J. Szanyi

Aging effect in pattern, motion and cognitive visual evoked potentials.

An electrophysiological study on the effect of aging on the visual pathway and various levels of visual information processing (primary cortex, associate visual motion processing cortex and cognitive cortical areas) was performed. We examined visual evoked potentials (VEPs) to pattern-reversal, motion-onset (translation and radial motion) and visual stimuli with a cognitive task (cognitive VEPs - P300 wave) at luminance of 17 cd/m(2). The most significant age-related change in a group of 150 healthy volunteers (15-85 years of age) was the increase in the P300 wave latency (2 ms per 1 year of age). Delays of the motion-onset VEPs (0.47 ms/year in translation and 0.46 ms/year in radial motion) and the pattern-reversal VEPs (0.26 ms/year) and the reductions of their amplitudes with increasing subject age (primarily in P300) were also found to be significant. The amplitude of the motion-onset VEPs to radial motion remained the most constant parameter with increasing age. Age-related changes were stronger in males. Our results indicate that cognitive VEPs, despite larger variability of their parameters, could be a useful criterion for an objective evaluation of the aging processes within the CNS. Possible differences in aging between the motion-processing system and the form-processing system within the visual pathway might be indicated by the more pronounced delay in the motion-onset VEPs and by their preserved size for radial motion (a biologically significant variant of motion) compared to the changes in pattern-reversal VEPs.

Motion-onset and pattern-reversal visual evoked potentials in diagnostics of neuroborreliosis.

Summary: Neuroborreliosis is a form of borreliosis that affects the central and/or peripheral nervous system. Although it can mimic neurologic and ophthalmologic disorders such as multiple sclerosis and optic neuritis, visual evoked potential (VEP) examination is usually not used in neuroborreliosis diagnostics. Combined VEP testing (pattern-reversal VEPs and VEPs produced in response to linear and radial motion) was performed in 81 patients with neuroborreliosis verified by laboratory results (positive polymerase chain reaction or intrathecal antibodies production). Thirty-four patients reported diplopia or blurred vision related to borreliosis. In 33 (40%) patients the VEPs were delayed: motion-onset VEPs were pathologic in 22 (27%) patients, reversal VEPs in 5 (6%) patients, and both VEP types in 6 (7%) patients. The findings suggest that VEP testing (especially the motion-onset VEP testing) can confirm CNS involvement. Much higher sensitivity of motion-onset VEPs in comparison with reversal VEPs can result from rather selective (earlier) involvement of the magnocellular system or the dorsal stream of the visual pathway.

Visual mismatch negativity in the dorsal stream is independent of concurrent visual task difficulty

The manipulation of attention can produce mismatch negativity-like components that are not necessarily connected to the unintentional sensory registration of the violation of probability-based regularity. For clinical purposes, attentional bias should be quantified because it can vary substantially among subjects and can decrease the specificity of the examination. This experiment targets the role of attention in the generation of visual mismatch negativity (vMMN). The visual regularity was generated by a sequence of two radial motions while subjects focused on visual tasks in the central part of the display. Attentional load was systematically varied and had three levels, no-load, easy, and difficult. Rare, deviant, and frequent standard motions were presented with a 10/60 ratio in oddball sequences. Data from 12 subjects was recorded from 64 channels and processed. vMMN was identified within the interval of 142–198 ms. The mean amplitude was evaluated during the aforementioned interval in the parietal and fronto-central regions. A general linear model for repeated measures was applied to the mean amplitude with a three-factor design and showed a significant difference [F(1, 11) = 17.40, p = 0.002] between standard and deviant stimuli and between regions [F(1, 11) = 8.40, p = 0.01]; however, no significant effect of the task [F(2, 22) = 1.26, p = 0.30] was observed. The unintentional detection of irregularity during the processing of the visual motion was independent of the attentional load associated with handling the central visual task. The experiment did not demonstrate an effect of attentional load manipulation on mismatch negativity (MMN) induced by the motion-sequence, which supports the clinical utility of this examination. However, used stimulation paradigm should be further optimized to generate mismatch negativity that is stable enough to be usable not only for group comparisons but also for a single subject assessment.

Pattern and motion-related visual-evoked potentials in neuroborreliosis: follow-up study.

