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

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.

Role of latency jittering correction in motion-onset VEP amplitude decay during prolonged visual stimulation.

Visual evoked potentials to motion-onset stimulation (M-VEPs) gradually attenuate in amplitude during examination. The observed decline in averaged responses can be caused by decreases in single response magnitudes and/or increased variability in a response delays, that is, latency jittering. To illuminate the origins of the suppression of M-VEPs during stimuli repetition, we used correlation technique to estimate an upper bound of possible latency jittering of single sweeps and we evaluated the effect of its correction on the amplitudes of three M-VEP dominant peaks P1, N2 and P3. During prolonged visual motion stimulation, the variability of corrective latency shifts in the occipital region increased (r = 0.35: 0.44) and the number of single responses corresponding to the average curve declined in occipital and parietal derivations (r = -0.48: -0.62). While the P1 peak amplitude did not exhibit any time-specific behaviour, the N2 amplitude exhibited a significant decay of 29.4% that was partially reduced to 16.6% in the central occipital derivation by the latency jitter and non-correspondence corrections. The strongest attenuation (32.7%) was observed in the P3 amplitude and was less sensitive to the corrections, dropping only to 27.9%. The main part of the response suppression to repeated motion stimulation was caused by amplitude drop and represents non-stationary process that likely correspond to a fatigue model. The rise of variability in latency jitter correction and the reduction in single responses correlated with the M-VEP were significant factors associated with prolonged motion stimulation. The relation of these parameters to a hypothetical veridical response is ambiguous and can be caused by a time shift of the response or by a change of signal-to-noise ratio. Using selective averaging and latency jitter correction, the effect of response suppression was partially removed.

Visual evoked potentials to pattern, motion and cognitive stimuli in Alzheimer's disease.

The aim of our study was to verify reported visual dysfunctions of patients with Alzheimer disease with the use of several variants of VEPs and visual ERPs and to learn whether these methods can be useful in diagnostics of AD. We tested 15 patients (6 women and 9 men, aged from 58 to 87) with mild to moderate Alzheimer disease (12-23 points of Mini Mental State Examination) and 15 age, gender and education level matched controls. The examination consisted of VEPs to pattern-reversal and motion-onset stimulation (to translational and radial movement) and of visual ERPs recorded during an odd-ball test. The subjects were instructed to signalize target stimuli by pressing of a button, which enabled to evaluate also the reaction time. While pattern-reversal VEPs were comparable in patients and controls, there were significantly smaller N2 peak amplitudes of motion-onset VEPs in patients with AD (in particular in radial moving stimuli outside the central 20 deg of the visual field), which suggests a dysfunction of the motion-processing (magnocellular) system or the dorsal cortical stream. ERPs, having significantly longer latencies in patients than in controls, distinguished well both groups. However, the individual AD diagnostics based on ERPs seems to be limited by rather high inter-individual variability of the ERP latencies. The ERPs might, however, be useful in disease progress and therapy effect estimation. Electrophysiological parameters did not correlate with neuropsychological ADAS cog test (Alzheimer Disease Assessment Scale--cognitive part).

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.

Using visual direction in three-dimensional motion perception.

The eyes receive slightly different views of the world, and the differences between their images (binocular disparity) are used to see depth. Several authors have suggested how the brain could exploit this information for three-dimensional (3D) motion perception, but here we consider a simpler strategy. Visual direction is the angle between the direction of an object and the direction that an observer faces. Here we describe human behavioral experiments in which observers use visual direction, rather than binocular information, to estimate an object's 3D motion even though this causes them to make systematic errors. This suggests that recent models of binocular 3D motion perception may not reflect the strategies that human observers actually use.

Simple and powerful visual stimulus generator.

We describe a cheap, simple, portable and efficient approach to visual stimulation for neurophysiology which does not need any special hardware equipment. The method based on an animation technique uses the FLI autodesk animator format. This form of the animation is replayed by a special program ('player') providing synchronisation pulses toward recording system via parallel port. The 'player is running on an IBM compatible personal computer under MS-DOS operation system and stimulus is displayed on a VGA computer monitor. Various stimuli created with this technique for visual evoked potentials (VEPs) are presented.

Advanced electrophysiological diagnostics of hepatic and portosystemic encephalopathy.

