| 1. |
- Drissi, Natasha Morales, 1980-
(författare)
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Brain Networks and Dynamics in Narcolepsy
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Narcolepsy is a chronic sleep disorder, characterised by excessive daytime sleepiness with frequent uncontrollable sleep attacks. In addition to sleeprelated problems, changes in cognition have also been observed in patients with narcolepsy and has been linked to the loss of Orexin-A in a number of studies. Results from previous functional and structural neuroimaging studies would suggest that the loss of Orexin-A has numerous downstream effects in terms of both resting state glucose metabolism and perfusion and reduction in cortical grey matter.Specifically, studies investigating narcolepsy with positron emission tomography (PET) and single photon emission computed tomography (SPECT) have observed aberrant perfusion and glucose metabolism in the hypothalamus and thalamus, as well as in prefrontal cortex. A very recent PET study in a large cohort of adolescents with type 1 narcolepsy further observed that the hypoand hypermetabolism in many of these cortico-frontal and subcortical brain regions also exhibited significant correlations with performance on a number of neurocognitive tests. These findings parallel those found in structural neuroimaging studies, where a reduction of cortical grey matter in frontotemporal areas has been observed.The Aim of this thesis was to investigate mechanisms and aetiology behind the symptoms in narcolepsy through the application of different neuroimaging techniques. I present in this thesis evidence supporting that the complaints about subjective memory deficits in narcolepsy are related to a misallocation of resources.I further describe how this has its seat in defective default mode network activation, possibly involving alterations to GABA and Glutamate signaling. In addition to this, I present our findings of a structural deviation in an area of the brainstem previously not described in the aetiology of narcolepsy.This finding may have implications for further understanding the aetiology of the disease and the specific neuronal populations involved.In addition to this, I show evidence from adipose tissue measurements in specific compartments, confirming that weight gain in narcolepsy is characterized by centrally located weight gain and may be specifically related to OX changes, but maybe not brown adipose tissue volume.The findings presented in this thesis provides new insights to the pathophysiology of narcolepsy beyond the well-known depletion of OX producing neurons in the hypothalamus.
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| 2. |
- Lundengård, Karin, 1985-
(författare)
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Mechanistic modelling - a BOLD response to the fMRI information loss problem
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Functional Magnetic Resonance Imaging (fMRI) is a common technique for imaging brain activity in humans. However, the fMRI signal stems from local changes in oxygen level rather than from neuronal excitation. The change in oxygen level is referred to as the Blood Oxygen Level Dependent (BOLD) response, and is connected to neuronal excitation and the BOLD response are connected by the neurovascular coupling. The neurons affect the oxygen metabolism, blood volume and blood flow, and this in turn controls the shape of the BOLD response. This interplay is complex, and therefore fMRI analysis often relies on models. However, none of the previously existing models are based on the intracellular mechanisms of the neurovascular coupling. Systems biology is a relatively new field where mechanistic models are used to integrate data from many different parts of a system in order to holistically analyze and predict system properties. This thesis presents a new framework for analysis of fMRI data, based on mechanistic modelling of the neurovascular coupling, using systems biology methods. Paper I presents the development of the first intracellular signaling model of the neurovascular coupling. Using models, a feed-forward and a feedback hypothesis are tested against each other. The resulting model can mechanistically explain both the initial dip, the main response and the post-peak undershoot of the BOLD response. It is also fitted to estimation data from the visual cortex and validated against variations in frequency and intensity of the stimulus. In Paper II, I present a framework for separating activity from noise by investigating the influence of the astrocytes on the blood vessels via release of vasoactive sub- stances, using observability analysis. This new method can recognize activity in both measured and simulated data, and separate differences in stimulus strength in simulated data. Paper III investigates the effects of the positive allosteric GABA modulator diazepam on working memory in healthy adults. Both positive and negative BOLD was measured during a working memory task, and activation in the cingulate cortex was negatively correlated to the plasma concentration of diazepam. In this area, the BOLD response had decreased below baseline in test subjects with >0.01 mg/L diazepam in the blood. Paper IV expands the model presented in Paper I with a GABA mechanism so that it can describe neuronal inhibition and the negative BOLD response. Sensitization of the GABA receptors by diazepam was added, which enabled the model to explain how changes to the BOLD response described in Paper III could occur without a change in the balance between the GABA and glutamate concentrations.The framework presented herein may serve as the basis for a new method for identification of both brain activity and useful potential biomarkers for brain diseases and disorders, which will bring us a deeper understanding of the functioning of the human brain.
