This thesis examines how the context in which an item is studied affects the phenomenological experience of the rememberer. Previous research has extensively studied how the match between study and test context affect subsequent memory performance; however, little work has attempted to examine how visual context information provided at study affects later recollection when that context information is not re-presented at retrieval. In particular, the quality of the memory retrieved may be enhanced when highly meaningful visual context information is provided at study. In each of seven experiments in the current thesis, participants studied words presented with context information high or low in meaningful content, and on a later recognition memory test made a Remember, Know, or New response to the words presented alone. Experiment 1 showed that participants had better overall memory, specifically recollection, for words studied with pictures of intact as opposed to scrambled faces. In Experiment 2, these results were replicated and recollection was shown to be higher for words studied with versus without pictures of faces. Experiment 3 showed that participants had higher memory performance, and recollection in particular, for words studied with upright compared to inverted faces. In Experiment 4, participants showed equivalent memory for words studied with novel or familiar faces. These results suggest that recollection benefits when visual context information high in meaningful content accompanies study words, and that this benefit is not related to the novelty of the context. To further test the claim that participants engage in elaborative processes at study to bind item and context information, improving subsequent recollection, the subsequent set of experiments examined how normal, healthy aging affects participants’ ability to use context information provided at study to benefit subsequent recollection. Older adults have been shown to experience deficits both in memory for context and in recollection, suggesting that they might fail to use context effectively to increase recollection, in contrast to younger adults. Experiment 5 found that younger, but not older, adults showed higher recollection for words studied with faces as compared to rectangles. To determine the type of cognitive processing required to obtain recollection benefits, and to examine whether instruction could alleviate age-related deficits, in Experiment 6, the type of processing engaged during the encoding of context-word pairs was manipulated. Younger and older adults studied words presented with a picture of a face under a surface feature or binding feature instruction condition. Both age groups showed higher recollection in the binding than surface instruction condition. Results suggest that older adults do not spontaneously engage in the processes required to boost recollection when visual context information is provided at study, although instructional manipulation during encoding lessens this deficit. This is in line with the Associative Deficit Hypothesis (Naveh-Benjamin, 2000), suggesting that older adults’ recollection deficit involves a specific difficulty in binding item and context information. The final experiment used functional Magnetic Resonance Imaging (fMRI) to examine the neural correlates of recollection, specifically testing the hypothesis that sensory-specific reactivation of context information occurs during item recollection. In Experiment 7, brain activation for Remember responses given to words studied with and without meaningful context information was compared. Behaviourally, 8 of the 14 participants showed a higher proportion of Remember responses to words studied with faces than scrambled faces, and 6 did not. Whole brain analysis showed that, for only those participants who showed higher memory performance for words studied with faces, activation in the fusiform gyrus and hippocampus was higher, and a region-of-interest analysis showed increased activation in the functionally-defined FFA (identified in a localizer task), for Remember responses given to words studied with faces compared to scrambled faces. A regression analysis additionally showed that activation in the fusiform gyrus increased as the relative recollection benefit for words studied with meaningful (face) compared to non-meaningful (scrambled face) context information increased across participants. Results suggest that encoding context can influence the pattern of recollection responses on a recognition task and that sensory-specific reactivation is related to behavioural performance. The findings of these experiments suggest that participants can use context information high in meaningful content at study to improve subsequent recollection and I suggest that this involves the use of elaborative processes at encoding that integrates item and meaningful contexts. Such recollection benefits can also be observed in older adults when they are provided experimental instructions to bind item and context at encoding. In addition, the brain regions used to process context information are reactivated at retrieval and, importantly, that this neural pattern determines whether a boost in recollection, from the encoding manipulation, is observed. Participants can thus use context information provided at study to boost subsequent recollection, and I suggest that this involves cognitive processes that bind item and context information at encoding and the reactivation of sensory-specific brain regions at retrieval.

