Emerging evidence suggests that hippocampal memory processing is modulated by midbrain regions under conditions of reward, resulting in enhanced encoding of episodic information—long-term memory for events. Current theories further suggest that hippocampal subregions may have distinct roles in episodic memory formation, and may be differentially influenced by dopaminergic midbrain inputs. Using high-resolution functional magnetic resonance imaging (fMRI), the present study investigated hippocampal subregional function as well as activation in surrounding medial temporal lobe (MTL) cortex, midbrain, and nucleus accumbens during associative encoding and cued recall under varying conditions of reward. A high-value or low-value monetary cue preceded a pair of objects indicating potential reward for successful retrieval of the association. At test, participants performed cued recall followed by match (correct association) or mismatch (incorrect association) probe decisions and received feedback on their performance. Behaviorally, cued recall performance was superior for pairs preceded by high reward cues at encoding relative to pairs preceded by low reward cues. FMRI analysis revealed regions within hippocampus, parahippocampal cortex, nucleus accumbens, and midbrain showing subsequent memory effects (greater encoding activation for remembered, compared to forgotten associations) and reward effects (greater activation for high-value, compared to low-value associations) during stimulus encoding. Within several of these regions, individual differences in reward-related encoding activation were correlated with the degree of the behavioral reward effect (better memory for high-value compared to low-value object pairs). At retrieval, regions in midbrain and subiculum predicted successful associative recall, and regions within hippocampus, parahippocampal cortex, nucleus accumbens, and midbrain showed reward effects in the absence of explicit reward cues. Within several MTL regions, activation was greater for match than mismatch probes. These findings are consistent with theories suggesting that reward-based motivation influences memory formation through interactions between dopaminergic midbrain and hippocampus. / text

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Research conducted over the past two decades has contributed a wealth of new knowledge to the field's understanding of stress effects on memory. It has been widely demonstrated that stress can either facilitate or impair memory, depending on 1) the phase of memory processing influenced by stress hormones and 2) the valence or arousing nature of the encoded information. It has also been reported that, when stress levels are significantly elevated at encoding, emotional memory is preserved (or enhanced) while memory for non-emotional information is impaired. These effects have been discussed at the neurobiological level with respect to the stress hormone, cortisol, and the impairing and facilitating modulatory effects it has on regions of the brain involved in emotional learning and memory. Whether diurnal shifts in basal levels of cortisol modulate these effects remains unknown. Additionally, it remains unknown whether enhancing and impairing effects of stress on memory result in memory traces that are more or less open to alteration by subsequent experiences, such as observed in the so-called "misinformation" effect.The current dissertation aimed to investigate the effects of stress on encoding of thematically negatively arousing and non-emotional events, composed of negatively arousing and neutral stimuli. Our goal in using more complex materials, in lieu of stimuli (e.g. word lists, images) traditionally used in studies of emotion and memory, was to examine the effects of stress on encoding of information more representative of a real-world event. Within this framework we examined 1) the effects of basal cortisol levels on stress modulation of memory encoding, and 2) the integration of subsequent misinformation on memory for negatively arousing versus non-arousing events encoded under stress. The research included in this dissertation aims to further the field's current understanding of the effects of stress on memory processes. Findings are relevant to the literature on traumatic memory, eyewitness testimony, and the effects of moderate to severe emotion on long-term episodic memory.

APOE ε4 is the major genetic risk factor for Alzheimer’s disease, a dementia characterized by memory impairment and hippocampal atrophy. While associated with episodic impairment and reduced hippocampal volume in healthy aging, APOE ε4 has been related to increased episodic memory performance in young adults. The effect of APOE ε4 on hippocampal volume in young age is uncertain, with studies showing comparable or smaller volumes in ε4 carriers. This thesis aims to further explore the effects of APOE ε4 on episodic memory and hippocampal volume in young adults. In addition to episodic memory, spatial memory will also be assessed, as both these memory types are hippocampus-dependent. Furthermore, potential modulating effects of sex are assessed, as sex differences has been found in relation to APOE-related pathology, episodic and spatial memory and hippocampal volume. Study I examined the effects of APOE ε4 on episodic and spatial memory and hippocampal volume in young adults. Hippocampal volume was assessed by manual tracing of the hippocampal head, body and tail. Study II considered whole-brain structural covariance patterns of the anterior and posterior hippocampus. Furthermore, the association between these patterns and episodic and spatial memory performance was assessed. Study III investigated the effects of APOE ε4 on episodic and spatial memory and hippocampal volume in three different age groups. This was done in order to further explore the different effects of APOE ε4 on cognition and hippocampal volume seen in young and older age. In summary, APOE ε4 was positively associated with spatial function and episodic memory in young adults. Although there were no effects of APOE ε4 on hippocampal volume, structural covariance patterns of the anterior and posterior hippocampus differed as a function of APOE ε4 and sex. Thus, structural covariance may provide an early measure of APOE ε4-related effects on brain structure. Moreover, sex was found to modulate the effects of APOE ε4 to the disadvantage of women. This was seen in both age-related hippocampal volume effects and in structural covariance patterns in young adults, as well as in spatial memory performance across age groups.

