视觉图形诱发的瞳孔反应

以图形变化刺激进行瞳孔反应研究,实验表明：（１）空间平均亮度守恒的光栅或棋盘格图形翻转能激发起瞳孔反应,为瞬态收缩波形,与ｐｕｐｉｌｌａｒｙ ｅｓｃａｐｅ相似;（２）光栅或棋盘格的空间频率的变化也能引起瞳孔反应,且反应幅度随空间频率差别增大而变大;（３）从均匀亮背景变化到棋盘格图形或者从棋盘格图形变化到黑暗背景,虽然不存在任何局部亮度增强,皆能引起瞳孔反应。实验结果明确证明了人的瞳孔反应系统除接收     

Visual potentials in humans with multiple sclerosis evoked by checkboard pattern of different contrast with additional noise

A hypothesis is advanced of an effect of internal noise upon signal conduction along visual nerve in an early stage of multiple sclerosis. Visual evoked potentials in response to chess patterns against a homogeneous background and against a noise background were studied in healthy subjects and in patients with multiple sclerosis. Contrast between internal noise in the patients was found to be twice as great as in healthy subjects.     

Visual evoked potentials in the vicinity of the optic tract during stereotactic pallidotomy

We recorded visual evoked responses in eight patients with Parkinson's disease, using a depth electrode either at or below the stereotactic target in the ventral part of the globus pallidus internus (GPi), which is located immediately dorsal to the optic tract. Simultaneously, scalp visual evoked potentials (VEPs) were also recorded from a mid-occipital electrode with a mid-frontal reference electrode. A black-and-white checkerboard pattern was phase reversed at 1 Hz; check size was 50 min of arc. Pallidal VEPs to full field stimulation showed an initial positive deflection, with a latency of about 50 ms (P50), followed by a negativity with a mean latency of 80 ms (N80). The mean onset latency of P50 was about 30 ms. P50 and N80 were limited to the ventralmost of the GPi and the ansa lenticularis. Left half field stimulation evoked responses in the right ansa lenticularis region while right half field stimulation did not, and vice versa. These potentials thus seemed to originate posterior to the optic chiasm. The scalp VEPs showed typical triphasic wave forms consisting of N75, P100 and N145. The location of the recording electrode in the ansa lenticularis region did not modify the scalp VEP. These results suggest that P50 and N80 are near-field potentials reflecting the compound action potentials from the optic tract. Therefore, N75 of the scalp VEPs may represent an initial response of the striate cortex but not of the lateral geniculate nucleus.     

VEP Correlates of Feedback in Human Cortex

It is known that neural responses become less dependent on the stimulus size and location along the visual pathway. This study aimed to use this property to find evidence of neural feedback in visually evoked potentials (VEP). High-density VEPs evoked by a contrast reversing checkerboard were collected from 15 normal observers using a 128-channel EEG system. Surface Laplacian method was used to calculate skull-scalp currents corresponding to the measured scalp potentials. This allowed us to identify several distinct foci of skull-scalp currents and to analyse their individual time-courses. Response nonlinearity as a function of the stimulus size increased markedly from the occipital to temporal loci. Similarly, the nonlinearity of reactivations (late evoked response peaks) over the occipital, lateral-occipital, and frontal scalp regions increased with the peak latency. Response laterality (contralateral vs. ipsilateral) was analysed in lateral-occipital and temporal loci. Early lateral-occipital responses were strongly contralateral but the response laterality decreased and then disappeared for later peaks. Responses in temporal loci did not differ significantly between contralateral and ipsilateral stimulation. Overall, the results suggest that feedback from higher-tier visual areas, e.g., those in temporal cortices, may significantly contribute to reactivations in early visual areas.     

视力与视觉诱发电位的相关分析

对104例病人的图形翻转VEP的瞬态波形各参数,以及9例正常或近视学生的稳态曲线功率谱与视力之间的关系进行了多元相关统计分析,旨在探讨VEP的哪些参数可客观地评估视力.结果表明,瞬态VEP的波形参数中以13’格诱发的N_1P_1、P_1N_2的峰峰值及P_(100)潜伏期与视力的相关系数最大,故认为,分析视力时以平均P_(100)波的波幅值和P_(100)波潜伏期作指标较为灵敏;而稳态、VEP能谱曲线则显示,视力与平均相叶能谱或刺激频率点的能谱相关性较大,与二次谐波的相关性则小.     

