Visual Evoked Responses Research Articles

Binocular interaction and steady-state visual evoked potentials. I. A study in normal subjects and in subjects with defective binocular vision.

A correlate of binocular-neuron activity was found in some properties of visual evoked potentials (VEPs), such as facilitation (defined as a binocular response greater than the sum of the monocular responses) and changes in latency (shortening of binocular VEP latency as compared to that of monocular VEPs). Monocular and binocular steady-state VEPs in response to phase-alternating gratings of different contrast and both spatial and temporal frequency were recorded in three normal subjects. Fourier analysis of the responses was performed to isolate the component at the reversal frequency. Binocular VEPs showed facilitation in the low-contrast range (3%-10%). Facilitation was highest for gratings that had spatial frequency of 0.6-2 cycles/degree (c/d), alternating at 16 reversals per second. Phase shortening was found across a parameter range larger than that at which amplitude facilitation occurred. These results suggest that both amplitude facilitation and phase shortening in binocular VEPs may provide an objective measure of binocular visual function in clinical ophthalmology.

Pharmacokinetic-pharmacodynamic modeling of midazolam effects on the human central nervous system.

The effect of midazolam on alpha-activity of the EEG and latency of the P-100 of the visual evoked response (VER) was studied in six healthy subjects. Drug concentration was related to effect with the Emax model that was used with either a threshold drug concentration or a sigmoid exponent. An effect compartment was included in the pharmacokinetic-pharmacodynamic model. Four subjects showed hysteresis, and mean values of half-lives-k(eo) ranged from 0.26 to 0.60 hour. Mean values of EC50 ranged from 42.0 to 48.1 ng/ml. Goodness of fit did not differ significantly between the sigmoid Emax model and the threshold Emax model. The sigmoid exponent estimated was 3.7 +/- 1.8 (EEG, mean +/- SD) and 2.9 +/- 1.4 (VER); the threshold concentration was estimated at 15.7 +/- 11.1 ng/ml (EEG) and 11.3 +/- 7.0 ng/ml (VER). We conclude that the Emax model adequately describes the relationship between midazolam concentration and effect and that the sigmoid exponent can be substituted by a threshold drug concentration, with a comparable fit of the model to the data.

Objective evaluation of binocular function with pattern reversal VER. IV. Effect of spatial and temporal frequency.

The effects of changing spatial and temporal frequencies on the amplitude of pattern reversal monocular and binocular visual evoked response (VER) were investigated. The pattern reversal VER and the degree of binocular summation (binocular VER amplitude/monocular VER amplitude) were lowest at the spatial frequency (check size) of 0.3 cycles per degree (CPD) and highest at the spatial frequency of 4.0 CPD. The largest VER amplitudes were observed at 1.2 CPD under both the binocular and monocular recording conditions. Regarding the effects of changing temporal frequency (alteration or reversal rate) on the pattern reversal VER, the transient condition (1.5 to 3.0 Hz) did not produce significant binocular summation. At the higher temporal frequencies (6 to 12 Hz), significant binocular summation was produced compared with the transient stimulus condition. At very high temporal frequencies, the degree of the binocular summation showed a decrease. From these results, we selected a pattern with an element around 1.2 CPD with a relatively swift temporal frequency for evaluating binocular function with the pattern reversal VER.

Steady-state visual evoked potentials to asymmetrical contrast.

The temporal frequency components in the steady-state visual evoked response (VEP) depend on the method of stimulus presentation; a first harmonic is generated to "on-off" patterns while a second harmonic occurs to both "on-off" and counterphase patterns. This study examined the VEP response in humans to patterns between these two extremes. In the main experiment, a 1 c/d sinusoidal grating was phase reversed sinusoidally at 8 Hz. The DC offset, however, was adjusted such that two different levels of peak contrast occurred during a temporal cycle. Within this context, a counterphase pattern would represent complete contrast symmetry and an "on-off" pattern would represent maximum contrast asymmetry during a temporal cycle. With this manipulation, the a) integrated luminance change; b) local luminance change; and c) total contrast remained constant. Only mean contrast varied. The amplitude of the first harmonic strongly depended on mean contrast. The amplitude and phase of the second harmonic, however, changed little across experimental conditions suggesting a dependence on one or more of the above three listed stimulus attributes which remained constant. In a supplementary experiment, this phase constancy was confirmed using other temporal frequencies.

