Hemifield pattern-reversal visual evoked potentials (VEPs) in retrochiasmal lesions with homonymous visual field defect

This study was designed to examine the clinical significance and the reliability of hemifield pattern reversal VEPs in the assessment of homonymous visual field defects due to retrochiasmal lesions.13 patients with traumatic, neoplastic or ischemic lesions of the cerebral parenchyma, and 18 normal subjects were studied.The results show that amplitude asymmetries over 4 V (between responses evoked by right and left hemifield stimulation, recorded ipsilaterally to the stimulated hemifield) are clinically relevant for hemianopic visual field defect.Significant correlations were found between the VEP features and the site of the damage: lesions of the occipital cortex were generally found to cause more pronounced bioelectrical abnormalities than those due to lesions affecting the visual pathways, with cortical sparing.

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Sommario Viene discussa la utilità clinica dello studio dei PVE da pattern-reversal nella diagnosi dei difetti campimetrici emianopsici omonimi da lesioni retrochiasmatiche (documentate dalla TAC).Sono stati studiati 13 pazienti affetti da lesioni cerebrali di natura traumatica, neoplastica o ischemica, e 18 soggetti normali.Dai risultati si deduce che asimmetrie di ampiezza superiori a 4 V, tra le risposte evocate per stimolazione dei singoli emicampi destro e sinistro (registrate da elettrodi posti omolateralmente all'emicampo stimolato), sono clinicamente suggestive della presenza di emianopsia omonima.Sono emerse, inoltre, correlazioni tra quadro bioelettrico ed anatomo-lesionale: le lesioni della corteccia occipitale provocano, generalmente, anomalie bioelettriche più evidenti rispetto a quelle dovute a lesioni interessanti le vie ottiche con risparmio della corteccia stessa.

     

Objective visual field evaluation using multifocal visual evoked potentials in patients with intracranial disease complicated by mental disorders

OBJECTIVES: We investigated whether visual field defects can be objectively evaluated using multifocal visual evoked potentials (mfVEPs) in patients with intracranial disease complicated by mental disorders. PATIENTS AND METHODS: First, to determine the normal pattern of mfVEPs, recordings were performed using a VERIS Junior Science recording apparatus (Mayo, Aichi, Japan) in 40 healthy subjects. Responses from 8 sites in each subject were divided into 4 quadrants (superior and inferior temporal quadrants and superior and inferior nasal quadrants). In each quadrant, two response waves were grouped and averaged, and the peak latency and amplitude were used for assessment. mfVEP recordings were also performed in 3 patients with intracranial disease complicated by mental disorders, in whom dynamic or static perimetry was impossible, or in whom reliable data could not be obtained, and quadrants showing abnormalities were compared with the sites of intracranial lesions observed by imaging techniques. RESULTS: In the 40 normal subjects, no significant differences were observed in the peak latency among the 4 quadrants, but the amplitude was significantly higher in the inferior than in the superior semi-field. mfVEPs in the 3 patients revealed abnormal waves, which corresponded to the lesions observed by imaging techniques. CONCLUSION: The objective evaluation of visual field defects using mfVEPs may be useful in patients with intracranial disease complicated by mental disorders, in whom kinetic/static perimetry as a subjective examination is difficult.     

Changes in subcortical visual and auditory evoked potentials following amygdaloid kindling in cats

In this study we dealt with the changes in visual and auditory evoked potentials following kindling, to reveal the distant effects of epileptic activity. The experiments were performed using cats. Visual and auditory evoked potentials were obtained initially. Daily stimulation of 60 Hz (rectangular wave, 1 ms in duration, 500 microA in peak current, 2-s train) was given to the right amygdala, for kindling. After the completion of kindling, evoked responses were recorded again. In the auditory system the changes of responses in the cortex, medial geniculate nucleus, and cochlear nucleus were distinguished. The changes of potentials in the subcortex were larger than those at the cortical level. For visual evoked potentials there was a discrepancy between stimulation with light and electrical stimulation of the optic chiasm. There was no significant change in amplitude of visual evoked potentials by flash. In the case of optic chiasm stimulation, an enlargement of evoked responses was obtained. These results indicate modality-specific change of the auditory system and widespread subcortical change. These results might be caused by some vulnerability of the auditory system in the case of amygdaloid kindling, as a result of the epileptogenic process.     

