Visually Evoked Potentials to Electronic Pattern Reversal: Latency Variations with Gender, Age, and Technical Factors

Resolving a "W-Shaped" P100 Waveform: Is It Normal or Abnormal?

SUMMARY

Pattern-reversal visual evoked potentials are used to assess the visual pathways. The main waveform of interest is the P100, which is best recorded with electrodes over the mid-occipital region. Most often, the P100 waveform has negative-positive-negative components. Occasionally, it is "W-shaped," with positive-negative-positive components. Although most often a W-shaped P100 waveform indicates an abnormality in the visual pathway, occasionally, it can be normal. A case is presented in which a W-shaped P100 waveform is seen after monocular full-field stimulation of both eyes with 30' checks. To resolve this finding, the pattern-reversal visual evoked potentials is repeated with 60' and 15' checks. With 15' checks a single typical single-peak P100 waveform is seen with normal latency. Evaluation of a W-shaped P100 waveform should involve analysis of various montages, stimulation with different check sizes, and hemifield stimulation to confirm whether the W-shaped waveform is normal or abnormal.

True pattern-reversal LED stimulator and its comparison to LCD and CRT displays: visual evoked potential study

A rapid checkerboard pattern change is used to elicit pattern-reversal visual evoked potentials (PR VEPs). CRT or LCD monitors do not allow immediate reversal of the entire pattern. The study aimed to construct a new stimulator whose characteristics approximate an instantaneous reversal and verify whether the improvement is reflected in PR VEPs. A new stimulator using a matrix of 12 × 48 independent white square LEDs was designed and compared with LCDs and CRTs. The effect on the PR VEP peak times and amplitudes of N70, P100, and P140 waves was evaluated in ten subjects. The LED stimulator showed significantly better performance in the rate of change of illuminance, change of pattern, luminance settling and stability. The PR VEP amplitudes of N75, P100, and N140 did not show significant differences. The sum of interpeak amplitudes was significantly larger for the LCD than for the other monitors. The peak times of the waves evoked by the LED were shorter than those evoked by the LCD and CRT for the N75 wave and a check size of 30´. LED stimulators are a better alternative to CRTs for PR VEPs than current LCDs. LEDs also seem to be better than CRTs, but further research is necessary to obtain significant results.

Developmental trajectory of transmission speed in the human brain

The structure of the human connectome develops from childhood throughout adolescence to middle age, but how these structural changes affect the speed of neuronal signaling is not well described. In 74 subjects, we measured the latency of cortico-cortical evoked responses across association and U-fibers and calculated their corresponding transmission speeds. Decreases in conduction delays until at least 30 years show that the speed of neuronal communication develops well into adulthood.

Normative values of visual evoked potential in adults

PURPOSE

Visual evoked potentials (VEP) are used to determine the function of visual pathway from the optic nerve to visual cortex. Various factors may affect VEP response, viz., technical and environmental. The aim of this study is to obtain the normative value of VEP latency and amplitude parameters in adulthood in Indonesia, as well as the relationship of height, weight, body mass index (BMI), head circumference, and visual acuity with the variety of latency and amplitude values of VEP parameters.

METHODS

It is a cross-sectional study on 120 healthy subjects consisting of 60 males and 60 females between 18 and 65 years old. Height, weight, BMI, head circumference, and visual acuity were measured and continued with VEP examination using a 26' checkerboard pattern on the left and right eyes alternately. All data were collected and analyzed with the Shapiro-Wilk test using statistical software R version 3.5.2.

RESULTS

Mean value of P100 latency (interocular latency) of left and right eye were 104.6 ± 3.4 ms and 104.1 ± 3.4 ms, respectively, as well as 9.8 ± 4.7 μV and 10.3 ± 5.4 μV for the amplitude. There was no significant difference between the male and female group, as well as on the age group. Female significantly exhibited a higher P100 amplitude than male. The greater the age, the lower amplitude of P100 significantly.

CONCLUSION

Gender and age do not affect the P100 latency value but only affect P100 amplitude. Height, weight, BMI, head circumference, and visual acuity also do not affect the P100 latency and amplitude.

Acute effect of caffeine on pattern-reversal visual evoked potential: a randomized-controlled study