Recovery of the visual evoked response in the cat following administration of diisopropylfluorophosphate, an irreversible cholinesterase inhibitor

Visual evoked responses (VER) to counterphased gratings were recorded from area 17 of cat visual cortex prior to and following administration of diisopropylfluorophosphate (DFP). The VER and acetylcholinesterase (AChE) activity of blood, retina, and visual cortex were reduced significantly following DFP administration. Approximately two hours after exposure to 4 mg/kg DFP, the VER began to recover and in some cats returned to base line levels. In contrast, blood, retina, and cortex AChE activity showed little, if any, tendency for recovery throughout the experiment. Since atropine sulfate provided at least partial recovery of the VER following DFP without affecting AChE inhibition, an accumulation of acetylcholine (ACh) probably is involved in the initial visual loss. However, recovery of the VER over time while AChE remained severely inhibited implicates mechanisms other than, or in addition to, accumulation of ACh at receptor sites.

Subclinical optic neuropathy in multiple sclerosis. A neuro-ophthalmological investigation by means of visually evoked response, Farnworth-Munsell 100 Hue test and Ishihara test and their diagnostic value.

Affection of the optic nerves play a central role in multiple sclerosis (MS) symptomatology. In reported autopsy series the prevalence of optic neuropathy has approached 100%. In the present study subclinical affection of the optic nerves was investigated by visual evoked response (VER), Farnworth-Munsell 100 Hue test (FM 100 Hue test) and Ishihara plates in 17 patients with normal visual acuity and without a history of acute optic neuritis. Optic neuropathy was demonstrated in 72% of the eyes. The occurrence of optic neuropathy was also investigated by the same methods in 16 patients with previous acute optic neuritis, which was bilateral in 5 patients. Affection of the optic nerves was demonstrated in 95% in this group. The affection of also the fellow eye in patients with previous monolateral optic neuritis is unexplained. It may be an analogue to the symmetry of plaques found in the brain and the spinal cord. The cause of this peculiar distribution of lesions is, like the ethiology of MS, unexplained at present. In comparing the different methods of demonstrating optic neuropathy, VER is recommended as the method of choice.

Captive bolt stunning of cattle: Effects on brain function and role of bolt velocity

The effects of captive bolt stunning on brain function in adult, anaesthetized cattle were examined. In particular, the role of bolt velocity was considered, using visual evoked responses (VER) as an index of brain damage and to assess the time course to recovery. Bolt velocities of 41, 47, 55 and 58 m/sec were compared. At all velocities examined, shooting with the captive bolt failed to abolish VERs in some animals. Increasing bolt velocity reduced the incidence of animals with VERs present following shooting, and also increased the time to recovery of VERs. Bolt velocities of 55 and 58 m/sec significantly increased the extent and duration of brain damage compared to 41 and 47 m/sec, and this result is discussed from the standpoint of humane stunning.

VISUAL ACUITY PREDICTION USING THE VISUAL EVOKED RESPONSE*

A technique is described for predicting visual acuity in adult humans by using the visually evoked response (VER). This involves using a pattern-reversal checkerboard with a small check size (5.5. min arc) as the stimulus, and measuring the peak-to-trough amplitude of the VER wave arising from it. The technique is therefore both rapid and convenient. The pattern-reversal rate was varied in order to assess the influence of the temporal modulation on the VER waves. The results suggest that a rapid pattern reversal rate produces a VER which displays a reduced association with spatial processing.

