<p>Emotion is known to influence multiple aspects of memory formation, which may include the initial encoding of the memory trace, its consolidation over time, and the efficacy of its retrieval. However, prior investigations have tended to treat emotional modulation of episodic memory as a unitary construct, thus conflating the contributions of these different stages to emotion-mediated memory enhancements. The present thesis aims to disentangle the component processes of emotional memory formation and retrieval through a series of studies using cognitive behavioral and functional magnetic resonance imaging (fMRI) methods. In the first 2 studies, neural activity was evaluated during the initial viewing of emotionally arousing and neutral scenes and, in the 3rd study, neural activity during this initial viewing period was compared to that during a recognition memory task. The findings are compatible with the proposal that two distinct networks support successful emotional memory formation: an amygdala-medial temporal lobe (MTL) network that modulates the consolidation of memories over time and a prefrontal-MTL network that translates emotion effects on controlled elaboration into superior memory encoding. The superlative quality of emotional memories is furthermore marked by heightened similarity between neural states at encoding and retrieval, suggesting another line of evidence through which emotion effects can be observed. Taken together, the results presented here highlight the heterogeneity of processes that confer mnemonic advantages to emotionally significant information.</p> / Dissertation

The main objective of this master thesis is to clarify the nested structure in time consciousness, depending on mental time travel and episodic memory. Time consciousness, mental time travel and episodic memory are connected, and function depending on each other. Mental time travel ability enables us to imagine personal future events. Episodic memory allows us to travel mentally into both past and future. Similarity between remembering the past and imagining the future indicates that episodic memory system contribute to future-directed personal mental time travel competence, and justifies the relation between episodic memory and mental time travel into both past and future. Episodic memory requires autonoetic consciousness, which can be applied to mental time travel competence, and mental time travel is a function of episodic memory. Distinguishing humans and non-humans is a method to understand the role of episodic memory and mental time travel in time consciousness. Episodic memory and mental time travel indicate to a higher-level time consciousness in humans, because mental time travel, episodic memory, autonoetic consciousness and recursive language are unique to humans, while non-humans show future-directed acts, possess episodic-like memory, and communicate with limited ways. Time consciousness is derived from the notion of autonoetic consciousness and it is a sort of temporal consciousness which enables us to be conscious of ourselves who travels in time and aware of ourselves along the temporal line. Non-humans have a rudimentary form of time consciousness, even they are deprived of autonoetic consciousness.

The current study explored the influence of priming vantage point at retrieval on the recall of younger and older adults, in addition to the effects of visualization ability on recall. Based on McIsaac and Eich’s (2002) findings of the effects on younger adults’ recall, it was hypothesized that recollections would be more likely to include certain features when retrieved through the field vantage point (FVP) than through the observer vantage point (OVP) and vice-versa. Additionally, it was expected that older adults would recall more detailed memories from the OVP than from the FVP. Finally, it was hypothesized that visualization ability would influence memory vividness and that it would be more influential in older adults than in younger adults. The experiment was conducted across two sessions. In Session 1, participants completed a visual imagery assessment, and memories were created in the laboratory with younger (n = 20; 18-21 years old) and older (n = 18; 63-88 years old) adults through the completion of two activities. In Session 2, participants recalled the activities from either the FVP or the OVP. Participants’ recollections were coded for various memory characteristics, which acted as dependent variables in analyses. A significant interaction effect (p = .003) between age and vantage point was found on the characteristic of psychological state, such that older adults referred to their psychological state in FVP memories more than in OVP memories (p = .002), while younger adults demonstrated no significant difference. Imagery ability significantly predicted several aspects of participants’ subjective recall experience. Overall, the results indicate that retrieval vantage point does not change the content of one’s recollections on most measures for either younger or older adults and that visual mental imagery ability predicts several aspects of one’s recall experience.