Purpose: This study was aimed to investigate the acute effect of caffeine intake on pattern-reversal (PR) visual evoked potential (VEP). Methods: This randomized controlled study included 40 participants who were divided into two groups randomly (group 1 [study group, n = 20] and group 2 [control group, n = 20]). While the study group received coffee beverages made from 6 g pure coffee beans (36 mg of caffeine per gram) containing approximately 216 mg caffeine, the control group was given beverages containing 200 mg lactose without caffeine. PR-VEP test was performed at baseline and 1 h after the beverage intake. The right eyes of both groups were used for the statistical analysis. Results: The median age of group 1 (8 male and 12 female) and group 2 (7 male and 13 female) were 31.0 (range, 21-59) and 36.5 (range, 20-59) years, respectively. No statistically significant difference was found between two groups in terms of age (p = 0.398) and gender (p = 0.744). Before the caffeine intake, median P100 latency and amplitudes were 109.90 ms (range: 99.60-120.60) and 12.45 µV (range: 5.20-19.30), respectively. One hour after caffeine intake, corresponding values were 110.70 ms (range: 99.00-114.60) and 12.45 µV (range: 5.70-20.0). Baseline P100 latency and amplitude values were not significantly different from the values recorded 1 h after caffeine intake (p > 0.05). Conclusions: This study showed that ingesting moderate amounts of caffeine did not affect PR-VEP parameters. Therefore, caffeine restriction does not seem to be required before the PR-VEP test. Further studies are needed to confirm our findings.

Sex differences in the human visual system

This Mini-Review summarizes a wide range of sex differences in the human visual system, with a primary focus on sex differences in visual perception and its neural basis. We highlight sex differences in both basic and high-level visual processing, with evidence from behavioral, neurophysiological, and neuroimaging studies. We argue that sex differences in human visual processing, no matter how small or subtle, support the view that females and males truly see the world differently. We acknowledge some of the controversy regarding sex differences in human vision and propose that such controversy should be interpreted as a source of motivation for continued efforts to assess the validity and reliability of published sex differences and for continued research on sex differences in human vision and the nervous system in general. © 2016 Wiley Periodicals, Inc.

Optimal Check Size and Reversal Rate to Elicit Pattern-reversal MEG Responses

Objective:

To determine the impact of check size and interstimulus interval (ISI) on neuromagnetic visual cortical responses.

Methods:

We recorded visual evoked fields to pattern-reversal stimulation with central occlusion in ten subjects. The ~100 ms magnetic activation (P100m) was analyzed by single dipole modeling.

Results:

With 1 s ISI, P100m strengths increased as check size increased from 15' up to 120' of visual arc, and larger checks elicited less P100m activation. With 120' checks, we found no P100m attenuation as ISI decreased from 4 s to 0.16 s. P100m sources around the calcarine sulcus did not vary with check size or ISI.

Conclusions:

The magnitude of cortical activation during visual contrast processing is check size-dependent and the 120' checks are optimum for future studies on neuromagnetic visual cortical functions using central-occluded stimulation. The corresponding neuronal activation demonstrated a short refractory period less than 0.16 s. We also found significantly overlapping cortical representation areas for different check sizes or ISIs.

Association of Height With Pattern Reversal Visual Evoked Potentials

PURPOSE

This study was conducted to investigate whether pattern reversal visual evoked potential parameters in a large sample of healthy subjects are influenced by height of the subjects.

DESIGN

It was an institutional, cross-sectional study.

METHODS

Pattern reversal visual evoked potential (PRVEP) recordings from 400 eyes from 200 normal subjects were performed in the Neurophysiology unit of the Department of Physiology in accordance to the standardized methodology and montages were kept as per 10-20 International System of electroencephalogram electrode placements. VEP latencies, duration and amplitude were measured in all subjects. The correlation of all the electrophysiological parameters with height was evaluated by Pearson's correlation co-efficient (r) and its statistical significance was evaluated.

RESULTS

On correlating mean height with mean VEP parameters of both eyes in the subjects it was found that there is a positive correlation of P100 latency and N155 latency in the subjects and a highly significant negative correlation of P100 amplitude with height in the subjects of various age groups. N70 latency was found to be significantly positively correlated with height whereas P100 Duration showed a non-significant negative correlation with height of the subjects.

CONCLUSION

Our findings suggest that VEP latencies, duration and amplitude are influenced by the height of the individual. The positive correlation between VEP latencies and increasing height may all reflect the increase in length between the optic nerve head and the visual processing areas-the striate and the extra striate cortex which are the main generators of the various PRVEP waveforms.

Electrophysiological Evaluation of Cranial Neuropathies

BACKGROUND

Cranial nerve abnormalities occur frequently in both focal and diffuse neurologic disorders and can be evaluated by electrophysiological techniques available in most clinical neurophysiology laboratories.

REVIEW SUMMARY

The optic nerve is evaluated by visual evoked potentials. Measurements of latency, amplitude, and waveform morphology are especially useful in detecting demyelinating lesions. Brain stem auditory evoked potentials evaluate the auditory portion of the eighth cranial nerve. Using an auditory stimulus, a number of waveforms are generated, and changes in the normal patterns of response can detect abnormalities. Assessment of the trigeminal and facial nerves is done using a series of electrical stimulation techniques including the blink, masseter, and masseter inhibitory reflexes and facial motor nerve conduction studies. The blink reflex detects lesions of the first division of the trigeminal nerve and the facial nerve. The masseter reflex evaluates the third division of the trigeminal nerve. Changes in responses are measured and, using a combination of these techniques, localization of lesions at specific sites can be made. Accessory motor nerve conduction is useful not only in focal nerve injury, but repetitive stimulation on the accessory and facial nerves is used in diagnosing neuromuscular junction disorders. In addition, many of the voluntary muscles innervated by the cranial nerves are accessible to needle electrode examination, and evaluation can aid in identification of focal nerve lesions, as well as diagnosis in diffuse nerve and muscle disorders.