In this master thesis methods for increasing temporal resolution when reconstructing radially sampled MRI data have been developed and evaluated. This has been done in two steps; first the order in which data is sampled in k-space has been optimized, and second; temporal filters have been developed in order to utilize the high sampling density in central regions of k-space as a result of the polar sampling geometry to increase temporal resolution while maintaining image quality.By properly designing the temporal filters the temporal resolution is increased by a factor 3–20 depending on other variables such as imageresolution and the size of the time varying areas in the image. The results are obtained from simulated raw data and subsequent reconstruction. The next step should be to acquire and reconstruct raw data to confirm the results. / This Master thesis work was performed at Dept. Radiation Physis, Linköping University, but examined at Dept. Radiation Physics, Umeå University

We examined the neural and cognitive processes engaged during auditory verbal recognition performance under full attention (FA) and divided attention (DA) conditions in younger and older adults. Recognition was disrupted by a word (DA-word), but not digit-based (DA-digit) distracting task, performed concurrently with retrieval. In Study 1, a multivariate functional magnetic resonance imaging analysis technique, Partial Least Squares (PLS) was used to identify distributed patterns of brain activity most related to the different conditions and behaviours. We found that similar retrieval networks were recruited during the FA and DA-digit, but not DA-word, condition in both age groups, mirroring behavioural performance. There was, however, an age-related change in the brain regions that predicted successful memory performance. In addition, we found that a neural network relating to hippocampal activity predicted memory success during the FA and DA-digit, but not DA-word, condition in younger, but not older, adults. In study 2, we used a Remember-Know paradigm to examine how manipulations of DA affect recollective and familiarity-based retrieval processes. Younger and older adults showed an increase in false Remember responses during both DA conditions and decreased accuracy in Know responses only during the word-based DA condition. In addition, aging was associated with decreased accuracy in Remember, but not Know, responses, in both DA conditions. In a follow-up experiment, we showed that these results cannot be accounted for by differences in difficulty level of the chosen distracting tasks. Results suggest that recollective processes rely on attentional resources during retrieval. Together these studies show that declines in available attentional resources, common with advancing age, affect both the neural networks used during retrieval, and the qualitative nature of the memories that are retrieved. Results also suggest that familiarity processes rely on the reactivation of content-specific representations, mediated by a neural network relating to hippocampal activity in younger, but not older, adults.

The neural correlates of bilateral upper limb movement are poorly understood. It has been proposed that interhemispheric pathways contribute to the modulation of motor cortical excitability during bimanual movements, possibly via direct connections between primary motor areas (M1), or via a central cortical structure, such as the supplementary motor area (SMA). The ability of one hemisphere to facilitate activation in the other presents a unique opportunity for motor rehabilitation programs using bilateral movements. The focus of this thesis was to investigate the mechanisms underlying bimanual movements in a group of healthy control participants using functional magnetic resonance imaging (fMRI), and subsequently to identify the types of movements that are most likely to maximize M1 activity. It was hypothesized first, that movements involving more proximal muscles, which are known to have a greater number of transcallosal connections, would produce a larger facilitation of M1 activity; and secondly, that the greatest facilitation would occur during those phases of movements where homologous muscles are active simultaneously (i.e. in-phase bilateral movements). The current results demonstrate that the M1 regions and the SMA work together to modulate motor cortical excitability, and that the greatest modulation of activity is seen during movements involving proximal muscles. The findings presented may have clinical relevance to motor rehabilitation programs involving bilateral movements.