Brain stem auditory and visual evoked potentials in multiple sclerosis

The diagnostic value of the checkerboard pattern-reversal visual evoked potential (VEP) and the random, low rate stimulated brain stem auditory evoked potential (BAEP) was compared in 99 patients with established or suspected multiple sclerosis (MS). In normal subjects examined by both techniques no abnormal recordings were found. In 49 patients with definite MS an incidence of abnormality was found in 100% of VEP and in 84% of BAEP recordings. In 50 patients with probable or possible MS an abnormal VEP was found in 70% and an abnormal BAEP in 50%. When the two examinations were combined, the diagnostic yield increased to 100 and 80%, respectively. 22 patients had only spinal symptoms; in these the VEP gave 73%, the BAEP 55% and the combination 82% abnormalities. The combination of the two techniques was found useful for demonstrating demyelinating lesions in the central nervous system, the diagnostic value being greatest when these lesions were clinically silent.     

Superior colliculus lesions and flash evoked potentials from rat cortex

It is generally assumed that the primary response of the rat flash evoked potential (FEP) is activated by a retino-geniculate path, and that the secondary response reflects input to the cortex by way of the superior colliculus (SC) or other brainstem structures. In the present study, male Long-Evans rats were implanted with monopolar screw electrodes placed over the left visual cortex, and a pair of twisted monopolar depth electrodes, which were used to produce electrolytic lesions, were placed in each SC. One half of the animals did not receive the electrolytic treatment (controls). FEP waveforms were obtained from all animals prior to treatment, and 2 and 5 days after treatment. Histological analysis was performed to verify electrode placement and determine lesion size. Electrolytic lesions resulting in massive destruction of the SC produced no decrement in any portion of the rat FEP but did produce an increase in amplitude of the N2P3 component. The data show that the secondary response is not generated by SC in rats, but that SC may modulate amplitude of the response.     

Cortical visual evoked potentials recorded after optic tract near field stimulation during GPi-DBS in non-cooperative patients

Object

Neurophysiologic monitoring during deep brain stimulation (DBS) interventions in the globus pallidus internum (Gpi) for the treatment of Parkinson's disease or primary dystonia is generally based upon microelectrode recordings (MER); moreover, MER request sophisticated technology and high level trained personnel for a reliable monitoring. Recordings of cortical visual evoked potentials (CVEPs) obtained after stimulation of the optic tract may be a potential option to MER; since optic tract lies just beneath the best target for Gpi DBS, changes in CVEPs during intraoperative exploration may drive a correct electrode positioning.

Patients and methods

Cortical VEPs from optic tract stimulation (OT C-CEPs) have been recorded in seven patients during GPi-DBS for the treatment of Parkinson's disease and primary dystonia under general sedation. OT C-VEPs were obtained after near-field monopolar stimulation of the optic tract; recording electrodes were at the scalp. Cortical responses after optic tract versus standard visual stimulation were compared.

Results

After intraoperative near-field OT stimulation a biphasic wave, named N40-P70, was detected in all cases. N40-P70 neither change in morphology nor in latency at different depths, but increased in amplitude approaching the optic tract. The electrode tip was positioned just 1 mm above the point where OT-CVEPs showed the larger amplitude. No MERs were obtained in these patients; OT CVEPs were the only method to detect the Gpi before positioning the electrodes.

Conclusions

OT CVEPs seem to be as reliable as MER to detail the optimal target in Gpi surgery: in addition they are less expensive, faster to perform and easier to decode.     

Comparative study of visual evoked potentials in spinocerebellar ataxias and multiple sclerosis

Visual evoked potentials (VEPs) were delayed in 11 out of 18 patients with Friedreich's ataxia, in 1 out of 8 patients with Strumpell's hereditary spastic ataxia, in 2 out of 5 cases with cerebellar atrophy and in 42 out of 50 patients with multiple sclerosis (MS). Responses were normal in 5 cases with Pierre Marie's disease. Amplitude and temporal dispersion were statistically analyzed in the above-mentioned groups of patients with respect to controls. An abnormal temporal dispersion, also considered as interpeak N1P2, was frequently found in MS but only occasionally in spinocerebellar ataxias. Amplitude was statistically reduced in Friedreich's ataxia group, where an inverse relationship between latency and amplitude was found. No relation was found between VEP delay and duration of the disease, in any group considered.     