CONCLUSION

Electrophysiological techniques offer reliable means of measuring the integrity of the cranial nerves and their central pathways.

The bifid visual evoked potential-normal variant or a sign of demyelination?

OBJECTIVE

To prospectively evaluate the diagnostic significance of bifid VEP at initial presentation.

MATERIALS AND METHODS

A hundred and sixteen patients (46 males and 70 females, age 15-54, mean 28.8), with a clinical suspicion of multiple sclerosis (MS), underwent pattern-shift VEP investigation between 1992 and 1998. They were further followed by clinical, CSF, MRI means for at least 5 years (mean 7.2). Twenty-six patients remained healthy, while 90 developed demyelinating disease (in 71 MS and in 19 optic neuritis was the final diagnosis). Fifty healthy persons (20 males aged 18-51, mean 28.8 and 30 females aged 18-48, mean 26.2) represented the control group. The number of persons with bifid VEP in each group are analyzed.

RESULTS

In the controls one out of 50 exhibited bifid VEP configuration. Of 26 patients with unconfirmed suspicion for MS again one had such responses. Bifid VEP were significantly more frequent in patients with demyelinative pathology (nine out of 90, 10.0%, P (chi-squared) < 0.01).

CONCLUSIONS

Bifid VEP is rarely observed in healthy persons. Its presence should suggest the possibility of demyelinating disease and prompt further investigation and follow-up.

The Relationship of Physical Activity History to Pattern-Reversal Evoked-Potential Components in Young and Older Men and Women

Latencies and peak-to-peak amplitudes of pattern-reversal evoked-potential (PREP) components of active and inactive community-dwelling healthy 61- to 77-year-olds were compared with those of active and inactive 18- to 31-year-olds to determine whether long-term physical activity involvement was associated with attenuation of age-related changes in sensory processes. Binocular PREPs were derived for each of 2 check sizes (22 × 15 ft and 41 × 30 ft of visual angle) to provide increasing challenge of spatial resolution. Analyses of the latencies revealed significant effects for age, gender, and check size such that latencies were longer for older than for young participants, men than for women, and small than for larger check sizes. Amplitudes were larger in older adults for the P100-N150 peak-to-peak difference, but physical activity history was not associated with reduction of the observed age-related increases in component latencies and amplitude. As such, physical activity does not appear to attenuate age-related decline in visual sensory processing.

Age-related changes of evoked potentials

The aim of this review is to analyse the current state of our knowledge on evoked potentials (EPs) in ageing and to report some conclusions on the relation between EPs and elder age. Evoked potentials provide a measure of the function of sensory systems that change during the different stages of life. Each sensory system has its own time of maturation. The individuation of the exact period of life when brain ageing starts is difficult to define. Normally, the amplitude of EPs decreases, and their latency increases from adult to elder life. Many authors speculate that these modifications might depend on neuronal loss, changes in cell membrane, composition or senile plaques present in older patients, but there is no evidence that these changes might modify the cerebral function in healthy aged individuals. This review emphasises some incongruities present in different studies confirmed by daily neurophysiologic practice. Different techniques as event-related desynchronization (ERD), contingent negative variation (CNV) and Bereitschaftspotential, are available to study central neuronal changes in normal and pathologic ageing.

Pattern-evoked potential latencies from central and peripheral visual fields

Median P100 and N70 latencies for peripheral field (>8 degrees) TV-generated pattern visual-evoked potentials were 6 and 8 milliseconds less than for central field patterns in subjects with normal pattern visual-evoked potentials. These differences held for patient subgroups with P100 latency maxima from 140 to 100 milliseconds, and for left and right eye data separately compiled. Latencies for central field stimulation exceeded those for peripheral field stimulation in 233 (85%) of 274 eyes for the N70 potential and in 210 (77%) of 274 eyes for the P100 potential. Such data suggest that the faster conducting peripheral visual system, conveying location and motion information, prepares the occipital cortex for the later arriving central data conveying more intricate details.

Evoked potentials in clinical trials for multiple sclerosis

Multiple sclerosis produces disruption of conduction in the central nervous system by a variety of mechanisms, relating, in part, to loss of the myelin sheath. Although often not well correlated with the clinical course of the disease in individual patients, the resulting evoked potential (EP) disturbances can serve as measures of an accumulating disease burden, particularly in longitudinal population studies. Accordingly, EPs can serve as useful instruments for assessing the effectiveness of therapeutic agents which may alter the course of the multiple sclerosis. Furthermore, since EPs measure conduction within the central nervous system, they provide a means of directly assessing symptomatic treatments designed to improve central conduction.

