The close proximity of the Nicoya Peninsula to the Cocos-Caribbean Subduction zone plate boundary makes it a prime location to use GPS to study episodic tremor and slip. Nicoya Peninsula currently has operating networks of both continuous GPS (CGPS) and seismic stations designed to identify and characterize the pattern of episodic tremor and slip (ETS) events along the seismogenic zone under Costa Rica's Pacific Margin. The occurrence of slow slip events has been previously postulated in this region based on correlated fluid flow and seismic tremor events recorded near the margin wedge in 2000 and from sparse GPS observations in 2003. Paucity of data prevented details of these events from being resolved. In May 2007 a slow slip event was recorded on our densified GPS network. This slow slip event was also accompanied by seismic tremor, worked up by colleagues at the University of California - San Diego. I will present the GPS time series, correlated with the seismic tremor for the event in May 2007. I will also present the inferred pattern of slip on the plate interface from elastic half space inversion modeling compared with the tremor and Low Frequency Earthquake (LFE) locations. The geodetic slip and seismic tremor co-locate temporally very well. Spatially the seismic tremor and LFE locations are offset but not independent of both the up dip and down dip patches of geodetic slip. The identification of these slow slip events enhances our understanding of the nuances of the interseismic period. Previous studies of the interseismic strain accumulation patterns in the region of the Nicoya Peninsula have not accounted for the occurrence of slow slip, thus underestimating the magnitude of locking on the fault plane. My study resolves this bias by using our CGPS network to estimate the interseismic surface velocity field, accounting for the May 2007 slow slip event. I will present the results of this velocity field estimation and the results of inversions for locking patterns on the fault plane. My study has also elucidated a potential temporal variability in the locking pattern on the fault plane beneath Nicoya.

Functional brain images are extraordinarily rich data sets that reveal distributed brain networks engaged in a wide variety of cognitive operations. It is a substantial challenge both to create models of cognition that mimic behavior and underlying cognitive processes and to choose a suitable analytic method to identify underlying brain networks. Most of the contemporary techniques used in analyses of functional neuroimaging data are based on univariate approaches in which single image elements (i.e. voxels) are considered to be computationally independent measures. Beyond univariate methods (e.g. statistical parametric mapping), multivariate approaches, which identify a network across all regions of the brain rather than a tessellation of regions, are potentially well suited for analyses of brain imaging data. A multivariate method (e.g. partial least squares) is a computational strategy that determines time-varying distributed patterns of the brain (as a function of a cognitive task). Compared to its univariate counterparts, a multivariate approach provides greater levels of sensitivity and reflects cooperative interactions among brain regions. Thus, by considering information across more than one measuring point, additional information on brain function can be revealed. Similarly, by considering information across more than one measuring technique, the nature of underlying cognitive processes become well-understood. Cognitive processes have been investigated in conjunction with multiple neuroimaging modalities (e.g. fMRI, sMRI, EEG, DTI), whereas the typical method has been to analyze each modality separately. Accordingly, little work has been carried out to examine the relation between different modalities. Indeed, due to the interconnected nature of brain processing, it is plausible that changes in one modality locally or distally modulate changes in another modality. This thesis focuses on multivariate and multimodal methods of image analysis applied to various cognitive questions. These methods are used in order to extract features that are inaccessible using univariate / unimodal analytic approaches. To this end, I implemented multivariate partial least squares analysis in study I and II in order to identify neural commonalities and differences between the available and accessible information in memory (study I), and also between episodic encoding and episodic retrieval (study II). Study I provided evidence of a qualitative differences between availability and accessibility signals in memory by linking memory access to modality-independent brain regions, and availability in memory to elevated activity in modality-specific brain regions. Study II provided evidence in support of general and specific memory operations during encoding and retrieval by linking general processes to the joint demands on attentional, executive, and strategic processing, and a process-specific network to core episodic memory function. In study II, III, and IV, I explored whether the age-related changes/differences in one modality were driven by age-related changes/differences in another modality. To this end, study II investigated whether age-related functional differences in hippocampus during an episodic memory task could be accounted for by age-related structural differences. I found that age-related local structural deterioration could partially but not entirely account for age-related diminished hippocampal activation. In study III, I sought to explore whether age-related changes in the prefrontal and occipital cortex during a semantic memory task were driven by local and/or distal gray matter loss. I found that age-related diminished prefrontal activation was driven, at least in part, by local gray matter atrophy, whereas the age-related decline in occipital cortex was accounted for by distal gray matter atrophy. Finally, in study IV, I investigated whether white matter (WM) microstructural differences mediated age-related decline in different cognitive domains. The findings implicated WM as one source of age-related decline on tasks measuring processing speed, but they did not support the view that age-related differences in episodic memory, visuospatial ability, or fluency were strongly driven by age-related differences in white-matter pathways. Taken together, the architecture of different aspects of episodic memory (e.g. encoding vs. retrieval; availability vs. accessibility) was characterized using a multivariate partial least squares. This finding highlights usefulness of multivariate techniques in guiding cognitive theories of episodic memory. Additionally, competing theories of cognitive aging were investigated by multimodal integration of age-related changes in brain structure, function, and behavior. The structure-function relationships were specific to brain regions and cognitive domains. Finally, we urged that contemporary theories on cognitive aging need to be extended to longitudinal measures to be further validated.

