A model of episodic memory: Mental time travel along encoded trajectories using grid cells

The definition of episodic memory includes the concept of mental time travel: the ability to re-experience a previously experienced trajectory through continuous dimensions of space and time, and to recall specific events or stimuli along this trajectory. Lesions of the hippocampus and entorhinal cortex impair human episodic memory function and impair rat performance in tasks that could be solved by retrieval of trajectories. Recent physiological data suggests a novel model for encoding and retrieval of trajectories, and for associating specific stimuli with specific positions along the trajectory. During encoding in the model, external input drives the activity of head direction cells. Entorhinal grid cells integrate the head direction input to update an internal representation of location, and drive hippocampal place cells. Trajectories are encoded by Hebbian modification of excitatory synaptic connections between hippocampal place cells and head direction cells driven by external action. Associations are also formed between hippocampal cells and sensory stimuli. During retrieval, a sensory input cue activates hippocampal cells that drive head direction activity via previously modified synapses. Persistent spiking of head direction cells maintains the direction and speed of the action, updating the activity of entorhinal grid cells that thereby further update place cell activity. Additional cells, termed arc length cells, provide coding of trajectory segments based on the one-dimensional arc length from the context of prior actions or states, overcoming ambiguity where the overlap of trajectory segments causes multiple head directions to be associated with one place. These mechanisms allow retrieval of complex, self-crossing trajectories as continuous curves through space and time.     

Environmental enrichment improves behavioral performance and auditory spatial representation of primary auditory cortical neurons in rat

Environmental enrichment (EE) has an important role in brain plasticity. Early research has shown that EE increases the response strength of neurons in the auditory cortex, but it remains unknown whether EE can influence the process of spatial localization in the auditory system. In this study, we raised rats in enriched and standard conditions from postnatal day 10 to day 56. By testing behavioral tasks via auditory cues, we have shown that EE improved the number of correct scores, but decreased the reaction time and azimuth deviation in behavioral performance of sound-azimuth discrimination. By in vivo extracellular recording, we have shown that EE enhanced the directional sensitivity of neurons in the primary auditory cortex. For example, EE rats had a smaller spatial receptive field, sharper frequency tuning curve and directional selective curve of auditory neurons compared with normal rats. Our findings indicate that early exposure to EE increases directional sensitivity. These results provide an insight into developmental plasticity in the auditory system.     

前额叶损害对个体一般智力、认知策略与自我监控能力影响的研究

本研究随机挑选了15名因外伤而造成的前额叶损害者和15名正常成人,采用韦氏成人智力量表和自编的图片分类作业,考查了他们在一般智力、认知策略与自我监控能力方面的差异,研究结果表明:(1)前额叶损害对个体的一般智力产生显著的影响,但是其智力仍然处于正常范围,可见智力的脑结构范围极为广泛,智力是一个具有多重性的系统。(2)前额叶损害者对无关刺激的抑制,对有效信息的提取与加工放大的心理活动受到极大影响,认知策略转换能力明显低于正常人,表现出了明显的认知不随意性,额叶可能更多的与个体的计划、认知策略选择、自我监控密切相关;(3)前额叶损害者对具体概念与抽象概念的自我监控能力表现出了不同的影响,对前者的损害显著大于后者,这表明个体依据具体概念进行的形象思维与凭借抽象概念进行的逻辑思维有不同的脑机制。     

Neuropsychological correlates of psychopathic traits in a non-incarcerated sample

The present study examined the association between neuropsychological behavioral performance and psychopathic personality traits, measured via the Psychopathic Personality Inventory (PPI), in a non-incarcerated sample. Specifically, performance involving general executive cognitive functioning (ECF) and response inhibition was investigated in regards to the two main psychopathy factors (affective-interpersonal and social deviance) of the PPI. A group of 95 student volunteers were administered the PPI and a variety of neuropsychological measures. Analyses revealed that total PPI scores were related to deficits in response inhibition but not general ECF. However, this relationship was qualified by the differential associations observed for the two PPI factors. The social deviance factor was associated with deficits in general ECF and response inhibition, whereas the affective-interpersonal facet was associated with enhanced general ECF performance but not response inhibition. The results suggest that cognitive functioning shows predicted associations with a self-report measure of psychopathy among non-incarcerated young adults, providing further evidence for psychopathy conceptualizations from a normal-range personality perspective.     