Gender differences in gating of the auditory evoked potential in normal subjects

Central nervous system (CNS) inhibitory mechanisms hypothesized to "gate" repetitive sensory inputs have been implicated in the pathology of schizophrenia. The present study investigated gender differences in inhibitory gating of evoked brain responses to repeated stimuli in normal subjects (30 women and 30 men) using an auditory conditioning-testing paradigm. Pairs of click stimuli (S1 and S2) were presented with a 0.5 s intrapair and a 10 s interpair interval. The amplitudes and latencies of the P50, N100, P180 components of the auditory evoked response to the conditioning (S1) and test response (S2) were measured, and the gating ratios were computed (T/C ratio = S2/S1 * 100). The amplitudes to S1 were not significantly different between men and women at P50, N100, or P180. However, women had significantly higher amplitudes to S2 at P50 (p = 0.03) and N100 (p = 0.04). The T/C ratios for women were higher (i.e., less suppression of response to S2) for P50 (p = 0.08) and N100 (p = 0.04) compared to men. The results suggested that differences in auditory gating between men and women were not due to biological differences in the P50 and N100 generators but possibly to differential influence of inhibitory mechanisms acting on the generator substrates of these evoked responses.

Influence of age on cerebral potentials evoked by oesophageal balloon distension in humans

The recording of viscerosensory cerebral evoked potentials is a new field in the research on gastrointestinal perception. The aim of our study was to assess the relationships between age and peak amplitudes and latencies of cerebral potentials evoked by balloon distension of the human oesophagus. In 16 healthy volunteers (aged 21-59 years), cerebral evoked potentials were recorded from a midline scalp electrode, using a series of 50 rapid balloon inflations with 13 ml of air. Peak to peak amplitudes (N1-P1, P1-N2) and peak latencies (N1, P1, N2) were assessed. Inverse correlations were found between age and N1-P1 amplitude (P < 0.05), and between age and P1-N2 amplitudes (P < 0.05). N1 and P1 latencies were significantly longer in elderly patients (N1: P < 0.05; P1: P < 0.05). Amplitudes and peak latencies of cerebral potentials evoked by balloon distension of the oesophagus are age-dependent. In cerebral evoked potential studies, patients and healthy controls should be age-matched.

Pattern reversal evoked potentials: gender differences and age-related changes in amplitude and latency

This report is intended to complement the current body of literature by describing pattern reversal evoked potential (PREP) component amplitudes and latencies in a larger sample than has been previously studied and providing comparisons of males and females across the lifespan. Binocular PREPs were measured from 406 normal subjects, 6-80 years of age. In general, latencies were found to decrease during maturation, stabilize across early adulthood, then begin to increase sometime after the late 20s. There were minimal gender differences in latencies during development but males tended to have longer latencies than females during adulthood. Across the lifespan, amplitudes were larger for females. Results of regression analyses using the entire data set were compared to results of separate regression analyses for developmental years (6-20) and adulthood (21-80). Separate analyses appear to provide more useful descriptions of PREP latency and amplitude changes across the lifespan. It is clear that predicted normal values can vary depending on age range and relative proportion of males and females comprising a reference sample. Appropriate clinical values should be based on age- and sex-matched normal subjects and should be specific with regard to technical and methodological variables.

Differences in the pattern visual evoked potential between pregnant and non-pregnant women

It has been proposed that latencies of some components of the pattern-reversal visual evoked potential (PRVEP) are shorter in women than in men because of differences in levels of circulating sex steroids. Pregnancy is a time when serum levels of oestrogen and progestogen are considerably greater than in the non-pregnant state. Whole and half field PRVEP latencies and amplitudes have been compared in 16 pregnant and 38 healthy non-pregnant women. The mean P100 latencies for all responses were shorter in the pregnant women, with statistically significant differences for the left eye whole field latency (P < 0.05) and the left eye right and left half field latencies (P < 0.005 and P < 0.05, respectively) and the right eye right half field latency (P < 0.05). The latencies in women in the pregnant group showed a negative correlation with gestation, which reached statistical significance for the REWF (r = -0.55, P < 0.05). These observed differences in PRVEP latencies in pregnant and non-pregnant women and the association between latency and gestation are likely to be due to differences in circulating sex steroids, and this effect may be the principal reason for latency differences between the sexes.

Visual evoked potentials: phenotypic and genotypic variability

Evoked potentials (EPs) provide a unique way of analyzing the relationship between genes and behavior. Individual differences in EPs, in response to light flashes of two intensities and pattern reversal, were studied in families from the isolated population Mechelta in the Northern Caucasus. While there were no age or sex differences in EP latency, or many age effects on amplitude, there were sex differences on the amplitude measures. Variation in the additive genetic determination of latency and amplitude measures is discussed. The largest estimates of additive genetic variation were found for the complexes of amplitude measures between the positive and negative waveforms.

