F. Vit

Properties of visual evoked potentials to onset of movement on a television screen

In 80 subjects the dependence of movement-onset visual evoked potentials on some measures of stimulation was examined, and these responses were compared with pattern-reversal visual evoked potentials to verify the effectiveness of pattern movement application for visual evoked potential acquisition. Horizontally moving vertical gratings were generated on a television screen. The typical movement-onset reactions were characterized by one marked negative peak only, with a peak time between 140 and 200ms. In all subjects the sufficient stimulus duration for acquisition of movement-onset-related visual evoked potentials was 100ms; in some cases it was only 20ms. Higher velocity (5.6°/s) produced higher amplitudes of movement-onset visual evoked potentials than did the lower velocity (2.8°/s). In 80% of subjects, the more distinct reactions were found in the leads from lateral occipital areas (in 60% from the right hemisphere), with no correlation to handedness of subjects. Unlike pattern-reversal visual evoked potentials, the movement-onset responses tended to be larger to extramacular stimulation (annular target of 5°–9°) than to macular stimulation (circular target of 5° diameter).

Motion-onset VEPs reflect long maturation and early aging of visual motion-processing system

Pattern-reversal and motion-onset visual evoked potentials (VEPs) were simultaneously tested in a group of 70 healthy subjects between the ages of 6-60 years to verify suspected differences in maturation and aging dynamics of the pattern and motion processing subsystems of the visual pathway. The motion-onset VEPs displayed dramatic configuration development and shortening of latencies up to 18 years of age (correl. coeff. -0.85; p < 0.001) and systematic prolongation from about 20 years of age (correl. coeff. 0.70; p < 0.001). This confirms long-lasting maturation of the magnocellular system and/or motion processing cortex and their early age related changes. Less significant changes of pattern-reversal VEPs in the tested age range can be interpreted as a sign of early maturation of the parvocellular system and its enhanced functional endurance in the elderly.

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.

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”.

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.

P21.5 Motion-onset visual evoked potentials provide unique diagnostic info II. Clinical studies

Objectives: To determine if a second-scale inter-stimulus interval (ISI) of single-pulse TMS affects the amplitudes of the induced MEPs. The aim was to reduce the duration of the MEP measurements while maintaining response stability. Methods: Nine healthy subjects were studied. The left hemisphere was mapped for the cortical representation area of the dominant hand thenar muscle, and resting motor threshold (MT) was determined. MEPs were analyzed from 30 responses to navigated TMS with a stimulation intensity of 120% of the MT. The investigated ISIs were 1, 2, 3, 5 and 10 s as well as randomized ranges of 1 3 s, 3 5 s and 5 10 s. MEP amplitudes were analyzed over the stimulation trains and compared between different ISIs. Results: The mean amplitude of 10 first MEPs were lower (p < 0.05) at short ISIs when compared to those measured at long ISIs. This difference was not observed when the last 10 MEPs were compared. Also, no differences were observed between the MEPs at different ISIs, when the means of all 30 MEPs were compared. Significant increase (p < 0.05) in the MEP amplitudes (sliding mean of 10 MEPs) was observed during the stimulation train at constant ISIs of 1 to 5 s and at random ISI of 1 3 s. Conclusions: The ISI does not affect MEP amplitudes when >20 stimuli are applied. However, with short ISIs several stimuli may have to be rejected from the analysis from the beginning of the measurement. The MEPs in the beginning of the stimulation train at short ISI may be prone to voluntary muscle relaxation which could decrease the MEP size of a relaxed muscle. This has not been reported earlier in case of MEPs and likely this may not be an issue when MEPs from an active muscle are recorded.