记忆过程中海马CA1区神经元的集群放电特征

观察空间工作记忆过程中海马CA1区神经元群的放电特征。应用多通道神经元集群放电记录技术, 同步观察和记录清醒大鼠在执行延迟选择任务时的行为轨迹以及海马CA1区神经元的放电活动。发现：海马CA1区位置细胞的位置野是在学习过程中逐渐形成并可消退; 部分位置细胞的放电对未来目标定向性行为具有预测作用; 在空间工作记忆过程中, 神经元放电之间的相关性加强, 神经元之间以及神经元与局部场电位之间存在相位编码方式。结果提示海马CA1区神经元参与对空间信息的初级编码和加工, 并为未来行为决策提供有效信息, 而且海马对信息的加工是通过局部神经网络进行, 时间编码可能是海马信息加工的重要方式之一。     

情绪记忆权衡效应:对复杂情绪刺激的记忆

情绪记忆研究最近一致发现了情绪记忆权衡效应,即人们对情绪事件的中心或核心特征的记忆增强,而对情绪事件的周围或背景特征的记忆受损.该效应证明情绪记忆具有选择性,情绪唤醒可以诱发出多种记忆选择性效应,并具有相当强的普遍性和稳定性,同时受较多主、客观因素的影响.相关理论逐步深入地阐述了该效应发生的可能机制,该效应在注意分配、编码以及编码后加工上的行为证据不断积累,但相关神经机制研究十分缺乏.未来研究应重视该效应的神经与遗传机制以及探讨面孔情绪诱发的记忆权衡效应等.     

触觉刺激对触觉注意启动作用的研究

目的：探讨触觉刺激对触觉注意的影响,以揭示选择性注意的机制。方法：利用在体电生理记录技术,记录了288个丘脑腹侧基底核（ventrobasal nuleus of thalamus,VB）神经元放电活动,并着重考察了不同强度触觉刺激对丘脑神经元细胞自发放电活动的影响。结果发现：触觉刺激对大部分的触觉神经元的自发放电活动均有抑制性影响。提示触觉刺激降低背景噪声可能是触发选择性触觉注意的神经机制。     

从ERP研究看前瞻记忆的神经基础和认知加工机制

关于前瞻记忆的ERP研究主要关注两个方面：神经基础和认知加工机制。神经基础方面的研究发现：前瞻记忆诱发了两种特异性的ERP成分—— N300和前瞻性正波; 前瞻记忆与回溯性记忆的神经基础有相似又有不同; 老年人的前瞻记忆可能存在一种不同于年轻人的神经机制。认知加工机制方面的研究主要为前瞻记忆的预备注意加工和记忆加工理论提供了ERP方面的证据支持。     

学习和记忆的神经生物学研究的若干进展

近年来,学习和记忆的神经机制研究有了很大的发展,在分子水平和细胞水平上都取得了好成绩,开辟了新的研究途径。学习记忆的神经机制研究是神经生理和生理心理的新兴研究领域。这一研究领域还有神经化学、神经解剖、神经药理、动物学、临床神经学乃至信息论和控制论等多种学科的参加。一些新兴学科,如神经科学、神经生物学、     

文字与面孔识别的半球偏侧化互补模式的竞争性发展机制

成人的大脑左侧VWFA对正字法信息更敏感,而右侧FFA优先处理面孔信息。然而,这种偏侧化互补模式的发展机制还亟待阐明。神经元再利用假设认为,在文字阅读学习过程中,文字识别会与面孔表征在左侧FG竞争神经加工资源,导致文字识别出现VWFA的左侧化,并推动了面孔识别FFA的右侧化。分布式半球组织的观点提出了神经计算加工三原则,试图系统阐释文字与面孔偏侧化竞争性发展的多层次双向动态加工机制。近期,FG的结构分区与功能特征研究取得了一些新成果,并据此构建了一个文字与面孔识别的多维度计算加工模型。因此,有必要基于神经元再利用假设和分布式半球组织的观点,并结合FG的结构与功能特征和近期研究证据,以系统探讨文字与面孔识别的半球偏侧化互补模式竞争性发展的认知神经加工机制。未来研究应进一步探究文字与面孔竞争加工的皮层空间位置和功能神经组织学基础、汉字与面孔竞争的加工机制、面孔识别的右侧化发展机制以及数字和音符阅读学习导致大脑可塑性改变的机制。     

