多感觉整合的研究进展

环境中的不同信息通过不同的感觉模态如视觉、听觉、躯体觉的通路传递到动物的大脑皮层,已有研究表明这些传入的相关信息之间存在跨模态的相互整合,这种多感觉整合效应对于动物的感知、学习和记忆都具有非常重要的作用。本文主要对听觉-视觉、听觉-躯体感觉多感觉整合的研究进展进行综述,分析可能的整合机制并对未来的研究方向进行展望。     

自然感觉刺激对脑发育的影响

大脑的正常认知功能依赖于其复杂而精细的神经网络。来自环境的刺激,特别是自然的感觉刺激,对大脑皮层的多个脑区中神经元的生长、突触的形成,以及神经网络的建立至关重要。感觉输入不仅可以影响其对应感觉皮层的功能,而且可以通过跨模态机制影响其他感觉皮层的功能。然而,前人关于跨模态可塑性机制的研究主要集中在成年个体上,基本没有涉及发育早期的机制。为了研究自然感觉刺激对大脑皮层的调节,中科院神经所于翔研究组建立了对新生小鼠进行感觉刺激或剥夺的行为范式,包括通过胡须拔除对小鼠进行特异的触觉剥夺、黑暗环境饲养对小鼠进行特异的视觉剥夺,和丰富环境饲养对小鼠进行多模态的自然感觉刺激。研究发现,从出生起对小鼠进行触觉或视觉剥夺,不仅影响了对应大脑皮层的发育,而且还减缓了其他感觉皮层的发育,而通过丰富环境饲养增加感觉刺激可以促进多个感觉皮层的发育。该研究揭示了一种新型的发育早期感觉经验依赖的感觉皮层跨模态可塑性机制,并发现了催产素这种由下丘脑分泌的神经肽是介导该跨模态可塑性的关键分子。催产素由于其与情绪和社交行为的相关性,已成为孤独症治疗的热点分子之一。该研究提示催产素在发育更早期就对感觉皮层的神经环路形成有重要的促进作用。鉴于孤独症患儿经常伴随有感觉输入的异常,该发现对进一步解析孤独症的致病机制有重要的借鉴意义。     

电刺激家兔大脑皮层感觉区对丘脑束旁核痛敏单位放电活动的影响

本工作目的在于探讨大脑皮层与丘脑束旁核痛觉信息活动之间的关系。用玻璃微电极记录了60只清醒麻痹状态下家兔束旁核痛敏单位的诱发放电活动。按其对外周伤害性刺激的反应型式而分成两类,分别称为痛兴奋单位和痛抑制单位。观察到在电刺激大脑皮层感觉区时,多数痛兴奋单位呈抑制性改变,并且有时施予皮层的每一单个刺激均能立即遏止一阵痛放电,少数呈易化性改变;痛抑制单位则对伤害性刺激呈现抑制反应解除,而施予皮层的每一单个刺激均可使之先有一阵短暂的放电,然后出现抑制的现象。本组实验观察过程,完整的总例数共32个单位,包括25个痛兴奋单位(18个呈抑制改变,7个呈易化改变)和7个痛抑制单位(全部呈易化改变)。实验结果表明,大脑皮层感觉区传出系统对机体的痛觉信息传递活动具有下行调制作用。由于皮层刺激对束旁核放电的影响是逐渐发展起耒的,因此考虑在上述过程中可能有体液因素的参与。     

清醒猕猴前额叶和运动前区神经元多感觉活动的观察

本实验对清醒猕猴前额叶和运动前区神经元多感觉活动进行了观察。在动物进行课题操作中记录单神经元放电。课题中包括视、痛、热三种感觉刺激。在所记录的338个课题相关神经元中,对一种感觉刺激呈现反应者156个,对两种刺激反应者94个,对三种刺激都反应者88个。为了观察不具有信号意义的感觉刺激的作用,在课题操作的间歇期给动物以痛、热、视、听、触等自然刺激。在测试的176个课题相关神经元中,仅72个神经元对自然刺激呈现反应。其中对一种感觉刺激反应者45个,对两种刺激反应者19个,三种者5个,四种者3个。多数神经元对痛(N=33),视(N=30)和热(N=29)刺激呈现反应,仅有3个神经元对声音,9个神经元对触刺激出现反应。绝大多数神经元位于弓状沟上支内侧的颗粒和无颗粒皮层内。本实验表明,痛、热、触、视、听觉等投射到额叶皮层的相同部位,不同程度地会聚到同一神经元上。有信号意义的刺激与没有信号意义的刺激相比,前者可激活更多的神经元。     

