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.     

自传记忆的加工机制研究进展

自传记忆是关于个人生活经验的记忆,它有悖于Ehbinghaus的记忆研究传统。在国外．90年代以来自传记忆研究已成为继内隐记忆研究后．记忆领域的又一研究热点。自传记忆加工机制的研究是认知心理学对自传记忆研究的核心领域。本文主要评析了自传记忆的知识表征．自传记忆提取机制的研究进展。目前已有的研究结论是：（1）自传记忆是以个人生活片段知识、一般事件知识和具体事件知识三种方式表征的;（2）自传记忆的提取方式主要通过生成提取和直接提取方式来实现。     

记忆提取研究的新进展

该文从3个方面回顾了记忆提取研究领域内的最新进展:(1)记忆编码和提取之间的关系,主要针对提取过程的自动性和控制性及相应的神经机制进行了讨论;(2)基于记忆提取的抑制机制,主要涉及指向性遗忘、提取-练习范式的研究及负启动范式在记忆提取研究中的应用;(3)工作记忆能力与记忆提取之间的关系,主要集中于工作记忆能力与控制性记忆提取及记忆提取中的抑制机制之间的关系。     

舌尖效应产生和解决的词汇提取年老化机制：两阶段范式研究

舌尖效应年老化机制受语言特异性因素的影响。本研究把Stroop效应作为协变量,在统计分析控制个体抑制能力的基础上,采用两阶段范式考察舌尖效应产生和解决过程中词汇提取的年老化机制。结果发现：（1）老年人的舌尖效应产生率和语音提取缺陷均显著高于青年人,而语义提取缺陷的年龄差异不显著;（2）老年人的舌尖效应解决率和语音促进效应量均显著低于青年人;（3）语义启动影响老年人舌尖效应解决时的语言促进效应,而对青年人没有影响。上述结果表明,舌尖效应产生和解决的词汇提取年老化与语音提取衰退有关,与语义提取衰退无关,支持语言特异性衰退的观点。     

Ontogeny of early event memory: I. Forgetting and retrieval by 2- and 3-month-olds

In 2 experiments, 2-month-olds, trained in the mobile conjugate reinforcement paradigm for two daily sessions, showed retrieval deficits relative to 3-month-olds. In Experiment 1, tests of simple forgetting administered to 2-month-olds after retention intervals of 1, 3, 6, and 9 days (a period over which 3-month-olds remember the contingency) indicated that their forgetting was complete after delays greater than 1 day. In Experiment 2, reactivation treatments administered to 2- and 3-month-olds alleviated forgetting after a retention interval of 28, but not 35, days in the 3-month-old group only. Previously, alleviated forgetting by a reactivation treatment had been demonstrated in 2-month-olds after a delay of 18 days. In both of the present experiments, performance of the two age groups did not differ during the immediate retention test at the end of training. These results suggest that neither the age of the infant nor the age of the memory determines memory retrieval after long delays; instead, it appears to be determined by the length of time that a memory has been inaccessible (i.e., forgotten). We propose that factors which delay simple forgetting will correspondingly increase the length of the interval over which a retrieval cue can still be effective in a reactivation paradigm, irrespective of the age of the infant or the age of the memory.     

The Influence of Episodic and Thematic Frames on Policy and Group Attitudes: Mediational Analysis

An experiment examined how episodic and thematic political message frames affect attitudes toward older adults and Social Security. When exposed to messages about abolishing Social Security, participants exposed to episodic frames were significantly more likely to endorse message‐consistent attitudes than participants exposed to a thematic frame. In mediation analyses, an episodic frame featuring a counterstereotypical exemplar increased endorsement of individual responsibility for retirement planning, which then led to more negative attitudes toward Social Security. These effects did not occur with a stereotypical exemplar in an episodic frame. The same mediated pathway influenced attitudes toward older adults in a more complex manner. Results provide support for individual responsibility attributions as a mediating mechanism underlying the effects of certain episodic frames.     

Mood-dependent retrieval in visual long-term memory: dissociable effects on retrieval probability and mnemonic precision

Although memories are more retrievable if observers’ emotional states are consistent between encoding and retrieval, it is unclear whether the consistency of emotional states increases the likelihood of successful memory retrieval, the precision of retrieved memories, or both. The present study tested visual long-term memory for everyday objects while consistent or inconsistent emotional contexts between encoding and retrieval were induced using background grey-scale images from the International Affective Picture System (IAPS). In the study phase, participants remembered colours of sequentially presented objects in a negative (Experiment 1a) or positive (Experiment 2a) context. In the test phase, participants estimated the colours of previously studied objects in either negative versus neutral (Experiment 1a) or positive versus neutral (Experiment 2a) contexts. Note, IAPS images in the test phase were always visually different from those initially paired with the studied objects. We found that reinstating negative context and positive context at retrieval resulted in better mnemonic precision and a higher probability of successful retrieval, respectively. Critically, these effects could not be attributed to a negative or positive context at retrieval alone (Experiments 1b and 2b). Together, these findings demonstrated dissociable effects of emotion on the quantitative and qualitative aspects of visual long-term memory retrieval.     

Why do older adults have difficulty with semantic fluency?

Aging involves many cognitive declines, particularly in fluid intelligence, with relative maintenance of crystallized intelligence. This paradox is evident in the language domain: lexical retrieval becomes slower and less accurate, despite well preserved vocabularies. Verbal fluency assesses both crystallized and fluid aspects of language. Semantic fluency hypothetically reflects semantic knowledge, while letter fluency putatively reflects executive functioning, which would predict a greater impact of aging on the latter. However, the opposite is typically observed.

To investigate factors contributing to such asymmetries, we examined verbal fluency in 86 adults (30-89 years). Multiple regression analyses indicated that semantic fluency depends largely on lexical retrieval speed, as well as visualization strategies to support controlled retrieval, skills which may disproportionately decline with age. By contrast, letter fluency relies heavily on vocabulary knowledge, providing some protection against age-related declines. These findings contribute to our understanding of the mechanisms of typical age-related declines in word retrieval.