Cortical sources of visual evoked potentials during consciousness of executive processes

What is the timing of cortical activation related to consciousness of visuo‐spatial executive functions? Electroencephalographic data (128 channels) were recorded in 13 adults. Cue stimulus briefly appeared on right or left (equal probability) monitor side for a period, inducing about 50% of recognitions. It was then masked and followed (2 s) by a central visual go stimulus. Left (right) mouse button had to be clicked after right (left) cue stimulus. This “inverted” response indexed executive processes. Afterward, subjects said “seen” if they had detected the cue stimulus or “not seen” when it was missed. Sources of event‐related potentials (ERPs) were estimated by LORETA software. The inverted responses were about 95% in seen trials and about 60% in not seen trials. Cue stimulus evoked frontal–parietooccipital potentials, having the same peak latencies in the seen and not seen data. Maximal difference in amplitude of the seen and not seen ERPs was detected at about +300‐ms post‐stimulus (P3). P3 sources were higher in amplitude in the seen than not seen trials in dorsolateral prefrontal, premotor and parietooccipital areas. This was true in dorsolateral prefrontal and premotor cortex even when percentage of the inverted responses and reaction time were paired in the seen and not seen trials. These results suggest that, in normal subjects, the primary consciousness enhances the efficacy of visuo‐spatial executive processes and is sub‐served by a late (100‐ to 400‐ms post‐stimulus) enhancement of the neural synchronization in frontal areas. Hum Brain Mapp, 2009. © 2008 Wiley‐Liss, Inc.     

Pattern-reversal visual evoked potentials in patients with newly diagnosed epilepsy

PURPOSE: The possible occurrence of evoked potential (EP) abnormalities in patients with newly diagnosed epilepsy has been little investigated. The main purpose of the present study was to investigate possible changes in pattern-reversal visual evoked potential (P-VEP) responses in newly diagnosed epilepsy patients. METHODS: By using P-VEPs, latency values of the N75 and P100 together with amplitude values of P100 were recorded in newly diagnosed idiopathic epilepsy patients. The patients comprised two groups; nonphotosensitive (non-PS), and photosensitive (PS) patients. RESULTS: Shortened N75 and normal P100 latencies of the P-VEP with higher than normal P100 amplitudes were detected in PS patients. In non-PS patients, N75 latencies of the P-VEPs were unaffected; however, P100 latencies were prolonged, and P100 amplitudes were unchanged. CONCLUSIONS: P-VEPs are different from those of controls in previously untreated idiopathic epilepsy patients. Results also indicate different P-VEP features in patients with and without photoparoxysmal responses. The changes might be the result of a disorder of one or more neurotransmitters or subtle morphologic damage such as microdysgenesis.     

Comparison between electric evoked potentials, source dipole components and magnetic evoked fields elicited by noise/square-wave stimuli

The aim of this study was to compare auditory evoked electric potentials (AEPs), source dipole components calculated from AEPs, and auditory evoked magnetic fields (AEFs). Noise/square-wave stimuli were presented either to the left or to the right ear. AEPs were measured from scalp electrodes on a coronal plane and AEFs were recorded over frontotemporal regions of both hemispheres. An increase of the ISI from 2 to 4-6 s did not change the scalp topography of AEPs nor the ratio of the tangential and radial source components. The 100-ms deflections of AEFs were higher in amplitude and shorter in latency to contra- than ipsilateral stimuli; a similar behaviour was seen in the tangential source components of AEPs. The similarity of the tangential components and the magnetic responses suggests that the method to calculate source dipole components can be useful in differentiating between the hemispheric differences in the activation of the auditory cortices and in discerning the tangential and the radial sources.     

Visual and auditory evoked potentials in the early diagnosis and follow-up of neurosarcoidosis

Visual and brainstem auditory evoked potentials (VEPs, BAEPs) were recorded in 23 patients with neurosarcoidosis. Eight patients (35%) had abnormal BAEPs, and 10 (43%) had abnormal VEPs. Four of the 8 patients with abnormal BAEPs had facial paresis, one had impaired memory and only 3 had symptoms and signs compatible with brainstem lesion. Seven of the patients with abnormal VEPs had no visual symptoms. These findings suggest that BAEP and VEP can reveal subclinical nervous system involvement in sarcoidosis and can also help in the early diagnosis of neurosarcoidosis. Successive recordings of 5 patients showed that BAEP and VEP were useful in the follow-up of these patients.     

