaine was injected. Trigeminal somatosensory evoked potentials were recorded bilaterally from C5/C6 scalp positions. Pupil diameters were also measured. Electrical stimulations were applied to the left-side lower lip, and trigeminal somatosensory evoked potentials waveforms derived from both sides of the scalp were recorded. Then, electrical stimulations were applied to the right-side of the lower lip, and recording was again performed. Recordings were performed at 5, 15, and 30 minutes after CSB. On the CSB side, pupil diameter decreased at 5 and 15 minutes after CSB. Trigeminal somatosensory evoked potentials at contralateral stimulation showed a prolongation of the latency in both P20 and N25 components on bilateral recording sites 5 and 15 minutes after CSB. Trigeminal somatosensory evoked potentials' amplitude at contralateral stimulation was smaller than at ipsilateral stimulation 5 minutes after CSB. Cervical sympathetic block prolongs the latency and reduces the amplitude of trigeminal somatosensory evoked potentials on the contralateral side.

The effect of progressively increased physical efforts on visual evoked potentials in volleyball players and non-athletes

We assessed the effect of physical effort with increasing intensity on neural activity in the visual pathway in volleyball players (n = 10) and non-athletes (n = 10). Participants performed three 10-min tests of increasing intensity on a cycle ergometer. Each participant was assigned individual workloads below the lactate threshold (40% [Vdot]O2max), at the lactate threshold (65–75% [Vdot]O2max), and above the lactate threshold (80% [Vdot]O2max). Four recordings of visual evoked potentials were made: pre-exercise and immediately after each of the three subsequent tests. We assessed neural activity of the visual pathway by examining the amplitude and latency of the N75, P100, and N135 components of the visual evoked potentials waveform. Pre-exercise P100 wave latency was shorter (P < 0.05) in volleyball players than in non-athletes. In non-athletes, the latency of P100 following the first and second effort (40% and 65–75% [Vdot]O2max) was reduced compared with pre-exercise (P < 0.01). However, P100 latency increased and P100 amplitude decreased after the third test (80% [Vdot]O2max) in non-athletes. In contrast, no significant changes in the latency or amplitude of visual evoked potentials were observed in the athletes in the three tests. Neural conductivity in the visual pathway after exercise might be at least partially dependent on the individual's personal training adaptation status.

Possibility of an Electrophysiological Experimental model using Brainstem Evoked Potentials with multi-channel dural electrodes array in rats

The rat is one of the most popular experimental animals in medical fields. However, the rat is not so often used in complicated neurological studies because of its size of the brain. To investigate the localization of waveform of auditory brainstem responses (ABRs), two rats were examined. Twelve or 13 platinum-rhodium coated electrodes were implanted on the dura mater through the cranial bone. The waveform of ABRs with 6 peaks was clearly recorded. These peaks were comparable with those of the human. However, the latency of these peaks was slightly shorter compared with that of the human. These 6 peaks were clearly identified in the waveform measured on the occipital area. On the other hand, these peaks recorded in frontal region were fused together. From these results, electrodes should be placed on the occipital area of the cranial bone to identify these peaks originated from brainstem by the auditory stimulation. Therefore, it is expected that latency changes can be evaluated clearly. This measurement system has a new possibility to analyze the details of various kinds of evoked potentials waveforms.

Stimulation threshold potentials of intraoperative cortical motor mapping using monopolar trains of five in pediatric epilepsy surgery

Direct cortical stimulation in commonly used for the accurate localization of the motor cortex but the electrical threshold stimulation parameters with this technique had not been fully established. A retrospective review of 15 cases of pediatric surgical cases were performed. The patients consisted of nine male patients and six female patients with age range from 2 to 18 years (mean: 10.8 years; median: 14 years). The most common pathology was cortical dysplasia (nine cases). Stimulation was performed with a train of five stimulations (range five-seven stimulations; <5% of stimulations required more than five stimulations) applied, each train of 50 micros pulse duration, with an interstimulus interval of 1.1 msec. Stimulation intensity commenced at 25 V and this was increased at 5-10 V increments until motor evoked potentials waveforms of sufficient duration and morphology were consistently generated. Monopolar electrical stimulation threshold for intraoperative motor cortical mapping were found to be more consistent in the upper limb compared to lower limb and facial muscles. Evoked responses from the extensor digitorium communis had the highest recorded rate (83.7%) and required the lowest stimulation voltage (36.0 V). The stimulation voltage was found to be statistically significant compared to threshold values for abductor hallucis, tibialis anterior, deltoid, and orbicularis oris with respective p values of 0.006, 0.021, 0,027, and 0.015. There was also a distinct trend that patients with cortical dysplasia/tuberous sclerosis have higher stimulation thresholds when compared to other pathology (p = 0.067). Monopolar electrical stimulation threshold for intraoperative motor cortical mapping were more consistent in the upper limb compared to lower limb and facial muscles. Evoked responses from the extensor digitorium communis had the highest recorded rate and required the lowest stimulation voltage. There was also a distinct trend that patients with cortical dysplasia/tuberous sclerosis have higher stimulation thresholds.

