Effects of the inter-stimulus interval on visual evoked potentials to patterned stimuli

Visual evoked potentials to patterned stimulation of the upper and lower half of the visual field were investigated in nine adult Ss. The inter-stimulus interval varied between 350 and 2,600 msec. With patterned stimulation, no inter-stimulus interval effects were obtained for occipital components. In contrast for the vertex lead, on the other hand, as inter-stimulus interval increased, the N140-P200 amplitude increased. Because of the heterogeneity subjects' responses evoked by upper half-field stimulation, this effect was more pronounced in lower half-field stimulation.     

Evoked potentials during the elaboration of a conditioned reflex to hippocampal stimulation in rats

In experiments on 9 rats, the study of evoked potentials (EPs) of the CA1 field of the dorsal hippocampus to stimulation of its symmetrical part serving as a signal of drinking conditioned reflex (CR) showed that during reflex elaboration, the amplitude of the main EP components significantly decreased; CR did not appear when the population spike (PS) was absent in the hippocampal response. PS always accompanying CR was not specific only of it, it was also recorded at other behavioural reactions. Changes of fascia dentata EPs in the process of CR elaboration to stimulation of its symmetrical part consisted in decrease of the initial negative wave and increase of the positive one. The obtained data point to a significant reconstruction of excitatory and inhibitory inputs to the hippocampus and fascia dentata under the influence of conditioned activity.     

Global brain dynamics of transient visual evoked potentials

The independent component analysis was applied to multichannel transient visual evoked potentials elicited by a high contrast pattern-reversal and motion-onset (motion velocity of 7 and 23 deg/s). Three overlapping independent components with different topographical distribution over the scalp were described. The first component displayed similar timing in response to all three stimuli (40-200 ms) but was a different in shape and scalp projection. This activation component is considered to reflect the stimulus properties. The second component (100-227 ms), related to negativity at about 160 ms, can be referred to visual processing of motion. The last component, attributed to positivity at 230 ms dominates in the fronto-central area and might represent a cognitive process.     

Manifestations of the genotypic causality of human evoked potentials during perception of various visual stimuli

Intrapair resemblance of the wave form and amplitude-temporal parameters of evoked potentials (EPs) to flashes, chess field, house image, the word "house" and a series of other stimuli was evaluated in 20 pairs of monozygotic and 20 pairs of homosexual dizygotic adult twins. In the occipital area the maximum of genetic dependence was characteristic of EPs to flashes, the minimum--of EPs--to the word "house". In vertex EPs parameters genotypic effects were manifest irrespectively of the stimulus type. Genotypic dependence differed for the amplitudes and latencies of separate EP components.     

The influence of emotionally significant visual stimuli on cortical evoked potentials

Electrophysiological correlates of the perception of emotional stimuli were studied by means of recording the visual evoked potentials (EP) in 20 derivations (Fz, Cz, Pz, Oz, Fp _1/2,F _3/4,F _7/8,C _3/4,P _3/4,T _3/4,T _5/6, andO _1/2) during the emotional test performance. The performance of a special task by subjects was assessed positively or negatively (by administering emotionally positive or negative stimuli, respectively). Factor analysis revealed seven factors, which described the EP component structure. Analysis of variance demonstrated the influence of the emotional stimuli sign on the factorsP ₁₀₀,P ₁₄₀,N ₁₆₀,P ₂₂₀,P ₃₄₀, and “slow wave.” Hemispheric difference in reactions to the stimuli of a different emotional sign were recorded. During presentation of the positive and negative assessments, the amplitudes of the factorsP ₁₀₀,P ₃₄₀, and “slow wave” were maximally different in the left hemisphere, while the factorsN ₁₆₀ andP ₂₂₀ were maximally different in the right hemisphere.     

Dipole tracing of visual evoked potentials in human brain

3D tracing of equivalent current dipoles (ECDs) of averaged human visual evoked potentials (VEP) by their distribution across a 34-electrode array was obtained under short presentation of pattern-onset stimuli (sets of 45 horizontal, vertical bars or crosses). Using a 2-dipole spherical three-layer model, we dynamically (step of 1 ms) localized dipoles in four healthy subjects. Dipole locations were matched to anatomical brain regions visualized in structural MRI. Best-fitting source parameters were superimposed on MR images of each subject to identify the anatomical structures giving rise to the surface patterns. It was found that during 50-300 ms following the onset of the stimuli, the ECDs in all subjects were localized in the occipital cortex and demonstrated reliable systematic shift in localization. Two local (1-2 cm3) zones of the preferable dipole attendance were found at 5-6 cm behind zero line: the first one was localized near the midline of the brain, whereas the other zone was situated in the right hemisphere at a distance of 6-7 cm from the first zone. Their localization and strength of activation were reliably different for crosses and lines and changed during VEP generation. Zones of relatively rare dipole attendance were found also. The data are discussed in relation to localization of initial and endpoint of ECDs trajectories, as well as with sensitivity of the visual cortex to line crossing and branching.     

Effect of genotype on evoked potentials of the left and right hemispheres during perception of visual stimuli

Intrapair similarity of evoked potentials (EPs) to light flash, checkerboard, house picture, the word "house" and a number of other stimuli was estimated in 20 pairs of monozygotic and 20 pairs of dizygotic adult twins of the same gender. In the right temporal area the level of the genotypic control of amplitude-temporal parameters of EPs on the whole is higher than in the left one; the more prominent this difference is in responses to spatial-structural stimuli. In the left temporal area, the genotypic control is manifested in latencies of components of EPs to linguistic stimuli.