The purpose for the present study was to examine working memory for what, where, and when information in rhesus monkeys (Macaca mulatta) and adult humans using a computerized task. In Experiment 1, monkeys and humans completed three delayed matching-to-sample (DMTS) tasks: 1) identity DMTS, 2) spatial DMTS, and 3) temporal DMTS. In Experiments 2, the identity and spatial tasks were combined so that monkeys had to report both what and where information about an event. In Experiment 3, the identity, spatial, and temporal tasks were combined in order to examine what-where-when memory integration. In Experiment 4, monkeys and humans were presented with two sequential events, and a memory cue indicated which event they were required to report. The rhesus monkeys and human participants were able to report all three components of the events and there was some evidence suggesting that these components were integrated in memory for the rhesus monkeys.

Aging is typically associated with declining mental abilities, most prominent for some forms of memory. There are, however, large inter-individual differences within the older population. Some people experience rapid decline whereas others seem almost spared from any adverse effects of aging. This thesis examined the neural underpinnings of such individual differences by using longitudinal observations of episodic memory change across 15-20 years, combined with structural and functional magnetic resonance imaging of the brain. Study I found significant correlations between volume and activity of the hippocampus (HC), and memory change over a 6-year period. That is, individuals with decline in HC function also had declining memory. In contrast, Study II showed that successfully aged individuals, who maintained high memory scores over 15-20 years, had preserved HC function compared to age-matched elderly with average memory change. The successful agers had HC activity levels comparable to those of young individuals, as well as higher frontal activity. Study III revealed that individual differences in memory ability and brain activity of elderly reflect both differential age-related changes, and individual differences in memory ability that are present already in midlife, when age effects are minimal. Specifically, memory scores obtained 15-20 years earlier reliably predicted brain activity in memory-relevant regions such as the frontal cortex and HC. This observation challenges results from previous cross-sectional aging studies that did not consider individual differences in cognitive ability from youth. Collectively the three studies implicate HC and frontal cortex function behind heterogeneity in cognitive aging, both substantiating and qualifying previous results from cross-sectional studies. More generally, the findings highlight the importance of longitudinal estimates of cognitive change for fully understanding the mechanisms of neurocognitive aging. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.</p>

Atkinson and Shiffrin's (1968) dual-store model of memory includes a structural memory store along with control processes conceptualized as a rehearsal buffer. I present a variant of Atkinson and Shiffrin's buffer model within a global memory framework that accounts for findings previously thought to be difficult for it to explain. This model assumes a limited capacity buffer where information is stored about items, along with information about associations between items and between items and the context in which they are studied. The strength of association between items and context is limited by the number of items simultaneously occupying the buffer. New findings that directly test the buffer assumptions are presented, including serial position effects, and conditional and first recall probabilities in immediate and delayed free recall, in a continuous distractor paradigm, and in experiments using list length manipulations of single item and paired item study lists. Overall, the model's predictions are supported by the data from these experiments, suggesting that control processes, conceptualized as a rehearsal buffer, are a necessary component of memory models.

This thesis considers cognitive narrative a component of intelligence that specializes in generality. In exploring the ubiquitous external (mediated) and internal (cognitive) functions of narrative it provides two contributions to the literature: a uniquely cross-discipline survey of narratology that bridges humanities, social science, and computational fields; and a theory to generate cognitive personal narratives from ongoing perception. The implications of narrative cognition and cognitive narrative are discussed as well as the limitations of this introductory theory and the grounds for promising future work.