网格对工作记忆中视觉客体空间位置编码的影响

为探究网格在工作记忆中对视觉客体位置编码的影响,本研究采用n-back范式,通过客体位置的确定性和网格出现的不同认知加工阶段,探索了网格线在空间工作记忆视觉客体位置记忆中的作用机制.实验1的结果表明,被试将依据客体的位置确定性强弱来选择类别编码或坐标编码.实验2的结果显示,网格在识记阶段可能有利于位置记忆,而在提取阶段可能有干扰作用.     

工作记忆与情景记忆的相互作用

虽然Baddeley的工作记忆模型得到大量实验研究的支持,但是有关工作记忆和长时记忆之间的关系未能得到详细阐述。来自神经心理学的证据表明,工作记忆与情景长时记忆任务均诱发了前额区的激活,但同时发现前额区存在不同的功能分区,可能在工作记忆与情景记忆过程中具有独立的执行功能。工作记忆与情景记忆的相互作用是当前记忆研究关注的问题。已有研究发现,在情景记忆对工作记忆的作用过程中,时间进程与头皮分布均显示了年龄效应与材料加工特点。而工作记忆对情景记忆的作用中,则发现工作记忆早期加工可能对情景记忆的成功形成有更大促进作用。今后的研究应在理论模型支持下,利用多种技术手段探讨两种记忆相互作用的神经加工机制     

自主控制眼跳：实验范式、神经机制和应用

自主控制眼跳是眼跳类型之一。自主控制眼跳实验范式为研究各种脑损伤,神经疾病和精神失调提供了一种新的研究手段,为研究眼跳的神经机制以及反应抑制、空间工作记忆等高级认知功能提供了重要的方法。文章介绍了自主控制眼跳的两种实验范式：反向眼跳和记忆导向眼跳,阐述了自主控制眼跳的神经机制及其实验范式的应用,指出自主控制眼跳实验范式为评定精神分裂症等脑功能失调病人的神经功能状态提供了重要的信息,为研究各种脑功能失调和精神疾病提供了重要的研究方法。今后的研究趋势是眼跳研究与神经成像技术和临床观察相结合     

不同注意形式调节听感觉门控的神经机制

前脉冲抑制(prepulse inhibition, PPI)是听感觉门控的测量模型, 反映了听觉系统的早期信息选择功能。尽管PPI的主要神经环路位于脑干, 研究发现PPI可以被注意自上而下调节。然而, 已有研究并未区分不同注意(特征注意和空间注意)对PPI的特异性调节, 并且神经机制方面的研究集中于听皮层区域, 仍缺乏对皮层下机制的探讨。在以往研究的成果基础之上, 借助听觉信息加工的双通路模型, 采用行为测量、脑电和脑成像技术, 揭示特征和空间两种注意调节PPI的神经活动在听觉系统中的层次性神经表达。包括1)建立特征注意和空间注意调节PPI的统一行为模型, 考察两种注意调节PPI的时间动态性异同; 2)两种注意调节PPI的脑干分离机制, 即前脉冲刺激包络和精细结构成分加工在注意调节PPI中的作用差异; 3)两种注意调节PPI的关键脑区和脑网络差异。     

Pattern separation, pattern completion, and new neuronal codes within a continuous CA3 map