Summary Visual-evoked potentials (VEPs) were used for objective testing of visual functions during treatment courses of Lyme neuroborreliosis (LNB) in adult patients in the Czech Republic. In 30 LNB patients with originally delayed VEP latencies, pattern-reversal (R-VEP) and motion onset (M-VEP) VEPs were repeatedly examined within 1 to 8 years. Six patients had Lyme optic neuritis (ON), five of them displayed prolonged latencies in both R-VEPs and M-VEPs, and one had only abnormal R-VEPs. The VEP recovery to normal latency values was in three of them. In the group of 24 LNB patients without ON, 14 patients displayed prolonged latencies only to motion stimuli, and 10 patients had abnormal latencies in both R-VEPs and M-VEPs. During the follow-up period, 7 patients displayed shortening to normal latencies. In 5 patients, VEPs latencies improved only partially, and in the remaining 12 patients, VEPs did not improve at all. This study provides objective evidence that in LNB, most of the patients without clinically manifesting ON display optic pathway involvement—predominantly magnocellular system/dorsal stream function changes. In patients with ON, however, mainly the parvocellular system is affected. About half of the patients without ON improved with a relatively long-time course of latency shortening.

Effect of Memantine in Alzheimerʼs Disease Evaluated By Visual-Evoked Potentials to Pattern-Reversal, Motion-Onset, and Cognitive Stimuli

The authors tested visual-evoked potentials to pattern-reversal, motion-onset, and visual cognitive event-related potentials in 17 patients with mild-to-moderate Alzheimers disease treated with Memantine (noncompetitive N-methyl-d-aspartic acid antagonist) to verify whether these objective methods can evaluate its therapeutic effect. The patients were examined before Memantine administration and after 3 and 6 months from the treatment onset. Besides electrophysiology, psychologic Alzheimer Disease Assessment Scale–cognitive part (ADAS-cog) test was also performed. Neither ADAS-cog nor any of the electrophysiological tests were able to prove a significant beneficial effect of Memantine therapy in our group of patients. The results of psychologic and electrophysiological tests did not correlate. An individual improvement of ADAS-cog score (decrease of score by 4 and more points) was present in only 29% of patients, improvement of event-related potentials (shortening of P300 peak latency by at least 20 milliseconds) occurred in 42% of patients. Conversely, in 52% of patients, Memantine therapy led to transitory decline of motion processing (delay of N2 peak latency of the motion-onset visual-evoked potentials by at least 10 milliseconds after the first 3 months of therapy, followed by return to pretherapy values in next 3 months).

Spared cognitive processing of visual oddballs despite delayed visual evoked potentials in patient with partial recovery of vision after 53 years of blindness

We examined the visual and cognitive functions of a 72-year-old subject, KP, who recovered his sight after 53 years of visual deprivation. We used visual evoked potentials (VEPs) to pattern-reversal and motion-onset stimuli and cognitive responses (ERPs) during the oddball paradigm to assess the effect of long-term deprivation on a mature visual system. KP lost his sight at the age of 17 years, and light projection onto his right retina was restored at 71 years by a corneal implant. Nine months after sight recovery we recorded reproducible responses to all examined stimuli. The response to pattern reversal contained two P100-like peaks with the later peak being dominant and significantly delayed (260 ms) when compared to the P100s of two control subjects, to whom the stimuli were adjusted in size and contrast to mimic KPs vision. KPs motion-onset VEPs to full-field and peripheral stimuli had a characteristic shape with a well-defined N2 peak; however, both peaks were significantly delayed (262 and 272 ms) compared to control responses. Unlike the P100 and N2 peaks, which represent sensory detection, the P3b/P300 component of the ERP to a target event in the oddball paradigm was not further delayed. In spite of degraded vision and sensory deprivation lasting 53 years, KP displayed reproducible responses to all reported stimuli. Long-term visual deprivation and retinal detachment degraded KPs visual sensory processing, assessed by pattern-reversal and motion-onset VEPs, whereas the cognitive processing of appropriate visual stimuli was not compromised.

06-Diagnostic substantiation and current possibilities of VEPS examination

The aim of this introductory lecture is to point out that despite the intensive use of modern imagine techniques (MRI, OCT, etc.), the diagnostic applications of visual evoked potentials (VEPs) need not be obsolete, if not preferable in many cases. This objective, fully non-invasive, low-cost electrophysiological method can detect functional problems of the optic pathway and various brain cortical areas even before a development of the first displayable morphological changes. For the increased sensitivity of VEPs, it is necessary to use a larger spectrum of visual stimuli (activating quite selectively different subsystems of the visual pathway and visual cortex) compared to standards recommended by ISCEV or IFCN. It should include not only flash or pattern-related stimuli (pattern-reversal, pattern-on/off) but also motion-related (motion-onset VEPs) and cognitive visual stimulation. Then, not only the early diagnostics of a large spectrum of neuro-ophthalmological and neuro-psychiatric disorders is possible but also the physiological aging of visual information processing or a drug abuse is recognisable. For a better availability of VEPs examination and their long-term monitoring also in home conditions, we have just introduced a “Mobile (wearable), low-cost device for examination of visual evoked potentials (VEPs)”, the use of which will be demonstrated during the lecture. Acknowledgements: Supported by the project of Charles University “Progres Q40/07”.