In 28 patients with liver cirrhosis, pre- and post-TIPS (transjugular intrahepatic porta-caval shunt), pattern-reversal visual evoked potentials (PREPs) and motion-onset visual evoked potentials (M-VEPs) examinations, EEG spectral analysis and Number Connection Test were performed. The M-VEPs (representing an activity of the magnocellular system of the visual pathway and reactions of the mediotemporal associate visual area) displayed the highest sensitivity (latencies delay) for detection of subclinical hepatic encephalopathy. The PREPs (originating in the primary visual cortex -area striata) were not significantly changed in comparison with a group of age matched controls. The EEG frequency spectrum exhibited significant slowing of the dominant frequency which was more pronounced in the post-TIPS examination. Combined analysis of the M-VEPs latency and EEG dominant frequency seem to be a recommendable method for early detection and objective classification of subclinical hepatic or portosystemic encephalopathy.

Video-signal synchronizes registration of visual evoked responses.

Autodesk Animator software offers the suitable technique for visual stimulation in the registration of visual evoked responses (VERs). However, it is not possible to generate pulses that are synchronous with the animated sequences on any output port of the computer. These pulses are necessary for the synchronization of the computer that makes the registration of the VERs. The principle of the circuit is presented that is able to provide the synchronization of the analyzer with the stimulation computer using Autodesk Animator software.

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 200 ms. In all subjects the sufficient stimulus duration for acquisition of movement-onset-related visual evoked potentials was 100 ms; in some cases it was only 20 ms. Higher velocity (5.6 degree/s) produced higher amplitudes of movement-onset visual evoked potentials than did the lower velocity (2.8 degrees/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 degrees-9 degrees) than to macular stimulation (circular target of 5 degrees diameter).

[The visual evoked response at the onset of structural movement]. / Zrakové vyvolané odpovedi na zacátek pohybu struktury.

Stimulation by means of moving the structure in the visual field is used to produce visual evoked responses (VER) only rarely. The authors attempted to verify the fact how VER to the movement depended on some stimulation parameters and to compare them with VER to the most frequently used stimulation method, i. e. reversal. Horizontally moving black and white vertical stripes were used with special frequency 2.3 cycles/deg on the screen. It was found that at least 3s interval between two stimuli (between the end of the preceding and onset of the following movements) was necessary and sufficient period of the moving was about 100 ms. Resultant VER are then a reaction on the onset of the movement and are characterized mostly only by marked negative peak with latency being 140 to 200 ms. Opposite to reversal VER, those to the onset of the movement were obtained just in 87.5% of the persons examined (n = 40), in five cases, however, the response to the onset of the motion was higher than that to reversal VER amplitudes were in the latter case highest in the unipolar lead from the right occipital region with the rate of the structure movement being 42 to 84 mm/s.

The use of rotating checkerboard patterns in the treatment of amblyopia.

Sixty-four amblyopic children (mean age 7.5 years, age range 4-12 years) were subjected to treatment using slowly rotating patterns of different spatial frequencies. In 20 amblyopes square-wave gratings (spatial frequencies 0.26-16.84 c/deg), in 44 checkerboard-patterned structures (spatial frequencies 0.04-5.2 c/deg) were used for stimulation. The mean improvement of the distance visual acuity was significantly higher in the checkerboard-stimulated group (3.59 equidistant optotype lines) than in the grating-stimulated group (2.71). As the highest spatial frequency of the checkerboards was substantially lower than of gratings, the results cannot be explained in terms of optical qualities of the stimulating patterns. Other factors, such as short-term occlusion, accomplishment of demanding visuomotor tasks and the quality of cooperation and attentiveness of the patients are considered to be more important for the success of treatment.

Visual evoked responses to pattern-reversal: the signal-to-noise ratio.

Visual evoked responses (VERs) to checkboard-reversal photic stimuli were recorded in 30 healthy experimental subjects with a mean age of 32 years. In 20 cases the stimuli were presented monocularly and in 10 cases binocularly. The estimated mean signal-to-noise ratio (SNR) of the individual VERs was found to be 0.245 +/- 0.092 for monocular stimulation and 0.444 +/- 0.23 for binocular stimulation. The power-based SNR of the averaged VERs was 24.5 and 44.4 respectively. The SNR was raised the most effectively by a new selective averaging variant applied after latency correction of the individual VERs; in the case of monocular stimulation the SNR rose to a mean 58.94 and in binocular stimulation to a mean 87.42. The mean proportion of discarded single VERs was 24%.

Pattern-reversal visual evoked potentials in patients with chronic renal insufficiency.

Visual evoked potentials (VEPs) were recorded from 88 patients with chronic renal insufficiency twice at a 6 month interval. In dialysed patients statistically significant decreases in amplitudes and prolongations of VEP peak latencies were found. Azotaemic non-dialysed patients showed related, but smaller, changes in their VEPs. In patients after kidney transplantation the VEP amplitudes were normal but peak latencies were prolonged. No systematic significant relationship between the VEPs and creatinine and urea levels in the blood could be shown.