Despite the tremendous amount of phonetic variability in speech across talkers, listeners seem to effortlessly process acoustic signals while attending to both the linguistic content and talker-specific information. Previous studies have explained this phenomenon by providing evidence for talker normalization, a process in which our perceptual system strips away information about a talker so that the abstract, canonical linguistic units are all that remain for further linguistic analysis. However, it is currently unknown whether or how talker normalization is facilitated by familiar talkers. In this study, we investigated whether talker familiarity had an impact on the speed in which listeners perceived highly confusable words under varying contexts. Over the course of three days, listeners were explicitly trained on the voices of four talkers. Baseline and post-test measures were administered to determine the effect of talker training and to see whether this effect was impacted by the presence of a carrier phrase as well as the variability of talker presentation. The results demonstrated that listeners adapted to the talker regardless of familiarity. Having immediate information about a talker from preceding speech appeared to play a larger role in managing talker variability than a long-term familiarity with the talker’s voice. Our findings suggest that talker normalization is a feedforward process that does not rely on prior memory traces.

<p>Gender differences favoring women have been found in face recognition, and in addition to this, it has been shown that women remember more female than male faces. This own-gender effect may be a result of women directing more attention towards female faces, resulting in a better memory. The aim of this study was to assess the role of attention for gender differences in face recognition and women’s own-gender bias by dividing attention at encoding of faces. Thirty-two participants completed two recognition conditions: one where faces at presentation were fully attended and one where a second task was performed simultaneously. Women remembered more female faces than men did when encoded under full attention. This difference disappeared when attention was divided. Less attentional resources might have hindered women from using their assumed expertise processing of faces.</p>

The present study investigated whether encoding manipulations which were supposed to make source monitoring of critical lures difficult could alter the levels of false recall for peoples names used as lures in the Deese-Roediger-McDermott list learning paradigm. The results demonstrated that most of manipulations used in the present experiments failed to increase the levels of false recall for the critical lures that were peoples names as it is assumed that, at the same time, the manipulations attenuated semantic encoding around the critical lures, and consequently lowered their activation levels, which is assumed to be essential to obtain high false recall of critical lures. On the other hand, manipulations which resulted in keeping participants from realizing the nature of the list organization, at least, hindered the decrease of false recall level. The question of why false recall for peoples names is rarely elicited in general was discussed.

Gender differences favoring women have been found in face recognition, and in addition to this, it has been shown that women remember more female than male faces. This own-gender effect may be a result of women directing more attention towards female faces, resulting in a better memory. The aim of this study was to assess the role of attention for gender differences in face recognition and women’s own-gender bias by dividing attention at encoding of faces. Thirty-two participants completed two recognition conditions: one where faces at presentation were fully attended and one where a second task was performed simultaneously. Women remembered more female faces than men did when encoded under full attention. This difference disappeared when attention was divided. Less attentional resources might have hindered women from using their assumed expertise processing of faces.

The objective of this research was to investigate the extent to which context contributes to the learning and recognition of episodic auditory-verbal memories (EAM). By combining the Hebb repetition paradigm (HRP) and continuous recognition paradigm (CRP), I capitalized on the advantages of both while manipulating the context in which EAM were retrieved. Through repetition, participants learned sequences of pseudowords in which word order and speaker were varied. A recognition test of either a pseudoword (Experiment I) or the speaker of a pseudoword (Experiment II) revealed temporal and sensory context effects. Results showed that the encoding manipulation did not impact short-term memory but did have an effect on long-term learning. This research helped to clarify the role of context in EAM in both short- and long-term memory, as well as added to the current literature of HRP and CRP. Future directions are discussed.