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．     

爬行动物皮层的细胞构筑与纤维联系

大脑进化到爬行动物阶段,端脑开始占据大脑的绝大部分,成为处理信息的高级中枢.皮层是爬行动物端脑的一个主要组成部分,与哺乳动物的大脑皮层相似,它位于端脑的表面,覆盖整个脑室下结构,参与各种信息的处理,嗅觉、视觉、听觉、学习和记忆都跟它相关.本文就爬行动物皮层的分区、细胞构筑、纤维联系等最近的研究进展进行介绍.     

自身运动感知中视觉-前庭整合的研究进展

日常生活中,机体利用自己的感官,以不同的感觉通路(视觉、听觉、味觉、嗅觉、触觉、前庭觉和本体觉等)获取环境中的信息以及自身相对于环境的信息,输入大脑进行加工处理,并作出反应。这些不同模态的感觉输入信息在大脑中存在跨模态(cross-modal,如视觉和听觉、听觉和嗅觉,甚至跨越三种或更多感觉模态信息)相互整合,从而对动物的感知、运动、学习记忆和决策等起着非常重要的作用。在过去的十几年里,多感觉整合研究领域吸引了一批学科交叉的科学研究人员,极大地推进了这一研究领域的发展。本文着重介绍自身运动感知过程中视觉和前庭信息整合机制的研究进展,分别从多感觉整合发生的脑区、神经元对多感觉信息的编码特性以及神经元活动与行为的关系三个方面进行综述,并对未来的研究方向进行展望。     

感觉神经元交互抑制调控秀丽线虫回避行为的发生

<正>感觉包括嗅觉、味觉等化学性感觉,以及视觉、听觉、触觉、温度觉和本体感觉等物理性感觉.感觉受体接受体内外刺激,并通过相应的电化学信号编码,将信息传导到中枢神经系统(如脑和脊髓).这些信息在中枢进行解码、加工和整合,进而引导相应的行为反馈以维持机体正常的生理活动和适应生存环境.此外,外周调节(peripheral modulation)对感觉和行为的形成也起着精细调节的作用.感觉受体神经元的受体表达量和亲和力、受体的磷酸化修饰、离子通道活性、突触活性和功能等,都可能受到外周调节     

离皮层纤维系统的下行调节作用与听觉可塑性

听觉离皮层纤维系统是指由听皮层直接投射到皮层下听觉核团和耳蜗的下行纤维,这些纤维较严格的遵守频率分布的原则,与上行传入纤维构成多重反馈环路。听皮层通过离皮层纤维系统高度聚焦的正反馈作用,易化与其生理特性相匹配的皮层下听觉神经元的电活动,同时通过广泛的侧枝抑制作用来抑制与其生理特性不相匹配的皮层下听觉神经元的电活动,从而调节和改善皮层下听觉信息的处理,参与中枢听觉系统的可塑性变化。离皮层纤维的下行调节作用还广泛存在于视觉和躯体感觉系统,它们可能具有类似的神经机制。     

应用基于内源信号的光学成像技术的视觉脑研究现状

基于脑内源信号的光学成像技术是近来国际上出现的一种脑功能成像方法。该技术既无毒,又具有较高的空间分辨率,因而被迅速应用于动物的视觉、听觉、体感皮层功能构筑的研究中。本文综述了这种光学脑功能成像在视觉脑研究方面所取得的重要进展,并分析了该方法与其他脑成像技术、微电极单细胞技术的关系。报道了国内自行研制第、套脑功能光学成像系统的研究工作,该系统已在猫初级视觉皮层不同深度获得了清晰的方位功能图,并已经和     