39. Electrophysiological diagnosis of early cns involvement in HIV-1 infection – Pilot study

Introduction The aim of our study was to verify the possibility of early identification of HIV-related neural injury using visual evoked potentials (VEPs) in neurologically asymptomatic HIV seropositives. In the CART (combination antiretroviral therapy) era, the prevalence of neurocognitive impairment remains high, up to 50%, and HIV-associated neurocognitive disorder (HAND) has shifted towards a milder clinical presentation. Such a mild clinical presentation can escape detection [1]. Methods The examination consisted of the Montreal Cognitive Assessment (MoCA) [2], and VEPs to pattern-reversal, motion-onset stimulation (radial movement), and of visual ERPs recorded during an odd-ball test (http://www.lfhk.cuni.cz/elf). Subjects: 9 homosexual men and 3 heterosexually infected women were examined in this study. All patients had ⩾350×106 CD4 cells/l blood at inclusion. The duration of the HIV infection was 0.5 – 7years, and mean age of the patients was 35 (24–50) years. Results P100 potential was recorded with no alteration in the VEP amplitude or latency. However, in 5 patients with CD4 counts 350–750×106cells/l, there was prolonged latency of the N160 peak compared to the reference values obtained in our laboratory, which suggests a dysfunction of the motion-processing (magnocellular system or the dorsal cortical stream) [3]. P300 latencies and MoCA results were within the normal range in all HIV patients. Conclusions Our data suggest that motion-onset VEPs may be a sensitive measure of subclinical visual pathway dysfunction in early HIV-1 infection, however, we did not reveal any cognitive decline in this pilot group. Subsequently, the patients will be investigated using VEPs and visual ERPs at six-month intervals to evaluate the long-term development of the visual pathway involvement in HIV patients.

9. Origins of VEP response suppression during prolonged visual motion stimulation

Superior temporal sulcus (STS) is a brain structure, which has been related to many cognitive functions recently. It can be presumed that it is a part of many cognitive functions and that in particular situation, its relationship with other brain areas is relevant. Our work aimed to its effective connectivity during processing of potentially relevant unusual events. Twenty healthy volunteers were investigated by functional magnetic resonance during visual oddball task – they were instructed to react to different visual stimuli, randomly dislocated among frequent ones. Further processing was done by SPM5 programme. Next step was psychophysiological interaction analysis, method of effective connectivity. We have detected two areas related to target stimuli detection in STS. The anterior area had increased connectivity with mesiotemporal cortices, the posterior one with anterior cingulate cortex. We have found decreased connectivity of the anterior area with dorsolateral prefrontal cortex and the posterior area with parietal cortex – attention related structures. We can hypothesize that STS in detection of rare events is not related to attention, but to later stages of stimuli processing. This hypothesis is supported by association of STS and mesiotemporal areas.

11. Pilot attempt to monitor Graves’ ophthalmopathy with pattern-reversal and motion-onset VEPS

Superior temporal sulcus (STS) is a brain structure, which has been related to many cognitive functions recently. It can be presumed that it is a part of many cognitive functions and that in particular situation, its relationship with other brain areas is relevant. Our work aimed to its effective connectivity during processing of potentially relevant unusual events. Twenty healthy volunteers were investigated by functional magnetic resonance during visual oddball task – they were instructed to react to different visual stimuli, randomly dislocated among frequent ones. Further processing was done by SPM5 programme. Next step was psychophysiological interaction analysis, method of effective connectivity. We have detected two areas related to target stimuli detection in STS. The anterior area had increased connectivity with mesiotemporal cortices, the posterior one with anterior cingulate cortex. We have found decreased connectivity of the anterior area with dorsolateral prefrontal cortex and the posterior area with parietal cortex – attention related structures. We can hypothesize that STS in detection of rare events is not related to attention, but to later stages of stimuli processing. This hypothesis is supported by association of STS and mesiotemporal areas.