Visual evoked potentials in monkeys.

Visual evoked potentials (VEPs) were recorded from 2 cortical sites in stump-tailed macaques. VEPs recorded from striate cortex were basically consistent between animals (especially at low light intensity), remained remarkably stable over time, and compared favorably to VEPs reported by other investigators. We concluded that the VEP recorded from the striate cortex of day-active monkeys consists of 5 major peaks within the first 250 msec. The potentials recorded from post-central gyrus were simpler and more individualized and did not show intensity-related latency changes or increases in inter-subject variability. However, amplitudes of potentials recorded from both electrode placements increased with light intensity apparently reflecting the amplitude of individual potentials rather than the variability of these potentials from which the average VEPs were derived.     

Somatosensory evoked potentials in a case of neurosyphilis

Here we report median and common peroneal nerve SEPs in a patient with tabes dorsalis. SEPs were within normal limits following median nerve stimulation, but of prolonged latency for common peroneal nerve. This was in keeping with clinical findings of posterior column involvement confined to the lumbosacral tract and with pathological features of tabetic neurosyphilis.

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Sommario Gli autori riportano le caratteristiche dei potenziali evocati somatosensoriali del nervo mediano e peroneo comune in un paziente affetto da tabe dorsale. I potenziali evocati somatosensoriali sono risultati nei limiti della norma stimolando il nervo mediano ma di latenza aumentata per il nervo peroneo comune. Ciò risultava in accordo sia con le caratteristiche cliniche di segni di interessamento dei cordoni posteriori limitato al tratto lombosacrale che con le caratteristiche anatomopatologiche della neurosifilide.

     

Visual evoked potentials in Reye's syndrome.

Visual evoked potentials (VEPs) induced by flash stimulation in a child who was recovering from Reye's syndrome with complaints of poor left-eye vision were recorded. Ophthalmological examination disclosed intact visual fields and normal visual acuity. Analysis of VEP's, however, showed a grossly abnormal configuration of wave forms, marked prolongation in latency and reduction in amplitude when the left eye was stimulated. Follow-up observation 3 weeks later showed parallel improvements in VEPs and subjective complaints. Thus, from VEP analysis, it may be possible to detect subtle changes in the visual system that have diagnostic and prognostic value.     

Visual evoked potentials in infants and children.

Visual evoked potential (VEP) studies are of great value in a wide variety of pediatric patients, including those with disorders of the sensory visual pathway and those at risk for visual pathway damage. VEPs are simple, non-invasive, and are particularly appropriate for infants and young children who cannot communicate visual symptoms or cooperate for standard vision assessment. VEPs in pediatric patients have the following main purposes: (1) detecting lesions causing dysfunction of the sensory visual pathways (the VEP is a sensitive indicator of subclinical lesions and can be used to differentiate visual impairment from visual inattention in young infants); (2) confirming functional loss when disorders of the visual system are present; (3) quantifying visual impairment in patients with known visual disorders, accomplished either empirically by noting the severity of the VEP abnormality to flash and pattern stimuli or by visual acuity estimation studies (early quantification of vision loss allows referral to early intervention programs, which can ameliorate the long-term consequences of the disability); (4) monitoring patients who are at risk for visual complications either from diseases (such as hydrocephalus or neurofibromatosis) or as a complication of therapeutic intervention (e.g., neurosurgery, chemotherapy) to help detect and avoid long-term sequelae of such therapies on the developing nervous system; (5) establishing prognosis for visual and systemic recovery based on flash VEPs for specific pediatric disorders including perinatal asphyxia in full-term neonates, acute-onset cortical blindness, and, to a fair extent, in comatose children; and (6) in some cases, contributing to the differential diagnosis. Abnormalities of flash and/or pattern VEPs are generally nonspecific to the type of exact location of the lesion, except in distinguishing prefrom postchiasmal lesions. However, in certain conditions, such as the hereditary ataxias of childhood, VEP abnormalities may help in the diagnosis. Similarly, deterioration in VEPs may help differentiate progressive from static encephalopathies. VEPs have become an indispensable tool in pediatric ophthalmology and neurology. They will probably play an increasingly important role in the future, primarily due to the difficulty in assessing visual system function in young or ill children and the VEP's sensitivity to subclinical damage in this aspect of the central nervous system.     

Visual evoked potentials in high-risk infants

Flash VEPs were recorded in 109 high-risk infants, and the result were compared with the clinical outcome of the infants at the age of one year. 87 of the infants (80%) had a normal outcome and also seemed to have normal VEP maturation. This material was used as a reference for infants with abnormal outcome. Altogether, 20 infants (18%) had abnormal VEPs. In most of these repeated VEPs were recorded. In 70 cases the first VEP was recorded at an age of less than three months. Among these 57 children had normal outcome, with abnormal VEPs in 8 cases (14%). 13 infants who had an abnormal outcome had abnormal VEPs in 7 cases (54%). 7 infants of them had poor outcome, and they had abnormal VEPs in 6 cases (86%). The difference between normal and abnormal outcome was statistically significant. The present results indicate that it is possible to predict the poor outcome but not the moderate abnormality by VEP. The absence of VEP or its abnormal wave form were the most important parameters to predict the prognosis. Our present opinion is that VEPs should be recorded selectively, e.g. according to the findings in ultrasound examination, at least twice, the first time as soon as possible after birth and the second time at the age of two months.     