Age-related changes in pattern visual evoked potentials: differential effects of luminance, contrast and check size

We recorded visual evoked potentials (VEPs) to checkerboard pattern-reversal stimulation in 109 normal subjects (51 males and 59 females; aged 19-84 years) in order to study the aging effect on the multiple channels of the visual system in humans. Transient VEPs to 3 check sizes (15', 30' and 50') were obtained by monocular stimulation. Two test conditions were employed: (1) a high luminance (180 cd/m2) and a low luminance (11 cd/m2) both with a fixed contrast (90%), and (2) a high contrast (85%) and a low contrast (10%) both at a fixed luminance (57 cd/m2). The major features of our results included: (1) the presence of a curvilinear relationship between P100 latency and age for all conditions, while the P100 amplitude did not show any such aging effect, (2) the age-latency function was similar between the two luminance conditions, while it was different between the two contrast conditions, and (3) the differential age effect on the P100 latency caused by changes in contrast depended on the check size. These results suggest that age-related changes in the human visual system are not uniform, but rather are different in the specific functional subdivisions. It is thus hypothesized that aging may differentially influence the separate channels of the human visual system.

Cerebral potentials evoked by oesophageal distension in patients with non-cardiac chest pain

Cerebral evoked potential recording was used to study the oesophagus-brain axis in 10 controls and 10 patients with non-cardiac chest pain with a manometric diagnosis of either nutcracker oesophagus or diffuse spasm and a positive edrophonium test. A series of 50 inflations (10/minute; inflation rate of 170 ml/second) of an intraoesophageal balloon (5 cm proximal to the lower oesophageal sphincter) was performed in each subject. Three different inflation volumes were used and were individually determined to cause no sensation, slight sensation, and definite sensation, respectively (volume ranges: 2-8 ml, 5-18 ml, and 8-22 ml). All signals were coded and their quality was scored on a scale from 0 (no recognisable pattern) to 5 (well defined potential of good quality) by four 'blinded' observers. The evoked potential quality scores and amplitude of the major peaks increased significantly (p less than 0.01) with increasing sensation, both in patients and in controls. In the patients, quality score and amplitude of all four peaks of the evoked potentials were lower (p less than 0.05) and latencies of two of the four peaks were longer (p less than 0.02) than in the controls. The volumes of air required to produce the various sensations were lower in the patients (p less than 0.01). When divided by the balloon volume, amplitude and quality of the evoked potential were no longer significantly different between the groups. These results suggest that the increased perception of oesophageal distension in patients with non-cardiac chest pain is caused by altered central processing rather than (functionally) abnormal receptors in the oesophageal wall.

Effects of age, heart rate, gender, tobacco and alcohol ingestion on R-R interval variability in human ECG

To evaluate the possibly confounding effects of age, gender, heart rate, tobacco and alcohol ingestion on the coefficient of variation of the electrocardiographic R-R interval (CVRR), ECGs in the supine posture were obtained in 68 healthy men and 33 healthy women. The C-CVRSA and C-CVMWSA (two component CVs reflecting respiratory sinus arrhythmia and Mayer wave related sinus arrhythmia, respectively) were computed in each subject from component spectral powers using autoregressive spectral and component analyses. Results of multiple regression analysis indicated that age was inversely related to CVRR, C-CVRSA and C-CVMWSA in both sexes. Heart rate was positively related to C-CVMWSA in males. However, no significant difference in the CVRR, C-CVRSA or C-CVMWSA was found between males and females. The C-CVMWSA was not correlated with the C-CVRSA in either males or females. These data indicate that the CVRR, C-CVRSA and C-CVMWSA are affected by age and partly by heart rate; gender, moderate smoking or drinking habits might not strongly influence autonomic nervous system function. On the other hand, the C-CVRSA in the supine posture appears to be independent of the C-CVMWSA. The positive relationship observed between the C-CVMWSA and heart rate suggests that the C-CVMWSA may be associated with sympathetic activity.

Sequence-dependent deterioration in the visual evoked potential in the absence of drowsiness

When visual evoked potentials (VEPs) are tested patients are often expected to focus on a pattern screen for prolonged periods of time. This may lead to fatigue, failure of concentration and drowsiness, and consequently to a deterioration in the recorded VEP. To determine whether there may be time-dependent changes in the VEP of normal subjects independent of the degree of alertness, attention and altertness were controlled using a reaction time (RT) task in which the subjects were required to re-illuminate the fixation point in the middle of the stimulating screen for the VEP. It was first established that the switching of the fixation point produced little contamination of the background VEP to pattern reversal and that the latency and amplitude of P100 to pattern reversal were identical whether or not the subject was engaged in the RT task. A sequence of 16 averages of the VEP to 256 pattern reversals was recorded, alternately with or without the RT task. The measured RTs decreased during the sequence, presumably due to practice. There was a progressive decrease in the amplitude N70-P100, accompanied by an increase in the variability of the latency of P100. These changes cannot be attributed to lack of alertness, given the improvement in RT. Clinicians should be aware of the possibility of a deterioration in the VEP due to physiological mechanisms when the testing protocol involves multiple averages.