Visual acuity thresholds of juvenile loggerhead sea turtles (Caretta caretta): an electrophysiological approach

Visual evoked potentials measure dynamic properties of the visual system by recording transient electric responses of neural tissue identified to correspond to a specific visual stimulus, such as light or a striped grid. In this study, visual evoked potentials were used to test the visual acuity of juvenile loggerhead sea turtles (Caretta caretta) in water. Subject animals were fitted with a Plexiglas goggle filled with filtered seawater. Stimuli of black and white striped gratings were presented to the turtles using a slide projector directing an image onto a screen via a rotatable mirror that shifted the striped pattern laterally one-half cycle. Bioelectric activity was collected using a digital averaging computer and subdermal platinum electrodes, implanted under the head scutes directly above the optic nerve and the contralateral optic tectum. To isolate the response signal from the noise, signal averaging techniques were used when collecting visual evoked potentials. The resulting response waveforms included a robust positive-negative compound that was used to track the turtle's response to visual stimulation. Acuity thresholds for these sea turtles, which were derived from linear regressions analysis of the positive-negative compound amplitudes versus stripe size, ranged from 0.130 to 0.215. This acuity level is comparable to other inshore, shallow water marine species.     

Visual evoked potentials in a sample of schizophrenic patients

Variations in evoked potentials utilizing a photic stimulus in a sample of psychiatric patients compared to a healthy sample were evaluated. A group of patients diagnosed as schizophrenic was tested against a sample of healthy volunteers in a trial combining visual evoked potentials and a simultaneous cognitive processing. The stimulus was a checkerboard pattern presented under three different conditions. The results indicate diminished P100 and lack the reactivity associated with cognitive processes in schizophrenic group. The P200 component also lacked, in the inpatient group the changes associated with the performance of the trial. Finally the multiple P300 component was shortened in latency and decreased in amplitude in the schizophrenia group. Besides, P300 interhemispheric shifts related to trials, were commonly inverted in schizophrenics. Results are interpreted as a lacked interhemispheric coordination in schizophrenics, rather than a fixed hemispheric alteration. Likewise, an attenuation in processing from specific cortical areas to association cortex is concluded.     

Analysis of visual evoked potentials through Wiener filtering applied to a small number of sweeps

We introduce a method for processing visual evoked potentials, on the basis of a Wiener filter algorithm applied to a small number of consecutive responses. The transfer function of the filter is obtained by taking into account both the average of 99 sweeps (as an estimate of the true signal) and the EEG signal just before the stimulus onset (as an estimate of the noise superimposed on each individual response). The process acts as a sweep-by-sweep filter (in the sense of the mean square error) which considers the possible non-stationarities of the EEG signal during a complete clinical procedure. The average of a small number of consecutive filtered sweeps reveals variations in the morphology of the evoked responses which produce a change in the principal latencies. Applications are foreseen in neurophysiological studies of visual evoked potential responses, and in the clinic, where it is important to evaluate adaptive mechanisms, dynamic changes in single groups of visual evoked potentials and cognitive responses.     

Comparative bioacoustical study of diurnal and nocturanl rodents from closed ranges

Studies have been made on the evoked potentials at the level of the colliculus inferior in the nocturnal rodent Glis glis and diuranl one--Eutamias sibiricus. In G. glis, the evoked potentials were recorded in a wide range of sonic and ultrasonic frequencies up to 90 kc, while in E. sibiricus these potentials were recorded in a range of frequencies up to 60 kc. The auditory threshold curves for G. glis exhibited two areas of minimum thresholds-- a low frequency area and an area at a boundary between sonic and ultrasonic frequencies. Threshold curves for E. sibiricus have no clear sensitivity maximum. In G. glis, correlation between the spectrum of their communication signals and acoustic noise in the habitat was observed. The species investigated differ in the rate of the recovery of the evoked potentials to paired stimuli and in the values of critical summation time.     