Use of epidurally derived evoked potentials for quantification of caudal nociception in ponies

To determine whether epidurally derived evoked potentials (EPs) can be used to reliably assess nociception and antinociception in ponies. 7 ponies. EPs and electromyograms (EMGs) from the quadriceps femoris muscles were recorded simultaneously, following electrical stimulation applied to the distal portion of the hind limb. The effect of increasing stimulus intensity, conduction velocities of the stimulated nerves, effect of epidurally applied methadone, and effect of systemically administered propofol were evaluated. In the EP and EMG waveforms, 2 distinct complexes, the EP N25 and P50 and the EMG P27 and N62, respectively, were identified. On the basis of their latency and calculated conduction velocities, the EP P50 and EMG N62 were considered to be related to nociception (AD-mediated). All complexes increased significantly in amplitude with increasing stimulus intensity and decreased significantly following epidural administration of methadone or systemic administration of propofol. Although the experimental setup allowed successful discrimination between tactile- and nociceptive-associated responses, the identified EPs, considered to reflect activity in the spinal cord, could not be definitively differentiated from activity in the lumbosacral epaxial musculature. Further research is required to refine measurement techniques to allow for discrimination between these 2 signals. Similar to other species, neurophysiologic variables such as EPs could potentially become a useful additional tool in quantifying nociception in equidae.

A new combination: scale-space filtering of projected brain activities

In the present study, well known scale-space filtering (SSF) algorithm is used in combination with a linear mapping approach (LMA) to obtain clear auditory evoked potential (EP) waveform. The proposed combination involves two sequential steps: At first, the EEG noise level is reduced from -5 to 0 dB owing to the LMA based on the singular-value-decomposition. In the secondary process, the EEG noise remaining on the projected data is removed by using the SSF. A small number of sweeps are composed as a raw matrix to project the data without using the ensemble averaging at the beginning of the proposed method. Then, single sweeps are individually filtered in wavelet domain by using the SSF in the secondary step. The experimental results show that the SSF can extract the clear single-sweep auditory EP waveform where the LMA is used as a primary filtering. As well, the results indicate that the EP signal and background EEG noise create different wavelet coefficients due to their different characteristics. However, this characteristic difference can be considered to distinguish the EP signal and the EEG noise when the Signal-to-Noise-Ratio is higher than 0 dB.

Estimation of individual evoked potential components using iterative independent component analysis

Independent component analysis (ICA) has been successfully employed in the study of single-trial evoked potentials (EPs). In this paper, we present an iterative temporal ICA methodology that processes multielectrode single-trial EPs, one channel at a time, in contrast to most existing methodologies which are spatial and analyze EPs from all recording channels simultaneously. The proposed algorithm aims at enhancing individual components in an EP waveform in each single trial, and relies on a dynamic template to guide EP estimation. To quantify the performance of this method, we carried out extensive analyses with artificial EPs, using different models for EP generation, including the phase-resetting and the classical additive-signal models, and several signal-to-noise ratios and EP component latency jitters. Furthermore, to validate the technique, we employed actual recordings of the auditory N100 component obtained from normal subjects. Our results with artificial data show that the proposed procedure can provide significantly better estimates of the embedded EP signals compared to plain averaging, while with actual EP recordings, the procedure can consistently enhance individual components in single trials, in all subjects, which in turn results in enhanced average EPs. This procedure is well suited for fast analysis of very large multielectrode recordings in parallel architectures, as individual channels can be processed simultaneously on different processors. We conclude that this method can be used to study the spatiotemporal evolution of specific EP components and may have a significant impact as a clinical tool in the analysis of single-trial EPs.

