跨通道学习及其认知神经机制

跨通道学习是指涉及从多个通道获取信息,对这些多通道的信息进行整合并加以利用的学习.多通道信息整合是跨通道学习的重要基础.尽管跨通道学习条件更接近人类学习的真实环境,但是目前多数研究依然采用单通道刺激,跨通道学习相关研究的结果还显得有些凌乱、不够系统.为了较好地概括跨通道学习的特点和机制,本文首先介绍了多通道信息整合的产生与影响因素,以及初级皮层具有通道非特异性的实验和理论研究,之后,系统梳理了跨通道学习的意识性、表征类型和迁移效应的相关研究,整理了采用神经元记录、ERP和f MRI等技术探讨跨通道学习神经机制的研究进展.最后,我们对目前跨通道学习的研究成果进行了总结,并对这些研究成果的潜在应用以及这一领域未来的研究方向进行了展望.     

CFTR型氯离子通道研究进展

囊性纤维化跨膜传导调节因子（CFTR）是一种重要的氯离子通道,突变易引起囊性纤维化病变,故得名。一系列研究表明,CFTR由5个结构域组成：两个跨膜结构域形成氯离子通道;两个核苷酸结合结构域调节通道的开闭;一个调节结构域主要影响氯通道的活动。这些结构域通过协同作用共同控制了氯离子的跨膜流动,而一些突变可以影响细胞功能而导致囊性纤维化的发生。本文通过介绍CFTR基本结构、调节机制、与囊性纤维化病变的关系及针对CFTR的治疗而对CFTR型氯离子通道有一个的全面的理解。     

明视人听词分类任务时的视皮层激活——跨感觉通道的新证据

近期的脑成像研究在盲人等感官缺陷被试者身上发现了感觉替换现象,即传统上认为仅对单一感觉通道刺激反应的皮层区域也参与其他感觉通道的信息加工．类似的效应在感觉剥夺(蒙住眼睛)的明视人被试中也被观察到,提示脑内可能预存着多感觉交互作用的神经通路．通常认为,上述神经通路在常态的人脑中是以潜伏形式存在的,只有当感觉剥夺时才显露出来或得到加强．但是,感觉剥夺是否是该类神经通路发挥作用的必要条件,已有的研究尚缺乏确切的证据．采用统计力度较强的实验设计,给未蒙眼明视人被试听觉呈现一组名词,要求其对听到的每一个词语做出是人工物体还是自然物体的语义判断．对同步采集的功能磁共振信号进行统计分析,观察到视皮层脑区有显著激活．这些结果表明,跨感觉通道的神经通路在未实施感觉剥夺的条件下依然能够显示出来,因而在常态人脑中也不是完全以潜伏形式存在的．上述研究为建立多感觉交互作用神经机制的具体理论模型提供了一个约束条件．     

电压门控钠离子通道疾病的研究进展

细胞膜上的电压门控钠离子通道（Voltage-gated Sodium Channels,VGSCs）是细胞形成动作电位过程中重要的组成构件,由一个大的α亚基和一个或多个不同的β亚基组成,中央是具高度选择性只允许钠离子通过的亲水通道。电压门控钠离子通道在调节细胞膜电位、维持细胞离子稳态、细胞增殖和凋亡等生理过程中发挥着重要作用,因而钠离子通道自身的异变或是相关基因的变异都可能引起一系列身体病变。本文主要介绍了电压门控钠离子通道的结构与功能,阐述了其与癌细胞侵袭转移和神经病理性疼痛的关系,并介绍了几种典型的由钠离子通道基因变异引起的疾病。随着对电压门控钠离子通道及其异常分子机制研究的不断深入,新成果将为生理学、药理学和病理学等领域的研究提供理论基础和新的研究思路,为离子通道疾病的临床预防、诊断与治疗找到新途径。     

综述: 渐近优先性及其机制

对渐近信号的优先加工被称为渐近优先性,该效应普遍存在于人类和动物的视觉、听觉和跨感觉通道中.人类神经影像学研究发现负责加工渐近信号的脑区涉及一个大规模相互协作和沟通的分布式神经网络,包括颞上沟、颞顶叶连接处以及一些运动区.对多种动物的细胞水平研究也发现了对渐近信号选择性敏感的神经元和神经通路.威胁论、注意捕获理论和自动加工理论从不同角度解释了渐近优先性产生的原因.未来研究可进一步考察刺激的社会、情绪等属性对渐近优先性的影响,探索多通道渐近渐远信息的整合和注意分配机制.     

