Representation of the visual field in the occipital striate cortex.

The representation of the field of vision in the human striate cortex is based on the Holmes map in which about 25% of the surface area of the striate cortex is allocated to the central 15 degrees of vision. Following the introduction of computed tomography of the brain, the accuracy of the Holmes map was apparently confirmed by clinical/radiological correlation, but a revision has been proposed by Horton and Hoyt based on a magnetic resonance imaging study of three patients with visual field defects due to striate lesions. They propose that the central cortical representation of vision occupies a much larger area. This study reviews the perimetric and imaging findings in a larger series of patients with striate cortical disease and provides support for the revised representation. The clinical phenomenon of macular sparing and its relation to representation of the macula at the occipital pole is also discussed.     

Visual areas and spatial summation in human visual cortex

Functional MRI measurements can securely partition the human posterior occipital lobe into retinotopically organized visual areas (V1, V2 and V3) with experiments that last only 30 min. Methods for identifying functional areas in the dorsal and ventral aspect of the human occipital cortex, however, have not achieved this level of precision; in fact, different laboratories have produced inconsistent reports concerning the visual areas in dorsal and ventral occipital lobe. We report four findings concerning the visual representation in dorsal regions of occipital cortex. First, cortex near area V3A contains a central field representation that is distinct from the foveal representation at the confluence of areas V1, V2 and V3. Second, adjacent to V3A there is a second visual area, V3B, which represents both the upper and lower quadrants. The central representation in V3B appears to merge with that of V3A, much as the central representations of V1/2/3 come together on the lateral margin of the posterior pole. Third, there is yet another dorsal representation of the central visual field. This representation falls in area V7, which includes a representation of both the upper and lower quadrants of the visual field. Fourth, based on visual field and spatial summation measurements, it appears that the receptive field properties of neurons in area V7 differ from those in areas V3A and V3B.     

Representation of fovea in the striate cortex of vervet monkey, Cercopithecus ˦thiops pygerythrus

The representation of 0°–4° in the visual field was studied in the vervet monkey from averaged gross responses on the dorsolateral occipital lobe. The vertical meridian lay at the boundary between the striate and parastriate cortex 2 mm from the lunate and occipital sulci. The 1° semicircle and the horizontal meridian intersected at a small hollow. The horizontal and vertical meridians intersected at the far lateral boundary of the striate cortex, and the centre of foveola was represented within 2 mm from this point. On the parastriate strip, representation was a mirror image of that of the striate cortex and the latency of the response to visual stimuli was longer. The magnification factor was 12 mm/deg in the region representing 0.2°–8° from the centre of gaze.     

Contralateral monocular dominance in anterior visual cortex confirmed by functional magnetic resonance imaging

PURPOSE: Although it is known that the damage to anterior striate cortex results in temporal peripheral visual field loss of the contralateral eye in patients with cerebral visual disturbance, the monocularity of anterior striate cortex has not been demonstrated in normal living humans. The aim of this study was to investigate whether this could be shown noninvasively using functional magnetic resonance imaging of the human visual cortex. METHODS: Eleven normal volunteers were studied with functional magnetic resonance imaging during alternating monocular visual stimulation using a 1.5 Tesla scanner. The data were motion corrected and spatially normalized to the standard brain. The monocular activation of the visual cortex was compared with the activation by the other eye. RESULTS: In the individual data analysis, contralateral eye dominance was always observed in the anterior striate cortex. In the group analysis from 11 subjects, the area with contralateral eye dominance was found in the most anterior part of primary visual cortex where the calcarine fissure merged with the parieto-occipital sulcus. CONCLUSIONS: This study shows that the contralateral eye dominance of anterior striate cortex can be detected noninvasively with functional magnetic resonance imaging during monocular visual stimulation. The finding confirms that the anterior striate cortex, where the monocular temporal crescent is represented, is primarily monocular, but the fact that greatest density of retinal ganglion cells and photoreceptors is in the nasal hemiretina must also be taken into account when interpreting these results.     