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| 3. |
- Sten, Sebastian, 1993-
(författare)
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Mathematical modeling of neurovascular coupling
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The brain is critically dependent on the continuous supply of oxygen and glucose, which is carried and delivered by blood. When a brain region is activated, metabolism of these substrates increases rapidly, but is quickly offset by a substantially higher increase in blood flow to that region, resulting in a brief oversupply of these substrates. This phenomenon is referred to as functional hyperemia, and forms the foundation of functional neuroimaging techniques such as functional Magnetic Resonance Imaging (fMRI), which captures a Blood Oxygen Level-Dependent (BOLD) signal. fMRI exploits these BOLD signals to infer brain activity, an approach that has revolutionized the research of brain function over the last 30 years. Due to the indirect nature of this measure, a deeper understanding of the connection between brain activity and hemodynamic changes — a neurovascular coupling (NVC) — is essential in order to fully interpret such functional imaging data. NVC connects the synaptic activity of neurons with local changes in cerebral blood flow, cerebral blood volume, and cerebral metabolism of oxygen, through a complex signaling network, consisting of multiple different brain cells which release a myriad of distinct vasoactive messengers with specific vascular targets. To aid with this complexity, mathematical modeling can provide vital help using methods and tools from the field of Systems Biology. Previous models of the NVC exist, conventionally describing quasi-phenomenological steps translating neuronal activity into hemodynamic changes. However, no mechanistic mathematical model that describe the known intracellular mechanisms or hypotheses underlying the NVC, and which can account for a wide variety of NVC related measurements, currently exists. Therefore, in this thesis, we apply a Systems Biology approach to develop such intracellular mechanisms based models using in vivo experimental data consisting of different NVC related measures in rodents, primates, and humans.Paper I investigates two widely discussed hypotheses describing the NVC: the metabolic feedback hypothesis, and the vasoactive feed-forward hypothesis. We illustrate through multiple model rejections that only a model describing a combination of the two hypotheses can capture the qualitative features of the BOLD signal, as measured in humans. This combined model can describe data used for training, as well as predict independent validation data not previously seen by the model before.Paper II extends this model to describe the negative BOLD response, where the blood oxygenation drops below basal levels, which is commonly observed in clinical and cognitive studies. The model explains the negative BOLD response as the result of neuronal inhibition, describing and adequately predicting experimental data from two different experiments.In Paper III, we develop a first model including the cell-specific contributions of GABAergic interneurons and pyramidal neurons to functional hyperemia, using data of optogenetic and sensory stimuli in rodents for both awake and anesthesia conditions. The model captures the effect of the anesthetic as purely acting on the neuronal level if a Michaelis-Menten expression is included, and it also correctly predicts data from experiments with different pharmacological inhibitors.Finally, in Paper IV, we extend the model in Paper III to describe and predict a majority of the relevant hemodynamic NVC measures using data from rodents, primates, and humans. The model suggests an explanation for observed bi-modal behaviors, and can be used to generate new insights regarding the underpinnings of other complicated observed behaviors. This model constitutes the most complete mechanistic model of the NVC to date.This new model-based understanding opens the door for a more integrative approach to the analysis of neuroimaging data, with potential applications in both basic science and in the clinic.