水通道蛋白

水通道蛋白 (aquaporin,AQP)是对水专一的通道蛋白 ,普遍存在于动、植物及微生物中。它所介导的自由水快速被动的跨生物膜转运 ,是水进出细胞的主要途径。1　水通道蛋白的发现长期以来 ,普遍认为细胞内外的水分子是以简单的跨膜扩散方式来透过脂双层膜。后来由于在生物物理学研究中发现红细胞及近端肾小管对渗透压改变引起的水的通透性很高 ,很难单纯以弥散来解释。因此 ,一些学者推测水的跨膜转运除了简单扩散外 ,还存在某种特殊的机制 ,并提出了水通道的概念。1988年 ,Agre等在鉴定人类 Rh血型抗原时 ,偶然在红细胞膜上发现了 1种新的 2…     

Ca^2＋激活Cl^-通道功能及分子基础研究进展

自从1983年Barish在爪蟾卵母细胞中发现钙激活的Cl^–通道以来,此种类型Cl^–通道一直在被广泛的研究,其在不同组织中的重要作用也被不断报道。但是,钙激活氯电流的分子机制一直未被阐明。直到2008年,由三个实验室分别发现了构成钙激活Cl^–通道的分子基础为跨膜蛋白16A（transmembrane protein 16A,TMEM16A）,这一发现使得人为通过基因手段调控钙激活Cl^–通道的功能与表达成为可能。该文综述了钙激活Cl^–通道在不同组织中的作用、TMEM16A的电生理和药理学特性以及TMEM16A在心肌肥厚和心衰中的可能作用,以及以Cl^–通道作为药物作用靶点的研究进展。     

跨膜蛋白16A：钙激活氯通道的最新进展

钙激活氯离子通道(calcium-activated chloride channels,CaCCs)介导了众多生理过程,包括跨上皮离子与液体分泌、心肌和神经兴奋、感觉传导、平滑肌收缩和受精过程等,但目前对于其分子基础等重要问题尚未研究清楚．综述了最新报道的CaCCs分子基础跨膜蛋白16A(TMEM16A)的发现过程、基因结构和功能、离子通道电生理特性、相关病理与药理功能的一些热点问题,并展望了该研究领域的发展趋势．     

成人数量加工系统的跨通道研究

目的:本研究以由视听通道交互作用产生的错觉性闪光为工具,对成人的数量认知系统进行了探讨.方法:采用声音信号引起视错觉的实验范式,改变实验中闪光和声音的数目进行研究.结果:错觉性闪光的数目随着闪光和声音的数目增加而增加.预示着多感觉通道交互过程中接受变化频率较快的信息的通道对知觉有特殊作用.多感觉通道接受信息无交互作用的情况下,普通成人数量认知与婴儿和其他人群相比达到高度的自动化,对数量的相对变化判断有较高的准确率和稳定性.结论:成人数量加工在有交互作用的认知过程中受到了感觉通道对信息加工的影响.并不是完全相对于感觉通道独立的.而且,知觉过程中大数和小数的反应差异也在一定程度上表现了二者加工机制的差异.     

水通道蛋白的基本结构与特异性通透机理

水通道蛋白是一个具有跨膜运输水分子功能的蛋白家族。从1988年Agre等发现水通道蛋白起,目前在不同物种中已经发现了200余种水通道蛋白,其中存在哺乳动物体内的有13种。概述了水通道蛋白的结构、组织特异性分布及特异性通透机理。     

Sound facilitates visual learning

Numerous studies show that practice can result in performance improvements on low-level visual perceptual tasks [1-5]. However, such learning is characteristically difficult and slow, requiring many days of training [6-8]. Here, we show that a multisensory audiovisual training procedure facilitates visual learning and results in significantly faster learning than unisensory visual training. We trained one group of subjects with an audiovisual motion-detection task and a second group with a visual motion-detection task, and compared performance on trials containing only visual signals across ten days of training. Whereas observers in both groups showed improvements of visual sensitivity with training, subjects trained with multisensory stimuli showed significantly more learning both within and across training sessions. These benefits of multisensory training are particularly surprising given that the learning of visual motion stimuli is generally thought to be mediated by low-level visual brain areas [6, 9, 10]. Although crossmodal interactions are ubiquitous in human perceptual processing [11-13], the contribution of crossmodal information to perceptual learning has not been studied previously. Our results show that multisensory interactions can be exploited to yield more efficient learning of sensory information and suggest that multisensory training programs would be most effective for the acquisition of new skills.     

