Pattern ERG and VEP maturation in schoolchildren.

OBJECTIVE: The maturation of the visual system has been studied with pattern electroretinograms (PERG) and pattern visual evoked potentials (PVEP) mostly in children under the age of 6 years. To address the question of maturation of the visual system in childhood and adolescence we investigated age-dependent PERG and PVEP changes in children aged 7-18 years. METHODS: PERG were recorded with skin electrodes attached to the lower eyelid, and PVEP were recorded with 5 electrodes. Visual stimuli, consisting of pattern-reversal 50' checks to full-field and to half-field stimulation, were applied to obtain macular (N70, P100, N145) and paramacular waves (P80, N105, N135). RESULTS: We found an age-dependent decrease (linear regression P<0.05) of PERG P50 amplitude and full-field PVEP P100 latency to monocular right and left eye stimulation, indicating central retinal and postretinal changes. In addition, waveform changes were found in responses to half-field stimulation. The paramacular wave N105 was typically enhanced in younger schoolchildren and diminished with age. The age-dependent decrease (linear regression P<0.01) of paramacular N105 amplitude indicated the increasing predominance of the macular structures of the visual system. CONCLUSIONS: Our findings suggest that central retinal and postretinal electrophysiological maturation persists throughout childhood. Age-dependent PVEP changes seem to correlate with the morphological and metabolic findings that maturation of the visual cortex continues until puberty and even later.     

Spatial distribution of potentials evoked by half-field pattern-reversal and pattern-onset stimuli.

Spatial distributions of visual potentials (VEPs) evoked by half-field checkerboard pattern-reversal and pattern-onset stimuli were studied in 13 subjects, using an 11 lead unipolar array. The main aim was to confirm findings, obtained by previous workers with bipolar recordings, that half-field pattern-reversal VEP's are confined to the contralateral hemisphere and that half-field pattern-onset VEPs are asymmetrical, with greater right hemisphere involvement. Pattern-reversal VEP's contained four consistent peaks, designated here by polarity and peak latency as: (a) P95, positivity contra-lateral and negativity ipsilateral to the field stimulated; (b) P125, predominantly ipsilateral positivity; (c) N165, predominantly ipsilateral negativity; (d) P225; predominantly midline positivity. Pattern-onset VEPs contained three consistent peaks: (a) P125, mainly contraleteral positivity; (B) N175, mainly contralateral negativity; (c) P225, midline positivity. Distributions of pattern-reversal and pattern-onset peaks resembled one another only for P225, suggesting different cortical representation for the other events of the two kinds of VEP. Bipolar pattern-reversal VEPs were largely contralateral, but unipolar recordings showed that this was due to steeper contralateral potential gradients, as ipislateral activity was widespread. Pattern-onset peaks did not differ in amplitude with respect to the half-field stimulated. Previously reported asymmetries were not confirmed. The P125 and N175 pattern-onset peaks were almost entirely restricted to the contralateral hemisphere, but the distributions by half-field were mirror-images of one another. Half-field pattern-onset stimuli could be used to investigate the responsiveness of each hemisphere, although differential hemispheric involvement was not shown. Several differences in amplitude and distribution resulted from varying the width of the vertical central dark strip.     

Sequential spatial maps of visual potentials evoked by checkerboard-pattern reversal: effect of the retinal field stimulated on response topography

Sequential color maps of visual potentials evoked by the reversal of various checkerboard patterns were recorded in 10 young adults using a 16 channel montage. It was found that each of the components of the N75-P100-N145 occipital complex had a specific spatial distribution on the scalp and was selectively influenced by the size, the spatial frequency, the luminance and possibly the wave length of the stimulus. Component N75 was found to be elicited by the more peripheral area of the TV stimulus (12 degrees X 16 degrees). Component P100 was associated with a frontal negativity of similar latency favoring the hypothesis of a dipolar occipital generator. With half-field stimulations the dipole orientation was modified, leading to a 'paradoxical' lateralization of P100 in most cases. However the reverse situation (P100 contralateral to the stimulated half-field) was observed in 4 and 3 subjects out of 10 with left and right half-field stimulations respectively. Thus VEP to full-field TV pattern reversal cannot be recommended to investigate hemianopic patients. Component N145 was of maximal amplitude when elicited by the reversal of small foveal patterns (2.18 degrees), especially red light emitting diodes.     