The general objective of the thesis was to examine aspects of declarative memory functioning across the adult life span. The four papers were based on data collected as part of the Betula Prospective Cohort Study (Nilsson et al., 1997) and included largescale population-based samples of participants in the age range 35 to 90. In study I and study II the possibility that age differences in episodic memory may be compensated for by provision of encoding support in the form of enactment was investigated, using free and cued recall and recognition portioned into components of recollective experience as the dependent measures. In Study III, unitary, two-, and multi-factorial models of declarative memory were compared and age-invariance was tested for. In Study IV cross-sectional age differences were contrasted with five-year longitudinal changes on aggregate measures of episodic and semantic memory within age groups ranging from 35 to 85 years. The results of Study I and Study II demonstrated that enactment constitutes an effective form of encoding support, but that the age differences generalize across this form of encoding support. Study II indicated that most of the age-related variance in recognition and levels of recollective experience following enacted and non-enacted encoding was shared by a measure of processing speed. Study III confirmed that a two-factor model of declarative memory (episodic and semantic memory) yields superior fit as compared with a unitary model of declarative memory. However, the best fitting model was a six-factor model with recall and recognition (episodic memory) and knowledge and fluency (semantic associated with different patterns of age-related differences, with some indications that the first-order factors show differential age-related patterns, indicative of variability that cross-sectional data may give a false impression of decline for adults in the age range 35-60 years for episodic memory. There was no evidence of time-related decline within these age groups, even though practice effects were taken into account. However, past this age, substantial time-related decline was observed for the older adults, in line with cross-sectional data. Semantic memory performance tended to improve across time for the younger groups, but decline in old age, although the magnitude of this decline was less pronounced than for episodic memory. Cohort differences in education may be one important factor underlying the discrepancy between the cross-sectional and longitudinal aging patterns, both in the case of episodic and semantic memory. In conclusion, the result of the present studies show that age-related functional losses occur in forms of declarative memory, especially memory) as first-order factors. Episodic and semantic memory were found to be within the episodic and semantic memory domains. The results of Study IV showed episodic memory, but that the onset of decline does not begin until old age.

Verbal information has predominantly been the to-be-remembered materials in human memory research for more than a century. In recent years some interesting deviations from the established rules of verbal memory have been observed in subjects who have been asked to motorically self-perform (enact) action sentences at the encoding phase of the memory task, instead of only hearing or reading them as in a traditional verbal task (VT). Marked enhancements in recall were also consistently demonstrated in such studies and the effect was named the subject-performed task (SPT) effect. Presently, the body of SPT research is large but little agreement has been reached regarding the mechanism at work in producing the SPT phenomenon. The present thesis addresses two major issues in SPT research. The enhancement of associative information and the significance of the motor component are evaluated. In Study A, the SPT effect was studied in two cued-recall tasks that relied on item-specific association and relational association, respectively. The results showed that SPT encoding interacts with item-specific associative cues at recall to produce a larger SPT effect as compared to free recall. This supports the notion that part of the SPT effect is due to enhanced item-specific association. In Study B, the associative effect in SPT was studied amongst age cohorts comprised of subjects between 40 and 85 years old. Normal age-related decline in episodic memory has elsewhere been suggested to be caused mainly by associative deficits connected with ageing. The results of Study B indicate that the item-specific associative effect in SPT was more age sensitive than recall of VT and the relational associative effect in SPT. In Study C, the question over whether the SPT effect is dependent on motor modality or not was addressed. Self-produced sign language encoding was argued to be qualitatively the same as self-produced oral/verbal encoding, with the motor modality component being the only exception. It was also argued that the motor modality component was the main similarity to performing SPT. Since the signing subjects performed at the same level as the SPT condition at recall, and better than the control conditions (e.g., VT), the conclusion was made that motor activation per se can contribute to memory enhancement in SPT. Whether SPT encoding results in qualitatively different memory traces is discussed as well as the effect of SPT on other types of associative information. The results are also briefly related to other controversies in SPT research. It is concluded, finally, that enactment produces differential effects on different types of associations. The association between verb and noun is clearly enhanced by SPT encoding. Moreover, it is concluded that overt motor activation is necessary for obtaining a full SPT effect. To explore these interactions further and to build upon these conclusions, an increased focus on motor processes and their relation to verbal processes is called for in future cognitive research.