[Evoked potentials and age: different aging by sex?]

Brainstem Auditory Evoked Responses, Pattern-Shift Visual Evoked Potentials, and Short-latency Somatosensory Evoked Potentials for upper and lower limbs have been recorded in 60 male and female normal control subjects, aged 20-84 years. Age and gender effects were analyzed from the comparison of linear regressions with age and from the comparison of the mean values calculated in 3 age groups (20-40 years, 40-60 years, over 60 years). No noticeable effect of age was observed on Brainstem Auditory Evoked Responses. A gender-differential aging process is discussed for some of the short-latency Somatosensory Evoked Potentials. The constitution of reference norms which differ for male and female subjects is considered to be necessary.

The effects of age on steady-state pattern electroretinograms and visual evoked potentials

Steady-state pattern-reversal electroretinograms and visual evoked potentials were simultaneously recorded in two groups of young and elderly normal volunteers. The young group consisted of 23 subjects (13 women and 10 men) aged 18 to 28 years, and the elderly group consisted of 24 subjects (11 women and 13 men) aged 58 to 77 years. Stimuli were square-wave gratings ranging in spatial frequency from 0.5 to 6 c/deg and phase reversed at a frequency of 4 Hz. Pattern-reversal electroretinograms and visual evoked potentials consisted of a prominent second and a smaller fourth harmonic response. Spatial frequency-amplitude functions of the pattern-reversal electroretinogram second and fourth harmonics were similar for the young and elderly groups. The mean fourth harmonic phase was significantly shifted in elderly subjects compared with young subjects for all spatial frequencies tested. Spatial frequency tuning was observed for amplitude and phase functions of the visual evoked potential second and fourth harmonic responses for both age groups. Age had a significant effect on phase for spatial frequencies above 1.5 c/deg. Amplitude of the fourth harmonic was significantly lower for the elderly group at 1.5-4 c/deg. Phase was significantly different between groups for spatial frequencies below 3 c/deg. Our results suggest that aging influences both retinal and central visual pathways. Aging differentially affected the visual evoked potential second and fourth harmonic responses, suggesting different neuronal origins for these components.

The clinical significance of the bifid or "W" pattern reversal visual evoked potential

Although the visual evoked potential (VEP) to an alternating checkerboard stimulus is usually recorded from the occipital midline as an N-P-N complex with a major positive deflection at 100 ms (P100), a wave form exhibiting a P-N-P or "W" morphology is occasionally encountered and its interpretation is the source of some controversy. A retrospective chart review identified 15 patients exhibiting the "W" VEP. This represented 7.6 percent of 197 VEP studies and 5.1 percent of 394 eyes. The response was encountered in 1.7 percent of 57 normal patients and 21.4 percent of 56 patients with definite, probable or possible multiple sclerosis (P less than .001). The "W" response was considered normal in only one patient. Of the remaining 14 cases, 13 had definite, probable or possible MS and one had ischemic optic neuropathy. It is concluded that the "W" VEP is an aberrant response that is rarely seen in normals and may have the same significance as a delayed P100 latency.

Power spectrum and optimal filtering for visual evoked potentials to pattern reversal

The optimal bandwidth for recording the visual evoked potential (VEP) to pattern reversal was investigated in 8 normal subjects by re-analyzing off-line data recorded on tape using an open bandwidth of 0.1 Hz-3 kHz. Power spectral analysis of the VEP revealed little energy above 50 Hz. With digital filtering, the amplitude N70-P100 was significantly attenuated only when the low-pass filter was reduced to 50 Hz or when the high-pass filter was raised to 8 Hz. With analogue filtering, there was significant prolongation of latency of P100 when the low-pass filter (12 dB/octave) was reduced to 250 Hz and a significant decrease in latency when the high-pass filter (6 dB/octave) exceeded 3 Hz. However, the effects of analogue filtering were not uniform across subjects: in 2 subjects the latency of P100 was prolonged using a low-pass filter of 600 Hz and in 2 other subjects the latency was shortened when the 1 Hz high-pass filter was introduced. If a restricted bandwidth is used, non-uniform distortion of latency could make a significant contribution to the variability in latency of P100. The optimal bandwidth is one which minimises this contribution to the variability, 0.3 Hz to greater than 600 Hz.

Cerebral electrical potentials evoked by balloon distention of the human esophagus

Cerebral evoked potentials provide a technique for evaluation of central nervous processing of information derived from a variety of sensory modalities. Evoked potentials associated with balloon distention of the smooth muscle esophagus were studied in 14 adult volunteers. Stimulation was applied via repeated inflation and deflation of a balloon attached to a pressure pump that cycled at 0.2 Hz. Cortical electrical responses were recorded from scalp electrodes at Cz, Cz', and Pz of the international 10-20 System for electroencephalographic recording. The recording electrodes were referenced to Fpz and averaged over a 1-s period for 100 repetitions. Latencies, amplitudes, and waveforms of the evoked potentials were compared with controls consisting of pump on/balloon detached, auditory masking, and conventional somatosensory posterior tibial nerve stimulation. Polyphasic evoked potentials were obtained in all subjects, and maximum positive deflections occurring with latencies of 202-396 ms. Maximal amplitudes ranged from 2.5-8.3 microV. Latencies and amplitudes of the evoked responses were highly reproducible in each subject with considerable variation among subjects.