Changeable cuttlefish camouflage is influenced by horizontal and vertical aspects of the visual background

Cuttlefish change their appearance rapidly for camouflage on different backgrounds. Effective camouflage for a benthic organism such as cuttlefish must deceive predators viewing from above as well as from the side, thus the choice of camouflage skin pattern is expected to account for horizontal and vertical background information. Previous experiments dealt only with the former, and here we explore some influences of background patterns oriented vertically in the visual background. Two experiments were conducted: (1) to determine whether cuttlefish cue visually on vertical background information; and (2) if a visual cue presented singly (either horizontally or vertically) is less, equally or more influential than a visual cue presented both horizontally and vertically. Combinations of uniform and checkerboard backgrounds (either on the bottom or wall) evoked disruptive coloration in all cases, implying that high-contrast, non-uniform backgrounds are responded to with priority over uniform backgrounds. However, there were differences in the expression of disruptive components if the checkerboard was presented simultaneously on the bottom and wall, or solely on the wall or the bottom. These results demonstrate that cuttlefish respond to visual background stimuli both in the horizontal and vertical plane, a finding that supports field observations of cuttlefish and octopus camouflage. Both A. Barbosa and L. Litman are first authors. An erratum to this article can be found at     

Amplitude asymmetry of hemifield pattern reversal VEPs in healthy subjects

The amplitudes of transient and steady-state visual evoked potentials (VEPs) were measured during hemifield stimulation of the left eye in 10 healthy adults. Pattern reversal of a checkerboard was produced at 4 stimulation frequencies: 1, 5, 10 and 15 Hz. The amplitudes of pattern VEPs were evaluated using the paired t test to determine significant differences between right and left hemifields. The transient VEP amplitudes from midoccipital, midparietal, ipsilateral occipital and contralateral occipital electrodes were significantly greater with right hemifield stimulation. The steady-state VEP amplitudes from the midoccipital electrode during 15 Hz stimulation were significantly greater with right hemifield stimulation. Our neurophysiological data may be compatible with neuroanatomical asymmetries of the occipital lobes in humans.     

The effect of selective attention on pattern-specific visual evoked potentials

In a complex choice reaction time experiment, patterned stimuli without luminance change were presented, and pattern-specific visual evoked potentials to lower half-field stimulation were recorded. Two experimental conditions were used. The first was the between-field selection, where square patterns were presented in either the lower or the upper half of the visual field. In a given stimulus run one of the half-fields was task-relevant, and the subjects' task was to press a microswitch to stimuli of higher duration value (GO stimuli), while they had to ignore shorter ones, i. e. stimuli of lower apparent spatial contrast (NOGO stimuli). They had to ignore the stimuli appearing in the irrelevant half-field (IRR stimuli). In order to ensure proper fixation, the subjects had to press another microswitch at the onset of a dim light at the fixation point (CRT stimuli). Our second experimental condition was the within-field selection, where the GO, NOGO, and IRR stimuli appeared in the lower half of the visual field. GO and NOGO were square patterns while IRR stimuli were constructed of circles, or vice versa. (The CRT stimuli were the same as in the previous condition.) Three pattern-specific visual evoked potential components were identified, i. e. CI (70 ms latency), CII (100 ms latency), and CIII (170 ms latency). There were marked selective attention effects on both the CI-CII and CII-CIII peak-to-peak amplitudes. In both experimental conditions, responses with the highest amplitude were evoked by the GO type of stimuli, while the IRR stimuli evoked the smallest responses. According to these results, attention effects on the pattern-specific visual evoked potentials in the first 200 ms cannot be attributed to a simple stimulus set kind of selection.     

Amplitude-frequency modulation of electroencephalogram associated with rhythmic movements

Evoked, motor and final potentials and some other EEG phenomena are suggested as additional components accompanying movements, external stimuli, imagination etc. Obviously, the EEG reactions are not restricted to them. On the basis of the method of synchronic averaging a way for detecting the amplitude-frequency modulation (AFM) related to the repeated movements is proposed. This method permitted to reliably single out the EEG effects which sometimes were detected by visual analysis. As the experiments showed the depth of AFM EEG accompanying the movements was about 3-6% (in this case spontaneous AFM plays the role of noise and equals 50% or more). Relations between changes in AFM for EEG recorded from various points, as well as for EEG rhythms were investigated.     

Visual evoked potentials in response to dichoptic presentation of sinusoidal grating and noise background

Dichoptic stimulation was used in comparison of visual evoked potentials (VEPs) with those obtained with monocular stimulation (recordings made from the occipital area). 16 subjects viewed sinusoidal gratings with the right eye while a visual noise was added via a mirror for the left eye. In presence of the noise, amplitude of the early VEP components' N1, P1b, and the late component P2 decreased, P1a is not changed in presence of the noise, and the late negative wave N2 increased for all spatial frequencies. The effect of noise on the amplitude of VEPs obtained for monocular and dichoptic stimulation was similar. The data suggest that external noise is filtered by the V1 cortical neurons--matched filters for the gratings.     

