Neural network model of the primary visual cortex: From functional architecture to lateral connectivity and back

The role of intrinsic cortical dynamics is a debatable issue. A recent optical imaging study (Kenet et al., 2003) found that activity patterns similar to orientation maps (OMs), emerge in the primary visual cortex (V1) even in the absence of sensory input, suggesting an intrinsic mechanism of OM activation. To better understand these results and shed light on the intrinsic V1 processing, we suggest a neural network model in which OMs are encoded by the intrinsic lateral connections. The proposed connectivity pattern depends on the preferred orientation and, unlike previous models, on the degree of orientation selectivity of the interconnected neurons. We prove that the network has a ring attractor composed of an approximated version of the OMs. Consequently, OMs emerge spontaneously when the network is presented with an unstructured noisy input. Simulations show that the model can be applied to experimental data and generate realistic OMs. We study a variation of the model with spatially restricted connections, and show that it gives rise to states composed of several OMs. We hypothesize that these states can represent local properties of the visual scene. Action Editor: Jonathan D. Victor     

屈光不正对儿童视觉皮层神经元活动影响的功能磁共振研究

目的：利用血氧水平依赖性功能性磁共振成像（BOLD-fMRI）技术及非金属MRI专用眼镜,分析探索屈光不正对儿童大脑皮层视觉功能区神经元活动的影响。方法：以1．5T磁共振成像系统采集8例屈光不正眼儿童屈光矫正前后枕叶视皮层兴趣区BOLD—fMRI数据,及8例正常眼凸透镜离焦前后枕叶视皮层兴趣区BOLD—fMRI数据,进行对比分析,比较屈光不正眼及其矫正后、正常眼及其离焦后皮层视觉功能区神经元活动的不同,分析其改变特点及原因。结果：屈光不正眼儿童矫正屈光后皮层视觉功能区神经元活动范围明显增加（P〈0．05）;正常眼离焦后皮层视觉功能区神经元活动范围明显减小（P〈0．05）。结论：屈光不正会明显降低儿童皮层视觉功能区的神经元活动。屈光不正患儿应尽早配镜矫正,以免影响视觉皮层功能发育。     

视皮层分区及其fMRI 研究进展

血氧水平依赖功能磁共振成像（BOLD—fMRI）作为一种无创、可精确定位的脑功能研究技术,已广泛应用于视觉系统的研究中,并取得了许多重要成果,本文就fMRI研究进展及其在大脑视觉皮层功能分区中的应用做一综述。     

Distribution of neuropeptide Y immunoreactivity in human visual cortex and underlying white matter

Immunocytochemical techniques have been used to study neuropeptide Y (NPY) distribution in the human visual cortex (Brodman's areas 17, 18 and 19) NYP cell bodies belong mostly to inhibitory (multipolar and bitufted) but also to excitatory (bipolar and some pyramidal) neuronal types. Their distribution is similar in the three cortical areas studied: 20 to 40% of the NPY perikarya are located in the cortical gray matter, mostly in the deep layers, while the remaining 60 to 80% are located in the underlying white matter. Immunoreactive NPY processes form a rich network of intersecting fibers throughout the entire visual cortex. A superficial plexus (layers I and II) and a deep plexus (deep layer V and layer VI) of NPY fibers are present in areas 17, 18 and 19. In area 17, an additional well developed plexus is present in layers IVb and IVc. These plexuses receive branches from long parallel fibers arising from deep cortical layers or underlying white matter and terminating in superficial layers. Local or extrinsic NPY terminals wind around vessels in the cortex as well as in the white matter, and either penetrate them or form clusters of club endings on their walls. Our results suggest a role for NPY in human visual circuitry and in cortical blood flow regulation.     

Gamma rhythms in the visual cortex: functions and mechanisms

Gamma-band activity, peaking around 30–100 Hz in the local field potential''s power spectrum, has been found and intensively studied in many brain regions. Although gamma is thought to play a critical role in processing neural information in the brain, its cognitive functions and neural mechanisms remain unclear or debatable. Experimental studies showed that gamma rhythms are stochastic in time and vary with visual stimuli. Recent studies further showed that multiple rhythms coexist in V1 with distinct origins in different species. While all these experimental facts are a challenge for understanding the functions of gamma in the visual cortex, there are many signs of progress in computational studies. This review summarizes and discusses studies on gamma in the visual cortex from multiple perspectives and concludes that gamma rhythms are still a mystery. Combining experimental and computational studies seems the best way forward in the future.     

