视交叉解剖与临床

视交叉为视路的主要组成部分，前连视神经，后与视束相连，是视觉传导的交通要道，视交叉病变随部位的不同会产生不同类型的视野改变，而根据视野的改变则可判断颅内病变的具体位置，有利于临床治疗。     

视觉诱发电位对眼挫伤患者的应用价值

目的:探讨视觉诱发电化(VEP)对眼挫伤视神经损伤的诊断、预后评估和出具鉴定意见的价值。方法:对55例眼挫伤患者(单眼挫伤53例,双眼挫伤2例)进行VEP检查,单眼损伤者以自体健侧眼为对照。视力≥0.1者行图形模式刺激视觉诱发电位(P-VEP)检查为A组;视力<0.1者行闪光视觉诱发电位(F-VEP)检查为B组。结果:55例中VEP正常16例(占29%),异常39例(占71%)。异常者中单纯P100波幅下降9例(占23%),单纯P100波潜伏期延长12例(占31%),P100波潜伏期延长伴波幅下降16例(占41%),P100波形完全消失2例(占5%)。所有眼挫伤后视力损害者与自体健侧眼作对比,A、B组间VEP P100波潜伏期延长和波幅降低,差异均有非常显著意义(P<0.01)。结论:VEP为挫伤性视力损害的视功能评价、临床早期诊断、预后评估以及伤残鉴定提供了重要的客观依据。     

脑诱发电位地形图诊断要点

(一)视觉诱发电位地形图(双眼全视野棋盘格翻转刺激)(VEP Mapping) 1.视神经炎及球后视神经炎 (1)急性期:视力明显下降时,①视诱发地形图显示在相当于P_(100)时相中枕叶双侧对称性正相高电位消失。②视诱发电位的自后向前空间电位变化消失。     

眼挫伤后视力损害患者视觉诱发电位分析

目的:探讨视觉诱发电位(VEP)在评价挫伤后视力损害中的价值。方法:对74例挫伤性视力损害患者进行图形翻转刺激VEP测定,并与自体健侧眼和正常对照组进行比较。结果:74例患者中,单眼挫伤57例,双眼挫伤17例,共91眼受伤,受伤眼均有不同程度视力损害。VEP检查结果:91 眼中波形不典型者5眼(6％);P100波幅下降异常者54眼(59％);P100潜伏期延长者23眼(25％)。其中单纯潜伏期延长12眼(13％);单纯波幅下降异常43眼(47％);潜伏期延长伴波幅下降者11眼 (12％),总异常66眼,异常率为73％。所有挫伤后视力损害者,与自体健侧服和正常对照组比较,P100 潜伏期延长和波幅降低,差异均有显著意义(P<0．01)。结论:VEP为挫伤性视力损害的视功能评价、临床早期诊断、预后评估以及伤残鉴定提供了重要的客观依据。     

人工晶体植入前后视觉诱发电位的临床分析

目的:(1)探讨白内障囊外摘除术前术后及人工晶体植入术后视觉诱发电位幅值及潜时变化特征;(2)探讨白内障囊外摘除术术前P—VEP,F—VEP,F—ERG联合预测的必要性。方法:采用重庆泰克医电仪器公司产TEC—100C视觉电生理仪。对白内障患者实行分组测量。术前均测F—ERG,P—VEP,部分病例增测F—VEP。结果:114例术前F—ERG正常,P—VEP测量其P_(100)波幅值潜时均异常:P_(100)波幅值降低,潜时延长,术后及人工晶体植入后幅值,潜时都有所改善,而并发性白内障,代谢性白内障变化不明显。结论:据视觉诱发电位的变化,老年性白内障组,外伤性白内障组术后应及时装入人工晶体,并发性白内障组,代谢性白内障组装入人工晶体临床意义不大。术前联合测试(VEP ERG)对视力预后、以及眼底病变的定量诊断意义重大。     

