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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.

Recent research has demonstrated that priming and recognition memory performance are not independent as traditionally thought. Evidence is accumulating suggesting that information recognized in great detail (recollected) also has higher levels of priming (Sheldon & Moscovitch, 2010; Turk-Browne, Yi, & Chun, 2006). The purpose of this dissertation was to delineate the conditions under which recognition processes (estimates of recollection and familiarity) are associated with priming, and how this changes with age. Results from a systematic crossing of level of encoding (deep versus shallow) with type of priming task (conceptual versus perceptual) suggests that the relation between priming and recognition is determined by the nature of the encoding task. Under deep encoding conditions, a greater magnitude of priming—both perceptual and conceptual—was related to subsequent recollection but only amongst younger adults. Under shallow encoding conditions, perceptual priming performance was related to subsequent familiarity in both younger and older adults. Taken together, this series of experiments suggests that the processing mode engaged during encoding dictates which processes will be engaged at retrieval (a recollection-based process, or a familiarity-based process; Henke, 2010). These findings also suggest that both recollection and familiarity have rapid and unconscious aspects that are measurable through behavioural priming tasks, aligning with a recently proposed model suggesting recollection is characterized by a two-stage process, an early, relatively automatic and unconscious stage and a later, controlled and conscious stage (Moscovitch, 2008). It is suggested that the rapid, unconscious aspects of recollection may decline across the lifespan, while the rapid, unconscious aspects of familiarity stay intact with age.

Recent research has demonstrated that priming and recognition memory performance are not independent as traditionally thought. Evidence is accumulating suggesting that information recognized in great detail (recollected) also has higher levels of priming (Sheldon & Moscovitch, 2010; Turk-Browne, Yi, & Chun, 2006). The purpose of this dissertation was to delineate the conditions under which recognition processes (estimates of recollection and familiarity) are associated with priming, and how this changes with age. Results from a systematic crossing of level of encoding (deep versus shallow) with type of priming task (conceptual versus perceptual) suggests that the relation between priming and recognition is determined by the nature of the encoding task. Under deep encoding conditions, a greater magnitude of priming—both perceptual and conceptual—was related to subsequent recollection but only amongst younger adults. Under shallow encoding conditions, perceptual priming performance was related to subsequent familiarity in both younger and older adults. Taken together, this series of experiments suggests that the processing mode engaged during encoding dictates which processes will be engaged at retrieval (a recollection-based process, or a familiarity-based process; Henke, 2010). These findings also suggest that both recollection and familiarity have rapid and unconscious aspects that are measurable through behavioural priming tasks, aligning with a recently proposed model suggesting recollection is characterized by a two-stage process, an early, relatively automatic and unconscious stage and a later, controlled and conscious stage (Moscovitch, 2008). It is suggested that the rapid, unconscious aspects of recollection may decline across the lifespan, while the rapid, unconscious aspects of familiarity stay intact with age.

No description available.

This dissertation looks at ways in which memories of traumatic events are revisited and reshaped by mnemonic communities during the Second Temple period. I focus on the social dimensions of traumatic memory that shape collective identity. I consider ways in which the earlier sites of memories of the exodus, the destruction of the first temple, and the Babylonian exile are reactivated and reshaped by mnemonic communities in constructing exclusive collective identities through discourses of exile, separation, and restoration. Drawing on theoretical frameworks from post-Holocaust thought that I outline in Chapter 1, I argue that the language in Ezra-Nehemiah (Chapter 2), 2 Maccabees (Chapter 3), Daniel (Chapter 4), and Damascus Document and Pesher Habakkuk (Chapter 5) is consistent with processes of identity formation in which trauma is construed as a founding, generative, and integrative identity. In developing themes of collective trauma and memory, I focus on Marianne Hirsch’s work on postmemory and Dominick LaCapra’s theories on founding traumas and the conversion of absence and loss. I apply these theories to the aforementioned Second Temple texts by arguing that notions of purity and impurity are established through the memory and postmemory of catastrophic events, including the destruction of the first temple, Babylonian exile, and the persecution by Antiochus IV Epiphanes in 167-164 B.C.E. The producers of these texts mask structural trauma (i.e., the transhistorical absence represented as the loss of an original identity) in its representation of historical trauma and narrate the process of restoration as the recovery of an original identity and unity, which never existed as it is represented in the texts. Chapter 6 is an analysis of notions of purification, hybrids, and multidirectional memory. Engaging with the work of Bruno Latour, I discuss the production and proliferation of hybrids, which emerge from discourses and practices of separation and purification. I use Latour as a segue into Michael Rothberg’s work on multidirectional memory, which shows that those whom some communities attempt to mnemonically and discursively eliminate or purify often share a collective pasts and/or identities.