Correlation between morphological abnormalities of Chiari malformation and evoked potentials]

We studied correlation between morphological abnormalities of Chiari malformation and evoked potentials (short-latency somatosensory evoked potential [SSEP] and auditory brainstem response [ABR]). On SSEP the inter-peak latency prolongation of P3-N1 was revealed in 6 out of 8 cases with Chiari malformations. The feature of positive wave between P3 and N1 was divided into 2 groups. The tendency of the positivity between P3 and N1 was more marked in cases of prolonged P3-N1 latency and correlated with the medullary kink. On ABR the prolongation of III-V inter-peak latency was revealed in one side in 3 patients Chiari malformations with malformed pons and tegmentum.     

Effects of luminance on the pattern visual evoked potential in multiple sclerosis.

Pattern visual evoked potentials (PVEPs) were recorded at 5 levels of luminance from 26 patients with multiple sclerosis and from age-matched normal subjects. In normal subjects, the latency of both the major positive peak (P100) and the early positive peak (P60) was an inverse logarithmic function of pattern luminance. The increase in latency per unit log decrease in luminance was 12.1 msec for P100 and 5.7 msec for P60. Only 2 patients had entirely normal results. In 9 patients, the increase in latency of P100 per unit log decrease in luminance was abnormal. Of the 18 luminance-latency functions obtained from testing both eyes, 10 were abnormal, 6 showing a greater than normal increase in latency with decreasing luminance and 4 a less than normal increase. The 6 luminance-latency functions with a greater than normal increase in latency with decreasing luminance were all from patients without other evidence of optic nerve involvement. Pattern luminance, therefore, as well as patient selection, can significantly affect the proportion of abnormal PVEP latencies in any group of patients with possible, probable or definite multiple sclerosis. The abnormal response of the PVEP to changes in luminance and the different effects upon P100 and P60 indicate that the delayed PVEPs in patients with multiple sclerosis cannot be attributed solely to slowing of conduction in the optic nerve.     

N200 latency and P300 amplitude in depressed mood post-traumatic brain injury patients

In order to examine the independent and combined effects of depressive symptoms and traumatic brain injury on event-related potential (ERP) components, we classified traumatic brain injury (TBI) patients as depressed and non-depressed mood according to their scores on the Zung Self-rating Depression Scale (SDS). Non-depressed mood post-traumatic brain injury patients (NondepTBI, n=9), depressed mood post-traumatic brain injury patients (DepTBI, n=26), and normal healthy control subjects (HC, n=10) were assessed for N100, N200, and P300 latencies and amplitudes by the auditory "oddball paradigm". DepTBI subjects had significantly prolonged N200 latency and low P300 amplitude compared with the NondepTBI and HC groups. A longer P300 latency in the NondepTBI and DepTBI than in the HC groups was found. A prolongation of N200 latency accompanied by low P300 amplitude may be a characteristic of post-traumatic brain injury patients with depressed mood. Prolonged P300 latency may be more closely associated with TBI than with depression, as it was significantly greater in both the DepTBI and NondepTBI, than in the HC group.     

N200 latency and P300 amplitude in depressed mood post-traumatic brain injury patients

In order to examine the independent and combined effects of depressive symptoms and traumatic brain injury on event-related potential (ERP) components, we classified traumatic brain injury (TBI) patients as depressed and non-depressed mood according to their scores on the Zung Self-rating Depression Scale (SDS). Non-depressed mood post-traumatic brain injury patients (NondepTBI, n = 9), depressed mood post-traumatic brain injury patients (DepTBI, n = 26), and normal healthy control subjects (HC, n = 10) were assessed for N100, N200, and P300 latencies and amplitudes by the auditory “oddball paradigm”. DepTBI subjects had significantly prolonged N200 latency and low P300 amplitude compared with the NondepTBI and HC groups. A longer P300 latency in the NondepTBI and DepTBI than in the HC groups was found. A prolongation of N200 latency accompanied by low P300 amplitude may be a characteristic of post-traumatic brain injury patients with depressed mood. Prolonged P300 latency may be more closely associated with TBI than with depression, as it was significantly greater in both the DepTBI and NondepTBI, than in the HC group.     

Cortical and spinal evoked potentials in parkinsonism. Part I. Visual potentials evoked with a checkerboard pattern

In 21 patients with parkinsonism and 20 healthy controls visual potentials evoked with checker pattern used as an alternating stimulus were studied. The left and right eye were examined separately recording visual cortical responses in the central occipital area. The analysed elements included the latency of the first highest positive wave P100 and the amplitude of the P100/N120 complex. Prolongation of the mean latency of P100 was found in patients with parkinsonism, but it was not significant statistically. No differences were found of the P100/N120 amplitude in the group with parkinsonism in relation to healthy controls. In the patients with parkinsonian syndrome (mainly of atherosclerotic origin) the mean latency of the visual potentials was longer and the amplitude was lower than in cases of Parkinson's disease. Attention is called to the high variability of the visual evoked potentials related to the clinical state and origin of the disease (parkinsonian syndrome and Parkinson's disease).     