视觉刺激功能磁共振成像在枕叶病变患者中的初步应用

目的 观察枕叶病变患者患侧与健侧的功能磁共振成像（fMRI）特点，评价fMRI在视觉中枢功能性病变检查、枕叶肿瘤定位、手术入路选择以及切除范围方面的临床应用价值。设计 病例系列。研究对象 伴有同侧偏盲的视觉中枢功能性病变及单侧枕叶肿瘤患者各1例。方法 对上述2例患者应用自行设计的双眼棋盘格刺激（5Hz）行脑fMRI检查。所得数据应用SPM软件处理（P〈0．01），与Goldmann视野计检查结果相比较，验证视野损害与其大脑皮层投影改变的一致性。主要指标 统计参数图，脑激活图，激活脑区信号变化的时间曲线，与标准化T1像叠加的脑激活图。结果 在视觉刺激on时，枕叶视功能区激活；off时无信号；2例患者fMRI检查右侧视功能区激活明确，左侧视功能区无信号与视野检查双眼右半视野缺损相一致。结论 视觉刺激程序能够很好地引出视觉中枢fMRI；fMRI的检查结果与视野结果一致性较好；fMRI在视觉中枢功能性检查、枕叶肿瘤范围定位的确定方面有良好的临床应用前景。     

Peripheral homonymous scotomas from a cavernous angioma affecting fibers subserving the intermediate region of the striate cortex

PURPOSE: To report the case of a pure peripheral homonymous visual field defect and to delineate the representation of the visual field on the striate cortex. METHODS: Observational case report. Neuro-ophthalmologic and neuroimaging assessment of a patient with a cavernous angioma of the right parieto-occipital lobe. RESULTS: The patient had left homonymous scotomas located 40 degrees to 60 degrees from the vertical meridian. Neuroimaging indicated that the lesion was affecting the optic radiations at their termination in the intermediate portion of the striate cortex or the striate cortex itself. CONCLUSION: Homonymous field defects are typically located within 10 degrees of fixation. This patient had a peripheral homonymous field defect from damage to the intermediate striate cortex. Correlation of the neuroimaging findings in this case with the most commonly used maps of the representation of the visual field on the striate cortex suggests that none of the maps correctly predicts the location or extent of lesions that affect the intermediate portion of the cortex.     

VISUAL REPRESENTATION AT THE CEREBRAL CORTEX: QUALITATIVE AND QUANTITATIVE ASPECTS

Abstracts— The cerebral representation of peripheral sensory surfaces is strictly ordered. In the case of the visual system, the scale of the cortical representation of visual space is non-linear: the area devoted to the fovea is greatly enlarged. Attempts have been made to quantify this retino-cortical relationship in animals and man: the result is the cortical magnification factor ( M ) which indicates the linear distance in mm along the striate cortex concerned with each degree of the visual field. The cortical magnification factor has indicated an alternative approach both to the theoretical interpretation of visual processing and to the clinical aspects of visual field examination. By M -scaling vision test stimuli, visual sensitivity, while quantitatively different at foveal and peripheral projections, remains qualitatively similar across the entire field.     

Treatment with flicker stimulation of lesions of the visual cortex surface

In this paper, the authors present the results of Flicker stimulation therapy in functional visual deficits secondary to occipital cortex lesions of miscellaneous origins. They formulate the hypothesis that the functional response obtained is subordinate to a variation or an integration of the macular cortical representation seat. Four cases were examined and the results obtained are significant.     

Automated perimetry and neuro-ophthalmology. Topographic correlation

Visual fields continue to be a key exploration for the diagnosis and follow-up of patients in neuro-ophthalmology. The pattern of visual field defects helps, and in many cases allows, the identification of brain damage location. Manual kinetic perimetry has been replaced by automated methods. 24-2 SITA (Humphrey Visual Field Analyser) and TOP (Octopus) are regarded as the standard perimetric explorations in neuro-ophthalmology. Goldmann perimetry remains as an useful exploration for temporal crescent detection in occipital lobe diseases, and it could be more accurate and consistent for studying lesions in the post-geniculate pathway. Frequency doubling perimetry could be useful for detecting neuro-ophthalmic visual field defects, but does not provide an accurate characterisation of the lesions. From the neuro-ophthalmic point of view, visual field defects could be divided in pre-chiasmatics, chiasmatics and post-chiasmatics. Pre-chiasmatic defects are strictly unilateral, do not respect the vertical meridian, often have a nasal step associated and are usually accompanied by ocular pathology detectable in an ophthalmic examination. The characteristic perimetric pattern of chiasmal disease is bi-temporal hemianopsia. Homonymous contralateral defects are the characteristic perimetric pattern of post-chiasmal disease, and their congruency increases when the lesions are closer to the occipital lobe. Neuroimage studies are mandatory in all patients with a perimetric defect pattern compatible with chiasmal or post-chiasmal lesions. Magnetic Resonance Imaging may be normal in a patient with homonymous defects in Alzheimer's disease, the Heidenhain variant of Creutzfeldt-Jakobs disease, carbon monoxide poisoning and mild occipital ischemia demonstrated by SPECT or PET imaging (Arch Soc Esp Oftalmol 2002; 77: 413-428).     