Visual evoked potentials in spinocerebellar degenerations

Pattern reversal visual evoked potentials were studied in 21 patients with spinocerebellar ataxias among whom 6 had Friedreich's ataxia, 10 had hereditary spastic ataxia and 5 had spinocerebellar degeneration with slow eye movements (olivopontocerebellar degeneration). The VHP abnormalities found in 4 cases of Friedreich's ataxia and one with spinocerebellar degeneration with slow eye movements, consisted of, bilaterally absent VEP in 3 patients and bilaterally abnormal responses with asymmetry in two. All the patients with spastic ataxia had normal VEP latencies. The N 70 – P 100 amplitudes, in patients with hereditary ataxias were significantly reduced compared to controls (P < 0.001). The VEP abnormalities correlated best with neuroopthalmic findings, but had no relation to age, sex, inheritance or duration of illness. The VEP findings are probably suggestive of progressive nerve fibre loss in the visual pathways with associated slowing of conduction. The higher incidence of visual pathway involvement in Friedreich's ataxia compared to other hereditary ataxias as reported in recent studies is confirmed.     

Visual evoked potentials in Creutzfeldt-Jakob disease

Neuropathological studies show frequent and extensive effects on the visual system in Creutzfeldt-Jakob disease (CJD), but deterioration of vision is not reported by all patients. We examined the function of the visual system by means of visual evoked potentials (VEP). We recorded monocular pattern-reversal VEP in six patients with sporadic CJD 1-13 months after first symptoms occurred. Three patients had normal vision, and in a further three, vision was impaired. All patients had pathological VEP with a delayed P100 component (six eyes) or loss of cortical response (five eyes). The patients with visual impairment vs those without were not different concerning VEP findings. The VEP are already pathological in initial CJD stages and point to an early effect on the visual system in CJD, irrespective of clinical visual deficits.     

Visual evoked potentials in pseudotumor cerebri

Pattern reversal visual evoked potentials in 13 patients with pseudotumor cerebri were significantly delayed (99 +/- 7.3 ms [mean +/- SD]) compared with the findings in 20 normal subjects (94 +/- 2.7 ms), although only four patients had latencies outside the normal range. There was, however, a significant correlation between the intracranial pressure and the latency of visual evoked potentials. After medical treatment of the intracranial hypertension, visual evoked potential latencies decreased in patients who recovered and in whom the papilledema disappeared. In one patient with progressive visual failure, the visual evoked potentials were abnormal before disturbances of visual fields and visual acuity were evident. Repeated examinations of visual evoked potentials might be of value in patients with pseudotumor cerebri to ensure neurosurgical intervention in due time to prevent visual loss in patients with impending optic nerve atrophy.     

Visual evoked potentials in ataxia telangiectasia

Summary Pattern reversal visual evoked potentials (VEPs) elicited in four patients with ataxia telangiectasia revealed normal results in two and absent responses in two. The pathogenesis of the VEP abnormalities is discussed. It is surmised that the VEP changes reflect progressive degeneration of the nerve fibres in the anterior visual pathway, as in Friedreich's ataxia.     

Visual evoked potentials in neonatal hyperbilirubinemia

The management of neonatal hyperbilirubinemia is very standardized. However, there is a lack of an objective method to evaluate the cerebral effects of bilirubin apart from brainstem auditory evoked potentials. There were few studies evaluating the effects of hyperbilirubinemia or phototherapy on the visual pathway in infants with hyperbilirubinemia. Serial visual evoked potentials of two groups of term neonates (N = 24)--group 1 with moderate hyperbilirubinemia (n = 16) and group 2 with severe hyperbilirubinemia (n = 8)--were evaluated prospectively. All infants had regular physical, neurologic, visual, and auditory evaluations until 3 years. Four (16%) had abnormal visual evoked potentials before 1 year, and the abnormalities returned to normal thereafter. There was no significant difference in visual evoked potentials between the two groups. All had normal neurodevelopmental status by 3 years, with the exception of one child from the severe group with ABO incompatibility with transient mild motor delay, hypotonia, and abnormal visual evoked potential. There were no abnormal effects of phototherapy on visual evoked potentials in infants with neonatal hyperbilirubinemia after 1 year of age. Although our sample size was small, the results suggest that the effects of hyperbilirubinemia on visual evoked potentials might be transient. (J Child Neurol 2006;21:58-62).     

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.     

Visual 'cognitive' evoked potentials in the behaving monkey.

Using a visual 'oddball' paradigm we studied ERPs in monkeys trained in a 'go' 'no-go' discrimination task. The stimuli were 2.5 cpd sinusoidal gratings differing only in orientation (0 degrees or 25 degrees). Monkeys released a lever during 1 of 2 response windows (RW), 480-1762 or 740-1672 msec, following target stimulus onset. Target stimulus presentation probabilities were 1.0, 0.5 and 0.3. The primary evoked potentials recorded to either the target or non-target stimulus were similar in all monkeys. P3 signals progressively emerged in the monkeys only to the target stimulus. P3 recorded at Cz, P3, and P4 had similar mean latencies and amplitudes. Eye movements showed no relationship to P3 potentials. Neither the primary visual potentials nor P3 changed significantly as a function of RW. P3 amplitude was inversely related to target probability. When the target stimulus was presented 100% of the time (P = 1.0) P3 disappeared over 4-5 blocks of trials, while the primary evoked potentials remained consistent.     

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).