Evoked potentials in chronic n-hexane intoxication

Somatosensory, brainstem auditory and pattern-reversal visual evoked potentials (SEP, BAEP and PVEP) were studied in 5 patients with n-hexane polyneuropathy to determine if the CNS was affected. In SEPs, the median central conduction (N13-to-N20) was normal but the tibial central conduction (N22-to-P40) was delayed. The central conduction time (I-to-V interval) of the BAEP was also prolonged. However, the P100 latency of the PVEP was normal. The present data indicate that the spinal cord and the brainstem are primarily affected in chronic n-hexane intoxication.     

Evoked potentials in HIV infection]

The study of the literature data on the multimodal evoked potentials in HIV infected patients shows many abnormalities as well in asymptomatic subjects without AIDS as in AIDS subjects with or without neurological signs. Visual evoked potentials (VEPs) reveal prolonged P100 wave latency in 22% of HIV asymptomatic subjects and in 26% of HIV symptomatic subjects; brainstem auditory evoked potentials (BAEPs) reveal an increase of the interpeak latency I-V in 16% of asymptomatic subjects and in 32% of symptomatic subjects; somatosensory evoked potentials (SEPs) by median nerve stimulation reveal prolonged central conduction time in 6% of asymptomatic subjects and in 11% of symptomatic subjects; somatosensory evoked potentials (SEPs) by tibial nerve stimulation reveal prolonged central conduction time in 4% of asymptomatic subjects and in 45% of symptomatic subjects; motor evoked potentials (MEPs) by magnetic stimulation reveal prolonged central motor conduction time in 46% of asymptomatic subjects.     

Evaluating the effects of spatial frequency on migraines by using pattern-reversal visual evoked potentials.

OBJECTIVE: To clarify the effects of contrast and spatial frequency in patients with migraine by means of pattern-reversal visual evoked potentials (PVEPs). METHODS: PVEPs were obtained from 14 patients who had migraine without aura (MO), 11 patients who had migraine with aura (MA), and 25 age-matched, healthy controls (CO). PVEPs were binocularly recorded with a reversal rate of 1Hz (2 reversal/s) at 3 spatial frequencies (0.5, 1.0 and 4.0 cpd) at high (98%), medium (83%) and low (29%) contrast. N75, P100 and N135 latency and the amplitudes of P50-N75, N75-P100 and P100-N135 were analyzed. RESULTS: Increased amplitude of PVEPs in patients with migraines were revealed at 3 different spatial frequencies in all components. The MO and the MA showed increased amplitudes mostly in high contrasts (98%). These findings were detected more at a high spatial frequency (4.0 cpd) than at a low spatial frequency (0.5 cpd). Increased amplitude with prolonged latency of N135 were found both in MO and MA at 4.0 cpd. CONCLUSIONS: We conclude that pattern stimuli of high contrasts may be particularly effective in uncovering abnormal cortical reactivity which may be modified in the primary and secondary visual cortex in the interictal state of migraine. SIGNIFICANCE: These findings indicate that there is abnormal visual cortex processing in patients with migraine.     

Visual evoked potentials in diabetes mellitus

25 diabetic patients have been studied in order to investigate the possible effects of the disease on the central nervous system by means of pattern shift visual evoked potentials. Patients with diabetic retinopathy, glaucoma and cataract were excluded from the study. Results obtained from a control group of 30 normal subjects were compared to those of the patient group in which sural nerve conduction velocities have also been determined to see whether there is a correlation between peripheral and central involvement of the nervous system. In diabetic patients latency prolongation in the P100 and N140 components were observed. The N90-N140 interpeak latency was also prolonged. In addition, in patients with longstanding diabetes mellitus the incidence of VEP abnormalities was found to be high. Pathologic changes in VEP latencies did not show any correlation with sural nerve conduction abnormalities.     

The cause of increased pupillary light reflex latencies in diabetic patients: the relationship between pupillary light reflex and visual evoked potential latencies.