CONCLUSIONS

(a) Reproducible evoked potentials with distinctive waveforms can be recorded in response to esophageal balloon distention in humans; (2) long latency of the evoked potentials suggests involvement of nonmyelinated visceral afferent pathways; (3) the evoked potentials are probably specific to mechanical stimulation rather than being nonspecific arousal responses; and (4) the results support this as a promising new method for investigation of the neurobiology of gastrointestinal sensation in humans that may help clarify pathological conditions of the irritable esophagus syndrome and esophagus-related chest pain.

Determinants of visual evoked potentials in preterm infants

The latency and amplitude of N1, the first negative peak of single flash visual evoked cortical potentials (VEP) were evaluated in 86 preterm infants (25-34 weeks of gestation), investigated during the first day of life. All infants were regarded stable at the time of investigation and none had experienced severe asphyxia. Both the VEP latency and amplitude were inversely related to gestational age. When latency was corrected for age it was longer in boys than in girls. Age corrected VEP amplitude was inversely related to head circumference, umbilical cord pH and EEG activity. There was no difference between VEP parameters in asymmetrically growth retardated infants compared to those with normal growth. Administration of dexamethasone to the mother before delivery, mode of delivery, presence of hyaline membrane disease, mode of assisted ventilation or imminent development of periintraventricular haemorrhage did not affect the VEP.

Visual evoked potentials in dementia: a meta-analysis and empirical study of Alzheimer's disease patients

A meta-analytic review of flash and pattern reversal visual evoked potential research indicates that elderly demented patients have longer P100 latencies than age-matched control subjects. In the present empirical research, patients with research diagnoses of probable Alzheimer's disease were compared with sex- and age-matched control subjects using P100 latencies of visual evoked potentials (VEP) elicited by flash and pattern reversal. As compared to control subjects, Alzheimer's disease patients showed significantly longer P100 latencies of the VEP elicited by pattern reversal; the flash P100 only marginally distinguished them. These findings are discussed within the context of VEP recording practices, patient selection, sex and age matching of control subjects, and the visual system.

Correlation with age and sex of flash-evoked electroretinogram and retinal oscillatory potentials recorded with skin electrodes

Electroretinograms and retinal oscillatory potentials to full-field flash stimulation were recorded by dermal electrodes in a population of subjects (1 to 84 yrs) balanced for age and sex (119 females, 133 males), without evidence or history of ocular and/or relevant systemic diseases. The electroretinogram latencies and b-wave amplitude increased, while the a-wave amplitude decreased linearly with age. The oscillatory potential amplitude initially increased, to decrease approximately at the age of 50, with an inverted U-shaped distribution.

The origin of the occipital lambda wave in man

The relationship between occipital lambda waves, saccadic eye movements, and pattern reversal visual evoked potentials (VEPs) has been investigated in 23 normal control subjects and 24 patients with suspected multiple sclerosis (MS). The VEP, electro-oculogram (EOG) and lambda waves were recorded similarly in both groups. The lambda waves were averaged, using pre-defined points in the saccadic eye movements for synchronisation. A comparison was made between the VEP and lambda waves recorded in patients with delayed VEP and in patients with a 'W'-shaped VEP morphology. In the normal subjects, the VEP and lambda waves recorded in response to full-field stimulation were compared with those recorded using a stimulus devoid of foveal pattern. In addition, the lambda waves from the control group were averaged according to different criteria, dependent on the presence of a secondary, corrective saccade. A hypothesis for the generation and transmission of lambda waves has been established. It is proposed that there are 2 different types of lambda wave. The first is generated as a result of retinal afferent activity due to the return of normal visual sensibility in the peripheral visual field, following its suppression during the saccadic eye movement. This activity is transmitted via the faster conducting Y fibres in the optic nerve. The second lambda wave results from the retinal afferent volley caused by the release of suppression of the central visual field, conducted via the slower X fibres in the optic nerve.