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| 4. |
- Georgiopoulos, Charalampos, 1984-
(författare)
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Imaging Studies of Olfaction in Health and Parkinsonism
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Olfactory loss is a common non-motor symptom of Parkinson’s disease (PD), often preceding the cardinal motor symptoms of the disease. The aim of this thesis was to: (a) evaluate whether olfactory examination can increase diagnostic accuracy, and (b) study the structural and functional neural basis of olfactory dysfunction in PD with different applications of Magnetic Resonance Imaging (MRI).Paper I was a comparison of the diagnostic accuracy between a simple smell identification test and DaTSCAN Single Photon Emission Computerized Tomography (SPECT), a nuclear medicine tomographic imaging technique that is commonly used in patients with suspected parkinsonism. The results indicate that smell test is inferior to DaTSCAN SPECT, but the combination of these two methods can lead to improved diagnostic accuracy.Paper II showed that diffusion MRI could detect discrete microstructural changes in the white matter of brain areas that participate in higher order olfactory neurotransmission, whereas MRI with Magnetization Transfer contrast could not.Paper III was a methodological study on how two different acquisition parameters can affect the activation pattern of olfactory brain areas, as observed with functional MRI (fMRI). The results indicate that brief olfactory stimulation and fast sampling rate should be preferred on olfactory fMRI studies.Paper IV used olfactory fMRI and resting-state fMRI in order to elucidate potentially altered activation patterns and functional connectivity within olfactory brain areas, between PD patients and healthy controls. Olfactory fMRI showed that olfactory impairment in PD is associated with significantly lower recruitment of the olfactory network. Resting-state fMRI did not detect any significant changes in the functional connectivity within the olfactory network of PD patients.In conclusion, the included studies provide evidence of: (a) disease-related structural and functional changes in olfactory brain areas, and (b) beneficial addition of olfactory tests in the clinical work-up of patients with parkinsonism.
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| 5. |
- Sundqvist, Nicolas, 1993-
(författare)
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Mathematical Modelling of Cerebral Metabolism : From Ion Channels to Metabolic Fluxes
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The brain is the most metabolically active organ in the human body and therefore rely on a continuous supply of oxygen and glucose. Neuronal stimulation in specific regions of the leads to the firing of action potentials, a process facilitated by voltage-gated ion channels in the neurons’ cell membranes. This activation of the ion channels significantly elevates the brain’s metabolic energy demand, compelling neurons to ramp up their metabolic activity in response. Concurrently, this neuronal activation also initiates a signalling cascade that induces vasodilation and increases blood flow, thereby ensuring that regions with elevated neural activity are adequately supplied with oxygen and nutrients. This dynamic interplay between neuronal activity and cerebral blood flow (CBF) regulation constitutes the neurovascular coupling (NVC). The NVC is a cornerstone in interpreting functional Magnetic Resonance Imaging (fMRI) Blood Oxygen Level-Dependent (BOLD) responses. The BOLD response is an indirect, non-invasive, and highly sensitive indicator of neuronal activity, reflecting changes in blood oxygenation and flow associated with the neuronal and metabolic activity in the brain. By examining these responses, we can gain insights into the complex interactions between neuronal activity, energy metabolism, and CBF.Additionally, techniques such as 13C Metabolic Flux Analysis (13C MFA) makes it possible to gain further insight into the cerebral metabolism. This method enables a detailed examination of metabolic pathways and fluxes by tracking the incorporation of 13C-labelled substrates into various metabolites. By using 13C MFA, researchers can quantify the flow of substrates through metabolic networks, offering a deeper understanding of how cell such as neurons adapt their metabolism during different functional states and conditions.Central to exploring these multifaceted aspects of cerebral metabolism is the use of mathematical modelling and systems biology. These disciplines provide a framework for integrating diverse biological data, allowing for the simulation and prediction of complex neurovascular interactions under various physiological and pathological conditions. Mathematical models can encapsulate the dynamics of ion channel kinetics, metabolic pathways, and neurovascular coupling, offering a comprehensive view of the interplay between neuronal activity, metabolism, and cerebral blood flow. This