Differences in waveforms of cerebral evoked potentials among healthy subjects, schizophrenics, manic-depres-sives and epileptics

The differences in the waveform of Cerebral EP (Evoked Potential)s; SEP, VEP and AEP, among healthy subjects, schizophrenics, manic-depressives and epileptics were investigated. In 585 subjects of both sexes comprising these diagnostic groups, 6 channels of EPs, each 2 channels for each sensory modality, were recorded simultaneously/parallelly from each subject, without assigning a mental task. Then, waveforms of the g-m (group mean) EPs of each diagnostic group were superimposed for inspection. Peak latencies and inter-peak amplitudes of individual EPs were statistically tested among (ANCOVA) and between (Scheffe's multiple comparison test) these diagnostic groups for each channel (modality), and for each sex. The waveforms of g-m EPs of each diagnostic group differed from each other. The differences of latencies and inter-peak amplitudes among these diagnostic groups attained to the significant level (P<0.05), with more significant differences between healthy subjects and each of these pathological diagnostic groups than between each of these pathological diagnostic groups, for each sex. Thus the differences in the waveform of EPs among these diagnostic groups were confirmed even taking the effect of medication on EPs into consideration. These results might suggest the existence of a waveform for individual EPs specific to each of these diagnostic groups, for each sex.

Single-trial evoked potential estimation: Comparison between independent component analysis and wavelet denoising

Objective Brain responses to repeated sensory stimuli are typically buried in the more prominent background activity, and thus analysis of these responses on a single-trial basis would require advanced procedures to estimate the brain activity related only to the experimental task. Recently, we have proposed a new iterative independent component analysis ( iICA) approach to estimate single-trial responses. In this paper, we compare the performance of iICA at estimating single-trial responses with ensemble averaging and wavelet transform (WT) denoising. Methods We analyzed simulated evoked potentials (EPs) and actual recordings of the auditory N100 component from 33 normal subjects, and the performance of each method was quantified in terms of the average root-mean-square error and average correlation before and after processing. Results We found that WT gave a smoother overall average EP, while iICA could isolate the N100 component out of the entire EP waveform. With simulated data, iICA provided significantly better estimates of the true EP compared to plain averaging ( p < 0.01) and WT ( p < 0.01). With actual data, iICA showed clear responses in single trials, in all subjects. Additionally, the corresponding average EPs had a sharper N100–P200 complex, with flatter preceding and following regions, resulting in an enhanced N100 component. Conclusions The iICA procedure can provide clear responses in each single trial, and the resulting average N100 component is significantly improved compared to plain averaging and wavelet denoising. Significance The proposed technique may have a significant impact as a clinical tool in the analysis of single-trial responses.

Update on Anesthetic and Metabolic Effects During Intraoperative Neurophysiological Monitoring (IONM)

ABSTRACT.Various agents are utilized in the operating room to produce anesthetic effects. These include barbiturates, halogenated inhalation agents, narcotics, non-barbiturate induction agents, and benzodiazepines. These agents have variable effects upon the EEG and EP (evoked potential) waveforms at different anesthetic levels. Metabolic changes such as body temperature and blood pressure can also elicit changes in the EEG and EPs.

Brain evoked potentials of 3‐D auditory stimuli

For evaluation of spatial cognitive function, we studied the brain evoked potentials (EP) of 3-D auditory stimuli in regard to the change of latencies in normal subjects aged 1-21 years and compared them with patients who have mental retardation (MR). A total of 144 normal subjects and 67 patients with MR were tested. The EP were elicited by 1000 Hz fixed and enlarged tones with Doppler effect randomly presented. No specific task was imposed in relation to the auditory stimuli. Electroencephalograms were recorded at the Fpz, Fz, Cz, Pz and Oz scalp locations (10-20 system), referenced to linked earlobes. The 64 responses of EP were averaged. The EP were measured from the difference in waveform by subtracting the EP of the fixed tone stimuli from that of the enlarged tone stimuli. The waveforms of EP consisted of the components P0, N1, P1, N2 and P2. These components (P0, N1, P1, N2 and P2) in the EP gradually shortened with increasing age in children. About 30% of patients with MR showed more prolonged latencies than normal subjects. These results suggest that these components indicated auditory kinetic evoked potentials. This developmental change could be related to maturational phenomena regarding spatial cognitive function. The EP of 3-D auditory stimuli may be used in children to evaluate the development of spatial cognitive function.