In 42 diabetic patients the relationship between the latency of the pupillary light reflex and the pattern reversal visual evoked potential (P100) was examined. Fifty-five percent of diabetic patients had pupillary light reflex latencies above the normal range. In 19% the visual evoked potentials were prolonged when compared to the normal range. Latencies of pupillary light reflexes and VEPs showed no correlation. There was a minimal correlation between the presence of retinopathy and prolongation of both the pupillary light reflex and the visual evoked response latency (kappa coefficients respectively: 0.31, P less than 0.01 and 0.36, P less than 0.02). The presence of an increased pupillary light reflex latency was positively correlated with a reduced respiratory sinus arrhythmia (kappa coefficient: 0.58, P less than 0.0001). Increased VEP latencies showed no correlation with signs of cardiovascular autonomic neuropathy. We conclude that the afferent optic pathway can be affected in diabetic patients. However, prolongation of pupillary light reflex latency in diabetic patients is primarily due to an efferent pupillary defect and represents parasympathetic dysfunction.     

Visual event-related potentials index focused attention within bilateral stimulus arrays. I. Evidence for early selection.

Event-related potentials (ERPs) were recorded from the scalp while subjects attended to sequences of bilaterally symmetrical arrays of 4 letters (2 in each visual half-field) that were flashed briefly at intervals of 280-520 msec. These sequences also included randomized presentations of unilateral 'probe' stimuli consisting of irrelevant bars (experiment 1) or potentially relevant letter pairs (experiment 2). The task was to pay attention to the letter pairs in either the left or the right half-field on a given run and to press a button when the two letters matched one another (targets). The ERPs to the bilateral arrays included an early positive wave (P1, peaking at 135 msec) that was enhanced over posterior scalp sites contralateral to the attended visual field. Both types of probe stimulus also elicited a larger early positivity in the P1 latency range (100-200 msec) when delivered to the attended half-field, followed in some cases by a more prolonged positive deflection. Notable for its absence was any sign of an enlarged posterior N1 component (160-200 msec), which was prominent in the ERP to attended-field stimuli in previous studies using randomized sequences of unilateral stimuli. Attended-field targets elicited large N2 and P3 (P300) components, which were greatly reduced or absent when targets occurred in the unattended field. The observed ERP effects were interpreted in terms of early sensory selection during visual spatial attention.     

The effect of experimental 'scotomata' on the ipsilateral and contralateral responses to pattern-reversal in one half-field.

The averaged cortical responses to a reversing checkerboard pattern presented monocularly in either left or right visual half-fields have been recorded from the occipital scalp using a transverse chain of widely spaced electrodes referred to a common mid-frontal electrode. The half-field responses showed a consistent asymmetry, the dominant feature of which was a positive wave (P100) that was widespread on the ipsilateral scalp and maximally recorded from the midline and ipsilateral electrodes. This formed part of the triphasic negative-positive-negative complex, the other two components being an N75 and an N145. On the contralateral scalp it was generally possible to record a triphasic complex of opposite polarity, but this was usually of smaller amplitude and its components (P75, N105, P135) showed greater variation in latency and morphology than the ipsilateral components. With progressive occlusion of the pattern stimulus from the central regions of the visual half-field, the ipsilateral positive wave (P100) was increasingly attenuated, while components of the contralateral complex were relatively unaffected, or, in some cases, enhanced. By contrast, reducing the radius of the stimulated area had relatively little effect on the ipsilateral P100, while the contralaterally recorded response was attenuated. These differential effects on the half-field response components are discussed in relation to the anatomy of the central and paracentral cortical representation of the visual field. The implications for the interpretation of evoked potential recordings in patients with field defects are considered.     

Combined electrophysiological assessment of the visual system in central serous retinopathy

Six subjects suffering from idiopathic central serous retinopathy were examined during the acute phase using a battery of neurophysiological tests. The records (using skin electrodes) included the electro-oculogram (EOG), the white light electroretinogram (ERG) during various stages of dark and light adaptation, and the flash and pattern reversal visual evoked potentials. Results obtained from the affected eye were compared with those from the healthy eye. The values of the healthy eye were not significantly different from our normal control group. The EOGs of the affected eyes were not significantly different from those of the healthy eyes. The 'a' wave of the ERG during light adaptation was significantly (P less than 0.05) smaller in the affected eye. The amplitudes of the other components and the latencies of all components were not affected. The latency of the PR-VEP of the affected eye in all subjects was prolonged in comparison with the unaffected eye. In 3 subjects the latency was prolonged by more than 2 S.D.s compared with our control group. The amplitude of the PR-VEP in 5 of our 6 subjects was slightly but significantly (P less than 0.02) smaller in the affected eye. There was no correlation between amplitude and latency changes.     