脑诱发电位地形图诊断要点

一、视觉诱发电位地形图(双眼全视野棋盘格翻转刺激)(VEP Mapping) 1.视神经炎及球后视神经炎 (1)急性期:视力明显下降时,①视诱发地形图显示在相当于P_(100)时相中枕叶双则对称性正相同电位消失。②视诱发电位的自后向前空间电位变化消失。 (2)随着视力的逐渐恢复枕区P_(100)时相的正     

单脉冲经颅磁刺激对视皮层神经活动抑制作用的初步实验研究

为了研究单脉冲经颅磁刺激(sTMS)对视皮层神经活动的影响,利用多通道生理记录仪,分别记录下11名右利手志愿者sTMS作用于视皮层前后的视觉诱发电位(VEP)。采用叠加平均和巴特沃斯低通滤波的方法处理后,对比分析这两种情况下的VEP峰时特征,发现sTMS刺激将引起VEP峰值发生的时间有一定延迟。初步的实验结果表明,sTMS对视皮层神经活动有抑制作用,从而引起VEP产生了滞后,为将经颅磁刺激应用于研究视觉中枢神经活动提供了实验证据。     

视觉诱发电位检测对视神经炎的诊断价值

视觉诱发电位(visual evoked potential,VEP)为检测视神经上行通路皮质下结构(包括视神经、视交叉、视束、外侧膝状体和视放射)的神经电生理检查方法之一,主要反映视网膜视锥细胞的电活动情况,从而检测视觉通路神经的功能.Halliday等[1]最先将棋盘格翻转视觉诱发电位(PS-VEP)用于临床并获得肯定结果,其后VEP被广泛应用,已成为神经眼科学重要的辅助诊断手段之一.     

边缘性人格障碍和焦虑障碍患者光诱发电位的对照研究

目的:探讨边缘性人格障碍(BPD)和焦虑障碍(AN)在光诱发电位(VEP)中的特点。方法:收集28例BPD组、36例AN组及49名正常成人对照(NC),应用美国仪器以及红光刺激,完成光诱发电位(VEP)检查。结果:与NC相比,BPD组潜伏期VEP/P1、P2前移,波幅VEP/N1-P2、P3增高,但波幅VEP/P2-N2、P2降低。与NC相比,AN组潜伏期VEP/P1、P3前移;波幅VEP/P2-N2、P2降低。BPD组与AN组相比,在潜伏期VEP/P2以及波幅VEP/N1-P2上两者有显著性意义,BPD组前移于AN组,波幅增高。结论:在VEP若干指标上,BPD组前移于AN组,波幅增高。BPD组光诱发电位特点,值得进一步跟踪随访。     

枕区脑血管病VEP—M及其临床应用

本文报导12例枕区脑血管病VEP—M表现,结果表明:半视野VEP—M可作为一种灵敏的诊断及监测手段,在脑皿管病的定位、定性、判断预后及疗效观察方面具有重要的临床应用价值。     

Spatial and temporal summation in impaired regions of the visual field

1. Spatial and temporal summation have been measured in perimetrically impaired regions of the visual field. Two classes of impairment have been studied: that resulting from lesions in the pre-geniculate visual pathways, and that resulting from post-geniculate lesions (optic radiation and/or striate cortex).2. Control measurements were made in the perimetrically normal visual fields of subjects without visual pathway damage.3. Spatial summation was found altered in all impaired visual fields: the greater the threshold elevation produced by the lesion, the more nearly complete was spatial summation.4. The above relation between threshold and spatial summation has also been given numerical form. This has been shown to be very nearly identical to the threshold-spatial summation relation which is seen as stimuli are increasingly peripherally presented in normal visual fields.5. It has been shown that the alterations of spatial summation brought about by a lesion are found only in those parts of the visual field which are perimetrically impaired: spatial summation is always normal in perimetrically normal regions of a visual field, even if other parts of the same field show impairment.6. Temporal summation has been found altered in visual fields impaired by post-geniculate lesions: the greater the threshold elevation produced by the lesion, the more nearly complete was temporal summation. These changes in temporal summation were found only in perimetrically impaired regions of the field.7. Temporal summation was normal in visual fields impaired by pregeniculate lesions.     