This thesis examines whether childhood family configuration influences performance on cognitive functions and health in adulthood and old age. All studies examined participants in the Betula Prospective Cohort Study aged 35 to 85 years (Nilsson et al., 1997). Study Ι established whether there are reliable effects of sibship size and birth order in a large sample of participants in adulthood and old age. The results showed that the effects previously demonstrated in children and adolescents (e.g., Belmont & Marolla, 1973; Mercy & Steelman, 1982) have a long-lasting effect and can be demonstrated in an adult sample. These studies concluded that intelligence and executive functioning decreased as the sibship size increased. Birth order, in contrast, had only influenced executive functions and working memory: earlier born siblings performed at a higher level than later born siblings. Study ΙΙ examined whether the effects of sibship size and birth order can be replicated and extended to episodic memory and whether the effects of family configuration are stable over a five-year interval. The results showed that early born siblings and siblings belonging to a smaller sibship size performed at a higher level and that these effects on both recall and recognition were stable over a five-year interval. Study ΙΙΙ explored whether childhood family configuration influences chronic adult diseases (myocardial infarction and circulatory disorders, stroke, and hypertension). The overall results showed that being born in a large sibship is a risk factor for stroke, myocardial infarction /circulatory disorders, and hypertension in old age. The results also suggest that being born early in a sibship is a predictor of stroke.

Recurrent stress has been found to impair brain structures essential to memory. The cognitive reserve model suggests that physical activity supplies protection against memory decline in neuropathologies. The purpose of the present study was to explore whether leisure physical activity modifies the predicted negative effect stress has on memory. A sub-sample derived from the Betula Study comprised 267 participants between 50 and 65 years. Memory was assessed by a SPT free recall and stress by a self-report. Low and High frequency exercisers were analyzed separately. After age, sex and education were controlled for in hierarchical regression, results showed that stress significantly improved memory performance in Low exercisers but no significant effect in High exercisers. Thus, frequency of physical activity did not explain variation in memory performance. However, higher age did not have a negative influence on memory performance for the High exercisers.

Research on children with Attention Deficit Hyperactivity Disorder (ADHD) has shown that they are extremely sensitive to distraction from external stimuli that lead to poor cognitive performance. This thesis shows that cognitive performance can be improved if this external stimulus is smooth and continuous (e.g. auditory white noise). Control children attenuate their performance under such conditions. The first Study proposes the moderate brain arousal model (MBA). This neurocomputational model predicts selective improvement from noise in ADHD children. Noise through a phenomenon called stochastic resonance (SR), can be beneficial in dopamine deprived neural systems. The statistical phenomenon of SR explains how the signal-to-noise ratio can be improved by noise in neural systems where the passing a threshold is required. The second Study provides experimental support for the MBA-model by showing that ADHD children improve performance in a free recall task while exposed to auditive noise. Control children declines in the same condition. The third Study generalizes this finding among low achieving children, which it is argued have low dopamine levels. Noise exposure improves performance in low achievers, but inhibits performance in high achievers. The conclusion is that external auditory noise can restore low dopamine levels and thus improve cognitive performance. It is also proposed that dopamine levels modulate the SR effect; this means that low dopamine persons require more noise to obtain an SR effect. Both excessive and insufficient dopamine is detrimental for cognitive performance. The MBA model can be used to explain several shortcomings where changes in the dopamine system have been identified. The MBA model can also help create appropriate and adaptive environments, especially in schools, for persons with a deficient dopamine function, such as ADHD children.

Previous findings have suggested that auditive white noise benefits cognitive performance under certain circumstances. The primary purpose of the present pilot study was to explore the effects of visual white noise on verbal episodic memory performance in a normal participant population. Performance was assessed by an immediate free recall test. A secondary purpose was to explore whether participants` eye blink rates and/or temporal processing alters in different noise conditions. The findings of the present study suggest that visual white noise does not affect recall performance among normal participants. However, partially different memory systems and/or memorizing techniques might be used in different noise conditions. Furthermore, noise was not found to affect participants` blink rates or temporal processing.

<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.