This thesis examines how the context in which an item is studied affects the phenomenological experience of the rememberer. Previous research has extensively studied how the match between study and test context affect subsequent memory performance; however, little work has attempted to examine how visual context information provided at study affects later recollection when that context information is not re-presented at retrieval. In particular, the quality of the memory retrieved may be enhanced when highly meaningful visual context information is provided at study. In each of seven experiments in the current thesis, participants studied words presented with context information high or low in meaningful content, and on a later recognition memory test made a Remember, Know, or New response to the words presented alone. Experiment 1 showed that participants had better overall memory, specifically recollection, for words studied with pictures of intact as opposed to scrambled faces. In Experiment 2, these results were replicated and recollection was shown to be higher for words studied with versus without pictures of faces. Experiment 3 showed that participants had higher memory performance, and recollection in particular, for words studied with upright compared to inverted faces. In Experiment 4, participants showed equivalent memory for words studied with novel or familiar faces. These results suggest that recollection benefits when visual context information high in meaningful content accompanies study words, and that this benefit is not related to the novelty of the context. To further test the claim that participants engage in elaborative processes at study to bind item and context information, improving subsequent recollection, the subsequent set of experiments examined how normal, healthy aging affects participants’ ability to use context information provided at study to benefit subsequent recollection. Older adults have been shown to experience deficits both in memory for context and in recollection, suggesting that they might fail to use context effectively to increase recollection, in contrast to younger adults. Experiment 5 found that younger, but not older, adults showed higher recollection for words studied with faces as compared to rectangles. To determine the type of cognitive processing required to obtain recollection benefits, and to examine whether instruction could alleviate age-related deficits, in Experiment 6, the type of processing engaged during the encoding of context-word pairs was manipulated. Younger and older adults studied words presented with a picture of a face under a surface feature or binding feature instruction condition. Both age groups showed higher recollection in the binding than surface instruction condition. Results suggest that older adults do not spontaneously engage in the processes required to boost recollection when visual context information is provided at study, although instructional manipulation during encoding lessens this deficit. This is in line with the Associative Deficit Hypothesis (Naveh-Benjamin, 2000), suggesting that older adults’ recollection deficit involves a specific difficulty in binding item and context information. The final experiment used functional Magnetic Resonance Imaging (fMRI) to examine the neural correlates of recollection, specifically testing the hypothesis that sensory-specific reactivation of context information occurs during item recollection. In Experiment 7, brain activation for Remember responses given to words studied with and without meaningful context information was compared. Behaviourally, 8 of the 14 participants showed a higher proportion of Remember responses to words studied with faces than scrambled faces, and 6 did not. Whole brain analysis showed that, for only those participants who showed higher memory performance for words studied with faces, activation in the fusiform gyrus and hippocampus was higher, and a region-of-interest analysis showed increased activation in the functionally-defined FFA (identified in a localizer task), for Remember responses given to words studied with faces compared to scrambled faces. A regression analysis additionally showed that activation in the fusiform gyrus increased as the relative recollection benefit for words studied with meaningful (face) compared to non-meaningful (scrambled face) context information increased across participants. Results suggest that encoding context can influence the pattern of recollection responses on a recognition task and that sensory-specific reactivation is related to behavioural performance. The findings of these experiments suggest that participants can use context information high in meaningful content at study to improve subsequent recollection and I suggest that this involves the use of elaborative processes at encoding that integrates item and meaningful contexts. Such recollection benefits can also be observed in older adults when they are provided experimental instructions to bind item and context at encoding. In addition, the brain regions used to process context information are reactivated at retrieval and, importantly, that this neural pattern determines whether a boost in recollection, from the encoding manipulation, is observed. Participants can thus use context information provided at study to boost subsequent recollection, and I suggest that this involves cognitive processes that bind item and context information at encoding and the reactivation of sensory-specific brain regions at retrieval.

Cross-education of strength is a neural adaptation defined as the increase in strength of the untrained contralateral limb after unilateral training of the opposite homologous limb. The neural mechanisms of the effect have remained elusive, although it appears to be a motor learning adaptation. Despite cross-education of strength being an inter-limb effect, no previous study has determined the influence of handedness and the direction of transfer (dominant to non-dominant or the reverse). Arguably, this is partly responsible for massive variation in the literature regarding the magnitude of the effect. The primary purpose of this document is to attempt to determine the central and peripheral neuro-physiological mechanisms controlling cross-education of muscular strength. Prior to determining the mechanisms of the effect, the influence of handedness and the preferred direction of transfer for cross-education of strength must be addressed. The secondary purpose is to determine the preferential direction of transfer of cross-education of strength in order to isolate the circumstances in which the effect is more pronounced. Two experiments were necessary to meet these objectives. <p>Experiment 1: The purpose was to determine the effect of the direction of transfer on cross-education in right-handed individuals. Subjects were randomized into a left-hand training (LEFT), right-hand training (RIGHT), or non-training control (CON) group. Strength training was 6 weeks of maximal isometric ulnar deviation, 4 times per week. The change in strength in the untrained limb was greatest in the RIGHT group (39.2%; p<.01), whereas no significant changes in strength were observed for the untrained limb of the LEFT group (9.3%) or for either of the CON group limbs (10.4% and 12.2%). There were no changes in muscle thickness of untrained limbs compared to CON. Changes in untrained limb EMG were not different compared to CON. Cross-education with hand strength training occurs only in the right-to-left direction of transfer in right-handed individuals. Cross-education of arm muscular strength is most pronounced to the non-dominant arm. <p>Experiment 2: The purpose of this study was to determine the central and peripheral mechanisms of cross-education of strength after actual and imagery training. Subjects were randomized into an actual training, imagery training, or non-training control group. A sub-sample of 8 subjects (4 actual, 4 imagery training) had brain activity during exercise assessed with functional magnetic resonance imaging (fMRI). Strength training was 6 weeks of maximal isometric handgrip ulnar deviation (Biodex) of the right arm, 4 times per week. Actual training was highly effective for increasing strength in trained (45.3%; p<.01) and untrained (47.1%; p<.01) limbs. Imagery training and control groups had no increases in strength for either arm. Muscle thickness increased only in the trained arm of the actual group (8.4%; p<.001). After actual training, there was an increase in activation of contralateral sensorimotor cortex and left temporal lobe during actual contractions with the untrained left arm (p<.001). Actual training was associated with a significantly greater change in agonist muscle activation pooled over both limbs, compared to the imagery and control groups (p<.05). Cross-education of strength is only significant after actual training, indicating that peripheral feedback is necessary for the effect. Cross-education of strength is accompanied by changes in cortical activation indicative of motor learning and the retrieval of memory of movement acquired by the trained limb. <p>General Conclusion: The neuro-physiological mechanism of cross-education of strength is that changes in cortical activation indicative of motor learning occur in both brain hemispheres after unilateral training. Cross-education of strength is influenced by strength asymmetries related to handedness, and the preferential direction of transfer is from dominant to non-dominant limb. Cross-education is a motor learning adaptation also reliant on peripheral feedback during training.