Neuronal representations of stimuli in the mouth: the primate insular taste cortex, orbitofrontal cortex and amygdala

The responses of 3687 neurons in the macaque primary taste cortex in the insula/frontal operculum, orbitofrontal cortex (OFC) and amygdala to oral sensory stimuli reveals principles of representation in these areas. Information about the taste, texture of what is in the mouth (viscosity, fat texture and grittiness, which reflect somatosensory inputs), temperature and capsaicin is represented in all three areas. In the primary taste cortex, taste and viscosity are more likely to activate different neurons, with more convergence onto single neurons particularly in the OFC and amygdala. The different responses of different OFC neurons to different combinations of these oral sensory stimuli potentially provides a basis for different behavioral responses. Consistently, the mean correlations between the representations of the different stimuli provided by the population of OFC neurons were lower (0.71) than for the insula (0.81) and amygdala (0.89). Further, the encoding was more sparse in the OFC (0.67) than in the insula (0.74) and amygdala (0.79). The insular neurons did not respond to olfactory and visual stimuli, with convergence occurring in the OFC and amygdala. Human psychophysics showed that the sensory spaces revealed by multidimensional scaling were similar to those provided by the neurons.     

宽周边视视网膜皮层映射的核磁共振研究

目的:人类视觉皮层的组织方式是视网膜皮层映射组织,先前研究已经证实视觉皮层在中心视采用这种组织方式,本文主要研究宽周边视的视觉皮层组织方式.方法:本文采用一种可以在核磁共振室中使用的光纤设备,设计了30度、40度、50度、60度的类圆环block刺激,使用1.5T的功能性核磁共振仪器,T1高分辨率图像分辨率为1*1*5.5mm,T2加权图像分辨率为4*4*5.5mm,TR反应时间为60,矩阵大小为64*64.核磁共振数据分析使用了SPM2和Brain voyager软件.结果:通过对试验者的数据处理分析,周边视的刺激的反应区域在枕叶上,主要分布在枕叶的前部,刺激反应区域随着偏心率的增大而沿着距状沟从距状沟的后部向前部移动.结论:周边视的视网膜皮层映射组织特性和中心视的特性非常相似.     

Information in the Neuronal Representation of Individual Stimuli in the Primate Temporal Visual Cortex

To analyze the information provided about individual visual stimuliin the responses of single neurons in the primate temporal lobevisual cortex, neuronal responses to a set of 65 visual stimuli wererecorded in macaques performing a visual fixation task and analyzedusing information theoretical measures. The population of neuronsanalyzed responded primarily to faces. The stimuli included 23 facesand 42 nonface images of real-world scenes, so that the function ofthis brain region could be analyzed when it was processing relativelynatural scenes.It was found that for the majority of the neurons significantamounts of information were reflected about which of several of the23 faces had been seen. Thus the representation was not local, forin a local representation almost all the information available canbe obtained when the single stimulus to which the neuron respondsbest is shown. It is shown that the information available about anyone stimulus depended on how different (for example, how manystandard deviations) the response to that stimulus was from theaverage response to all stimuli. This was the case for responsesbelow the average response as well as above.It is shown that the fraction of information carried by the lowfiring rates of a cell was large—much larger than that carried bythe high firing rates. Part of the reason for this is that theprobability distribution of different firing rates is biased towardlow values (though with fewer very low values than would bepredicted by an exponential distribution). Another factor is thatthe variability of the response is large at intermediate and highfiring rates.Another finding is that at short sampling intervals (such as 20 ms)the neurons code information efficiently, by effectively acting asbinary variables and behaving less noisily than would be expectedof a Poisson process.     

