Perinatal exposure to 60-Hz electric fields: Effects on the development of the visual-evoked response in rats

Two independent series of experiments were performed on 114 male Sprague-Dawley derived, albino rat pups, which represented 61 litters in experimental series I and 53 litters in experimental series II. Animals were exposed for 20 h/day from conception to testing (postnatal days 11–20) to a vertical, 65-kV/m, 60-Hz electric field or sham-exposed. Recordings of the visual-evoked response (VER) were obtained using a small silver ball electrode placed epidurally over the visual cortex. Visual stimuli consisted of 10-μS light flashes delivered at 0.2 Hz. Computer-averaged VERs were obtained and power spectral analyses (fast Fourier transform) were performed on the tapered (split cosine-bell window), averaged VERs. The expected age-related changes were clearly evident; however, a detailed analysis of VER component latencies, peak-to-peak amplitude, and power spectra failed to reveal any consistent, statistically significant effect of exposure to 60-Hz electric fields.     

Real-time modulation of perceptual eye dominance in humans

Ocular dominance (OD) has long served as the model for neural plasticity. The shift of OD has been demonstrated by monocular deprivation in animals only during early visual development. Here, for the first time, we show that perceptual eye dominance can be modulated in real time in normal human adults by varying the spatial image content of movies seen dichoptically by the two eyes over a period as short as 2.5 h. Unlike OD shifts seen in early visual development, this modulation in human eye dominance is not simply a consequence of reduced interocular correlation (e.g. synchronicity) or overall contrast energy, but due to the amplitude reductions of specific image components in one eye''s view. The spatial properties driving this eye dominance change suggest that the underlying mechanism is binocular but not orientationally selective, therefore uniquely locating it to layer 4 B of area V1.     

The refractive development of the eye of the American kestrel (Falco sparverius): a new avian model

Summary Most measures of avian visual performance are carried out on commonly available domestic species such as the chicken, and most of the data on avian induced refractive error deals with chickens. Raptors are predatory birds in which good visual resolving ability is particularly important. Behavioral studies indicate that the eyes of raptors have two to three times the resolving ability of the human eye. The domestic chicken is precocial at hatching whereas most raptors are semi-altricial. This study was an effort to determine if the effect of early visual deprivation on the refractive development of the chicken eye can be reproduced in the American kestrel, a species which is not domesticated and in which the need for acute vision is particularly important.Visual deprivation was achieved by unilaterally applying translucent plastic goggles over the eyes of kestrels two days after hatching. Refractive error was measured using a retinoscope and trial lenses. Ocular growth was monitored by A-scan ultrasonography, and frozen ocular sections of sacrificed birds. The effect of the experimental manipulation on the contralateral control eye and body weight was evaluated each day over a 42-day period. The goggles did not significantly affect the normal changes in body weight or the normal pattern of ocular growth and refractive development in the untreated eyes. An analysis of the refractive state changes as a result of form deprivation was made each week for 6 weeks after hatching on both the treated and untreated eyes in a separate group of experimental birds. Visual form deprivation caused a significant myopic shift in refractive error and a significant increase in the vitreous chamber depth in the treated eyes at 3 and 6 weeks of age. However, the amount of myopia produced is much less than that induced in chicks, and in certain cases hyperopia is produced. The kestrels recover from myopia and hyperopia within 10 days of goggle removal, after 3 to 4 weeks of deprivation.This study is the first indication that chickens may not be a representative bird model for studying form deprivation myopia. First, myopia is not always produced in kestrels in response to form deprivation. Second, kestrels are severely myopic at hatching and therefore, the direction of emmetropization is opposite to that found in hatchling chicks.     

The long-term effectiveness of different regimens of occlusion on recovery from early monocular deprivation in kittens.

