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.     

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.     

The evoked brain activity during hyperbaric exposure

Changes of amplitude-temporal parameters of visual evoked potentials (VEPs) under hyperbaric action testify to reconstruction of the activity of functional brain systems participating in the generation of responses to light stimulation. The revealed EP changes depend both on conditions of hyperbarism and on individual characteristics of subjects. The parameters of VEPs may manifest the estimation of common functional state under prolonged extreme influences.     

Objective measurements of visual acuity by visual evoked potentials

Electrophysiological measurements of the threshold spatial frequency were conducted in 26 healthy subjects by using visual evoked potentials with the purpose of objective determination of the visual acuity. For that we proposed a universal method of the visual stimulation and EEG processing (using ICA decomposition in particular) to minimize errors arising on account of individual differences in the visual system functioning. As a result, a correlation of 0.74 and a logarithmic dependence were obtained between spatial resolution measured by electrophysiological and psychophysical methods. The proposed methods of objective measurement of visual resolution has a high effectiveness, does not depend on specificity of individual EEG and domination of different channels in the visual system. Therefore it is possible to determinate objectively the visual acuity in humans independently of their responses.     

Rhythmic activity of the endbrain in the carp evoked by adequate visual stimulation

In acute experiments on immobilized carps, under dark adaptation conditions, studies have been made on the electrical activity of the telencephalon and midbrain tectum. It was found that in the latter photostimulation evokes local rhythmic activity which includes fast (30-50 Hz) phasic (200-300 ms) and slow (8-14 Hz) tonic (up to 3-4 s) components. High rhythm of this activity may be observed only in "healthy" preparations, coinciding with on-rhythm in the midbrain tectum. Low rhythm does not depend on the presence of rhythmic activity in the tectum. Various aspects of the development of the thalamo-telencephalic system in vertebrates are discussed.     

Optical and electrical recording of neural activity evoked by graded contrast visual stimulus

Background  

Brain activity has been investigated by several methods with different principles, notably optical ones. Each method may offer information on distinct physiological or pathological aspects of brain function. The ideal instrument to measure brain activity should include complementary techniques and integrate the resultant information. As a "low cost" approach towards this objective, we combined the well-grounded electroencephalography technique with the newer near infrared spectroscopy methods to investigate human visual function.     

Inhibition of sialyltransferase activity in cultured cells by a natural inhibitor from rat brain

Summary Brain from mature rats has been shown previously to contain a natural inhibitor of rat brain sialyltransferase I (CMP-sialic acid: lactosylceramide sialyltransferase activity). This same inhibitor preparation was effective against sialyltransferase I and a second sialyltransferase activity from different lines of cultured cells. Cardiolipin which stimulates sialyltransferase I activity in cultured cells apparently was not required for inhibition. Inhibition was specific for sialyltransferase activities while a third ganglioside biosynthetic enzyme, UDP-gal: glucosyl-ceramide galactosyltransferase activity, was not inhibited. Inhibition of sialyltransferase I was linear with time, heat-resistant, and increased with inhibitor concentration.Gangliosides are sialic-acid containing glycosphingolipids found in brain as well as extraneural tissues and cultured cells t,2. Although the functions of gangliosides are unknown, they appear to play a role in morphological differentiation³ sensory and visual stimulation 4 and as receptor for cholera toxin^5–8 and possibly thyroid stimulating hormone⁹. The monosaccharide units are added to the elongating oligosaccharide chain of the gangliosides in step-wise fashion and different glycosyltransferases catalyze each addition^10,11. The activities of these enzymes have been observed to change during development^12,14 malignant transformation¹³ and morphological differentiation³.Although little is known about the regulation of ganglioside synthesis, a natural inhibitor of CMP-AcNeu: GL-2 sialyltransferase (sialyltransferase I) from rat brain has been described^14,15. As the inhibitor activity increased with the age of the animal, the same authors suggested that it may regulate the biosynthetic pathway of gangliosides. In this paper, the effects of the rat brain inhibitor on the activities of ganglioside biosynthetic enzymes from several cultured cell lines are described.Abbreviations AcNeu N-acetylneuraminic acid - GL1 glucosylceramide - GL-2 lactosylceramide - G_M3 Nacetylneuraminylgalactosylglucosylceramide - G_M1 gal actosyl-N-acetylgalactosaminyl-(N-acetylneuraminylgalactosylglucosylceramide - G_D1a Nacetylneuraminylgalactosyl-N-acetylgalactosaminyl-(Nacetylneuraminyl)-galactosylglucosylceramide. DR. DUFFARD was a recipient of a Fogarty Center Fellowship.     