Evidence from functional magnetic resonance imaging of crossmodal binding in the human heteromodal cortex

BACKGROUND: Integrating information from the different senses markedly enhances the detection and identification of external stimuli. Compared with unimodal inputs, semantically and/or spatially congruent multisensory cues speed discrimination and improve reaction times. Discordant inputs have the opposite effect, reducing performance and slowing responses. These behavioural features of crossmodal processing appear to have parallels in the response properties of multisensory cells in the superior colliculi and cerebral cortex of non-human mammals. Although spatially concordant multisensory inputs can produce a dramatic, often multiplicative, increase in cellular activity, spatially disparate cues tend to induce a profound response depression. RESULTS: Using functional magnetic resonance imaging (fMRI), we investigated whether similar indices of crossmodal integration are detectable in human cerebral cortex, and for the synthesis of complex inputs relating to stimulus identity. Ten human subjects were exposed to varying epochs of semantically congruent and incongruent audio-visual speech and to each modality in isolation. Brain activations to matched and mismatched audio-visual inputs were contrasted with the combined response to both unimodal conditions. This strategy identified an area of heteromodal cortex in the left superior temporal sulcus that exhibited significant supra-additive response enhancement to matched audio-visual inputs and a corresponding sub-additive response to mismatched inputs. CONCLUSIONS: The data provide fMRI evidence of crossmodal binding by convergence in the human heteromodal cortex. They further suggest that response enhancement and depression may be a general property of multisensory integration operating at different levels of the neuroaxis and irrespective of the purpose for which sensory inputs are combined.     

Multisensory Perceptual Learning of Temporal Order: Audiovisual Learning Transfers to Vision but Not Audition

Background

An outstanding question in sensory neuroscience is whether the perceived timing of events is mediated by a central supra-modal timing mechanism, or multiple modality-specific systems. We use a perceptual learning paradigm to address this question.

Methodology/Principal Findings

Three groups were trained daily for 10 sessions on an auditory, a visual or a combined audiovisual temporal order judgment (TOJ). Groups were pre-tested on a range TOJ tasks within and between their group modality prior to learning so that transfer of any learning from the trained task could be measured by post-testing other tasks. Robust TOJ learning (reduced temporal order discrimination thresholds) occurred for all groups, although auditory learning (dichotic 500/2000 Hz tones) was slightly weaker than visual learning (lateralised grating patches). Crossmodal TOJs also displayed robust learning. Post-testing revealed that improvements in temporal resolution acquired during visual learning transferred within modality to other retinotopic locations and orientations, but not to auditory or crossmodal tasks. Auditory learning did not transfer to visual or crossmodal tasks, and neither did it transfer within audition to another frequency pair. In an interesting asymmetry, crossmodal learning transferred to all visual tasks but not to auditory tasks. Finally, in all conditions, learning to make TOJs for stimulus onsets did not transfer at all to discriminating temporal offsets. These data present a complex picture of timing processes.

Conclusions/Significance

The lack of transfer between unimodal groups indicates no central supramodal timing process for this task; however, the audiovisual-to-visual transfer cannot be explained without some form of sensory interaction. We propose that auditory learning occurred in frequency-tuned processes in the periphery, precluding interactions with more central visual and audiovisual timing processes. Functionally the patterns of featural transfer suggest that perceptual learning of temporal order may be optimised to object-centered rather than viewer-centered constraints.     

Modality distribution of sensory neurons in the feline caudate nucleus and the substantia nigra

Despite extensive analysis of the motor functions of the basal ganglia and the fact that multisensory information processing appears critical for the execution of their behavioral action, little is known concerning the sensory functions of the caudate nucleus (CN) and the substantia nigra (SN). In the present study, we set out to describe the sensory modality distribution and to determine the proportions of multisensory units within the CN and the SN. The separate single sensory modality tests demonstrated that a majority of the neurons responded to only one modality, so that they seemed to be unimodal. In contrast with these findings, a large proportion of these neurons exhibited significant multisensory cross-modal interactions. Thus, these neurons should also be classified as multisensory. Our results suggest that a surprisingly high proportion of sensory neurons in the basal ganglia are multisensory, and demonstrate that an analysis without a consideration of multisensory cross-modal interactions may strongly underrepresent the number of multisensory units. We conclude that a majority of the sensory neurons in the CN and SN process multisensory information and only a minority of these units are clearly unimodal.     