Colour-black pattern reversal visual evoked potentials (colour-black-PVEPs): neurobiological aspects and clinical applicability of a new method

The new method of Colour-Black-PVEPs was applied to 67 healthy subjects with normal colour vision who were subdivided into age groups (= AG) I (N = 40: 18-30 years) and AG II (N = 27: 31-60 years): 1. For the N80-, P100- latencies and the N80P100-amplitudes of all Colour-Black-PVEPs we obtained age-, sex- and eye-matched normative data. 2. The female subjects of AG I showed shorter (p less than or equal to 0.05 resp. 0.002) P100-latencies and higher (p less than or equal to 0.02 resp. 0.0001) N80P100-amplitudes in the Colour-Black-PVEPs than the male subjects. In AG II, however, the Colour-Black-PVEPs did not show any more sex-differences for the P100-latencies, whereas the N80P100-amplitudes remained significantly higher for the females. 3. In the Colour-Black-PVEPs the N80- and P100-latencies did not reveal age-dependent changes. The N80P100-amplitudes, however, decreased with increasing age, but this was significant for the females only. 4. The head sizes, although decreasing with age, were in both age groups significant smaller for the females only. 4. The head sizes, although decreasing with age, were in both age groups significant smaller for the females. Therefore, head size alone could not fully explain the sex-differences in the Colour-Black-PVEPs and their age-dependent changes. 5. In both age groups, the N80--and P100-latencies increased significantly for both sexes from the Green-Black- and Red-Black-PVEPs to the Blue-Black-PVEPs. The N80P100-amplitudes decreased in the same sequence. This method may become a valuable tool in the investigation of neurophysiological and ophthalmoneurological aspects of human colour vision.

Recording of visual-evoked potentials in dogs with scalp electrodes

Following unsuccessful attempts to record visual-evoked potentials (VEPs) in dogs with scalp electrodes, adoption of a new stimulation technique seems to be beneficial. Previously, flashes of white light administered after dark adaptation induced relatively high amplitude electroretinograms (ERGs) covering any VEP activity over the surface of the skull. ERG amplitude, however, can be significantly reduced using flashes of red light after light adaptation (mostly cone stimulation). Simultaneous ERG and VEP recording allows identification of VEPs composed of three significantly different negative peaks (N1, N2, and N3) measured in dogs anesthetized with chloralose and halothane. No more than two of the three peaks were seen in one recording. Only the N1 and N3 waves were consistently recorded in dogs anesthetized with thiopental and thiopental combined with halothane. In 50% of all recordings, N1 was seen alone. The other VEPs consisted of N1 and N2, or N1 and N3 occurring concurrently. The simultaneous occurrence of N2 and N3 waves, however, was never seen. Among all recordings, N1 was most frequently recorded (85% of measurements), followed by N3 and N2 (38% and 31% of measurements, respectively). Peaks of less than 90 ms are highly reproducible. Anesthesia is necessary to eliminate frequent artifacts obtained in conscious and sedated dogs. Thiopental and/or halothane had no effect on measured latencies compared with chloralose.

Effect of reference point on visual evoked potentials: clinical relevance

For clinical purposes the VEP is generally recorded from the mid-occipital region referenced to the vertex or mid-frontal region. This may lead to interpretive errors that can be avoided if a relatively inactive reference point, such as linked mastoids, is used simultaneously. The additional recording derivation may also be helpful in clarifying aberrant or ambiguous wave forms. The diagnostic yield from the two montages is similar, although the linked-mastoid reference provides a greater number of technically inadequate recordings due to smaller size of P100 and increased contamination by muscle artifact.

The use of weighted quadratic regression for the study of latencies of the P100 component of the visual evoked potential

The aim of this study was to determine the range of normal values of the latency of the P100 component of the VEP from a control population. Weighted least squares polynomial regression analysis showed that a quadratic curve best described the relationship between age and latency and separate curves, along with normal ranges, are presented for males and females. We would recommend the use of this statistical method for all determinations of the normal range of P100 latencies.

Neuronal generators of the visual evoked potentials: intracerebral recording in awake humans

Flash and pattern reversal visual evoked potentials were recorded in awake patients undergoing stereotactic procedures for severe dyskinetic disorders resistant to medical treatment. The nucleus ventralis lateralis thalami was reached via an occipital approach. VEPs were recorded on the scalp at the entrance of the intracerebral electrode, and serially from sites at different depths. A polarity reversal of the surface recorded wave form took place as the intracerebral electrode was advanced beneath the surface cortical layers. As concerns F-VEPs, most of the scalp activity mirrored the potentials recorded down to the depth of 70-65 mm from the thalamus. The largest amplitude of intracerebral F-VEPs was obtained from recording sites at 50-70 mm from the thalamus, i.e., in the depth of the calcarine fissure. A negative wave, peaking around 47-50 msec, became evident in recording sites at 30-40 mm from the thalamus but vanished as the electrode was advanced farther. In only one patient could we record a small negative wave, peaking at 33 msec, in the vicinity of the corpus geniculatum externum. Furthermore, the oscillatory activity recorded from the scalp appeared to be generated in the cortical layers. PR-VEPs also underwent polarity reversal as the electrode traversed the cortex. PR-VEPs disappeared more superficially than F-VEPs. No PR-evoked activity could be recorded in the vicinity of the corpus geniculatum externum. We conclude that slow and fast components of VEPs recorded from the scalp are entirely generated in cortical layers.