As a non-invasive method, functional MRI (fMRI) has been widely used for human brain mapping. Although many applications have been done, there are still some critical issues associated with fMRI. Perfusion-weighted fMRI (PWI) with exogenous contrast agent suffered from the problems of recirculation, which could contaminate the cerebral blood flow (CBF) estimation and make its ability of prediction "tissue-at-risk" in debate. We propose a rapid and effective method that combines matched-filter-fitting (MFF) and ICA where ICA was used for regions with a prolonged TTP and MFF was utilized for the remaining areas. The calculation of cerebral hemodynamics afterwards demonstrates that the proposed method may lead to a more accurate estimation of CBF. The extent to which CBF is reduced in relationship to normal values has been utilized as an indicator to discern ischemic injury. However, despite the well known difference in CBF between gray and white matter, relatively little attention has been given as to how CBF may be differently altered in gray and white matter during ischemia due to the inability to accurately separate gray and white matter. To this end, we propose a robust clustering method for automatic classification of perfusion compartments. The method is first to apply a robust principal component analysis to reduce dimension and then to use a mixture model of multivariate T distribution for clustering. Our results in ischemic stroke patients at the hyperacute phase show the clear advantage over the conventional technique. BOLD fMRI, as a feasible and preferred method for developmental neuroimaging, is seldom conducted in pediatric subjects and therefore the information about brain functional development in the early age is somewhat lacking. To this end, this dissertation also focuses on how functional brain connectivity may be present in pediatric subjects in a sleeping condition. We propose a statistical method to delineate frequency-dependent brain connectivity among brain activation regions, and an automatic procedure combined with spatial ICA approach to determine the brain functional connectivity. Our results suggest that functional connectivity exists as young as two weeks old for both sensorimotor and visual cortices and that functional connectivity is highly age-dependent. / Dissertation