Deoxyglucose mapping of nervous activity induced inDrosophila brain by visual movement

Summary The pattern of visually induced local metabolic activity in the optic lobes of two structural mutants ofDrosophila melanogaster is compared with the corresponding wildtype pattern which has been reported in Part I of this work (Buchner et al. 1984b). Individualoptomotor-blind ^H31 (omb) flies lacking normal giant HS-neurons were tested behaviourally, and those with strongly reduced responses to visual movement were processed for 3H-deoxyglucose autoradiography. The distribution of metabolic activity in the optic lobes ofomb apparently does not differ substantially from that found in wildtype. In the mutantlobula plate-less ^N684 (lop) the small rudiment of the lobula plate which lacks many small-field input neurons does not show any stimulus-specific labelling. The data provide further support for the hypothesis that small-field input neurons to the lobula plate are the cellular substrate of the direction-specific labelling inDrosophila (see Buchner et al. 1984b).Abbreviations DG deoxyglucose - omb optomotor blind^H31 - lop lobula plate-less^N684 - WT wildtype     

Deoxyglucose mapping of nervous activity induced inDrosophila brain by visual movement

Summary Autoradiographs of the brains of the visual mutantsouter rhabdomeres absent ^JK84 (ora),small optic lobes ^KS58 (KS58) andno object fixation E ^B12 (B12) have been obtained by the deoxyglucose method. The patterns of metabolic activity in the optic lobes of the visually stimulated mutants is compared with that of similarly stimulated wildtype (WT) flies which was described in Part I of this work (Buchner et al. 1984b).In the mutantKS58 the optomotor following response to movement is nearly normal despite a 40–45% reduction of volume in the visual neuropils, medulla and lobula complex. InB12 flies the volume of these neuropils and the optomotor response are reduced. In autoradiographs of both mutants the pattern of neuronal activity induced by stimulation with moving gratings does not differ substantially from that in the WT. It suggests that only neurons irrelevant to movement detection are affected by the mutation. However, in the lobula plate of someKS58 flies and in the second chiasma of allB12 flies, the pattern of metabolic activity differs from that observed in WT flies. Up to now no causal relation has been found between the modifications described in behaviour or anatomy and those observed in the labelling of these mutants.In the ommatidia ofora flies the outer rhabdomeres are lacking while the central photoreceptors appear to be normal. Stimulus-specific labelling is absent in the visual neuropil of these mutants stimulated with movement or flicker. This result underlines the importance of the outer rhabdomeres for visual tasks, especially for movement detection.Abbreviations DG deoxyglucose - KS58 small optic lobes^KS58 - B12 no object fixation E^B12 - JK84 ora outer rhabdomeres absent ^JK84 - WT wildtype     

Linking visual perception with human brain activity.

The past year has seen great advances in the use of functional magnetic resonance imaging (fMRI) to study the functional organization of the human visual cortex, to measure the neuronal correlates of visual perception, and to test computational theories of vision. Activity in particular visual brain areas, as measured with fMRI, has been found to correlate with psychophysical performance, with visual attention, and with subjective perceptual experience.     

Subjective visual perception: from local processing to emergent phenomena of brain activity