Spectral tuning of visual pigments: the rhodopsins of cottoid fish from Lake Baikal

Brain responses to repeated sensory stimuli are typically buried in the more prominent background activity, and thus analysis of these responses on a single-trial basis would require advanced procedures to estimate the brain activity related only to the experimental task. Recently, we have proposed a new iterative independent component analysis (iICA) approach to estimate single-trial responses. In this paper, we compare the performance of iICA at estimating single-trial responses with ensemble averaging and wavelet transform (WT) denoising.We analyzed simulated evoked potentials (EPs) and actual recordings of the auditory N100 component from 33 normal subjects, and the performance of each method was quantified in terms of the average root-mean-square error and average correlation before and after processing.We found that WT gave a smoother overall average EP, while iICA could isolate the N100 component out of the entire EP waveform. With simulated data, iICA provided significantly better estimates of the true EP compared to plain averaging (p < 0.01) and WT (p < 0.01). With actual data, iICA showed clear responses in single trials, in all subjects. Additionally, the corresponding average EPs had a sharper N100–P200 complex, with flatter preceding and following regions, resulting in an enhanced N100 component.The iICA procedure can provide clear responses in each single trial, and the resulting average N100 component is significantly improved compared to plain averaging and wavelet denoising.The proposed technique may have a significant impact as a clinical tool in the analysis of single-trial responses.

Spinal and cortical evoked potential studies in the ketamine-anesthetized rabbit: fentanyl exerts component-specific, naloxone-reversible changes dependent on stimulus intensity.

This study examined the changes in spinal and cortical evoked potentials (EPs) produced by fentanyl in the rabbit. The reversibility of these effects by naloxone and the effects of varying stimulus intensity also were examined. Eleven ketamine-anesthetized rabbits underwent analysis of spinal and cortical EPs produced by posterior tibial nerve electrical stimulation. Progressive fentanyl doses up to 100 micrograms/kg total were given intravenously. Stimulus intensities of two to eight times the motor threshold (MT) were used. The lowest stimulus (2 x MT) was insufficient to activate A delta fibers whereas the highest (8 x MT) produced consistent A delta activation. Two spinal potential waveform components (N1, P2), at 4 and 10 ms, and four cortical components (P1, N2, P3, N4), at 15, 30, 60, and 95 ms, were analyzed. Significant amplitude reductions in spinal P2 (46%), cortical N2 (54%), cortical P3 (47%), and cortical N4 (45%), P < 0.01, as well as latency prolongation in cortical P1 (11%), P < 0.01, resulted from administration of a total dose of 100 micrograms/kg of fentanyl. The effect of fentanyl was critically dependent on stimulus intensity for the cortical P3 component (P < 0.01). All changes were reversed by naloxone. Fentanyl produced dose-related changes in specific spinal and cortical EP waveform components in the ketamine-anesthetized rabbit. This effect was significantly dependent on stimulus intensity in at least one cortical component (P3). Such an interaction between drug dose and stimulus intensity may be relevant to interpreting other human and animal evoked potential studies.

Comparison of long-term enhancement and short-term exploratory modulation of perforant path synaptic transmission

Long-term enhancement (LTE/LTP) is an artificially induced form of synaptic change that may underlie memory storage in the hippocampus; however, there is as yet no evidence that this process occurs naturally as a result of normal neural activity. In the dentate gyrus, synaptic change does occur in conjunction with an animal's recent history of exploratory behavior. This change, which persists for a short time (ca. 30 min) following cessation of exploration, has been called short-term exploratory modulation (STEM). This experiment examined the relationship between LTE and STEM by comparing the magnitude of STEM before and after induction of LTE in rats with chronically implanted stimulating electrodes in the perforant path and recording electrodes in the fascia dentata. The absolute magnitude of STEM was the same before and after LTE saturation, suggesting that the processes are independently of each other. Furthermore, quantitative and qualitative analyses of the types of changes seen in the evoked-potential waveforms reveal different types of alteration. LTE includes an increase in EPSP slope, whereas STEM reflects an increase in EPSP onset. These data suggest that it is unlikely that STEM and LTE reflect the same synaptic process, and are at least partly consistent with recent reports suggesting that STEM may be mediated by activity-dependent changes in brain temperature.