Abnormal visual processing in migraine with aura: a study of steady-state visual evoked potentials

BACKGROUND: Although a number of studies reported different interictal findings between migraine with aura (MA) and migraine without aura (MO), the pathophysiology of the visual aura in migraine remains unclear. OBJECTIVE: To investigate the visual processing in patients who experience MA between attacks using steady-state visual evoked potentials (SSVEPs). METHODS: SSVEPs to high (98%) and low (29%) contrast black and white checkerboard gratings with two spatial frequencies (0.5 and 2.0 cpd) at 5 and 10 Hz (10 and 20 reversal/s) were recorded binocularly from 10 patients with MA, 10 patients with MO between attacks and 20 healthy controls (HC). The SSVEPs were Fourier analyzed to obtain the amplitude and phase of the second (2F) and fourth (4F) harmonic response. RESULTS: In the amplitude of 2F, at 0.5 cpd, there was significant increased amplitude in both MA and MO in comparison to HC at 5 Hz in high and low contrast. However, no significant differences were detected at 2.0 cpd in both 5 and 10 Hz in high and low contrast. In the amplitude of 4F, at 2.0 cpd, there was significant increased amplitude in MA in comparison to MO and HC at 10 Hz in high contrast. However, there were no significant differences at 0.5 cpd at both 5 and 10 Hz in high and low contrast. There were no significant phase differences between MA, MO, and HC. CONCLUSION: The high amplitude of the SSVEPs suggests that interictally migraine patients have abnormal excitability in the primary visual cortex, and this change in excitability may exist, at least partially, in the visual association cortex in MA.     

Visual evoked potentials in cerebral white matter hyperintensity on MRI

OBJECTIVES: To investigate the correlation of the cerebral white matter hyperintensities (WMH) on MRI, and latency and amplitude of visual evoked potentials (VEPs) in elderly subjects. PATIENTS AND METHODS: Pattern VEP (PVEP) and flash VEP (FVEP) were recorded in 25 patients with WMH consisting of 12 patients with frontal dominant WMH (FMH) and 13 patients with occipital dominant WMH (OMH) and 25 patients with basal ganglionic hyperintensities (BGH). RESULTS: In WMHs, there were significantly larger P100 and P2 amplitudes than in BGHs and controls. Regarding the distribution of WMH, OMH showed significantly larger P100 amplitudes than FMH. In OMH in males, there was significantly prolonged P100 latency compared with females, and in females, there were significantly larger P100 and P2 amplitudes compared with males. CONCLUSION: Appropriate clinical values in VEP should take into consideration WMH in addition to gender and age-related changes.     

Somatosensory and visual evoked potentials in children with cerebral palsy: Correlations and discrepancies with MRI findings and clinical picture

Purpose: To determine if there is any association between the findings of visual evoked potentials (VEPs), somatosensory evoked potentials (SEPs), and magnetic resonance imaging (MRI) findings with the neurodevelopment and severity in children with cerebral palsy (CP). Methods: The present study included 15 children with spastic diplegic CP and five children with spastic hemiplegic CP and 42 healthy children as controls. The number of the controls was two-times greater than the study group to increase statistical power of this study. VEPs and SEPs were recorded in the CP children and compared with healthy controls. All MR scans were obtained using a 1.5 T MR scanner. Results: A significant difference was found in the latencies P100 (VEP) between the CP and controls. No correlations between increased P100 latencies and asphyxia, prematurity, the CP severity, MRI findings and mental retardation were noted. A significant difference in N13–N20 conductions (SEPs) between the subjects with CP and the control group was found. SEPs were positively correlated with mental retardation in CP children. The brain lesions in MRI showed a significant correlation with the CP severity scores and mental retardation. Conclusion: The differences in VEPs and SEPs were determined between CP children and healthy children. The MRI findings were positively correlated with the CP severity and mental retardation.     