损毁大鼠双侧内嗅皮质对束缚应激反应的影响

采用大鼠急性束缚应激动物模型,用鹅羔氨酸损毁大鼠双侧内嗅皮质来建立内嗅皮质损伤模型,观察束缚应激1小时后下丘脑室旁核快反应基因c-Fos表达情况以及应激后血浆促肾上腺皮质激素含量的动态变化,并与对照组相比较,探讨内嗅皮质与束缚应激反应的关系。结果表明,损毁内嗅皮质,明显抑制了应激诱导的下丘脑室旁核c-Fos的表达和血浆促肾上腺皮质激素含量的上升。结果提示,内嗅皮质参与调节束缚应激反应时HPA轴功能。     

前扣带回功能的冲突监测理论

前扣带回在多种任务中的普遍激活使它成为当前认知控制研究的一个热点。一般认为它是执行控制网络的一个组成部分。针对它的功能尚缺乏一个综合的可以普遍接受的理论,前扣带回功能的冲突监测理论是一个影响十分广泛的理论。它认为前扣带回通过监测冲突提供控制信号,并将控制信号传达给具体负责控制的脑区。该文对冲突监测理论的观点及其实验支持做了简要的介绍,并对该理论存在的一些问题做了一些说明     

Memory deficits in young schizophrenics with normal general intellectual function

The aim of the present study was to examine different dimensions of memory functioning in young schizophrenics with normal general intellectual abilities. Thirty-three patients with schizophrenia and 33 healthy controls were included in the study. The results suggest that immediate short-term memory is intact, though there emerged a working memory deficit in the schizophrenia group. Deficient encoding of verbal material was observed in some, but not in other, testing conditions. There also seemed to be a retrieval deficit for verbal material in schizophrenia, though no storage deficit was indicated. Impaired memory for non-verbal material was also revealed. These results occurred in a context of intact executive functioning as measured by the Wisconsin Card Sorting Test. The results indicate that temporal and frontal structures, as well as their interconnections, may be compromised in schizophrenia.     

On the Correlation between Synchronized Oscillatory Activities and Consciousness

Recent experiments have shown that the amplitudes of cortical gamma band oscillatory activities that occur during anesthesia are often greater than amplitudes of similar activities that occur without anesthesia. This result is apparently at odds with the hypothesis that synchronized oscillatory activities constitute the neural correlate of consciousness. We argue that while synchronization and oscillatory patterning are necessary conditions for consciousness, they are not sufficient. Based on the results of a binocular rivalry study of Fries et al. (1997), we propose that the degrees of oscillatory strength and synchronization of neuronal activities determine the degree of awareness those activities produce. On the other hand, the overal firing rates of neurons in cortical sensory areas are not correlated with the degree of awareness the activities of those neurons produce. The results of the experiment of Fries et al. (1997) appear to conflict with the results of another binocular rivalry experiment, in which monkeys were trained to pull a lever in order to report which stimulus object was being perceived (Leopold & Logothetis, 1996). In the latter experiment, it was demonstrated that the firing rates of neurons in striate cortex did not change during perceptual alterations, while 90% of neurons in inferior and superior temporal cortices changed their firing rate when the perceived image changed. This result led to the conclusion that activities in temporal cortex are correlated with visual awareness, but those in striate cortex are not. We argue that activities in temporal cortex contribute little, if anything, to perceptual awareness, and that their primary function is computational. Thus the correlation between the firing rates of neurons in these areas and the responses of the monkeys is due to the recognition of a particular stimulus object, which in turn is due to the computations made there.     

压后皮质在空间导航的作用：认知地图与环境的映射

压后皮质在大脑中紧邻胼胝体压部,在空间导航中起到重要作用,但其具体功能尚未明确。目前存在空间更新、地标领航和参照系转换三种观点。本文通过梳理上述观点,认为压后皮质的功能为对认知地图与环境布局进行映射,这种映射功能有助于解释压后皮质在基于认知地图进行导航过程中的激活。未来研究应该关注对压后皮质的功能分区,也要关注压后皮质与不同脑区的连接,这将对进一步理解其功能有重要的意义。     

熟悉性能够支持联结记忆:一体化编码的作用

双加工理论认为熟悉性和回想是支持情景记忆的两种基本加工过程。一般认为熟悉性和回想都可以支持项目记忆,但只有回想能够支持联结记忆。然而,一体化假说提出,当刺激材料在学习阶段得到一体化编码,形成一个单一、整合的表征时,熟悉性也能够支持联结记忆。以往研究主要利用实验材料的固有特征,或使用定义法、交互表象法来实现对刺激材料的一体化编码,然后通过配对联结再认范式或来源记忆范式验证一体化假说。神经成像研究发现,位于内侧颞叶的嗅周皮层能够支持编码阶段一体化表征的形成和基于熟悉性对一体化表征的提取。未来研究应克服以往研究中存在的方法学缺陷、从功能神经网络的角度考察一体化加工的脑神经机制、并注重一体化编码策略在特殊人群中的应用价值。