Electron microscopy of the fate of exogenous ferritin in the feline visual cortex

Summary The ultrastructural changes occurring in the feline visual cortex 3 hours after the injection of 0.02 mls of ferritin in 1% trypan blue in artificial cerebrospinal fluid have been studied.Near the site of injection, disrupted cells contained free and membrane-bound ferritin. In less damaged areas, some signs of oedema were present in the cells, especially in astrocytes. Membrane-bound ferritin occurred occasionally in neurones and more frequently in astrocytes and oligodendrocytes. Considerable amounts of ferritin were also accumulated in phagocytic cells of unknown origin. In blood vessels, ferritin collected in the basement membrane and around collagen and, in membrane-bound form, in pale cells at the periphery of the vessels. Ferritin occurred in all parts of the intercellular space except in interglial junctions and tight junctions between vascular endothelial cells.This work was supported by a research grant from the National Health and Medical Research Council of Australia to Professor M. J. Blunt, of the School of Anatomy, University of New South Wales. The author wishes to thank Professor Blunt for his constant encouragement and support. The assistance of Mrs. Ruth Mather is gratefully acknowledged.     

Insular cortex neurons encode and retrieve specific immune responses

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Mapping of contextual modulation in the population response of primary visual cortex

We review the evidence of long-range contextual modulation in V1. Populations of neurons in V1 are activated by a wide variety of stimuli outside of their classical receptive fields (RF), well beyond their surround region. These effects generally involve extra-RF features with an orientation component. The population mapping of orientation preferences to the upper layers of V1 is well understood, as far as the classical RF properties are concerned, and involves organization into pinwheel-like structures. We introduce a novel hypothesis regarding the organization of V1’s contextual response. We show that RF and extra-RF orientation preferences are mapped in related ways. Orientation pinwheels are the foci of both types of features. The mapping of contextual features onto the orientation pinwheel has a form that recapitulates the organization of the visual field: an iso-orientation patch within the pinwheel also responds to extra-RF stimuli of the same orientation. We hypothesize that the same form of mapping applies to other stimulus properties that are mapped out in V1, such as colour and contrast selectivity. A specific consequence is that fovea-like properties will be mapped in a systematic way to orientation pinwheels. We review the evidence that cytochrome oxidase blobs comprise the foci of this contextual remapping for colour and low contrasts. Neurodynamics and motion in the visual field are argued to play an important role in the shaping and maintenance of this type of mapping in V1.     

Neurons and their synaptic organization in the visual cortex of the rat

Summary Cells in the visual cortex (area 17) of adult rats were impregnated by the rapid Golgi method and characterized by light microscopy. Selected cells were then sectioned for electron microscopy and their cytological characteristics and the pattern of synapses on their cell bodies and dendrites were studied Twelve classical pyramidal cells from layers II–VI, two pyramid-like cells from layer VI, two inverted pyramidal cells from layers V and VI, ten spine-free non-pyramidal cells from layers II–VI and two spinous non-pyramidal cells from layer IV were examined.The cytoplasmic features of the identified cells, where these could be discerned, corresponded to those previously reported for the different cell types in conventionally prepared tissue. Pyramidal Cells received exclusively type 2 synaptic contacts on their cell bodies, type 1 contacts on their dendritic spines and a mixture of synaptic types (type II predominating) on their shafts, where synaptic density was relatively low. This pattern of synaptic contacts was consistent for all portions of the dendritic tree; inverted pyramidal cells and pyramid-like cells showed the same synaptic organization as classical pyramids. The axon collaterals of pyramidal cells established type I contacts with dendritic spines (or, rarely, shafts) of unknown origin. Non-Pyramidal Cells received both type 1 and type 2 contacts (the former predominating) on their cell bodies and dendrites. The spinous variety also received type I contacts on their dendritic spines. Axon terminal of spine-free non-pyramidal cells established type II synaptic contacts with dendritic shafts of unknown origin. The similarity in synaptic organization between the spine-free and spinous non-pyramidal cells examined in this study suggest that the latter correspond to the sparsely spinous stellate cells rather than to the spinous stellate cells of cat and monkey visual cortex.We thank the Medical Research Council for financial support     

Goldfish's visual information processing patterns in food-reinforced discrimination learning between compound visual stimuli

Summary To examine how goldfish process and store information on compound visual stimuli, goldfish were trained with visual discriminative stimuli composed of varied colors and patterns using a Y-maze instrumental conditioning technique. The fish showed some very different types of information processing patterns depending upon the degree of discrimination difficulty of each constituent aspect (color and pattern). Those trained with compound stimuli with both a more easily discriminated aspect and a more difficult aspect learned the former selectively but did not learn the latter at all in spite of a high rate of training. Contrary to this, the fish trained with compound stimuli composed of two aspects with similar degrees of discrimination difficulty learned both aspects. In this case, only when fish were trained with compound stimuli composed of relatively more difficult aspects did they learn to discriminate between the stimuli more rapidly than the fish in each group trained with the constituent colored or patterned stimuli. These results were discussed in relation to visual processing patterns reported in other species and the mechanism of aspect selection.Abbreviations CP compound stimuli composed of VR and HB (7-mm ISBBs) - Cp compound stimuli composed of VR and HB (14-mm ISBBs) - cP compound stimuli composed of VG and HB (7-mm ISBBs) - cp compound stimuli composed of VG and HB (14-mm ISBBs) - HB horizontal patterns on blue background - HGra horizontal patterns on gray background - ISBBs interval spaces between bars - VG vertical patterns on green background - VGra vertical patterns on gray background - VR vertical patterns on red background     