Functional development of the visual system in normal and protein‐deprived rats. IV. Latencies in the specific visual pathway of adult rats

It was recently shown that an increase in latency of the cortical visual evoked response (VER) seen in young malnourished animals persists in adult rats given a low protein diet. In the present paper the VER latencies of the specific visual pathway were measured in order to establish the level at which the latency increase occurs in protein-deprived rats. The VER in the dorsal lateral geniculate nucleus (dLGN) showed no significant differences to onset or peak latencies between control (C) and the protein-deprived (PD) rats. The dLGN activity was higher in C rats than in PD rats. Late components differed in median values between the two groups, but the individual variations were large. Generally, the VER of the dLGN in PD rats was more stereotype compared with the C rats. Intracortical VER at a depth of 0.4-0.5 mm showed a small negative component of short onset latency in both C and PD rats. This component preceded the onset of the initial positivity recorded from the cortical surface by 1-2 ms in C rats and by 3-6 ms in PD rats. Following electrical stimulation of the dLGN, no differences in onset latency of the first cortical activity (monosynaptic response) were recorded between C and PD rats, whereas later activity was significantly delayed in PD compared with C rats. The laminar potential pattern was less distinct in PD compared with C rats, and the late components of the evoked response from deep cortical layers were markedly attenuated or lacking.(ABSTRACT TRUNCATED AT 250 WORDS)

Visual function and pattern visual evoked response in optic neuritis.

The disparity between clinical visual function and pattern visual evoked response (VER) was studied in 53 patients who had suffered an attack of optic neuritis (ON) more than six months before. The visual functions tested included Snellen visual acuity, colour vision, visual field, and contrast sensitivity. The effect of pattern presentation, check size, and luminance was tested by recording VERs with several stimulus configurations. VER amplitudes were found to be associated with the outcome of all four clinical tests, independently of check size, luminance, or the presentation method used. On the other hand VER latencies were hardly ever related to the results of any of the four clinical visual tests. These findings support the idea that VER amplitude provides information about visual spatial perception, while VER latency is more related to the extent of demyelination.

Evaluation of central nervous system involvement in uncomplicated optic neuritis after prolonged follow-up.

Magnetic resonance imaging (MRI), multimodal evoked responses (ER) and HLA antigens were examined in 10 patients with idiopathic acute optic neuritis (ON) without any clinical symptoms or signs of multiple sclerosis (MS) during 9-14 years. In MRI, abnormalities compatible with MS were seen in 4 patients. In spite of clinically unilateral ON, a bilateral abnormality in visual evoked responses (VER) was seen in 3 of 9 cases. Brain stem auditory evoked responses (BAER) were normal in all cases, short latency somatosensory evoked response (SER) in all but one. The cerebrospinal fluid at time of ON showed signs of demyelination in one case only. The frequency of HLA antigens DR2 (78%) and B18 (40%) was significantly increased in comparison to healthy controls. MRI seems to be the most sensitive method in the detection of cerebral lesions of MS, especially in mild or asymptomatic forms of the disease. The present techniques are, however, mostly unable to demonstrate optic nerve lesions which more reliably can be evaluated by VERs. The question whether idiopathic ON represents a form of MS solely, cannot be resolved.

Neurofibromatosis

Neurofibromatosis (NF) is a spectrum of disorders that manifest in a variety of ways. As part of the NF spectrum, many different anatomic abnormalities can develop that cause neurologic problems. The central nervous system may be directly involved or may be affected by tumor impingement. Optic pathway gliomas may also occur. The multiple neurofibromas characteristic of the most common form of NF, Von Recklinghausen disease, have a propensity to grow anywhere along nerve pathways. Therefore, the peripheral nervous system can be extensively involved. The neurofibromas may range in size from small, circumscribed tumors to gigantic plexiform tumors that insinuate into adjacent normal tissues and may compromise their function. Other neurologic problems of a functional nature can occur as well: learning disabilities, seizures, incoordination, and sensory abnormalities, among others. Computerized tomography (CT) and magnetic resonance imaging (MRI) scans are valuable diagnostic studies for identification and follow-up of tumors and other neurologic problems that may be investigated with these techniques. Plain radiographs are useful for investigating skeletal abnormalities in the skull, the ribs, the spine, and the limbs. Neurologic studies, including electroencephalography (EEG), brain-stem evoked response (BSER) or auditory brain stem response (ABR), visual evoked response (VER), nerve conduction velocity (NCV), and electromyography (EMG) provide additional information regarding specific symptom-indicated problems.