Both striate cortex and superior colliculus contribute to visual properties of neurons in superior temporal polysensory area of macaque monkey

Although the tectofugal system projects to the primate cerebral cortex by way of the pulvinar, previous studies have failed to find any physiological evidence that the superior colliculus influences visual activity in the cortex. We studied the relative contributions of the tectofugal and geniculostriate systems to the visual properties of neurons in the superior temporal polysensory area (STP) by comparing the effects of unilateral removal of striate cortex, the superior colliculus, or of both structures. In the intact monkey, STP neurons have large, bilateral receptive fields. Complete unilateral removal of striate cortex did not eliminate visual responses of STP neurons in the contralateral visual hemifield; rather, nearly half the cells still responded to visual stimuli in the hemifield contralateral to the lesion. Thus the visual properties of STP neurons are not completely dependent on the geniculostriate system. Unilateral striate lesions did affect the response properties of STP neurons in three ways. Whereas most STP neurons in the intact monkey respond similarly to stimuli in the two visual hemifields, responses to stimuli in the hemifield contralateral to the striate lesion were usually weaker than responses in the ipsilateral hemifield. Whereas the responses of many STP neurons in the intact monkey were selective for the direction of stimulus motion or for stimulus form, responses in the hemifield contralateral to the striate lesion were not selective for either motion or form. Whereas the median receptive field in the intact monkey extended 80 degrees into the contralateral visual field, the receptive fields of cells with responses in the contralateral field that survived the striate lesions had a median border that extended only 50 degrees into the contralateral visual field. Removal of both striate cortex and the superior colliculus in the same hemisphere abolished the responses of STP neurons to visual stimuli in the hemifield contralateral to the combined lesion. Nearly 80% of the cells still responded to visual stimuli in the hemifield ipsilateral to the lesion. Unilateral removal of the superior colliculus alone had only small effects on visual responses in STP. Receptive-field size and visual response strength were slightly reduced in the hemifield contralateral to the collicular lesion. As in the intact monkey, selectivity for stimulus motion or form were similar in the two visual hemifields. We conclude that both striate cortex and the superior colliculus contribute to the visual responses of STP neurons. Striate cortex is crucial for the movement and stimulus specificity of neurons in STP.(ABSTRACT TRUNCATED AT 400 WORDS)     

Left hemiparalexia of Chinese characters: neglect dyslexia or disruption of pathway of visual word form processing?

The objective of the study was to further elucidate the potential mechanisms underlying left hemiparalexia induced by a splenium lesion in corpus callosum. A patient KY, who had infarctions in the splenium and the left ventral medial occipitotemporal area, was examined with neuropsychological tests and fMRI. KY presented left hemiparalexia when he read aloud characters presented in central foveal field tachistoscopically as well as in free-view field. KY also showed left hemialexia for characters in left visual field, while no left hemiparalexia occurred when characters were presented in the right visual field. KY performed poorly in lexical decision tasks. He could judge the directions of Landolt’s rings gaps in the left or right visual field equally. The result of fMRI indicated that characters in the left visual field could not activate the visual word form area (VWFA), such as left mid-fusiform cortex. All the above neuropsychological and fMRI findings have provided evidences against the assumption of left hemineglect dyslexia. Instead, they support the mechanism of disconnection of visual word form processing pathway. In conclusion, the evidences suggested that the visual information transmission of characters in the left visual field from right occipital area to the VWFA in the left hemisphere was interrupted by the splenium lesion.     

Massive restructuring of neuronal circuits during functional reorganization of adult visual cortex

The cerebral cortex has the ability to adapt to altered sensory inputs. In the visual cortex, a small lesion to the retina causes the deprived cortical region to become responsive to adjacent parts of the visual field. This extensive topographic remapping is assumed to be mediated by the rewiring of intracortical connections, but the dynamics of this reorganization process remain unknown. We used repeated intrinsic signal and two-photon imaging to monitor functional and structural alterations in adult mouse visual cortex over a period of months following a retinal lesion. The rate at which dendritic spines were lost and gained increased threefold after a small retinal lesion, leading to an almost complete replacement of spines in the deafferented cortex within 2 months. Because this massive remodeling of synaptic structures did not occur when all visual input was removed, it likely reflects the activity-dependent establishment of new cortical circuits that serve the recovery of visual responses.     