approach is instrumental in bridging the gap between molecular-scale events and observable physiological phenomena, enhancing our understanding of cerebral metabolism and its critical role in the brain’s function.Paper I sets the foundation by developing a mechanistic model that integrates the mechanisms of the NVC with the metabolism. This model connects cerebral regulation of blood flow and metabolism, using small mechanistic model to represent the central metabolism. By integrating experimental data based on nuclear magnetic resonance spectroscopy (NMRS), the model successfully captures the dynamics of metabolites in response to neuronal stimuli, providing a crucial link between metabolic changes and NVC.Paper II extends the investigation to the realm of ion channel kinetics. By developing a generic model structure for voltage-gated ion channels, this paper explores how ion channel activity, a fundamental aspect of neuronal function, influences cerebral metabolism. The model, validated against experimental data and existing kinetic models, accurately predicts various channel behaviours and action potential characteristics. It includes mechanisms like voltage sensor movements and rate constants dependent on membrane voltage, offering a universal approach for studying all types of voltage-gated ion channels in neural networks and other applications.Paper III further explores the neurovascular relationship by examining the influence of inhibitory neurons on CBF and metabolism. This study introduces an expanded mathematical model that integrates the effects of γ-aminobutyric acid(GABA)ergic inhibitory neurons on vascular responses, aligning with new experimental evidence and enhancing understanding of neurovascular coupling (NVC). The model, validated with data from various studies, not only captures vascular changes triggered by inhibitory neuron activation but also reveals how these neurovascular responses vary with stimulation frequency, underscoring the important role of inhibitory neuron in the NVC.Paper IV tackles the critical aspect of accurately measuring metabolic fluxes in cells, focusing on 13C MFA. This study introduces a novel approach for model selection in MFA, ensuring that the chosen models accurately represent the underlying metabolic processes. This method enhances our ability to identify and understand key metabolic pathways and reactions, providing deeper insights into various metabolic conditions. Connecting back to the cerebral metabolism, application of 13C MFA to neuronal systems offers a powerful tool for studying metabolically linked neuropathology such as the development of Alzheimer’s disease.In Conclusion, this thesis establishes key components for understanding the mechanisms of the cerebral metabolism. The integration of mathematical modelling across different scales, from ion channels to cerebral blood flow, is used to provide a comprehensive perspective on how cerebral metabolism is regulated and how it interacts with other physiological processes. This work not only advances our basic scientific knowledge but also holds significant potential for improving our understanding of neurological disorders where metabolism and neurovascular function are impaired.
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| 6. |
- Aryuwat, Pimwalunn, et al.
(författare)
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Factors Associated with Resilience among Thai Nursing Students in the Context of Clinical Education : A Cross-sectional Study
- 2024
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Ingår i: Education Sciences. - 2227-7102. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Resilience aids nursing students in dealing with adversities during their nursing education. This study examined the relationship between nursing students’ resilience and relevant variables in the context of clinical education. Methods: A cross-sectional study was conducted to collect data from 319 undergraduate nursing students in Northeast Thailand. The Connor–Davidson Resilience Scale, the Multidimensional Scale of Perceived Social Support, the Learning Experience Scale or the Personal Responsibility Orientation to Self-Direction in Learning Scale, and the Stressors in Nursing Students scale were administered. A multiple regression analysis was performed for factors presumed to be associated with resilience. Results reported that Thai nursing students’ average resilience score was 71.79 ± 16.33. Multiple regression analysis indicated factors associated with resilience, in which social support (β = 0.354, p < 0.001, 95%CI: 0.240 to 0.469) and self-directed learning (β = 0.787, p < 0.001, 95%CI: 0.606 to 0.968) showed a positive association, while stress (β = −0.083, p = 0.025, 95%CI: −0.083 to −0.006) had a negative association. The final model accounted for 43.4% of the variance in the resilience score. In conclusion, self-directed learning, social support, and perceived stress among nursing students during clinical education are associated with their resilience.