Throughout adulthood, the brain continuously generates new neurons in two neurogenic regions: the subgranular zone of the hippocampus and the subventricular zone on the lateral wall of the lateral ventricles. These neurons have been shown to integrate into hippocampal and olfactory bulb circuitry, respectively. Nevertheless, their specific contribution to hippocampal or olfactory function remains unclear. Previous studies have tried to assess adult born neuron contribution to memory function by suppressing neurogenesis and examining the impact on memory acquisition. Although ablation of neurogenesis has been shown to impair performance in hippocampus dependent and olfactory tasks, many studies fail to see an effect. Compensation from residual cells in either system after ablation may underlie these contradictory findings. Thus, a more direct approach to answer this question would be to ablate adult born neurons after their incorporation into the memory trace. To do this, we established a double transgenic strategy to tag and selectively ablate adult born neurons with temporal control. Ablation of a population of predominantly mature, adult generated dentate granule cells did not prevent acquisition of contextual fear conditioning or Morris Water Maze memories. Removal of that same population of cells after training, however, led to memory degradation in three hippocampus dependent tasks. Similarly, post-training ablation of a population of adult generated olfactory interneurons iii impaired performance in an associative odour memory task, whereas pre-training ablation had no impact. Together, these data show that adult generated neurons form a crucial component of both hippocampal and olfactory memory traces.

Biophysical simulations of memory must choose which aspects of known neurophysiology and neuroanatomy to model. Relevant aspects were constrained by functional requirements determined for on-line acquisition in context dependent memory, memory that is retrieved by contextual cues. In an on-line task, the protocol of data presentation and the tunes at which encoding or retrieval in memory is needed are not predetermined. A sequence of neuronal spike patterns representing items may be presented only once. Yet, episodic memory of the sequence immediately encodes the temporal context of familiar items, a process known to depend on hippocampal function. For this, interference caused by overlapping spike patterns must be avoided, a requirement that suggested the relevance of coincidental spiking. Overlap in the input to the hippocampus was reduced by recruiting such spikes in a model of encoding in dentate gyrus. Durable encoding is required in the hippocampus, since hippocampal damage can cause retrograde amnesia in context dependent memory that spans years. Long-lasting synaptic changes involved modeling relevant neurophysiology concerning protein production elicited by the spaced reactivation of spike patterns. The likelihood of reactivation was increased by the well-known process of long-term potentiation of synaptic transmission. Such potentiation is elicited when a presynaptic spike precedes a postsynaptic spike within a specific time window repeatedly. The intervals in a sequence of spike patterns must be compressed and the sequence repeated, requirements that were achieved with a model of short-term memory based on persistent spiking. Retrieval may be concurrent with these encoding processes due to effects of different phases of a brain rhythm at theta frequency (3-12 Hz) that modulate transmission and plasticity. A model of short-term memory by Lisman and Idiart (Science 267:1512-15), extended by Jensen et al. (Learning and Memory 3:243