Behavioral analysis of two distinct visual responses in the larva of the tiger beetle (Cicindela chinensis)

The tiger beetle larva shows two distinct visual responses, a predatory jump and an evasive withdrawal into the burrow (escape). In the present study the visual stimuli controlling these two responses have been behaviorally analyzed in the larva of Cicindela chinensis. The threshold size needed for a target to elicit both responses is a visual angle of 5–7°. The velocities of moving targets needed to elicit the responses are 0.4–33° s⁻¹ for the jump and 0.76–90° s⁻¹ for the escape. Choice between the two responses appears to be controlled by the actual target size rather than by the angular size. It also appears to be controlled by the target height. As the height of the target increases, the probability for the jump decreases, whereas the probability for the escape increases. Response properties of the larva with only a single functional stemma, the other stemmata being occluded, are different from those of the intact larva, which suggests cooperation of at least two stemmata for the release of different visual responses. Visual responses of the one-stemma larva still vary, however, with target size and target height, which suggests the visual responses are partially controlled even by a single stemma. Although our data do not resolve these conflicting results, more than one stemma is necessary for a firm choice between the two responses. Accepted: 13 May 1997     

Locomotion-induced gain of visual responses cannot explain visuomotor mismatch responses in layer 2/3 of primary visual cortex

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吡哆胺对糖尿病大鼠视皮质AGE-RAGE系统的影响

目的观察吡哆胺对糖尿病大鼠视皮质高级糖基化终末产物(AGE)及其受体(RAGE)表达的影响,探讨吡哆胺对视皮质的保护作用。方法健康SD大鼠随机分为正常对照组(NC组)、糖尿病未治疗组(DM组)、糖尿病吡哆胺治疗组(PM组)和氨基胍治疗对照组(AG组)各20只,用链脲佐菌素(STZ)建立糖尿病模型,PM组和AG组分别于造模成功后第二天开始予吡哆胺和氨基胍灌胃。各组于治疗4w和12w后取材,用酶联免疫吸附(ELISA)法定量检测大鼠视皮质中AGEs含量,荧光免疫组化及图像分析半定量检测各组视皮质RAGE的表达。结果糖尿病治疗组和未治疗组血糖无显著性差异。4w时各组AGEs含量无明显差异,12w时PM组视皮质中AGEs含量与AG组、NC组比较差异无统计学意义,与DM组相比显著降低,差异具有统计学意义(P0.05)。PM组视皮质中RAGE表达比DM组显著减少,差异具有统计学意义(P0.05),但高于NC组(P0.05)。结论糖尿病大鼠12w后视皮质中AGEs含量和RAGE的表达高于正常对照组,吡哆胺类似氨基胍可减少AGEs的堆积,还能抑制RAGE的表达,减轻AGEs-RAGE通路作用导致的组织损伤,对视皮质具有一定的保护作用。     

Adaptation to visual stimulation modifies the burst firing property of V1 neurons

The mean firing rate of visual cortical neurons is reduced after prolonged visual stimulation, but the underlying process by which this occurs as well as the biological significance of this phenomenon remains unknown. Computational neuroscience studies indicate that high-frequency bursts in stimulus-driven responses can be transmitted across synapses more reliably than isolated spikes, and thus may carry accurate stimulus-related information. Our research examined whether or not adaptation affects the burst firing property of visual cortical neurons by examining changes in the burst firing changes of V1 neurons during adaptation to the preferred visual stimulus. The results show that adaptation to prolonged visual stimulation significantly decreased burst frequency (bursts/s) and burst length (spikes/burst), but increased burst duration and the interspike interval within bursts. These results suggest that the adaptation of V1 neurons to visual stimulation may result in a decrease of feedforward response gain but an increase of functional activities from lateral and/or feedback connections, which could lead to a reduction in the effectiveness of adapted neurons in transmitting information to its driven neurons.     

Age-associated reduction of nuclear shape dynamics in excitatory neurons of the visual cortex

Neurons decline in their functionality over time, and age-related neuronal alterations are associated with phenotypes of neurodegenerative diseases. In nonneural tissues, an infolded nuclear shape has been proposed as a hallmark of aged cells and neurons with infolded nuclei have also been reported to be associated with neuronal activity. Here, we performed time-lapse imaging in the visual cortex of Nex-Cre;SUN1-GFP mice. Nuclear infolding was observed within 10 min of stimulation in young nuclei, while the aged nuclei were already infolded pre-stimulation and showed reduced dynamics of the morphology. In young nuclei, the depletion of the stimuli restored the nucleus to a spherical shape and reduced the dynamic behavior, suggesting that nuclear infolding is a reversible process. We also found the aged nucleus to be stiffer than the young one, further relating to the age-associated loss of nuclear shape dynamics. We reveal temporal changes in the nuclear shape upon external stimulation and observe that these morphological dynamics decrease with age.