Study of visual evoked potentials in diabetics without retinopathy: correlations with clinical findings and polyneuropathy

To evaluate central optic pathways' involvement in diabetics, visual evoked potentials (VEP), in particular the latency of positive peak (LP100), were studied in 35 patients without retinopathy (4 insulin-dependent, 31 non-insulin-dependent) and 35 normal controls using reversal pattern stimulation. LP100 was significantly delayed in diabetics at both binocular and monocular stimulation. Furthermore, the delay in LP100 was significantly longer in the diabetics with polyneuropathy than in those without, particularly after binocular stimulation. A positive correlation was found between latencies of VEP and HbA1, duration of disease, and neurologic score. VEP measurement seems a simple and sensitive method for detecting early alterations in central optic pathways in diabetics.     

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.     

Asymmetric scalp distribution of pattern visual evoked potentials during interictal phases in migraine

The N70 and P100 components of transient pattern visual evoked potentials (P-VEPs) were measured in migraine patients, with and without aura, and in normal subjects in order to evaluate their latency, amplitude and occipital scalp distribution. The aim was to find any typical electrophysiological abnormalities in migraine. P-VEP N70 and P100 were analyzed in 59 patients without any known visual field defect. Mean latency and amplitude values were within normal ranges for either N70 and P100 all over the occipital scalp; the only significant abnormality we found was related to the absolute right-left amplitude ratio either for N70 and P100 waves, providing an asymmetry in P-VEP scalp distribution; this finding was detected in 78.9% of patients with aura and 72.5% without aura. Our results show that in migraine patients, both P-VEP waves N70 and P100, have an asymmetric topographic distribution, even during interictal phases, that can be explained by a cortical disturbance in agreement with the neural hypothesis of headache.     

Evaluation of visual pathways in multiple sclerosis. I. After-images compared to visual evoked potentials

The value of flight of colours (FOC), i.e. the succession of coloured afterimages following light stimulation, in diagnosing and following visual impairment was evaluated in 65 patients with multiple sclerosis (MS). Previous optimistic reports of the use of a pocket flashlight (PFL) method could not be confirmed, and are ascribed to inadequate methods. An electronic flashlight (EFL) method developed by us, proved a significantly better diagnostic tool (61% abnormal versus 18% abnormal). The EFL method was diagnostically less sensitive than pattern reversal visual evoked potential (PR-VEP) (80% abnormal). It did, however, add to PR-VEP by diagnosing 16 eyes with normal PR-VEP latency. The EFL method reflected the degree of degenerative changes in the central visual pathways and may be of value in following the disease activity in MS. The potential of the EFL method may be further improved by proposed modifications.     

Luminance and chromatic visual evoked potentials in type I and type II diabetes: relationships with peripheral neuropathy

Abstract The objective of the study was to investigate the subclinical visual deficit in type I and II diabetes, and its relationship with peripheral neuropathy. Thirty-two healthy volunteers, 20 patients with type I diabetes and 30 patients with type II diabetes were studied in a clinical neurophysiology setting. Luminance (VEPs) and chromatic visual evoked potentials (CVEPs) were recorded, with white-black, grey-black, red-green and blue-yellow sinusoidal gratings. The peak latencies of the VEP positive wave and CVEP negative wave were recorded. Ten patients with type I and 8 with type II diabetes had peripheral neuropathy. VEPs were slower in patients with type II diabetes and CVEPs were slower in patients with type I and type II diabetes than in controls. Blue-yellow CVEPs were slower in type II than in type I diabetes. VEPs and red-green CVEPs were slower in patients with diabetes with neuropathy than in those without. In conclusion, we found that visual system impairment differs in diabetes with and without peripheral neuropathy.     

Brainstem auditory evoked potentials in tuberous sclerosis

Brainstem auditory evoked potentials were recorded in 4 subjects and pattern reversal evoked potentials in 1 subject, all with tuberous sclerosis. Alterations were found (absence or delay of components and prolonged interpeak intervals) which may suggest impaired nervous conduction also at brainstem level in patients with tuberous sclerosis.

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Sommario Sono stati registrati i potenziali evocati auditivi troncoencefalici in 4 soggetti con sclerosi tuberosa, in uno di essi sono stati registrati anche i potenziali evocati visivi da pattern reversal. Sono state ritrovate alterazioni delle risposte (assenza o ritardo di alcune componenti ed intervalli interpicco prolungati) che possono suggerire l'esistenza di una conduzione nervosa alterata anche a livello del tronco dell'encefalo nei pazienti con sclerosi tuberosa.