VEP Recording Research Articles

Normative data of Visual Evoked Potential in children and correlation with age

Background: Visual Evoked Potential is the assessment of the visual pathway and the visual cortex. The present study was descriptive analysis of normal VEP between the age of 6 months to 4 years of age and the determination of the neuronal development among healthy children of above age group.Materials and Methods: The study was conducted in neurological lab of BPKIHS on healthy children (n=36) of well-baby clinic between the age of 0.5 to ≤4 years (yr). Subjects were divided into subgroup 1(0.5 to ≤2 yr), subgroup 2(2 to ≤3 yr) and subgroup 3(3 to ≤4 yr). Visual stimulator provided with flash light emitting diode (LED) goggle was used to stimulate the retina and VEP recording was done. Flash VEP parameters: latencies (N90, P120) and amplitude (N90-P120) were recorded. Post hoc (Bonferroni) analysis was done for comparing VEP variables. Pearson correlation and scatter plot with trend line analysis were done for VEP with respect to ageResults: VEP latencies of children, age-group 3 to Μ4 yr showed significantly less N90 latency on right eye stimulation comparing age-group 0.5 to Μ2 yr (103.75±22.54 vs. 79.09±17.77ms, p=0.012). P120 latency was significantly less on right eye stimulation (148.5±15.38 vs. 116.67±13.65ms p=0.001) and on left eye stimulation (145.91±18.11 vs. 116.67±13.65 ms, p=0.001) in age-group 3 to Μ4 yr children as compared to age-group 0.5 to Μ2 yr.Conclusion: Significant decrement of VEP latencies as age advances which explains the maturation of central nervous system and functionally approaching to adult value at around 3 to 4 yr.Asian Journal of Medical Sciences Vol.7(2) 2015 39-43

Is lack of habituation a biomarker of migraine? A critical perspective.

Processing of sensory stimuli has been supposed to be dysfunctioning in migraine. A basis for such abnormality has been identified in a defective ability to habituate to repetitive sensorial stimulation. Habituation, i.e. the way the nervous system attenuates response to repeated non noxious stimuli is a fundamental function of sensory systems, that allows appropriate adaptation of neural responses to the relevance of incoming stimuli. In humans, habituation can be studied by evoked potentials where it is indexed by a reduction of amplitude of the evoked response to repeated stimulation. After the first evidence by Schoenen et al in 1995[1] of reduced habituation to visual evoked potentials in migraine the defect was confirmed in other studies, not only with visual stimuli, but also with other sensory modalities (acoustic, somatosensory) and even with nociceptive stimulation. For such a consistency lack of habituation has been considered a neurophysiological hallmark of the disease. However, critical aspects concerning this statement have been recently raised because the requirement for a disease hallmark appeared not to be met by lack of habituation[2, 3]. A disease hallmark should be intrinsic to the pathophysiology of a disease and as such ubiquitous or quite so and specific for that disease. This however, does not seem to be the case for lack of habituation in migraine. Some authors indeed were not able to find defective habituation in this disease and recently relevant criticism about this dysfunction has been raised by the group of Sand and Omland[2]. These authors indeed applying a different methodological approach (with a blind procedure for both VEP recording and analysis) in a series of studies (exploring a wide range of stimulation parameters) were not able to replicate, at least for visual modality, the habituation defect and attributed this to a likely expectancy bias not adequately controlled in previous studies. Moreover, dysfunctioning habituation is not specific for migraine as it has been found in several other diseases ranging from chronic pain states, to deafferentation diseases like tinnitus, or degenerative pathologies like Parkinson's disease. Thus, more than strictly related to migraine pathophysiology, lack of habituation could represent a more general marker of neural dysfunction that migraine can share with several other diseases.

Conscious Wireless Electroretinogram and Visual Evoked Potentials in Rats

The electroretinogram (ERG, retina) and visual evoked potential (VEP, brain) are widely used in vivo tools assaying the integrity of the visual pathway. Current recordings in preclinical models are conducted under anesthesia, which alters neural physiology and contaminates responses. We describe a conscious wireless ERG and VEP recording platform in rats. Using a novel surgical technique to chronically implant electrodes subconjunctivally on the eye and epidurally over the visual cortex, we are able to record stable and repeatable conscious ERG and VEP signals over at least 1 month. We show that the use of anaesthetics, necessary for conventional ERG and VEP measurements, alters electrophysiology recordings. Conscious visual electrophysiology improves the viability of longitudinal studies by eliminating complications associated with repeated anaesthesia. It will also enable uncontaminated assessment of drug effects, allowing the eye to be used as an effective biomarker of the central nervous system.

Physiological State Evaluation of VEP Recording by Combination of Image and EEG

Physiological State Evaluation of VEP Recording by Combination of Image and EEG

Faster and more sensitive VEP recording in children.

In the difficult-to-test paediatric population, shorter test procedures are desirable. This study investigates whether Laplacian analysis of a three occipital-electrode montage detects steady-state VEPs (ssVEPs) more often or faster in children than a conventional montage, and if so, in which age groups. Steady-state VEPs (7.78 reversals/s; checkerboard stimulus) to various checksizes (60-3', 0.07-14 cpd equivalent) were recorded from 80 normal children aged from 1 month to 13 years and 19 adults. Active occipital electrodes were placed at Oz and symmetrically either side at 15% of the subject's half-head circumference (right occipital and left occipital, RO and LO). The Laplacian analysis used 2Oz-(RO+LO) instead of the conventional Oz-Fz. Fourier analysis and a circular T2 statistic was used to determine VEP detection time (DT). The number of responses detected overall by each analysis method and the effects of age and checksize on DT differences between analysis methods were investigated. The Laplacian analysis detected more VEPs than the conventional Oz-Fz (95 versus 84%, p = 0.001) in children's age groups. The Laplacian analysis also provided faster response detection to 3' checks in all subjects over the age of five, and to 6' and 9' in 7-9-year-olds. A Laplacian analysis offers increased sensitivity and faster VEP detection over conventional (Oz-Fz) recording in children over five for threshold-sized VEPs. Simultaneous use of both conventional (Oz-Fz) VEP recording and a Laplacian analysis in all patient ages is likely to give faster, more accurate VEP assessments.