Visual evoked potential abnormalities in Charcot-Marie-Tooth disease and comparison with Friedreich's ataxia

Pattern-reversal visual evoked potentials (VEPs), recorded in 15 visually asymptomatic patients fulfilling the clinical and electrophysiological criteria of Charcot-Marie-Tooth disease (CMTD), were abnormal in 5 and possibly abnormal in another 3. Five patients showed a prolongation of P100 latency, one a reduction of amplitude and one a possibly abnormal "scotomatous" waveform. In 9 cases abnormalities were detected on neuro-ophthalmological examination. These were poorly correlated with VEP abnormalities, except for patients with 2 or more clinical eye signs. Relative central scotomata were found in the patient with an abnormal waveform. VEP abnormalities, where present, were usually fairly comparable in the 2 eyes. In comparison with a group of Friedrich's ataxia cases there was a lower overall incidence of VEP abnormalities in CMTD, but little to suggest a qualitative difference in the nature of the visual pathway pathology. All 4 patients with unequivocally abnormal VEPs had experienced atypical symptoms suggestive of CNS involvement. In none of these was it possible to sustain an alternative diagnosis. It is concluded that a minor degree of visual pathway involvement may be present in many CMTD cases, in spite of the fact that optic atrophy is only rarely reported, and that the VEP latency may reflect the degree to which other parts of the CNS are involved.     

Spatial dissociation of early and late colour evoked components

Evoked potentials to the primary colours red, green, yellow and blue were recorded and compared with those evoked by white. The unpatterned 10 degrees X13 degrees stimuli were generated with the aid of a colour monitor. Activity was depicted with 5 electrodes, the central electrode 5 cm above the inion and two on each side 5 and 10 cm apart from the central electrode. With equally bright colour stimuli a previously described early negative colour-dominated component N87 was localized in all subjects at the central occipital electrode while the following positivity P100 was clearly more lateralized to the peripheral electrodes. With half-field stimulation N87 showed a similar--paradoxical--lateralization to the ipsilateral electrodes as has been demonstrated for pattern reversal. The existence and localization of N87 could be confirmed also for blue colours, its amplitude independent of the blue luminance, its latency decreasing for definite additional brightness increments and decrements. The N87 to blue was of the same latency as the N87 components to other colours. N87 is mainly generated foveally and parafoveally, its amplitude saturates with stimuli larger than 6-8 degrees in diameter.     

Cocaine-dependence and cocaine-induced paranoia and mid-latency auditory evoked responses and sensory gating

Cocaine-dependence has been shown to affect the amplitudes of the P50 mid-latency auditory evoked response (MLAER) as well as P50 sensory gating. The effects on subsequent MLAERs (N100 and P200) have not been examined. The objective of the current study was to further assess the effects of chronic cocaine use on the P50, N100, and P200 components. Thirty-four, at least three weeks abstinent, cocaine-dependent individuals and 34 age and gender matched healthy controls were examined. The amplitudes, latencies and gating measures were calculated and compared between the groups. The N100 and P200 were significantly smaller in patients as compared to control subjects. Sensory gating of the P50, the N100, and the P200 were deficient in cocaine-dependent subjects. Latencies of all measured components were prolonged in subjects who reported developing paranoia while intoxicated. Finally, a positive correlation was found between length of abstinence and evoked response amplitudes. We conclude that the effects of cocaine on sensory gating extend beyond the P50 to the N100 and the P200 components. The data also suggest that prolonged latency of the evoked potentials may be a correlate of cocaine-induced psychosis. Finally, the data suggest that some recovery of amplitude and gating occurs with abstinence.     

A study on visual evoked responses in childhood epilepsy with occipital paroxysms.

As some apparently idiopatic epilepsies may occasionally pose diagnostic difficulties in regard to their precise status of etiology, evoked potentials, particularly visual evoked potential (VEP), may contribute to the diagnosis of childhood epilepsy with occipital paroxysms (CEOP) as a subsidiary method of evaluation. This study includes 19 children (10 boys 52.6%; 9 girls 47.4%) ranging in age from 5 to 17 years (mean SD = 9.68 3.28) suffering from CEOP and a control group of 30 normal children, matched for chronological age and sex. Peak amplitudes and latencies of the P100 component for pattern-shift VEP (PVEP) and of major positivity for flash VEP (FVEP) are measured, respectively. The results from this study demonstrate that amplitude and latency values in patients with CEOP differs insignificantly when compared with controls. Although, non-significantly, mean values of amplitudes for both PVEP and FVEP were higher in the patients than in the normal children, whereas latencies in FVEP were somewhat longer. There may be some tendency for the amplitudes to increase and the latencies to be delayed in VEPs in patients with CEOP, when an overall interpretation of our and similar studies are considered. In certain cases of diagnostic difficulty, VEP values may provide further information for the clinician, regarding either a symptomatic or an idiopathic nature of the underlying disorder.