The Crossmodal Congruency Task as a Means to Obtain an Objective Behavioral Measure in the Rubber Hand Illusion Paradigm

The rubber hand illusion (RHI) is a popular experimental paradigm. Participants view touch on an artificial rubber hand while the participants'' own hidden hand is touched. If the viewed and felt touches are given at the same time then this is sufficient to induce the compelling experience that the rubber hand is one''s own hand. The RHI can be used to investigate exactly how the brain constructs distinct body representations for one''s own body. Such representations are crucial for successful interactions with the external world. To obtain a subjective measure of the RHI, researchers typically ask participants to rate statements such as "I felt as if the rubber hand were my hand". Here we demonstrate how the crossmodal congruency task can be used to obtain an objective behavioral measure within this paradigm.The variant of the crossmodal congruency task we employ involves the presentation of tactile targets and visual distractors. Targets and distractors are spatially congruent (i.e. same finger) on some trials and incongruent (i.e. different finger) on others. The difference in performance between incongruent and congruent trials - the crossmodal congruency effect (CCE) - indexes multisensory interactions. Importantly, the CCE is modulated both by viewing a hand as well as the synchrony of viewed and felt touch which are both crucial factors for the RHI.The use of the crossmodal congruency task within the RHI paradigm has several advantages. It is a simple behavioral measure which can be repeated many times and which can be obtained during the illusion while participants view the artificial hand. Furthermore, this measure is not susceptible to observer and experimenter biases. The combination of the RHI paradigm with the crossmodal congruency task allows in particular for the investigation of multisensory processes which are critical for modulations of body representations as in the RHI.     

Multisensory contributions to the 3-D representation of visuotactile peripersonal space in humans: evidence from the crossmodal congruency task.

In order to determine precisely the location of a tactile stimulus presented to the hand it is necessary to know not only which part of the body has been stimulated, but also where that part of the body lies in space. This involves the multisensory integration of visual, tactile, proprioceptive, and even auditory cues regarding limb position. In recent years, researchers have become increasingly interested in the question of how these various sensory cues are weighted and integrated in order to enable people to localize tactile stimuli, as well as to give rise to the 'felt' position of our limbs, and ultimately the multisensory representation of 3-D peripersonal space. We highlight recent research on this topic using the crossmodal congruency task, in which participants make speeded elevation discrimination responses to vibrotactile targets presented to the thumb or index finger, while simultaneously trying to ignore irrelevant visual distractors presented from either the same (i.e., congruent) or a different (i.e., incongruent) elevation. Crossmodal congruency effects (calculated as performance on incongruent-congruent trials) are greatest when visual and vibrotactile stimuli are presented from the same azimuthal location, thus providing an index of common position across different sensory modalities. The crossmodal congruency task has been used to investigate a number of questions related to the representation of space in both normal participants and brain-damaged patients. In this review, we detail the major findings from this research, and highlight areas of convergence with other cognitive neuroscience disciplines.     

Multimodal sensory integration in weakly electric fish: a behavioral account.

The ability to integrate multisensory information is a fundamental characteristic of the brain serving to enhance the detection and identification of external stimuli. Weakly electric fish employ multiple senses in their interactions with one another and with their inanimate environment (electric, visual, acoustic, mechanical, chemical, thermal, and hydrostatic pressure) and also generate signals using some of the same stimulus energies (electric, acoustic, visual, mechanical). A brief overview provides background on the sensory and motor channels available to the fish followed by an examination of how weakly electric fish 'benefit' from integrating various stimulus modalities that assist in prey detection, schooling, foraging, courtship, and object location. Depending on environmental conditions, multiple sensory inputs can act synergistically and improve the task at hand, can be redundant or contradictory, and can substitute for one another. Over time, in repeated encounters with familiar surrounds, loss of one modality can be compensated for through learning. Studies of neuronal substrates and an understanding of the computational algorithms that underlie multisensory integration ought to expose the physiological corollaries to widely published concepts such as internal representation, sensory expectation, sensory generalization, and sensory transfer.     

Multisensory integration in cortex: shedding light on prickly issues

Interactions between different sensory modalities can be observed in unimodal areas of the cortex, as revealed by recent neuroimaging studies. A new report by Macaluso and colleagues ( [this issue of Neuron]) shows that crossmodal effects of tactile stimulation in visual cortex critically depend on the spatial congruence of multisensory inputs. This work is discussed in relation to neural and computational models of multisensory integration.