Influences of lesions of parietal cortex on visual spatial attention in humans

Summary Several brain areas have been identified with attention, because damage to these regions leads to neglect and extinction. We have tested elements of visual attentional processing in patients with parietal, frontal, or temporal lesions and compared their responses to control subjects. Normal humans respond faster in a reaction time task when the spatial location of a target is correctly predicted by an antecedent stimulus (valid cue) than when the location is incorrectly predicted (invalid cue). The cue is hypothesized to shift attention towards its location and thereby facilitate or impede response latencies. The reaction times of individuals with damage to the parietal lobe are somewhat slowed for targets ipsilateral or contralateral to the side of the lesion if the targets are preceded by valid cues. These same patients are extremely slow in responding to targets in the visual field contralateral to the lesion when the cue has just appeared in the unaffected (ipsilateral) visual field. In addition, these individuals are especially slow in responding to targets in either visual field when the lights are preceded by weak, diffuse illumination of the entire visual field. Patients with lesions of the frontal lobe have very slow reaction times in general and, as is the case for patients with lesions of the temporal lobe, are slow in all conditions for targets in the field contralateral to the lesion. These patterns are probably not associated with attentional defects. For patients with parietal lesions, these studies demonstrate a further deficit in a cued reaction-time task suggesting abnormal visual attention. Since different sites of brain damage yield different patterns of responses, tests such as these could be of analytic and diagnostic value.     

Enhanced responsiveness of human extravisual areas to photic stimulation in patients with severely reduced vision

Lesions in the primary visual cortex induce severe loss of visual perception. Depending on the size of the lesion, the visual field might be affected by small scotomas, hemianopia, or complete loss of vision (cortical blindness). In many cases, the whole visual field of the patient is affected by the lesion, but diffuse light-dark discrimination remains (residual rudimentary vision, RRV). In other cases, a sparing of a few degrees can be found (severely reduced vision, SRV).In a follow-up study, we mapped visually induced cerebral activation of three subjects with SRV using functional magnetic resonance imaging. We were especially interested in the visual areas that would be activated if subjects could perceive the stimulus consciously although information flow from V1 to higher visual areas was strongly reduced or virtually absent. Because subjects were only able to discriminate strong light from darkness, we used goggles flashing intense red light at a frequency of 3 Hz for full visual field stimulation. Besides reduced activation in V1, we found activation in the parietal cortex, the frontal eye fields (FEF), and the supplementary eye fields (SEF). In all patients, FEF activation was pronounced in the right hemisphere. These patterns were never seen in healthy volunteers. In a patient who recovered completely, we observed that extrastriate activation disappeared in parallel with the visual field restitution. This result suggests that damage to the primary visual cortex changes the responsiveness of parietal and extravisual frontal areas in patients with SRV. This unexpected result might be explained by increased stimulus-related activation of attention-related networks.     

Recovery of visual functions in patients with cerebral blindness

Summary Patients with homonymous visual field defects after damage to the geniculo-striate pathway were forced to make saccadic eye movements to light targets presented briefly in their perimetrically blind regions. This specific type of saccadic localization led to an increase in visual field size in the region subjected to this practice. Visual acuity and color identification also improved in the restored region, provided that the lesion was mainly limited to the striate cortex. The enlargement of the visual field strongly depended on a specific practice. The degree of recovery was related to the sharpness of the visual field border. In patients with a rather shallow gradient of light sensitivity in the area between the intact visual field and the scotoma, a fairly good recovery was obtained, whereas in patients with a steeper gradient the enlargement of the visual field was small. It is suggested that recovery takes place at the level of the striate cortex and is probably mediated by the retino-tectal pathway.Supported by the Deutsche ForschungsgemeinschaftDedicated to Professor D. Ploog on his 60th birthday     