Set-Related Activity in the Premotor Cortex of Rhesus Monkeys: Effect of Triggering Cues and Relatively Long Delay Intervals

“Set-related activity” has been defined as a significant alteration in neuronal discharge rate during an “instructed delay period,” a period when a previously instructed movement is being withheld. It has been argued that set-related activity in the primate premotor cortex, or at least a significant proportion of it, reflects motor preparation. In most previous investigations, however, in which visual stimuli have triggered the movement and simultaneously indicated its target, set-related activity might reflect either the anticipation of or attention to the trigger stimulus. The present report shows that set-related activity is robust and can be directionally selective when trigger stimuli do not indicate the target and when a trigger stimulus is absent. Another feature of previous studies has been the relatively brief intervals between the instruction and trigger stimuli (typically 3 sec or less). In the present study, we were able to observe the activity of a small number of cells during longer delay periods. Set-related activity persists, although it becomes less consistent, for as much as 7.5 sec after an instruction stimulus. These results support the hypothesis that set-related activity reflects the preparation for specific limb movements.     

Coding processes involved in the cortical representation of complex tactile stimuli

To understand how information is coded in the primary somatosensory cortex (S1) we need to decipher the relationship between neural activity and tactile stimuli. Such a relationship can be formally measured by mutual information. The present study was designed to determine how S1 neuronal populations code for the multidimensional kinetic features (i.e. random, time-varying patterns of force) of complex tactile stimuli, applied at different locations of the rat forepaw. More precisely, the stimulus localization and feature extraction were analyzed as two independent processes, using both rate coding and temporal coding strategies. To model the process of stimulus kinetic feature extraction, multidimensional stimuli were projected onto lower dimensional subspace and then clustered according to their similarity. Different combinations of stimuli clustering were applied to differentiate each stimulus identification process. Information analyses show that both processes are synergistic, this synergy is enhanced within the temporal coding framework. The stimulus localization process is faster than the stimulus feature extraction process. The latter provides more information quantity with rate coding strategy, whereas the localization process maximizes the mutual information within the temporal coding framework. Therefore, combining mutual information analysis with robust clustering of complex stimuli provides a framework to study neural coding mechanisms related to complex stimuli discrimination.     

Responses of Neurons of the Extrastriate Area 21b of the Cat Brain Cortex to Changes in Orientation of Moving Visual Stimuli

We studied the responses of neurons of the extrastriate cortical area 21b of the cat to changes in orientation of the movements of visual stimuli within the receptive field (RF) of the neuron under study. Our experiments demonstrated that 24 of 108 cells (22%) responded differentially to a certain extent to orientation of the movements of visual stimuli. As a whole, neurons of the area 21b did not demonstrate fine tuning on the optimum angle of orientation. In many cases, neuronal responses to different orientations of the movement of visual stimulus depended significantly on specific parameters of this stimulus (its shape, dimensions, and contrast). Some directionally sensitive neurons responded to a change in orientation of the movement of visual stimuli by modification of the index of directionality. We also studied spatial organization of the RF of neurons with the presentation of stationary visual stimuli. Comparison of the neuronal responses to a change in orientation of the movements of stimuli and to presentation of stationary stimuli showed that the correlation between the orientation sensitivity of the neuron under study and the stationary functional organization of its RF was insignificant. We hypothesize that inhibitory processes and subthreshold influences from a space surrounding the RF play a special role in the formation of the neuronal responses generated in the associative visual cortical regions to visual stimulation.     

Distributed representation of perceptual categories in the auditory cortex

Categorical perception is a process by which a continuous stimulus space is partitioned to represent discrete sensory events. Early experience has been shown to shape categorical perception and enlarge cortical representations of experienced stimuli in the sensory cortex. The present study examines the hypothesis that enlargement in cortical stimulus representations is a mechanism of categorical perception. Perceptual discrimination and identification behaviors were analyzed in model auditory cortices that incorporated sound exposure-induced plasticity effects. The model auditory cortex with over-representations of specific stimuli exhibited categorical perception behaviors for those specific stimuli. These results indicate that enlarged stimulus representations in the sensory cortex may be a mechanism for categorical perceptual learning.     