The hippocampal CA3 subregion is critical for rapidly encoding new memories, which suggests that neuronal computations are implemented in its circuitry that cannot be performed elsewhere in the hippocampus or in the neocortex. Recording studies show that CA3 cells are bound to a large degree to a spatial coordinate system, while CA1 cells can become more independent of a map-based mechanism and allow for a larger degree of arbitrary associations, also in the temporal domain. The mapping of CA3 onto a spatial coordinate system intuitively points to its role in spatial navigation but does not directly suggest how such a mechanism may support memory processing. Although bound to spatial coordinates, the CA3 network can rapidly alter its firing rate in response to novel sensory inputs and is thus not as strictly tied to spatial mapping as grid cells in the medial entorhinal cortex. Such rate coding within an otherwise stable spatial map can immediately incorporate new sensory inputs into the two-dimensional matrix of CA3, where they can be integrated with already stored information about each place. CA3 cell ensembles may thus support the fast acquisition of detailed memories by providing a locally continuous, but globally orthogonal representation, which can rapidly provide a new neuronal index when information is encountered for the first time. This information can be interpreted in CA1 and other downstream cortical areas in the context of less spatially restricted information.     

Modularity of object and place memory in children

The present study investigated modularity of object and place memory in children with the reaction time/accuracy paradigm. The memory task was presented in two spatial arrays, a frame with landmarks and a grid. Modularity was tested using perceptual size judgment (what-interference) and movement direction judgment (where-interference). Latencies of object memory were increased by same-system what-interference in all age groups indicating limited capacity of an object memory system. With respect to accuracy of object and place memory, only young children's performance was susceptible to same-system interference of perceptual judgment.     

The effects of spatial representation on memory for verbal navigation instructions

Three experiments investigated effects of mental spatial representation on memory for verbal navigation instructions. The navigation instructions referred to a grid of stacked matrices displayed on a computer screen or on paper, with or without depth cues, and presented as two-dimensional diagrams or a three-dimensional physical model. Experimental instructions either did or did not promote a three-dimensional mental representation of the space. Subjects heard navigation instructions, immediately repeated them, and then followed them manually on the grid. In all display and experimental instruction conditions, memory for the navigation instructions was reduced when the task required mentally representing a three-dimensional space, with movements across multiple matrices, as compared with a two-dimensional space, with movements within a single matrix, even though the words in the navigation instructions were identical in all cases. The findings demonstrate that the mental representation of the space influences immediate verbatim memory for navigation instructions.     

Arc length coding by interference of theta frequency oscillations may underlie context-dependent hippocampal unit data and episodic memory function

Many memory models focus on encoding of sequences by excitatory recurrent synapses in region CA3 of the hippocampus. However, data and modeling suggest an alternate mechanism for encoding of sequences in which interference between theta frequency oscillations encodes the position within a sequence based on spatial arc length or time. Arc length can be coded by an oscillatory interference model that accounts for many features of the context-dependent firing properties of hippocampal neurons observed during performance of spatial memory tasks. In continuous spatial alternation, many neurons fire selectively depending on the direction of prior or future response (left or right). In contrast, in delayed non-match to position, most neurons fire selectively for task phase (sample vs. choice), with less selectivity for left versus right. These seemingly disparate results are effectively simulated by the same model, based on mechanisms similar to a model of grid cell firing in entorhinal cortex. The model also simulates forward shifting of firing over trials. Adding effects of persistent firing with reset at reward locations addresses changes in context-dependent firing with different task designs. Arc length coding could contribute to episodic encoding of trajectories as sequences of states and actions.     

Spatial frameworks in imagined navigation

The spatial framework model proposes that people use the extensions of their body axes as a reference frame for encoding spatial layouts in memory, and that the physical and functional properties of our bodies and the world determine the accessibility of egocentric locations from memory representations. The present experiment provides evidence that spatial framework results can be obtained even with perceptual scenes that contain no objects to be held in memory. Using a paradigm in which participants interpreted direction and distance information to follow a mental path within a checkerboard grid, the present study shows that spatial framework results are obtained when reasoning occurs from a perspective that is misaligned with respect to the physical reference frame of the participant. The theoretical implications of these results are discussed.     