<p>Humans must integrate information to make decisions. This thesis is concerned with studying neural mechanisms of decision making, and combines tools from economics, psychology, and neuroscience. I employ a neuroeconomic approach to understand the processing of reward information and motivation in the brain, utilizing neural data from functional magnetic resonance imaging (fMRI) to make connections between cognitive neuroscience and economics.</p><p>Chapter 1 lays the groundwork for the thesis and provides background on neuroscience, fMRI, and neuroeconomics. Chapter 2 sketches the central challenges of using neuroscience to address economic questions. The first half of the chapter discusses familiar arguments against the integration of neuroscience and economics: behavioral sufficiency and emergent phenomenon. The second half constructs principles for interdisciplinary research linking mechanistic (neuroscience) data to behavioral (economic) phenomena: mechanistic convergence across experiments and biological plausibility in models.</p><p>Chapters 3 and 4 employ a nonstandard analysis technique, multivariate pattern analysis (MVPA), to identify brain regions that contain information associated with different types of economic valuation. Chapter 3 uses a combinatoric approach to evaluate how brain regions uniquely contribute to the ability to predict different types of valuation (probabilistic or intertemporal). MVPA shows that early valuation phases for these rewards differ in posterior parietal cortex and suggests computational topographies for different rewards. Chapter 4 employs within- and cross-participant MVPA, which rely on potentially different sources of neural variability, to identify brain regions that contain information about monetary rewards (cash) and social rewards (images of faces). Cross-participant analyses reveal systematic changes in predictive power across multiple brain regions, and individual differences in statistical discriminability in ventromedial prefrontal cortex relate to differences in reward preferences. MVPA thus facilitates mapping behavior to both individual-specific functional organization and general organization of the brain across individuals. </p><p>Chapter 5 employs a reward anticipation task to measure variation in relative motivation without observing choices between rewards (money and candy). A reaction-time index captures individual differences in motivation, and heterogeneity in this index maps onto variability in two brain regions: nucleus accumbens and anterior insula. Further, the nucleus accumbens activation mediates the predictive effects of anterior insula. These results show that idiosyncrasies in reward efficacy persist in the absence of a choice environment.</p><p>Chapters 6 and 7 conclude the thesis. Chapter 6 complements discussions of neuroeconomics with text analysis of an exhaustive corpus from top economics journals and references from a large set of review articles. The analysis shows a mismatch between topics of importance to economics and prominent concepts in neuroeconomics. I show how neuroeconomics can grow by employing cognitive neuroscience to identify biologically plausible and generalizable models of a broader class of behaviors.</p> / Dissertation

<p>Functional Magnetic Resonance Imaging, fMRI, can be used for analyzing brain activity in subjects performing language tasks. The purpose of this study was to develop aphasia-friendly information adjusted to aphasic subjects participating in fMRI studies. The objectives were to investigate if adjusted information was important for the ability to perform language tasks and if the information could be used for different types of aphasia.</p><p>Sixteen aphasic subjects participated in the study, six of these underwent fMRI. The participants varied in grade and type of aphasia. They had Swedish as their native language and were aged between 26 and 89, mean 57. Information was developed in three versions. The participants performed word generation and sentence completion language tasks.</p><p>Results showed that all the participants produced significantly more words (p < 0.05), and completed significantly more sentences (p < 0.001) in the final version. The fMRI results showed high intersession variability, therefore intra- or intersubject comparisons were difficult to make.</p><p>It was found that increased amount of time to solve the task and removal of the control task together with aphasia-friendly, concrete information improved performance. This applies to all participants, irrespective of aphasia type.</p>

While episodic and spatial memory both depend on the hippocampus, opposite gender differences in these functions suggest they are partly separate, with different neural underpinnings. The anterior and posterior hippocampus differ  in structure and whole-brain connectivity, and studies point to the posterior hippocampus being more involved in spatial memory while the anterior hippocampus’ role in episodic memory is less clear. This thesis aims to explore the role of the anterior and posterior hippocampus, and associated brain regions, in episodic and spatial memory. Paper I studied gender differences in hippocampal activation underlying differences in spatial memory performance. Better performance in men was accompanied by greater right-lateralization of hippocampal activation compared to women. Paper II investigated regions of gray matter that covaried in volume with the anterior and posterior hippocampus, and whether these covariance patterns depended on gender and were related to behavior. The anterior and posterior hippocampus showed different patterns of covariance, with the anterior hippocampus covariance pattern observed in women and the posterior hippocampus covariance pattern primarily in men. Paper III considered whether the location of hippocampal recruitment in episodic memory depends on memory content. Verbal stimuli were associated with more anterior, and left-lateralized, encoding activations than pictorial stimuli, which in turn were associated with more posterior and bilateral encoding activations. This was not observed during retrieval. Paper IV investigated whether resting-state connectivity associated with the anterior and posterior hippocampus predicts episodic and spatial memory performance, respectively. Resting-state connectivity associated with the anterior, not posterior, hippocampus predicted episodic memory performance, while resting-state connectivity associated with the posterior, not anterior, hippocampus predicted spatial memory performance. This thesis lends further support to differences in function and structure between the anterior and posterior hippocampus suggesting that these two sub–segments play different roles in episodic and spatial memory. Further, it suggests that gender differences in anterior and posterior hippocampus function underlies gender differences in episodic and spatial memory, respectively. Considering the anterior and posterior hippocampus, as well as men and women, separately, is hence important when studying the effect of age and pathology on the hippocampus and associated memory functions.