The visual field representation in striate cortex of the macaque monkey: Asymmetries,anisotropies, and individual variability

The topographic organization of striate cortex in the macaque was studied using physiological recording techniques. Results were displayed on two-dimensional maps of the cortex, which facilitated the quantitative analysis of various features of the visual representation. The representation was found to be asymmetric, with more cortex devoted to lower than to upper fields. Over much of striate cortex the representation is anisotropic, in that the magnification factor depends upon the direction along which it is measured. There is considerable individual variability in these features as well as in the overall size of striate cortex. Outside the fovea, the cortical representation shows only modest deviations from a logarithmic conformai mapping, in which the magnification factor is proportional to the inverse of eccentricity in the visual field. Comparison of receptive field size with cortical magnification was used to estimate the “point image size” in the cortex (i.e. the extent of cortex concerned with processing inputs from any given point in the visual field). Our evidence supports a previous report that point-image size varies significantly with eccentricity. This is of interest in relation to anatomical evidence that the dimensions of columnar systems in striate cortex are largely independent of eccentricity.     

Resolution, separation of retinal ganglion cells, and cortical magnification in humans

We present direct comparisons of resolution thresholds and quantitative estimates of retinal ganglion cell separation in humans with reported functional magnetic resonance imaging estimates of the human linear cortical magnification factor. Measurements of resolution thresholds (MAR), retinal ganglion cell (GC) densities, and linear cortical magnification factor (M) values were taken from the literature. Our objective was to analyse the apparent overrepresentation of human central vision in the visual cortex and to determine whether the cause of this is an effect of the uneven distribution of GC in the retina and/or that central GC have more devoted cortical area per cell. The reserved amount of cortical distance per retinal unit, i.e. the product of M on the one hand and effective GC separation, MAR, and GC receptive field separation on the other, indicates an overrepresentation of the fovea and immediately surrounding retina in the human striate cortex due to an increase in devoted cortical distance per central GC or resolution unit. This cannot be explained by lateral displacement of foveal ganglion cells nor by peripheral scaling, but rather by an additional magnification in the retino-cortical pathway.     

A comparison of tangent screen, goldmann, and humphrey perimetry in the detection and localization of occipital lesions

OBJECTIVE: To compare manual kinetic perimetry with tangent screen and Goldmann techniques and automated static perimetry with the Humphrey Field Analyzer in the detection and localization of occipital lobe lesions. DESIGN: Prospective consecutive comparative case series. PARTICIPANTS: Twelve patients with well-defined occipital lobe infarcts on magnetic resonance (MR) imaging were studied. MAIN OUTCOME MEASURES: The patients were tested by tangent screen, Goldmann, and Humphrey perimetry (central 30-2 threshold program). The three visual fields were compared and correlated with MR images. RESULTS: All three perimetric techniques detected the presence of postchiasmal lesions. However, localization of lesions differed with perimetric technique. Visual fields obtained from tangent screen and Goldmann perimetry were similar and corresponded well with the location of lesions on MR images in all 12 patients. Humphrey perimetry inaccurately localized the lesion to the proximal part of the postchiasmal pathway by revealing incongruous fields in two patients, failed to detect sparing of the posterior occipital cortex or occipital pole in four patients, and estimated a larger extent of damage in one patient when compared with MR images and manual perimetry. CONCLUSIONS: All three perimetric techniques are satisfactory screening tests to detect occipital lesions. However, tangent screen and Goldmann perimetry provide information about the location and extent of lesions that is more consistent with prevailing knowledge of the effects of the lesion in the postgeniculate visual pathway.     