Method for single-trial recordings of somatosensory evoked potentials

Evoked potentials (EPs) in response to stimuli are recorded from a human scalp contaminated with noise. To improve the signal-to-noise ratio, averaging methods have been widely used for the recorded data. However, when the waveforms of EP for each stimulus are not identical, the average waveform of the EP deteriorates. Variation of the EP waveform to each stimulus itself is important information for the EP. In this paper, a recording method for single somatosensory evoked potential (SEP) waveform is proposed, in which three kinds of band-pass filters were selectively used during three specific time sectors for each interstimulus interval. For the late section of the interval, an EEG waveform prediction method was applied to eliminate contaminated alpha rhythm components. By using the proposed method, we were successful in detecting the single SEP waveform.

Evoked potential topography in major depression. I. comparisons with nonpatients and schizophrenics

This study compared evoked potential (EP) topography in major depression (MD), schizophrenia and nonpatient controls. EPs to four kids of stimuli were recorded from 15 locations. Patients were 69 MDs and 52 schizophrenics, currently unmedicated. EP waveforms of 195 controls were subjected to principal component factor analysis (PCA). The structures of 32 factors so extracted have been shown to encompass the data space of disparate groups; they were used to compute factor scores for all subjects. Age and gender-matched groups were compared. Factor scores were normalized across leads (Z-transform) to distinguish between topographic and mean level differences. Topographic differences ( P < 0.05) between MD and controls were demonstrated for scores of 8 factors, with 2 others at P = 0.053. Unlike those for schizophrenia/control comparisons, these topographic differences did not converge regionally in MD. EP findings were not related to duration of withdrawal from drugs. There were few differences between bipolar and unipolar patients. Topographies of 5 factors differed between MDs and schizophrenics; these involved all modalities and reflected long latency, cognition-related events, such as P300. These topographic differences were antero-posterior (AP); values were greater posteriorly in MDs and anteriorly in schizophrenics. Deviant AP gradients appear specific to MD; gradients were similar in schizophrenics and controls.

Topography of the evoked potential to spatial localization cues.

Visual tasks that are perceptually diverse might be expected to elicit unique evoked-potential waveforms that exhibit differing topographic maps. To investigate this possibility, multichannel visual-evoked potentials (VEPs) were recorded in response to several dot spatial localization stimuli that are physically similar yet produce different percepts (vernier offsets, steroscopic disparity, bisection, orientation, and relative displacement) to determine if the unique percepts arising from these stimuli reflect the activation of different cortical neural populations. The resulting evoked potentials were all similar in waveform, although the stereoscopic VEPs were relatively delayed. Topographic maps of the evoked-potential activity to each stimulus revealed a late major component with two independent foci: one 7 or more centimeters above the inion lateral to the midline, and the other at least 6 cm lateral to OZ. The scalp localization of both peaks was independent of both the position of the stimulus in the visual field and the particular stimulus cue presented. An asymmetric response to pattern appearance vs. disappearance indicated strong pattern specificity for each stimulus type except unreferenced motion. The timing of the VEP responses and relative insensitivity to retinal locus of stimulation suggest the involvement of higher cortical areas. The two map foci might be interpreted as activation of inferotemporal and parietal cortices whose roles are thought to be visual object interpretation and spatial attention and localization, respectively.

Evoked potential topography in unmedicated and medicated schizophrenics

The main purposes were to determine whether: (1) evoked potential (EP) topography differs from normal in schizophrenics; (2) EP topography is altered by psychotropic drugs. Unmedicated ( n=72) and medicated ( n=57) schizophrenics were compared with age- and sex-matched non-patients and with one another. EPs to left and right median nerve, visual pattern and auditory stimuli were recorded from 15 leads. EP data were reduced by principal component analysis (PCA) of EP waveforms, with separate PCAs for later and earlier poststimulus times; 32 factors were extracted. Factor scores, based on factor structure of 195 non-patients, were computed for all subjects. Topographic effects were evaluated by ANOVAs on Z-transformed factor scores. The results were: (1) topographies differed between groups in about one-third of the factors, but variables yielding effects differed between comparisons; (2) topographic differences from normal in unmedicated patients converged at left temporoparietal (higher in schizophrenics) and right fronto-central-temporal areas (lower in schizophrenics); (3) similar convergence was absent in medicated patients; (4) most medicated vs unmedicated patient topographic differences persisted in groups matched for psychopathology. Results appear consistent with “focal cortical arousal” of the left posterior quadrant in schizophrenics (Morihisa and Duffy, 1986) and suggest that medication alters EP topography.