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| 7. |
- Bednarska, Olga, 1973-
(författare)
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Peripheral and Central Mechanisms in Irritable Bowel Syndrome : in search of links
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Irritable bowel syndrome (IBS) is a chronic visceral pain disorder with female predominance, characterized by recurrent abdominal pain and disturbed bowel habits in the absence of an identifiable organic cause. This prevalent and debilitating disease, which accounts for a substantial economic and individual burden, lacks exact diagnostic tools and effective treatment, since its pathophysiology remains uncertain. The bidirectional and multilayered brain-gut axis is a well-established disease model, however, the interactions between central and peripheral mechanisms along the brain-gut axis remain incompletely understood. One of the welldescribed triggering factors, yet accounting for only a fraction of IBS prevalence, is bacterial gastroenteritis that affects mucosal barrier function. Altered gut microbiota composition as well as disturbed intestinal mucosal barrier function and its neuroimmune regulation have been reported in IBS, however, the impact of live bacteria, neither commensal nor pathogenic, on intestinal barrier has not been studied yet. Furthermore, abnormal central processing of visceral sensations and psychological factors such as maladaptive coping have previously been suggested as centrally-mediated pathophysiological mechanisms of importance in IBS. Brain imaging studies have demonstrated an imbalance in descending pain modulatory networks and alterations in brain regions associated with interoceptive awareness and pain processing and modulation, particularly in anterior insula (aINS), although biochemical changes putatively underlying these central alterations remain poorly understood. Most importantly, however, possible associations between these documented changes on central and peripheral levels, which may as complex interactions contribute to disease onset and chronification of symptoms, are widely unknown.This thesis aimed to investigate the peripheral and central mechanisms in women with IBS compared to female healthy controls (HC) and to explore possible mutual associations between these mechanisms.In Paper I, we studied paracellular permeability and passage of live bacteria, both commensal and pathogenic through colonic biopsies mounted in Ussing chambers. We explored the regulation of the mucosal barrier function by mast cells and the neuropeptide vasoactive intestinal polypeptide (VIP) as well as a correlation between mucosal permeability and gastrointestinal and psychological symptoms. We observed increased paracellular permeability and the passage of commensal and pathogenic live bacteria in patients with IBS compared with HC, which was diminished by blocking the VIP receptors as well as after stabilizing mast cells in both groups. Moreover, higher paracellular permeability was associated with less somatic and psychological symptoms in patients.In Paper II, we aimed to determine the association between colonic mucosa paracellular permeability and structural and resting state functional brain connectivity. We demonstrated different patterns of associations between mucosa permeability and functional and structural brain connectivity in IBS patients compared to HC. Specifically, lower paracellular permeability in IBS, similar to the levels detected in HC, was associated with more severe IBS symptoms and increased functional and structural connectivity between intrinsic brain resting state network and descending pain modulation brain regions. Our findings further suggested that this association between mucosa permeability and functional brain connectivity was mainly mediated by coping strategies.In Paper III, we investigated putative alterations in excitatory and inhibitory neurotransmission of aINS, as the brain’s key node of the salience network crucially involved in cognitive control, in IBS patients relative to HC and addressed possible connections with both symptoms and psychological factors. We found decreased concentrations of the excitatory neurotransmitter Glx in bilateral aINS in IBS patients compared to HC, while inhibitory neurotransmitter GABA+ levels were comparable. Further, we demonstrated hemisphere-specific associations between abdominal pain, coping and aINS excitatory neurotransmitter concentration.In conclusion, this thesis broadens the knowledge on peripheral and central mechanisms in IBS and presents novel findings that bring together the ends of brain-gut axis. Our results depict association between mucosal permeability, IBS symptoms and functional and structural connectivity engaging brain regions involved in emotion and pain modulation as well as underlying neurotransmitter alterations.