Although the behavioural effects of an early period of monocular deprivation imposed on kittens can be very severe, resembling an extreme form of the human clinical condition deprivation amblyopia, they are not necessarily irreversible. Considerable behavioural as well as physiological recovery can occur if normal visual input is restored to the deprived eye sufficiently early, particularly if the other (initially non-deprived) eye is occluded at the same time (reverse occlusion). However, past work has shown that in many situations the improvement in the vision of the initially deprived eye that occurs during reverse occlusion is not retained following the subsequent introduction of binocular visual input. Furthermore, the vision of the other eye is often reduced as well, with the result that the eventual outcome is a condition of bilateral amblyopia. This study first examines the consequences of several periods of reverse occlusion whose onset and duration would be thought to maximize the opportunity for good and long-standing recovery of vision in the initially deprived eye. However, only in a very restricted set of exposure conditions did animals acquire good vision in one or both eyes; in most situations the final outcome was one of bilateral amblyopia. A second set of experiments examined the consequences of various regimens of part-time reverse occlusion, where the initially non-deprived eye was occluded for only part of each day to allow a period of binocular visual exposure, on kittens that had been monocularly deprived until 6, 8, 10 or 12 weeks of age. Whereas short or long daily periods of occlusion of the initially non-deprived eye resulted eventually in amblyopia in one, or usually both, eyes, certain intermediate occlusion times (3.5 or 5 h each day) resulted in recovery of normal acuities, contrast sensitivity and vernier acuity in both eyes, in animals that had been monocularly deprived until 6, 8 or 10 weeks of age, but not in animals deprived for longer periods. Experiments were done to establish some of the factors that contributed to the successful outcome associated with certain of the regimens of part-time reverse occlusion. It was established that recovery was just as good in animals in which the visual axes were vertically misaligned by means of prisms during the daily period of binocular visual exposure, thereby indicating that the visual input to the two eyes need not be concordant. However, animals that received equivalent visual exposure of the two eyes each day, but successively rather than simultaneously, all developed very severe bilateral amblyopia.(ABSTRACT TRUNCATED AT 400 WORDS)     

Evaluation of brain-stem auditory evoked potentials using dynamic time warping

Dynamic time warping is a procedure whereby portions of a temporal sequence of values are stretched or shrunk to make it similar to another sequence. This procedure can be used to align the brain-stem auditory evoked potentials recorded from different subjects prior to averaging. The resultant warp-average more closely resembles the wave form of a typical subject than the conventional average. Dynamic time warping can also be used to compare one brain-stem auditory evoked potential to another. This comparison can show the differences that result from changes in a stimulus parameter such as intensity or repetition rate. When a patient's wave form is compared to a normal template, warping can identify the peaks in the patient's wave form that correspond most closely to the peaks in the normal template. Compared to an experienced human interpreter, warping is very accurate in identifying the waves of normal brain-stem auditory evoked potentials (error rate between 0 and 4%) and reasonably accurate in identifying the peaks in abnormal wave forms (error rate between 3 and 18%).     

Early diagnostic value of optical coherence tomography in the clinical prediction model for optic nerve injury in saddle space occupying patients

In this study, 50 patients with anterior ischemic optic neuropathy due to saddle block were selected as the experimental group, and 50 healthy subjects were used as the control group to conduct a study. The best corrected visual acuity examination, optical coherence tomography and visual evoked potential examination were performed on the two groups. The results of the study showed that the majority of patients were middle-aged and older people over the age of 50, but the youngest patients were only 37 years old. After various examinations, it was found that patients with optic nerve injury had a significant reduction in the best corrected visual acuity compared with healthy people. After the onset of the disease, the optic nerve fiber layer will first increase and then decline. During the course of the disease, the patient's optic nerve fiber layer will gradually thin to a much lower level than healthy people. And in comparing the thickness of the optic nerve fiber layer in patients with systemic disease and no systemic disease, it is found that the degree of optic nerve damage is more serious in patients with systemic diseases. After the VEP examination, the difference between the P100 wave latency and the N75-P100 amplitude of the diseased eye and the unaffected eye was statistically significant. Moreover, the difference between the patient's diseased eye and the healthy human eye is almost the same as that of the unaffected eye.     

Neural mechanisms of recovery following early visual deprivation

Natural patterned early visual input is essential for the normal development of the central visual pathways and the visual capacities they sustain. Without visual input, the functional development of the visual system stalls not far from the state at birth, and if input is distorted or biased the visual system develops in an abnormal fashion resulting in specific visual deficits. Monocular deprivation, an extreme form of biased exposure, results in large anatomical and physiological changes in terms of territory innervated by the two eyes in primary visual cortex (V1) and to a loss of vision in the deprived eye reminiscent of that in human deprivation amblyopia. We review work that points to a special role for binocular visual input in the development of V1 and vision. Our unique approach has been to provide animals with mixed visual input each day, which consists of episodes of normal and biased (monocular) exposures. Short periods of concordant binocular input, if continuous, can offset much longer episodes of monocular deprivation to allow normal development of V1 and prevent amblyopia. Studies of animal models of patching therapy for amblyopia reveal that the benefits are both heightened and prolonged by daily episodes of binocular exposure.     