This paper describes two experiments, each of which investigated the impact of stress on human episodic memory. All participants watched narrated slide shows containing emotional and neutral information. Experiment 1 demonstrated that pre-learning exposure to a psychological stressor (the Trier Social Stress Test or "TSST"; Kirschbaum, Pirke &amp; Hellhammer, 1993) preserved or enhanced memory for emotional aspects of the slide show, but impaired memory for neutral aspects of the slide show. Moreover, stress exposure disrupted memory for information that was visually and thematically central to the slide show. Memory for peripheral information, on the other hand, was unaffected by stress. Experiment 2 replicated these results and extended them to a similar paradigm, where participants viewed separate emotional and neutral slide shows, and saliva was tested for the stress hormones cortisol and norepinephrine. Similar to the results of Experiment 1, stress disrupted memory for the neutral slide show, but enhanced memory for the emotional slide show. Salivary cortisol levels at retrieval were negatively correlated with memory for the neutral slide show. These results are consistent with theories invoking differential effects of stress on brain systems responsible for encoding and retrieving emotional memories (the amygdala) and non-emotional memories (e.g. the hippocampal formation, frontal cortex), and inconsistent with the view that memories formed under high levels of stress are qualitatively the same as those formed under ordinary emotional circumstances. These data, which are also consistent with results obtained in a number of studies using animals and humans, have implications for the traumatic memory debate and theories regarding human memory.

Repetition and the passage of time influence the consolidation of long-term episodic memories. The experiments presented here have explored the influence of repetition on recent and remote autobiographical memories both behaviorally with regard to qualitative and quantitative measures of content, and neuroanatomically, focusing on changes within the hippocampus and adjacent structures. The first experiment tested the prediction made by MTT that hippocampal memory traces expand and strengthen as a function of repeated memory retrievals. An fMRI paradigm was used to compare the effect of memory retrieval versus the mere passage of time on hippocampal activation. Participants retrieved remote autobiographical memories that had been previously retrieved either one month earlier, two days earlier, or multiple times during the preceding month. Behavioral analyses revealed that the number and consistency of memory details retrieved increased with multiple retrievals but not with the passage of time. Hippocampal activation did not change as a function of either multiple retrievals or the passage of time. The second behavioral investigation was a follow-up to the first experiment, examining the retrieval of those same memories one year later in order to determine whether the level of detail remained stable or whether the memories returned to their original state. Participants reported even more details than they had recalled at least one year earlier, including new details. This finding was consistent across both multiple and single retrieval conditions. These findings together with those of the first study suggest that both repetition and the passage of time are important factors that may result in an increase in recall. The third and final experiment explored the behavioral and neural influences of repeated reactivation of both recent and remote autobiographical memories. Participants were interviewed a total of five times throughout one month and retrieved 20 significant life event memories, from either within the past several months or more than five years ago. Additionally, two fMRI scan sessions were collected, which enabled a direct comparison of the same 20 memories before and after a series of repetitions. Activation increased with repetition in several brain regions including bilateral posterior cingulate and precuneus. Behaviorally, repetition resulted in increased accessibility as suggested by decreased reaction times between the initial and final retrieval sessions, and a general maintenance of the level of recall resulted with repetition.

The aim of the present doctoral thesis was to investigate the ability of patients with Alzheimer's disease (AD) to utilize cognitive support in order to improve episodic remembering. A review of previous research indicated that most studies have failed to find beneficial effects of encoding support on memory in AD patients. The ability to utilize cognitive support (i.e., motoric activities, semantic organization, and semantic knowledge) for episodic remembering was investigated in five studies (Bäckman &amp; Herlitz, 1990; Herlitz, Adolfsson, Bäckman, &amp; Nilsson, in press; Herlitz &amp; Bäckman, 1990; Herlitz &amp; Viitanen, in press; Karlsson et al., 1989). Patients with mild, moderate, or severe AD, and normal older adults participated in the studies. On the basis of the results from these studies and the review of the literature, it was concluded that (a) AD patients, irrespective of dementia severity, perform at a lower level than normal older adults in episodic memory tasks; (b) provided that support is supplied at retrieval, AD patients may be sensitive to manipulations at encoding; (c) the strength of the encoding manipulation determines the size of the memory improvement in AD patients; and (d) depending on dementia severity, the type of encoding support also determines the magnitude of memory improvement obtained. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1991, härtill 5 uppsatser.</p> / digitalisering@umu