Quantifying the benefits of additional channels of multifocal VEP recording.

For some individuals and for some locations, multifocal visual evoked potentials (mfVEP) may be too small or appear 'too noisy' to be reliably measured. By adding electrodes, especially electrodes placed lateral to the midline, and by recording with multiple channels, the amplitude of the signal can be increased in some field locations. However, the addition of electrodes involves certain costs; the set-up time is longer and the data analysis more time consuming and complex. The objective of this study was to assess the benefits of adding electrodes by quantifying these benefits using a signal-to-noise measure. In addition to the typical midline placement of electrodes, two electrodes were placed 1 cm above and 4 cm lateral to the inion on each side. This allowed for 3 channels of recording and 3 additional, derived channels. The mfVEPs were recorded with a 60 sector, pattern-reversing display presented to one eye. Two 7 min records were obtained from 14 individuals with no known visual problems. The two records were averaged and a signal-to-noise (SNR) measure was obtained for every response from all 6 channels. For each sector of the display and each subject, the benefits of additional electrodes were quantified by comparing the SNR from the traditional midline channel to the best SNR from amongst the 6 channels. The number of responses exceeding any given criterion SNR value was increased with the additional channels. For example, 79% of the responses for the typical midline channel exceeded a SNR of 0.6 (a false positive rate of about 2.5%) and this increased to 93% when the best SNR value was used. As expected, summing the mfVEP responses from contiguous sectors also increased the SNR values. Additional electrodes and multiple channels of recording substantially improve the quality of the mfVEP records and the SNR measure provides a useful metric for assessing these benefits.

WS-11-2 An application of several unique methods to pattern VEP recording

WS-11-2 An application of several unique methods to pattern VEP recording

Improved processing of the steady-state evoked potential

Two related procedures for estimating the parameters of steady-state evoked potentials (SSEPs) are introduced. The first procedure involves an initial stage of digital bandpass filtering followed by a Discrete Fourier Transform analysis. In the second method, a high resolution method based on parametric modelling is applied to the filtered data. The digital pre-filter consists of a non-phase shifting Chebychev bandpass filter. The parametric modelling method considers the evoked-response-plus-noise distribution to consist of a set of exponentially damped sinusoids. The frequency, amplitude, phase and damping factors of these components are estimated by calculating the mean of the forward and backward prediction filters and linear regression. We compared the signal-to-noise ratio (SNR) of the new procedures to the conventional Discrete Fourier Transform method for Monte Carlo simulations utilizing known sinusoids buried in white noise, known sinusoids buried in human EEG noise and for a sample of visual evoked potential data. Both of the new methods produce substantially more accurate and less variable estimates of test sinusoid amplitude. For VEP recording, the EEG background noise level is reduced by 5–6 dB over that obtained with the DFT. The new methods also provide approximately 5 dB better SNR than the DFT for detection of sinusoids based on the Rayleigh statistic. The parametric modelling approach is particularly suited for the analysis of very short data records including cycle-by-cycle analysis of the SSEP.

Follow-up of visual evoked potential in full-term and pre-term control newborns and in subjects who suffered from perinatal respiratory distress

Thirty-five healthy newborns (18 pre-term) and 13 subjects who had suffered from slight (5), middle (3) or severe (5) respiratory syndromes were examined with VEP recording and clinically. Twelve subjects (9 pre-term) affected by perinatal troubles of different kinds (dismetabolic, infectious, etc.) were used for further comparison. A total of 102 records were taken between the 5th and 15th days of life, while for 6 controls, 6 of the second group and 2 of the third one, VEP records and clinical examinations were performed at the 2nd, 6th and 9th months of life. The evoked response was analysed as follows: P 2 wave latency, number of waves, maximal driving frequency with intermittent stimulation and prevalent polarity of the evoked waves. VEPs in normals were well correlated with gestational age, chronological age and body weight for P 2 latency decrement (from about 200 msec at birth down to 110 msec at the 9th month), increase in number of evoked waves, progressively higher maximal frequency of flicker response and clear-cut prevalence of negative polarities in the final response. Neonatal respiratory distress (middle and severe types) induced a severely altered VEP (mainly with delayed peaks and positive polarity) even at the 9th month of extrauterine life.

Visual Evoked Potentials in Menstrual Migraine

SYNOPSISVisual evoked potentials (VEP) were recorded and plasma estrogen, progesterone, FSH and LH hormones were determined in a group of patients with menstrual migraine and in healthy controls. Consistent differences from controls were found in the VEPs of migraine patients, justifying the use of VEP recording as a method of investigating the neurophysiology of migraine. The VEPs were not dependent on the hormonal cycle, except for responses to flashes 10/sec which in healthy persons were higher in the luteal phase. This was less clear in migraine patients. Some of the patients showed strong asymmetrical VEP distortion, which was always transient; follow‐up revealed later normalisation. The transient and asymmetrical VEP distortion seemed to relate to the asymmetrical symptoms of migraine, but a direct connection between the two was not established.