Functional development of the visual system in normal and protein‐deprived rats. V. Specific cortical response and repetitive stimulation in adult rats

Recent studies on the specific visual system have indicated that early induced protein deprivation results in an impaired transmission from cell to cell in the cortex. To further investigate cortical mechanisms the response to repetitive light flashes and to electrical stimulation of the optic tract (OT) and the dorsal lateral geniculate nucleus (dLGN) were examined. The first potential of the surface visual evoked response (VER) and the monosynaptic response to OT and dLGN stimulation showed similar sensitivity to repetitive stimulation in C and PD rats. In PD rats later activity was significantly more sensitive to repetitive stimulation than in controls. By using paired stimuli with a short inter-stimulus interval, similar inhibitory mechanisms in PD and C rats were demonstrated. The results support the view that protein deprivation results in impaired cortical synaptic activation. The results are discussed in relation to previously described impairment at the cortical level in malnourished animals.

An evaluation of different techniques for removing eye-blink artifact from visual evoked response recordings.

ABSTRACTThis investigation compared four methods used to control eye‐blink artifact in visual evoked response (VER) recordings using the augmenting‐reducing paradigm: rejecting trials containing blinks, presenting the stimuli through closed eyelids, and two different techniques for subtracting a proportion of the averaged electro‐oculogram (FOG) from the averaged VER. The two subtraction procedures differed in the way in which they estimated the amount of EOG to be subtracted and in the case with which they could be applied. Twenty normal, female subjects were exposed to a series of four different intensity light flashes twice with eyes open and once with eyes closed. Blinking was monitored by recording the EOG and EEG was recorded from three midline electrodes. The results indicated that the two subtraction techniques were very similar. They effectively removed ocular artifact and produced corrected VERs that showed high retest stability. Presenting the flashes through closed lids yielded idiosyncratic data, and rejecting trials contaminated by blinks was found to have limited utility with the VER paradigm used in the present study.

Layout of a multiplexed electrode VLSI circuit for monitoring evoked responses in cerebral cortex.

This paper summarizes the details of the design of an integrated circuit layout usable as a multiple-electrode implantable cerebral cortex sensor. The purpose of implanting multiplexed electrode circuits in a cerebral cortex is to monitor the electroencephalograph (EEG) and visual evoked response (VER) generated while the subject performs normal visual functions. A summary of the human image processing system is given as a background for the circuit design work. A typical subject for the research would be a laboratory animal. External power, clocking, and analogue data lines required for its operation posed problems for the original electrode chip. The second generation brain chip includes self contained-power with on-board multiplexing and clocking circuits. The most significant improvement is the incorporation of analogue to digital (A/D) converters. Through the use of A/D converters, brain signal data can be converted at the site of implant, eliminating induced noise from analogue wires used on the original chip. Conversion at the implant site, the primary visual cortex, yields a more accurate indication of the actual brain data.

Clinical neurophysiology in the assessment of neurological symptoms in systemic lupus erythematosus

Neurophysiological studies were performed on 22 randomly selected patients with systemic lupus erythematosus in order to determine whether this form of assessment might be of value in the diagnosis and management of neurological lupus. Sixteen patients described neurological lupus. In eight, neurological symptoms were present at the time of neurophysiological testing. All eight had neurophysiological abnormalities. In six the abnormality was of central origin manifesting as a disorder of either visual evoked response (VER) or brain-stem auditory evoked response (BAER). In the remaining two, an isolated disorder of peripheral nerve conduction (PNC) was present. In the eight patients with previous neurological symptoms five (63%) had neurophysiological abnormalities, but a central disorder was observed in only one and abnormal PNC was present in all. Of the six patients with no neurological symptoms, three (50%) had central neurophysiological disorders. No correlation between individual neurophysiological disorders and specific neurological symptoms was observed. However, all four patients with active vasculitis and all seven with lymphopenia had a neurophysiological disorder. If these observations are extended and confirmed, neurophysiological studies may provide a useful test to the clinician in the evaluation and management of neurological lupus.

Neurological, electrophysiological and MRI abnormalities in infants with extensive cystic leukomalacia.