This thesis investigates implicit memory for music, as measured by repetition priming: a processing benefit for previously encountered items. Although repetition priming has been documented in many domains, including language, visual perception, and environmental sounds, it has not yet been demonstrated in music, a domain replete with pitch repetition. A novel methodology is presented in which participants sang back the final tone of a short melody. Experiments presented in Chapter 2 show that participants were faster to sing back a target tone when it was a repetition of a previous melodic tone than when it was not, and this effect was greatest when the repetition was closest to the target. These studies also showed a benefit for expected tonic tones, which were manipulated independently of the repetition effect. Chapter 3 presents a new analysis method for measuring response latencies in sung tones. A time-frequency representation that optimizes the tradeoff between time and frequency for each point in time yielded a measurement of singers' time to reach a target frequency, which takes into account both speed and accuracy of the vocal productions. The time-frequency measurement, applied to the data presented in Chapter 2, showed longer times to reach target frequency for higher pitches, as well as larger effects of tonal priming than were attained through traditional response latency measures. The experiments in Chapter 4 examine the time course of the effects of repetition and tonality. The singing-back paradigm used in Chapter 2 also was used with the additional manipulation of stimulus tempo. These studies implicated interference rather than decay as the cause of the decreased repetition priming effect. Stimulus tempo manipulations showed separate time courses for repetition and tonal priming. Together, these studies provide the first evidence of repetition priming in music, document its interaction with other factors including tonality and pitch height, and describe its time course. The findings are discussed in terms of sensory and cognitive theories of priming.

Although a plethora of data exists on the role of the prefrontal cortex in memory retrieval, it has been difficult to relate specific aspects of retrieval processing to the different prefrontal regions. The present thesis consists of one behavioural experiment and three functional neuroimaging studies that aimed at elucidating the role of the mid-ventrolateral region of the prefrontal cortex in memory retrieval. We hypothesized that the mid-ventrolateral prefrontal cortex, through its anatomical connections with posterior association areas, is in a key position to exert control over posterior association areas where information is processed and stored for the active retrieval of mnemonic information. In contrast to automatic retrieval, active retrieval is necessary when a person retrieves based on his/her plans and intentions a specific memory amongst multiple related mnemonic traces. / Previously, we had demonstrated that the mid-ventrolateral prefrontal cortex in the right hemisphere controls active retrieval of non-verbal stimuli. More specifically, we reported activity increases within this region during the delay period that followed the presentation of a retrieval cue. We proposed that these activity increases reflect the top-down control exerted by the mid-ventrolateral prefrontal cortex to focus attention on relevant aspects of encoded memories in preparation for the decision. The first study of my thesis focuses on the behavioural correlates of this active retrieval process. The results indicate that the subjects' performance improves (i.e. becomes faster) with longer retrieval periods. Thus, some aspect of retrieval is initiated during the delay before the presentation of a test stimulus for the decision. The results, however, also indicate that retrieval continues after the presentation of the test stimulus. / The three event-related fMRI studies that make up chapters three, four, and five of the thesis were designed on the basis of the results obtained in the behavioural study described in chapter two. For all three fMRI studies, we used an experimental paradigm in which the retrieval cue coincided with the test stimulus presentation. The experimental design for the three neuroimaging studies was similar but examined the retrieval of mnemonic information from different sensory modalities. A separate group of subjects was tested for each study with a common hypothesis: when subjects are performing active retrieval trials, selective activity increases will be observed within the mid-ventrolateral prefrontal cortex. The study presented in chapter three examined verbal active retrieval, the study presented in chapter four examined tactile active retrieval, and the one in chapter five examined active retrieval for auditory stimuli. Selective activity increases were reported within the mid-ventrolateral prefrontal cortex during the active retrieval trials in all three studies. Activity increases were stronger in the left mid-ventrolateral prefrontal cortex when subjects retrieved verbal information. For tactile and auditory stimuli, the activity increases were bilateral. Importantly, within the prefrontal cortex, there were no other activity increases, indicating that the role of the mid-ventrolateral prefrontal cortex in memory retrieval is specific and distinct from that of other prefrontal regions. Thus it can be concluded that, across sensory modalities, the mid-ventrolateral prefrontal cortex plays a key role in the top-down control necessary for the disambiguation of information in memory during retrieval.