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| 8. |
- Vigren, Patrick
(författare)
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On the Kleine-Levin Syndrome
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Populärvetenskaplig sammanfattning på svenska Kleine-Levins syndrom är en sömnsjukdom som beskrevs av Willi Kleine 1925 och därefter utvecklades i fallbeskrivningar av Max Levin och McDonald Chritchley. De symptom som beskrevs var återkommande sömnperioder (periodisk hypersomnia), en tendens att äta mycket i samband med dessa perioder (hyperfagi) och ökad sexdrift i samband med perioderna (hypersexualitet) och, i senare beskrivningar, kognitiva och beteendemässiga störningar. Enligt tidigare beskrivningar var patienterna återställda mellan sömnperioderna. Dessa varade i dagar-veckor och återkom flera gånger årligen. Sjukdomen debuterade vanligtvis i tonåren och beskrevs gå över efter åtta år.d avhandling beskriver diagnosens utveckling över tid och sätter forskningen i sitt teoretiska sammanhang. Med det senare menas att det diskuteras hur forskningen förhåller sig till en diagnos som förändras över tid och där olika läkare kan ha olika kunskap kring och förhållningssätt till diagnosen.De studier som ingår i avhandlingen har undersökt flera olika aspekter av Kleine-Levins syndrom. Den första studien undersökte arbetsminnet hos patienterna och kunde påvisa att det var nedsatt jämfört med friska försökspersoner, även mellan sömnperioderna, något som inte var visat systematiskt tidigare. Dessutom sågsandra aktiveringsmönster i hjärnan när patienterna försökte klara arbetsminnesuppgiften, jämfört med aktiveringsmönstren hos friska försökspersoner. Hos hälften av patienterna sågs dessutom avvikande blodflöde i delar av hjärnan även när ingen särskild arbetsuppgift utfördes. Detta sågs även hos patienter som tillfrisknat.Då det funnits hypoteser i annan forsking att sjukdomen kan ha ett genetiskt/ärftligt inslag undersöktes huruvida patienterna hade en gen som tidigare har kopplats till sjukdomen. I den grupp av patienter som undersöktes i avhandlingens sista artikel kunde dock ingen sådan koppling ses.Slutsatsen av forskningsresultaten är att (1) patienter med Kleine-Levins syndrom har en störning av arbetsminnet som verkar konstant. (2) De uppvisar andra hjärnaktiveringsmönster än friska personer som gör samma arbetsminnesuppgift. (3) Hälften av patienterna har ett avvikande blodflödesmönster även i vila och efter tillfrisknande. (4) En eventuell ärftlig komponent kan inte påvisas avseende de undersökta generna.
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| 9. |
- Pålsson, Ylva, 1971-
(författare)
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A pathway into the profession : The use, feasibility and outcomes of a peer learning intervention for nursing students and newly graduated nurses
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall aim of present thesis was to study the use, feasibility and outcomes of a peer learning intervention for nursing students and new graduates, including studies using a quasi-experimental (Study I and III), descriptive (Study II) and mixed-methods (Study IV) design. Data were collected using questionnaires, observations, checklists for intervention fidelity, individual interviews and group interviews. When studying peer learning outcomes among nursing students, peer learning seems to have a significant interaction effect on self-efficacy, based on a comparison of changes over time between the intervention (n=42) and comparison (n=28) groups. Studying each group separately over time, significant improvements were found in the intervention group on thirteen of the twenty variables, whereas the comparison group improved on four (Study I). Observations of how nursing students (n=16) used peer learning revealed that the student pairs collaborated to different extents and in different ways. All students were observed practicing several competencies together (Study II). Testing the peer learning model in new graduates’ workplace introduction (n=10) revealed that new graduates’ descriptions of peer learning were consistent with the theoretical description (Study III). Feasibility was tested in relation to compliance and acceptability, and lessons were learned. In Study IV, fidelity to the intervention was generally good. When first-line managers (n=8) described their perception of using the peer learning intervention with new graduates, predominantly positive outcomes were expressed. When examining the effect of peer learning in workplace introduction for newly graduated nurses (n=35), it was difficult to draw any conclusions due to recruitment problems (Study IV). The conclusions is that peer learning is a useful model for nursing students’ that seems to improve self-efficacy more than traditional supervision does. The model gives nursing students opportunities to practice several competencies on each other, and these competencies, e.g., leadership and organizational skills are useful in their future profession. The students practice teaching and supervision skills on each other, which seems to be a natural part of the peer relationship. Peer learning in the context of new graduates’ workplace introduction describes in a way consistent with the theoretical description of peer learning outcomes thus, also here it seems as a useful model. When developing and testing new interventions such as peer learning, it is important to do so systematically to minimize problems when conducting an evaluation, where the MRC framework can be useful. First-line managers generally expressed a positive attitude toward the peer learning model.
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