Twenty infants, diagnosed by cranial ultrasound as having extensive cystic leukomalacia, had visual evoked responses (VER) and electroencephalograms (EEG) in the neonatal period and MRI scans later in infancy. The early ultrasound findings and results from the electrophysiological tests were correlated with later MRI findings and functional abilities. In infants with periventricular leukomalacia (PVL), the cysts were usually no longer visible by ultrasonography, beyond 40 weeks postmenstrual age (PMA), but later MRI scans showed a consistent pattern of delayed myelination around the irregularly dilated occipital horns of the lateral ventricles. VER's were present in the neonatal period and vision was maintained, although all infants developed a marked squint. EEG's were either normal or abnormal initially, but improvement was noted within several weeks. In those with subcortical or mixed lesions, cysts were noted to persist beyond 40 weeks PMA. Later MRI scans showed very poor myelination, with poor progress on subsequent scans and cortical atrophy. VER's were absent and all infants later became cortically blind. EEG's were severely abnormal and recovery was very poor. The infants with PVL developed spastic diplegia with moderate developmental delay, while those with mixed or subcortical lesions developed quadriplegia with severe mental retardation. An integrated approach, consisting of ultrasound imaging and electrophysiological recordings in the neonatal period and MRI imaging later in infancy, may provide a more reliable prediction of the pattern of later deficits.

Visual evoked responses (VERs) and brain-stem auditory evoked potentials (BAEPs) in patients undergoing dialysis: A. Annigoni, [formula omitted], E. Ghidoni, T. Lusenti, F. Soliani and P. Borgatti (Divisione di Neurologia, Arcispedale S. Maria Nuova, Reggio Emilia, Divisione di Nefrologia e Dialisi, Arcispedale S.M.N., Reggio Emilia, Italy)

Visual evoked responses (VERs) and brain-stem auditory evoked potentials (BAEPs) in patients undergoing dialysis: A. Annigoni, [formula omitted], E. Ghidoni, T. Lusenti, F. Soliani and P. Borgatti (Divisione di Neurologia, Arcispedale S. Maria Nuova, Reggio Emilia, Divisione di Nefrologia e Dialisi, Arcispedale S.M.N., Reggio Emilia, Italy)

Value of visual evoked response and oligoclonal bands in cerebrospinal fluid in diagnosis of spinal multiple sclerosis.

To assess the predictive value of prolongation of visual evoked response (VER) plus the presence of oligoclonal bands in the cerebrospinal fluid (CSF) in the diagnosis of multiple sclerosis (MS) in patients with isolated cord lesions, the false-positive rate for the two tests combined was determined by a prospective analysis of 42 patients with a structural spinal cord lesion. The false-positive rate for the combination of VER and CSF abnormalities was zero, but the individual false-positive rates were 10% for VER and 12% for CSF protein oligoclonal bands. According to Bayes' theorem, and taking into account the false-positive rates of the tests in the population studied and the prevalence of MS and the true-positive rates for the tests as derived from published reports, abnormalities of VER and CSF protein together gave a probability of MS of 100%. However, if only either the VER or the CSF were abnormal, the probability of MS was 44% or 49%, respectively. An abnormal result for both tests thus indicates a sufficiently high probability of MS to exclude myelography, but a positive result in only one test warrants the procedure.

Progressive Neuronal Degeneration of Childhood (PNDC) with Liver Disease

Thirteen children with progressive neuronal degeneration and liver disease are reported. Clinical features included developmental delay after a normal initial period with later onset of intractable epilepsy. The EEG showed an unusual but characteristic pattern, and visual evoked responses (VER) were abnormal. Rapidly progressive cerebral atrophy was seen on computerized axial tomography (CAT). Inheritance was consistent with an autosomal recessive trait. Pathological findings were neuronal degeneration and spongy change of the cerebral cortex. The calcarine cortex was more severely affected than other areas. Hepatic lesions included severe fatty change and cirrhosis. In six patients liver disease was detected before the onset of epilepsy and exposure to anticonvulsants. Two others were reported to have died from sodium valproate (SV) toxicity, but both had abnormal liver enzymes before treatment with SV, and in both the neuropathological findings were indicative of PNDC. During life, PNDC may be indicated by the characteristic clinical course, abnormal liver function tests, and abnormalities of EEG, VER, and CAT.