The combination of electrophysiological recordings with ambiguous visual stimulation made possible the detection of neurons that represent the content of subjective visual perception and perceptual suppression in multiple cortical and subcortical brain regions. These neuronal populations, commonly referred to as the neural correlates of consciousness, are more likely to be found in the temporal and prefrontal cortices as well as the pulvinar, indicating that the content of perceptual awareness is represented with higher fidelity in higher-order association areas of the cortical and thalamic hierarchy, reflecting the outcome of competitive interactions between conflicting sensory information resolved in earlier stages. However, despite the significant insights into conscious perception gained through monitoring the activities of single neurons and small, local populations, the immense functional complexity of the brain arising from correlations in the activity of its constituent parts suggests that local, microscopic activity could only partially reveal the mechanisms involved in perceptual awareness. Rather, the dynamics of functional connectivity patterns on a mesoscopic and macroscopic level could be critical for conscious perception. Understanding these emergent spatio-temporal patterns could be informative not only for the stability of subjective perception but also for spontaneous perceptual transitions suggested to depend either on the dynamics of antagonistic ensembles or on global intrinsic activity fluctuations that may act upon explicit neural representations of sensory stimuli and induce perceptual reorganization. Here, we review the most recent results from local activity recordings and discuss the potential role of effective, correlated interactions during perceptual awareness.     

Reproducibility of human brain activity evoked by esophageal stimulation using functional magnetic resonance imaging

Functional MRI is a popular tool for investigating central processing of visceral pain in healthy and clinical populations. Despite this, the reproducibility of the neural correlates of visceral sensation by use of functional MRI remains unclear. The aim of the present study was to address this issue. Seven healthy right-handed volunteers participated in the study. Blood oxygen level-dependent contrast images were acquired at 1.5 T while subjects received nonpainful and painful phasic balloon distensions ("on-off" block design, 10 stimuli per "on" period, 0.3 Hz) to the distal esophagus. This procedure was repeated on two further occasions to investigate reproducibility. Painful stimulation resulted in highly reproducible activation over three scanning sessions in the anterior insula, primary somatosensory cortex, and anterior cingulate cortex. A significant decrease in strength of activation occurred from session 1 to session 3 in the anterior cingulate cortex, primary somatosensory cortex, and supplementary motor cortex, which may be explained by an analogous decrease in pain ratings. Nonpainful stimulation activated similar brain regions to painful stimulation, but with greater variability in signal strength and regions of activation between scans. Painful stimulation of the esophagus produces robust activation in many brain regions. A decrease in subjective perception of pain and brain activity from the first to the final scan suggests that serial brain imaging studies may be affected by habituation. These findings indicate that for brain imaging studies that require serial scanning, development of experimental paradigms that control for the effect of habituation is necessary.     

Effects of morphine on visual evoked responses recorded in five brain sites.

The effects of morphine on averaged evoked responses to visual stimulation were examined in specific brain structures relevant to pain, analgesia, tolerance and motor disturbances. Permanent electrodes (60 μ in diameter) were implanted stereotaxically in the central gray, mesencephalic reticular formation, caudate nucleus, parafasicular-centromedian complex and the lateral geniculate body as a control site. Visual evoked responses were obtained in unanesthetized, unrestrained rats prior to and following the administration of morphine in successive doses of 1, 5, 10 and 30 mg/kg and 1 mg/kg of naloxone (a morphine antagonist). The parafasicular-centromedian complex and the reticular formation exibited a progressive increase in response amplitude to increased dose of morphine. These effects were reversed by naloxone. In this study the parafasicular-centromedian complex was found to be the most sensitive structure to morphine, displaying the largest changes in response amplitude as a result of morphine administration.     

Spontaneous and evoked unit activity in the visual cortex in mutant mice

Spontaneous and evoked unit activity was investigated in the visual cortex of mice with the "ocular retardation" (or/or) mutation, in which the action of the gene is manifested phenotypically by defective development of the optic nerve, with the consequent total blindness of the animals. Control experiments were carried out on inbred C57Br mice. A raised level of spontaneous activity was found in the neurons of the mutant animals and also differences in the distribution of the cells on the basis of the types of their spontaneous activity: A regular type of activity was found 2.5 times more often in the "or/or" mice than in the control group, whereas the proportion of cells with a volley type of discharge was 2.7 times smaller. In addition, visual cortical neurons of the "or/or" mice were more able to respond to acoustic stimulation, when 78% of the responses were tonic in character. Of the unit responses to electrical stimulation of the skin 70% also were tonic, and most were responses of excitation. In 42% of visual cortical neurons of the mutants convergence of heteromodal afferent influences was observed. The functional features described are evidently phenotypical manifestations of the action of the mutant gene on cortical neurons.P. K. Anokhin Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 568–574, November–December, 1976.