The Measurement and Treatment of Suppression in Amblyopia

Amblyopia, a developmental disorder of the visual cortex, is one of the leading causes of visual dysfunction in the working age population. Current estimates put the prevalence of amblyopia at approximately 1-3%^1-3, the majority of cases being monocular². Amblyopia is most frequently caused by ocular misalignment (strabismus), blur induced by unequal refractive error (anisometropia), and in some cases by form deprivation.Although amblyopia is initially caused by abnormal visual input in infancy, once established, the visual deficit often remains when normal visual input has been restored using surgery and/or refractive correction. This is because amblyopia is the result of abnormal visual cortex development rather than a problem with the amblyopic eye itself^4,5 . Amblyopia is characterized by both monocular and binocular deficits^6,7 which include impaired visual acuity and poor or absent stereopsis respectively. The visual dysfunction in amblyopia is often associated with a strong suppression of the inputs from the amblyopic eye under binocular viewing conditions⁸. Recent work has indicated that suppression may play a central role in both the monocular and binocular deficits associated with amblyopia^9,10 .Current clinical tests for suppression tend to verify the presence or absence of suppression rather than giving a quantitative measurement of the degree of suppression. Here we describe a technique for measuring amblyopic suppression with a compact, portable device^11,12 . The device consists of a laptop computer connected to a pair of virtual reality goggles. The novelty of the technique lies in the way we present visual stimuli to measure suppression. Stimuli are shown to the amblyopic eye at high contrast while the contrast of the stimuli shown to the non-amblyopic eye are varied. Patients perform a simple signal/noise task that allows for a precise measurement of the strength of excitatory binocular interactions. The contrast offset at which neither eye has a performance advantage is a measure of the "balance point" and is a direct measure of suppression. This technique has been validated psychophysically both in control^13,14 and patient^6,9,11 populations.In addition to measuring suppression this technique also forms the basis of a novel form of treatment to decrease suppression over time and improve binocular and often monocular function in adult patients with amblyopia^12,15,16 . This new treatment approach can be deployed either on the goggle system described above or on a specially modified iPod touch device¹⁵.     

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%.     

连续全遮盖法治疗双眼屈光参差性弱视的有效性与安全性分析

目的:探讨连续q全遮盖法治疗双眼屈光参差性弱视的有效性与安全性。方法:选择2014年2月到2016年9月在我院诊治的126例双眼屈光参差性弱视患儿作为研究对象,根据治疗方法的不同分为阿托品组60例与遮盖组66例,遮盖组采用连续全遮盖法治疗,阿托品组给予阿托品治疗,两组都治疗观察3个月。比较两组治疗期间不良反应的发生情况、治疗后的总有效率、最佳矫正视力、电位潜伏期、波幅。结果:两组治疗期间都无严重不良反应发生。治疗后,遮盖组与阿托品组的总有效率分别为98.5%和88.3%,遮盖组的总有效率明显高于阿托品组(P0.05)。两组治疗后的最佳矫正视力都高于治疗前,且遮盖组治疗后的最佳矫正视力也明显高于阿托品组(P0.05)。两组治疗后的电位潜伏期都较治疗前明显缩短,而波幅明显增强(P0.05),且遮盖组治疗后的潜伏期明显短于阿托品组,而波幅显著强于阿托品组(P0.05)。结论:连续全遮盖法治疗双眼屈光参差性弱视具有很好的安全性,能提高患儿的治疗效果,改善视力,促进神经元的兴奋性。     

Influence of Retinal Image Shifts and Extra-Retinal Eye Movement Signals on Binocular Rivalry Alternations

Previous studies have indicated that saccadic eye movements correlate positively with perceptual alternations in binocular rivalry, presumably because the foveal image changes resulting from saccades, rather than the eye movement themselves, cause switches in awareness. Recently, however, we found evidence that retinal image shifts elicit so-called onset rivalry and not percept switches as such. These findings raise the interesting question whether onset rivalry may account for correlations between saccades and percept switches.We therefore studied binocular rivalry when subjects made eye movements across a visual stimulus and compared it with the rivalry in a ‘replay’ condition in which subjects maintained fixation while the same retinal displacements were reproduced by stimulus displacements on the screen. We used dichoptic random-dot motion stimuli viewed through a stereoscope, and measured eye and eyelid movements with scleral search-coils.Positive correlations between retinal image shifts and perceptual switches were observed for both saccades and stimulus jumps, but only for switches towards the subjects'' preferred eye at stimulus onset. A similar asymmetry was observed for blink-induced stimulus interruptions. Moreover, for saccades, amplitude appeared crucial as the positive correlation persisted for small stimulus jumps, but not for small saccades (amplitudes < 1°). These findings corroborate our tenet that saccades elicit a form of onset rivalry, and that rivalry is modulated by extra-retinal eye movement signals.     

