Comparison of psychophysical and evoked potential methods in the detection of visual deficits in multiple sclerosis

Pattern visual evoked potentials in Japanese patients with multiple sclerosis without history of visual pathway involvement

A delay of the peak latency of the pattern visual evoked cortical potentials (pVEP) is accepted as one of the paraclinical evidence for a diagnosis of multiple sclerosis (MS). The purpose of this study was to evaluate the pVEPs in Japanese patients with MS without a history of visual pathway involvement. We studied the medical records of 29 MS patients without any history of visual pathway involvement, and with visual acuity correctable to > or = 20/20. The Goldmann visual fields, pupillary light reflexes, and optic disks were normal in all. pVEPs elicited by 3 rev/s (transient) and 12 rev/s (steady-state) were recorded from the MS patients and compared with those recorded from normal subjects. The latency of the P100 component of the transient pVEPs was significantly prolonged in 9/29 (31%) MS patients. A phase lag in the steady-state pVEPs was found in 6/29 (21%) MS patients, and the mean amplitude was significantly smaller. The incidence of cases with abnormal pVEPs is lower than that reported from Europe and United State. This difference is possibly due to racial differences, and the use of different criteria for diagnosing optic neuritis.

A primer on motion visual evoked potentials

Motion visual evoked potentials (motion VEPs) have been used since the late 1960s to investigate the properties of human visual motion processing, and continue to be a popular tool with a possible future in clinical diagnosis. This review first provides a synopsis of the characteristics of motion VEPs and then summarizes important methodological aspects. A subsequent overview illustrates how motion VEPs have been applied to study basic functions of human motion processing and shows perspectives for their use as a diagnostic tool.

Motion-onset VEPs: Characteristics, methods, and diagnostic use

This review article summarises the research on the motion-onset visual evoked potentials (VEPs) and important motion stimulus parameters which have been clarified. For activation of the visual motion processing system and evocation of the motion-onset specific N2 peak (with latency of 160-200ms) from the extra-striate temporo-occipital and/or parietal cortex, the following stimulus parameters can be recently recommended: low luminance (<ca. 20cd/m(2)) and low contrast (<ca. 10%-sinusoidally modulated) of a moving structure with low velocity and temporal frequency (<ca. 6Hz). A short (up to 200ms) duration of motion and a long (at least 1s) inter-stimulus interval reduce adaptation to motion and predominance of a pattern-related P1 peak. Radial motion (with increasing velocity and decreasing spatial frequency towards the periphery) produces larger reactions as compared to a unidirectional translation. In view of the slow maturation (up to the age of 18 years) and early ageing of the visual motion processing system, the use of age-dependent latency norms may be necessary. Since early or selective involvement of the motion processing system is suspected in some CNS disorders, we suggest an evaluation of the utility of motion-onset VEPs as part of the electrophysiological CNS examination since this method may recognise motion processing involvement better than other methods. Motion-onset VEPs might increase the sensitivity of this examination for diagnosing CNS diseases including Multiple Sclerosis, Neuroborreliosis, Glaucoma, Dyslexia and Encephalopathies.

Visuoperceptual impairment in MS patients: nature and possible neural origins

Failures on visuoperceptual neuropsychological tasks (on neuropsychological tests of visuo-spatial perception or on tests concerning semantic properties of visual objects), may indicate focal deficits of visuoperceptual function, or could be the result of (an)other (peripheral) visual deficit(s), or be the effect of a more general cognitive decline. In multiple sclerosis (MS) patients exhibiting sufficient visual acuity and not showing severe cognitive deterioration, impairment on a comprehensive set of 31 visuoperceptual neuropsychological tasks was compared with spatial resolution deficits (SRD), temporal resolution deficits (TRD) for visual stimuli, abnormal pattern shift visual evoked potential (PSVEP) responses, and failing scores on neuropsychological tasks other than visuoperceptual tasks. Impairment on the visuoperceptual neuropsychological tasks was highly independent from the other abnormal visual and cognitive neurological impairments examined, suggesting that it mostly represented focal deficits. Only TRD in both eyes related to this impairment and this relationship was rather weak. Thus in some MS patients a slowed visual information processing may be one of the combined deficits underlying visuoperceptual neuropsychological task impairment. Given that SRD and TRD were not related to another stage of MS and reflect disturbances of a P (parvocellular channel and ventral stream projections) and M (magnocellular channel and dorsal stream projections) visual-system function respectively, demyelination of a certain M pathway may become a co-determinant of visuoperceptual neuropsychological task impairment more rapidly than damage to a certain P pathway.

Neurophysiological investigations in multiple sclerosis

The advent of magnetic resonance imaging techniques has greatly reduced the diagnostic value of neurophysiological tests, particularly evoked potentials, in multiple sclerosis patients, because of the higher sensitivity in revealing subclinical involvement of the central nervous system. Technical progress and new methods of investigating afferent and efferent nervous pathways would seem to increase the sensitivity in detecting neural dysfunction, but the 'clinical gain' is modest at best. More promising is the utilization of neurophysiological tests to quantify the severity of white matter involvement. Transversal and longitudinal studies have demonstrated good correlations between neurophysiological parameters and disability measures, indicating that a battery of neurophysiological tests could be useful in monitoring the disease evolution in single patients and as surrogate endpoints in clinical trials. Further studies are needed for a better definition of the applications of evoked potentials and other neurophysiological techniques. Finally, event-related potentials and advanced electroencephalogram techniques, such as coherence analysis, could provide useful information on the pathophysiology of cognitive dysfunction, so common in multiple sclerosis patients, and with a strong impact on the quality of life.

Temporal and spatial resolution in foveal vision of multiple sclerosis patients

Deficits of spatial and temporal resolution were compared in a group of 49 definite multiple sclerosis(MS) patients showing no major evidence of previous optic neuritis attack but representative of the population of the Belgian National MS Centre as to age and the most important disease variables. Resolution in the two domains was measured foveally with forced-choice staircase psychophysical procedures using Landoldt C and double flash stimuli, respectively. The two measurements were equally sensitive to MS-induced deficits and did not exhibit cross-sensitivity. Since discrete deficits of either kind were equally prevalent and outnumbered combined deficits, this suggests a nonselective but nonuniform destruction of M and P visual pathway function in these patients.

False perception of motion in a patient who cannot compensate for eye movements

We are usually unaware of the motion of an image across our retina that results from our own movement. For instance, during slow-tracking eye movements we do not mistake the shift of the image projected onto the retina for motion of the world around us, but instead perceive a stable world. Following early suggestions by von Helmholtz, it is commonly believed that this spatial stability is achieved by subtracting the retinal motion signal from an internal reference signal, such as a copy of the movement command (efference copy). Object motion is perceived only if the two differ. Although this concept is widely accepted, its anatomical underpinning remains unknown. Here we describe the case of a patient with bilateral extrastriate cortex lesions, suffering from false perception of motion due to an inability to take eye movements into account when faced with self-induced retinal image slip. This is indicated by the fact that during smooth-pursuit eye movements, he perceives motion of the stationary world at a velocity that corresponds to the velocity of his eye movement; that is, he perceives the raw retinal image slip uncorrected for his own eye movements. We suspect that this deficiency reflects damage of a distinct parieto-occipital region that disentangles self-induced and externally induced visual motion by comparing retinal signals with a reference signal encoding eye movements and possibly ego-motion in general.