Encoding Stimulus Information by Spike Numbers and Mean Response Time in Primary Auditory Cortex

Neurons can transmit information about sensory stimuli via their firing rate, spike latency, or by the occurrence of complex spike patterns. Identifying which aspects of the neural responses actually encode sensory information remains a fundamental question in neuroscience. Here we compared various approaches for estimating the information transmitted by neurons in auditory cortex in two very different experimental paradigms, one measuring spatial tuning and the other responses to complex natural stimuli. We demonstrate that, in both cases, spike counts and mean response times jointly carry essentially all the available information about the stimuli. Thus, in auditory cortex, whereas spike counts carry only partial information about stimulus identity or location, the additional availability of relatively coarse temporal information is sufficient in order to extract essentially all the sensory information available in the spike discharge pattern, at least for the relatively short stimuli (< ∼ 100 ms) commonly used in auditory research.     

Genetic variation in the serotonin transporter modulates neural system-wide response to fearful faces

A distributed, serotonergically innervated neural system comprising extrastriate cortex, amygdala and ventral prefrontal cortex is critical for identification of socially relevant emotive stimuli. The extent to which a genetic variation of serotonin transporter gene 5-HTTLPR impacts functional connectivity between the amygdala and the other components of this neural system remains little examined. In our study, neural activity was measured using event-related functional magnetic resonance imaging in 29 right-handed, white Caucasian healthy subjects as they viewed mild or prototypical fearful and neutral facial expressions. 5-HTTLPR genotype was classified as homozygous for the short allele ( S/S ), homozygous for the long allele ( L/L ) or heterozygous ( S/L ). S/S showed greater activity than L/L within right fusiform gyrus (FG) to prototypically fearful faces. To these fearful faces, S/S more than other genotype subgroups showed significantly greater positive functional connectivity between right amygdala and FG and between right FG and right ventrolateral prefrontal cortex (VLPFC). There was a positive association between measure of psychoticism and degree of functional connectivity between right FG and right VLPFC in response to prototypically fearful faces. Our data are the first to show that genotypic variation in 5-HTTLPR modulates both the amplitude within and the functional connectivity between different components of the visual object-processing neural system to emotionally salient stimuli. These effects may underlie the vulnerability to mood and anxiety disorders potentially triggered by socially salient, emotional cues in individuals with the S allele of 5-HTTLPR.     

Emotion-perception interplay in the visual cortex: "the eyes follow the heart"

Emotive aspects of stimuli have been shown to modulate perceptual thresholds. Lately, studies using functional Magnetic Resonance Imaging (fMRI) showed that emotive aspects of visual stimuli activated not only canonical limbic regions, but also sensory areas in the cerebral cortex. However, it is still arguable to what extent such emotive, related activation in sensory areas of the cortex are affected by physical characteristic or attribute difference of stimuli. To manipulate valence of stimuli while keeping visual features largely unchanged, we took advantage of the Expressional Transfiguration (ET) of faces. In addition, to explore the sensitivity of high level visual regions, we compared repeated with unrepeated (i.e. different) stimuli presentations (fMR adaptation). Thus, the dynamics of brain responses was determined according to the relative signal reduction during repeated relative to different presentations (adaptation ratio). Our results showed, for the first time, that emotional valence produced significant differences in fMR adaptation, but not in overall levels of activation of lateral occipital complex (LOC). We then asked whether this emotion modulation on sensory cortex could be related to previous personal experience that attached negative attributes of stimuli. To clarify this, we investigated Posttraumatic Stress Disorder (PTSD) and non-PTSD veterans. PTSD is characterized by recurrent revival of trauma-related sensations. Such phenomena have been attributed to a disturbed processing of trauma-related stimuli, either at the perceptual level or at the cognitive level. We assumed that PTSD veterans would differ from non-PTSD veterans (who have similar combat experience) in their high order visual cortex responses to combat-related visual stimuli that are associated with their traumatic experience. An fMRI study measured the cerebral activation of subjects while viewing pictures with and without combat content, in repeated or different presentation conditions. The emotive effect on the visual cortex was found, again, only in the fMR-adaptation paradigm. Visual cortical regions showed significant differences between PTSD and non-PTSD veterans only in repeated presentations of trauma-related stimuli (i.e. combat). In these regions, PTSD veterans showed less decrease in signal with repeated presentations of the same combat-related stimuli. This finding points to the possibility that traumatic experience modulates brain activity at the level of sensory cortex itself.