Central core control of developmental plasticity in the kitten visual cortex: I. Diencephalic lesions

Summary In five, dark-reared, 4-week-old kittens the posterior two thirds of the corpus callosum were split, and a lesion comprising the intralaminar nuclei was made of the left medial thalamic complex. In addition, the right eye was closed by suture. Postoperatively, the kittens showed abnormal orienting responses, neglecting visual stimuli presented in the hemifield contralateral to the side of the lesion. Sudden changes in light, sound, or somatosensory stimulation elicited orienting responses that all tended toward the side of the lesion. These massive symptoms faded within a few weeks but the kittens continued to neglect visual stimuli in the hemifield contralateral to the lesion when a second stimulus was presented simultaneously in the other hemifield. Electrophysiologic analysis of the visual cortex, performed after the end of the critical period, revealed marked interhemispheric differences. In the visual cortex of the normal hemisphere most neurons were monocular and responded exclusively to stimulation of the open eye, but otherwise had normal receptive field properties. In the visual cortex of the hemisphere containing the thalamic lesion, the majority of the neurons remained binocular. In addition, the selectivity for stimulus orientation and the vigor of responses to optimally aligned stimuli were subnormal on this side. Thus, the same retinal signals, which in the control hemisphere suppressed the pathways from the deprived eye and supported the development of normal receptive fields, failed to do either in the hemisphere containing the thalamic lesion. Apparently, experience-dependent changes in the visual cortex require both retinal stimulation and the functioning of diencephalic structures which modulate cortical excitability and control selective attention.     

Effects of unilateral frontal eye-field lesions on eye-head coordination in monkey

We studied the effects of unilateral frontal eye-field (FEF) lesions on eye-head coordination in monkeys that were trained to perform a visual search task. Eye and head movements were recorded with the scleral search coil technique using phase angle detection in a homogeneous electromagnetic field. In the visual search task all three animals showed a neglect for stimuli presented in the field contralateral to the lesion. In two animals the neglect disappeared within 2-3 wk. One animal had a lasting deficit. We found that FEF lesions that are restricted to area 8 cause only temporary deficits in eye and head movements. Up to a week after the lesion the animals had a strong preference to direct gaze and head to the side ipsilateral to the lesion. Animals tracked objects in contralateral space with combined eye and head movements, but failed to do this with the eyes alone. It was found that within a few days after the lesion, eye and head movements in the direction of the target were initiated, but they were inadequate and had long latencies. Within 1 wk latencies had regained preoperative values. Parallel with the recovery on the behavioral task, head movements became more prominent than before the lesion. Four weeks after the lesion, peak velocity of the head movement had increased by a factor of two, whereas the duration showed a twofold decrease compared with head movements before the lesion. No effects were seen on the duration and peak velocity of gaze. After the recovery on the behavioral task had stabilized, a relative neglect in the hemifield contralateral to the lesion could still be demonstrated by simultaneously presenting two stimuli in the left and right visual hemifields. The neglect is not due to a sensory deficit, but to a disorder of programming. The recovery from unilateral neglect after a FEF lesion is the result of a different orienting behavior, in which head movements become more important. It is concluded that the FEF plays an important role in the organization and coordination of eye and head movements and that lesions of this area result in subtle but permanent changes in eye-head coordination.     

Plasticity and rigidity in the representation of the human visual field

Summary Neuronal plasticity in the mammalian visual system has been studied with a variety of experimental methods like induction of artificial squint and eye rotation. To investigate neuronal plasticity in the human visual system, we examined a patient with a congenital convergent squint of his left eye, who later suffered a vascular lesion in his left occipital lobe that led to an incomplete hemianopia in his right visual field. The examination revealed that the visual field representation in the striate cortex is rigidly prewired with reference to the anatomical fovea. In contrast, plasticity in the oculomotor system enables the patient to use a functional visual axis that does not correspond to the anatomical fovea. Local alterations of sensitivity within the visual field that indicate interactions among non-corresponding retinal points provide additional evidence of functional plasticity.