Motion-reversal visual evoked responses.

Motion-reversal visual evoked responses (VERs) have remarkable waveform variability. In our opinion this is caused by the alternative predominance of either motion or pattern-onset/offset related components. The motion dependent component of motion-reversal VER closely resembles motion-onset VER (main negative peak with the latency of about 170 ms), the first positive peak (with the latency of about 100 ms) corresponds to the pattern-onset component and the second non-constant positive peak (with the latency of about 130 ms) seems to be identical with the pattern-offset positivity. The differences in expression of these components are dependent on some stimulus characteristics (mainly on the contrast of a structure, velocity of motion, retinal localization of the stimulus) and on substantial differences in the sensitivity of subjects to motion stimulation.     

Visual evoked potentials elicited by a moving unidimensional noise pattern

(1) Motion onset and offset visual evoked potentials (VEPs) were recorded in normal human subjects using a unidimensional noise pattern moving at 1, 8 and 64°/s. The maximum N1-P1 amplitude of the motion onset response was obtained when using a fine noise pattern (maximum energy at 5.2 cpd) moving at 8°/s. (2) At a velocity of 8°/s, the motion onset response (fine pattern, 0.70 contrast) showed a morphology similar to the pattern disappearance response. Both at a lower (1°/s) and a higher velocity (64°/s) the N1-P1 amplitude of the motion onset complex was significantly reduced. The latency of the motion onset response (8°/s) and the pattern disappearance complex were significantly different. (3) The effect of lowering the spatial content of the noise pattern on the amplitude of the motion onset response was different for the 3 velocities tested: the largest effect was at the lower velocity of 1°/s; there was no similar effect on the pattern disappearance response. (4) With decreasing contrast, the N1-P1 amplitude of the motion onset response at 8°/s decreased, but this reduction in amplitude was much less than that of the disappearance response. The contrast dependency of the motion onset complex was identical for binocular and monocular recordings. (5) Increasing the motion duration or the duration of the interstimulus interval did not alter the general morphology of the motion response.     

Anteroposterior dynamic balance reactions induced by circular translation of the visual field

The anteroposterior sway of subjects under conditions of spontaneous dynamic balance on a wobbly platform was measured during visual stimulation by a visual target executing a circular trajectory in the frontal plane. The target was either a component of the whole moving visual scene or moving on a stationary background. With the former stimulation, obtained through the use of rotating prismatic glasses, every point of the visual field appeared to describe a circular trajectory around its real position so that the whole visual field apeared to be circularly translated, undistorted, inducing a binocular pursuit movement. Under these conditions, stereotyped anteroposterior dynamic balance reactions synchronous with the position of the stimulus were elicited. The latter stimulation consisted of pursuing a luminous target describing a trajectory similar to that of the fixation point seen through the rotating prisms on the same, this time stable, visual background. Although pursuit eye movements were comparable, as demonstrated by electro-oculographic recordings, no stereotyped equilibration reaction was induced. It is concluded that the translatory motion of the background image on the retina in the latter experiments contributed to the body's stability as well as to the perception of a stable environment.     

Dissociating ocular dominance column development and ocular dominance plasticity: a neurotrophic model

 Recent experimental data indicate that both neurotrophic factors (NTFs) and intracortical inhibitory circuitry are implicated in the development and plasticity of ocular dominance columns. We extend a neurotrophic model of developmental synaptic plasticity, which previously failed to account correctly for the differences between monocular deprivation and binocular deprivation, and show that the inclusion of lateral cortical inhibition is indeed necessary in understanding the effects of visual deprivation in the model. In particular, we argue that monocular deprivation causes a differential shift in the balance between inhibition and excitation in cortical columns, down-regulating NTFs in deprived-eye columns and up-regulating NTFs in undeprived-eye columns; during binocular deprivation, however, no such shift occurs. We thus postulate that the response to visual deprivation is at the level of the cortical circuit, while the mechanisms of afferent segregation are at the molecular or cellular level. Such a dissociation is supported by recent experimental work challenging the assumption that columnar organisation develops in an activity-dependent, competitive fashion. Our extended model also questions recent attempts to distinguish between heterosynaptic and homosynaptic models of synaptic plasticity. Received: 17 April 2001 / Accepted in revised form: 7 November 2001     