Memory for two types of spatial location: effects of instructions, age, and format

Three experiments, with old persons (59-80 years) and college students (17-30 years) in Experiments 1 and 2 and with college students (17-24 years) in Experiment 3, investigated the differences between two types of spatial location memory: memory for the location of individual items in an array and memory for occupied, as opposed to unoccupied, locations in an array. Young persons performed better than old persons on both measures of location memory. However, an effect of instructions (intentional vs. incidental for spatial location) was consistently obtained for memory for occupied, as opposed to unoccupied, locations, whereas no effect of instructions was obtained for memory for individual item locations. In addition, item location memory was superior for objects as opposed to matched words (Experiment 2), whereas occupied location memory was not affected by presentation format (Experiments 2 and 3). These differences indicate that spatial memory is a complex process whose properties are affected by variations in stimulus characteristics and task demands. It was concluded that the distinction of Hasher and Zacks (1979) between automatic and effortful processes is not adequate for understanding spatial memory. A recognition of the complex nature of spatial processing suggests a resolution of discrepancies in the literature based upon differences in stimulus characteristics, task demands, and the effectiveness of task-appropriate mnemonic strategies.     

Spatial memory in the grey mouse lemur (Microcebus murinus)

Wild animals face the challenge of locating feeding sites distributed across broad spatial and temporal scales. Spatial memory allows animals to find a goal, such as a productive feeding patch, even when there are no goal-specific sensory cues available. Because there is little experimental information on learning and memory capabilities in free-ranging primates, the aim of this study was to test whether grey mouse lemurs (Microcebus murinus), as short-term dietary specialists, rely on spatial memory in relocating productive feeding sites. In addition, we asked what kind of spatial representation might underlie their orientation in their natural environment. Using an experimental approach, we set eight radio-collared grey mouse lemurs a memory task by confronting them with two different spatial patterns of baited and non-baited artificial feeding stations under exclusion of sensory cues. Positional data were recorded by focal animal observations within a grid system of small foot trails. A change in the baiting pattern revealed that grey mouse lemurs primarily used spatial cues to relocate baited feeding stations and that they were able to rapidly learn a new spatial arrangement. Spatially concentrated, non-random movements revealed preliminary evidence for a route-based restriction in mouse lemur space; during a subsequent release experiment, however, we found high travel efficiency in directed movements. We therefore propose that mouse lemur spatial memory is based on some kind of mental representation that is more detailed than a route-based network map. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of verbal and nonverbal interference on spatial and object visual working memory

We tested the hypothesis that a verbal coding mechanism is necessarily engaged by object, but not spatial, visual working memory tasks. We employed a dual-task procedure that paired n-back working memory tasks with domain-specific distractor trials inserted into each interstimulus interval of the n-back tasks. In two experiments, object n-back performance demonstrated greater sensitivity to verbal distraction, whereas spatial n-back performance demonstrated greater sensitivity to motion distraction. Visual object and spatial working memory may differ fundamentally in that the mnemonic representation of featural characteristics of objects incorporates a verbal (perhaps semantic) code, whereas the mnemonic representation of the location of objects does not. Thus, the processes supporting working memory for these two types of information may differ in more ways than those dictated by the "what/where" organization of the visual system, a fact more easily reconciled with a component process than a memory systems account of working memory function.     

Investigating neural representations: the tale of place cells

While neuroscientists often characterize brain activity as representational, many philosophers have construed these accounts as just theorists’ glosses on the mechanism. Moreover, philosophical discussions commonly focus on finished accounts of explanation, not research in progress. I adopt a different perspective, considering how characterizations of neural activity as representational contributes to the development of mechanistic accounts, guiding the investigations neuroscientists pursue as they work from an initial proposal to a more detailed understanding of a mechanism. I develop one illustrative example involving research on the information-processing mechanisms mammals employ in navigating their environments. This research was galvanized by the discovery in the 1970s of place cells in the hippocampus. This discovery prompted research in what the activity of these cells represents and how place representations figure in navigation. It also led to the discovery of a host of other types of neurons—grid cells, head-direction cells, boundary cells—that carry other types of spatial information and interact with place cells in the mechanism underlying spatial navigation. As I will try to make clear, the research is explicitly devoted to identifying representations and determining how they are constructed and used in an information processing mechanism. Construals of neural activity as representations are not mere glosses but are characterizations to which neuroscientists are committed in the development of their explanatory accounts.