视路疾病患者脑功能性磁共振成像初步观察

目的 观察视路疾病患者视网膜拓扑投射的分布及脑功能性磁共振成像(fMRI)与视野检查结果的关系.方法 3例经病理检查确诊为垂体瘤和颅咽管瘤的鞍区占位患者(患者组)6只眼以及年龄24～30岁的3名健康志愿者纳入研究.患者组6只眼最佳矫正视力无光感～1.0;健康志愿者矫正视力1.0,除近视外无其他眼疾.受检者均无fMRI检查禁忌.常规行最佳矫正视力、直接和(或)间接检眼镜眼底检查,Octopus101电脑全自动视野计32程序策略趋势导向检查法行中心静态视野检查.fMRI检查采用GE signa VH/I 3.0T扫描机.视觉刺激占据12°视角,采用对比度接近100%的黑白棋盘格,背景为棋盘格的平均亮度,包括周期性扩张或收缩的环形刺激和顺时针或逆时针旋转的楔形刺激两种模式.功能图像采用梯度回波的平面同波序列的血氧水平依赖扫描序列,垂直于距状裂冠状位扫描,三维采集方式的扰相梯度回波序列矢状位采集高分辨率解剖结构数据.数据分析采用AFNI软件,并且应用Freesurfer进行皮层的分割、膨胀处理.结果 6只患眼中,视野颢侧缺损3只眼,颞上方缺损2只眼,不能完成检查1只眼.环形刺激的功能图像显示,枕叶视觉皮层产生了时相对应的激活图像,枕叶后极沿距状裂向前迁移对应黄斑中心区向周边视野的迁移.楔形刺激的功能图像显示,初级视觉皮层的极角拓扑投射的空间序列与视野相反.距状裂下方的视皮层主要对应对侧上方视野,距状裂上方主要对应对侧下方视野.刺激患眼不能诱导出与相应视野缺损相关的初级视觉皮层的激活,存在相应视觉皮层反应的减少.结论 fMRI检查结果与常规视野计检查的结果有很好的对应关系,可以反映视路疾病患者的视野缺损对应的皮层反应.     

Macular sparing investigated by means of Haidinger brushes.

Haidinger brushes, an entoptic phenomenon perceived only through the most central macular retina, have been used in addition to kinetic and static perimetry with the Tubingen perimeter for determining macular sparing and splitting in hemianopic patients. Seven patients were examined: 2 with a bitemporal hemianopia resulting from traumatic damage to the optic chiasma, and 5 with a homonymous hemianopia resulting from extensive lesions of the optic radiations and/or the occipital cortex (including 2 cases of hemidecortication). On perimetric examination some exceptions could be observed in the correspondence of macular splitting and sparing respectively with pre- and postgeniculate lesions, but this was not the case when Haidinger brushes were used. Half of the figure was then perceived by the patients with lesions of the chiasma and the entire figure by all the patients with geniculostriate lesions. We consider that results obtained by this simple method are more reliable than those obtained by perimetry and that Haidinger brushes should be used for macular field examination in neuro-ophthalmic practice.     

Reorganization of visual processing in macular degeneration: replication and clues about the role of foveal loss

We previously reported large-scale reorganization of visual processing (i.e., activation of "foveal" cortex by peripheral stimuli) in two individuals with loss of foveal input from macular degeneration [Baker, C.I., Peli, E., Knouf, N., & Kanwisher, N. G. (2005). Reorganization of visual processing in macular degeneration. Journal of Neuroscience, 25(3), 614-618]. Here, we replicate this result in three new individuals. Further, we test the hypothesis that this reorganization is dependent on complete loss of foveal input. In two other individuals with extensive retinal lesions but some foveal sparing we found no evidence for reorganization. We conclude that large-scale reorganization of visual processing in MD occurs only in the complete absence of functional foveal vision.     

Functional magnetic resonance imaging of visual cortex in a patient with cerebrovascular insufficiency

We compare the findings of functional magnetic resonance imaging (MRI) of the visual cortex in a patient with moyamoya disease with other neuro-imaging techniques. Automated static perimetry demonstrated a slight depression of the left visual field in both eyes. MRI of the brain showed diffuse atrophy of the right cerebral hemisphere, sparing the occipital lobe. Single-photon emission computed tomography showed relatively preserved perfusion to the right occipital lobe. Functional MRI during visual stimulation, however, demonstrated an apparent lack of activation of the right primary visual cortex, which did not correlate with the known retinotopic map of the visual cortex. The patient seems to have had a lack of reserved ability to respond to visual stimuli with maximal autoregulatory vasodilatation in the visual cortex, even though apparent morphologic change and dense visual field defects had not been observed.     

正常人视觉皮层视网膜拓扑投射的功能磁共振研究

目的研究功能磁共振（fMRI）检测正常人视觉皮层的视网膜拓扑投射分布特征,探讨功能定位的V1／V2边界的解剖特征。方法以3名健康志愿者作为实验对象,年龄25～30岁,右利手。视觉刺激占据12度视角,采用对比度接近100％的棋盘格,背景为黑白棋盘格的平均亮度,包括周期性扩张或收缩的环形刺激和顺时针或逆时针旋转的楔形刺激两种模式。应用GE Signa VH/I 3．0 T fMRI扫描机。功能图像采用GRE-EPI的BOLD扫描序列,垂直于距状裂冠状位扫描,3D-SPGR序列矢状位采集高分辨率解剖结构数据。采用AFNI软件进行数据分析,应用Freesurfer软件进行皮层的分割、膨胀及切开展平处理。结果（1）环状刺激自中心向周边扩张时,视皮质枕叶后极至距状裂前部先后兴奋,并存在皮层放大效应;（2）楔形刺激揭示V1区的极角坐标方向与视野相反,相邻功能区的极角坐标方向相反;（3）功能定位的V1／V2边界位于脑回顶部附近。结论时相编码的视觉刺激是获得视觉皮层视网膜拓扑投射的有效手段,功能定位V1／V2边界的解剖特征支持了白质纤维最优化连接假说。     