双眼和单眼视觉剥夺猫外膝体细胞的图形适应

为测定丘脑外膝体细胞的图形适应是否依赖于早期视觉经验,在细胞外记录了双眼和单眼缝合的猫外膝体中断细胞对手工时间运动光栅刺激的反应。在双眼剥夺猫,占６８％的记录到的细胞在３０ｓ内反应下降到稳定值,其平均反应值下降３３％,适应程度较正常猫显著。在单眼剥夺猫,记录到的剥夺眼驱动的和非剥夺眼驱动的细胞中,分别有占５３％和４４％的细胞显示图形适应,两者差别不大。研究表明,早期视剥夺能增强或保持图形适应,提示     

Reading and Visual Search: A Developmental Study in Normal Children

Studies dealing with developmental aspects of binocular eye movement behaviour during reading are scarce. In this study we have explored binocular strategies during reading and during visual search tasks in a large population of normal young readers. Binocular eye movements were recorded using an infrared video-oculography system in sixty-nine children (aged 6 to 15) and in a group of 10 adults (aged 24 to 39). The main findings are (i) in both tasks the number of progressive saccades (to the right) and regressive saccades (to the left) decreases with age; (ii) the amplitude of progressive saccades increases with age in the reading task only; (iii) in both tasks, the duration of fixations as well as the total duration of the task decreases with age; (iv) in both tasks, the amplitude of disconjugacy recorded during and after the saccades decreases with age; (v) children are significantly more accurate in reading than in visual search after 10 years of age. Data reported here confirms and expands previous studies on children''s reading. The new finding is that younger children show poorer coordination than adults, both while reading and while performing a visual search task. Both reading skills and binocular saccades coordination improve with age and children reach a similar level to adults after the age of 10. This finding is most likely related to the fact that learning mechanisms responsible for saccade yoking develop during childhood until adolescence.     

Experience in early infancy is indispensable for color perception

Early visual experience is indispensable to shape the maturation of cortical circuits during development. Monocular deprivation in infancy, for instance, leads to an irreversible reduction of visually driven activity in the visual cortex through the deprived eye and a loss of binocular depth perception. It was tested whether or not early experience is also necessary for color perception. Infant monkeys were reared for nearly a year in a separate room where the illumination came from only monochromatic lights. After extensive training, they were able to perform color matching. But, their judgment of color similarity was quite different from that of normal animals. Furthermore, they had severe deficits in color constancy; their color vision was very much wavelength dominated, so they could not compensate for the changes in wavelength composition. These results indicate that early visual experience is also indispensable for normal color perception.     

Visual cortical responses to the input from the amblyopic eye are suppressed during binocular viewing

Amblyopia is a visual disorder caused by an anomalous early visual experience. It has been suggested that suppression of the visual input from the weaker eye might be a primary underlying mechanism of the amblyopic syndrome. However, it is still an unresolved question to what extent neural responses to the visual information coming from the amblyopic eye are suppressed during binocular viewing. To address this question we measured event-related potentials (ERP) to foveal face stimuli in amblyopic patients, both in monocular and binocular viewing conditions. The results revealed no difference in the amplitude and latency of early components of the ERP responses between the binocular and fellow eye stimulation. On the other hand, early ERP components were reduced and delayed in the case of monocular stimulation of the amblyopic eye as compared to the fellow eye stimulation or to binocular viewing. The magnitude of the amblyopic effect measured on the ERP amplitudes was comparable to that found on the fMRI responses in the fusiform face area using the same face stimuli and task conditions. Our findings showing that the amblyopic effects present on the early ERP components in the case of monocular stimulation are not manifested in the ERP responses during binocular viewing suggest that input from the amblyopic eye is completely suppressed already at the earliest stages of visual cortical processing when stimuli are viewed by both eyes.     

Brief daily periods of binocular vision prevent deprivation-induced acuity loss

The role of experience in the development of the central visual pathways has been explored in the past through examination of the consequences of imposed periods of continuously abnormal or biased visual input. The massive changes in the visual cortex (area 17) induced by selected early visual experience, especially monocular deprivation (MD) or experience (ME) where patterned visual input is provided to just one eye, are accompanied by profound and long-standing visual deficits. Although the use of exclusively abnormal experience permits identification of those aspects of the visual cortex and of visual function that can be influenced by visual experience during development, this approach may provide a distorted view of the nature of the role of visual experience because of the absence of any normal visual input. In this study a different approach was used whereby animals were provided daily with separate periods of normal (i.e., binocular exposure) and abnormal (monocular exposure) visual experience. We show that 2 hr of daily normal concordant binocular experience (BE) can outweigh or protect against much longer periods of monocular deprivation (MD) and permit the development of normal visual acuities in the two eyes. This result is not what would be expected if all visual input had equal influence on visual development.