Mechanisms of interaction between the parietal association and projection areas of the cat neocortex

Changes in evoked potentials in the first visual (VI), first somatic (SI), and parietal areas of the cortex during local cooling of each area were investigated under pentobarbital anesthesia. Two types of interaction were distinguished. Type I interaction was found in all areas in the early stages of local cooling and was reflected in a similar decrease in amplitude of evoked potentials in intact parts of the cortex. In the thalamic association nuclei — the pulvinar and posterolateral nucleus — somatic evoked potentials were unchanged but visual were transformed differently from those in the cortex. Type IIinteraction was found in the later stages of cooling and only between the association area and each of the projection areas. It was reflected in a greater change in amplitude of the evoked potentials and also in their configuration. In response to somatic stimulation in the early stage of type II interaction transformation of evoked potentials in the cortex took place sooner than in the nuclei; in the later stage it took place immediately after transformation of the "subcortical" evoked potentials. In response to photic stimulation transformations of cortical evoked potentials were always preceded by the corresponding transformations in the nuclei. It is suggested that type I interaction is formed by intercortical connections and type II by direct and subcortical relay connections. Differences in the role of the association area in interaction of types I and II when activated by stimuli of different modalities are discussed.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 573–581, November–December, 1978.     

Spatiotemporal specificity of neuronal activity directs the modification of receptive fields in the developing retinotectal system

The precise temporal relation between pre- and postsynaptic activity modulates the strength of synaptic connections. Despite its extensive characterization in vivo and in vitro, the degree to which spike timing-dependent plasticity can shape receptive field properties is unclear. We use in vivo patch-clamp recordings of tectal neurons in developing Xenopus tadpoles to control the precise timing of action potentials with respect to the arrival of a subset of visual inputs evoked by local light stimulation on the retina. The pattern of visual inputs onto a tectal neuron was tracked over time by rapid reverse correlation mapping of receptive fields. Spike timing-dependent potentiation or depression of a subset of synapses reliably shifts the spatial receptive fields toward or away from the trained subregion of visual space, respectively. These results demonstrate that natural patterns of activity evoked by sensory stimuli play an instructive role in the developing nervous system.     

Bioelectrical activity and neuromediator metabolism in different brain structures during chronic haloperidol administration]

First haloperidol administration is followed by the reorganization of evoked potentials in visual cortex. During haloperidol administration (10-12 days after the beginning) variations of evoked potentials is visual cortex and in subcortical structures uniform evoked potentials took place.     

Interhemispheric transmission of visual information: behavioral and electrophysiologic aspects

Efficiency of callosal and extracallosal channels of interhemispheric transfer of visual information was studied by behavioural and electrophysiological methods on cats with sections of classical and commissural pathways of the visual system. The results showed a high ability of the operated animals to form conditioned defensive reflex to visual stimuli. The primary complexes of evoked potentials to light flashes in the projection cortex of both hemispheres were also preserved. The data show the significant role of the callosal and extracallosal pathways of the transmission of visual information across the midline.     

Modeling the Formation of Steady State Visual Evoked Potentials at Different Frequencies of Photostimulation

Biophysics - The formation of steady-state visual evoked potentials on the basis of visual evoked potentials was analyzed. Using the regression model, it was shown that the accumulation of...     

Contrast transfer function of the visual system]

Visually evoked potentials were used to determine the spatial contrast response function of the visual system and the visual acuity of the pigeon. The spatial contrast response describes the relationship between the contrast in a pattern of vertical stripes, whose luminance is a function of position, and the amplitude of the visually evoked response at various spatial frequencies for a given temporal frequency (pattern reversal frequency); it indicates how particular spatial frequencies are attenuated in the visual system. The visually evoked responses were recorded using monopolar stainless steel electrodes inserted into the stratum griseum superficiale of the optic tectum; the depth of penetration was determined on the basis of a stereotactic atlas. The stimulus patterns were generated on a video monitor placed 75 cm in front of the animal's eye perpendicular to the optic axis. The spatial contrast response function measured at 10% contrast and 0.5 Hz reversal frequency shows a peak at a spatial frequency of 0.5 c/deg, corresponding to 1 degree of visual angle, and decreases progressively at higher spatial frequencies. The high-frequency limit (cut-off frequency) for resolution of sinusoidal gratings, estimated from the contrast response function, is 15.5 c/deg, corresponding to a visual acuity of 1.9 min of arc.