Ocular integration in the human visual cortex

Human striate cortex contains an orderly map of the contralateral visual field, which is distorted to make a disproportionate amount of tissue available for the representation of the macula. Engrafted on the retinotopic map is a system of alternating inputs known as ocular dominance columns. These columns consist of interleaved bands of geniculocortical afferents in layer 4C serving either the right eye or the left eye. They can be revealed in humans with a history of prior visual loss in one eye by processing striate cortex for cytochrome oxidase at autopsy. Because their geniculate input is segregated, cells within ocular dominance columns in layer 4C respond to stimulation of one eye only. These monocular cells converge onto binocular cells in other layers, integrating signals from the two eyes. The columns in humans appear similar to those found in many primate species, including the macaque. In the squirrel monkey, however, the occurrence of ocular dominance columns is highly variable. Some squirrel monkeys lack columns, yet they seem to have no impairment of visual function. In animals with weakly expressed columns, one can detect a cortical pattern of metabolic activity corresponding to retinal blood vessels. It appears because visual deprivation from shadows cast by blood vessels induces remodeling of geniculocortical afferents, in a manner akin to the shrinkage of ocular dominance columns from congenital cataract. Although the function of ocular dominance columns is unknown, their metabolism is altered in strabismus, suggesting a role in visual suppression.     

Nasotemporal overlap of retinal ganglion cells in humans: a functional study

PURPOSE: A zone of overlap along the vertical retinal meridian where ipsi- and contralaterally projecting ganglion cells intermingle has been demonstrated histologically in nonhuman primates. The widening of the zone of overlap in the foveal region was thought to produce a foveal sparing extending 1.5 degrees in the blind hemifield in human hemianopia. The functional relevance of the nasotemporal overlap is still unclear and cannot be shown definitely by conventional perimetry, because of insufficient spatial accuracy, light-scattering effects, and insufficient fixation control. Therefore, this study was undertaken to investigate the vertical field border by a perimetric method that does not have these shortcomings. METHODS: A scanning laser ophthalmoscope (SLO) was used to scan vertical triplets of dots along the vertical field border in 20 patients (36 eyes) with homonymous hemianopia without macular sparing. Stimuli and fundus were imaged simultaneously for fixation monitoring. RESULTS: None of the patients showed a field border that coincided exactly with the vertical midline. In 34 eyes, the seeing area extended from the vertical meridian into the blind hemifield and formed a vertical strip of perception. None of the patients showed additional foveal sparing. Twenty-two eyes showed a concave shape of the seeing area within the foveal region of the blind hemifield. CONCLUSIONS: Our results show that the nasotemporal overlap exists in humans. It consists of a strip of intact perception reaching into the blind hemifield. The concave shape can be explained by the size and distribution of the receptive fields of the retinal ganglion cells.     

Residual visual function after loss of both cerebral hemispheres in infancy

PURPOSE: To investigate whether and what kind of visual function is still present in the absence of both cerebral hemispheres. METHODS: Binocular visual function of five children who had suffered the loss of both cerebral hemispheres and the visual fields of 30 controls 5 to 12 months of age were examined according to a perimetric method based on forced-choice, preferential-looking methods. RESULTS: Results show that after the destruction of both cerebral hemispheres, a stimulus presented binocularly beyond 5 degrees eccentricity did not elicit a response. However, two children were still able to fixate steadily and to follow a stimulus presented binocularly within the central 5 degrees , with eye and head movements despite the absence of both cerebral hemispheres. One child responded only to a moving face or a moving drum with black and white stripes presented binocularly within the central 5 degrees but not to a moving spot of light. The binocular visual field of 30 controls 5 to 12 months of age almost reached the dimensions of the adult binocular visual field. CONCLUSIONS: Neural structures in the midbrain, including the superior colliculi and the pretectum, seem to be able to mediate visual function in the foveal and macular regions. These structures are, however, unable to mediate the presence of a functional visual field beyond 5 degrees eccentricity.