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Dissertation
Persistant remembering and directed forgetting : Appraising emotional memory attenuation techniques
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Year: 2020 Publisher: Leuven KU Leuven. Faculteit Psychologie en Pedagogische Wetenschappen

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Dissertation
The role of childhood adversities in fibromyalgia a multiple level approach The role of childhood adversities in fibromyalgia
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Year: 2019 Publisher: Leuven KU Leuven. Faculteit Psychologie en pedagogische wetenschappen

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Dissertation
Role of the Microbiome in the etiology and pathophysiology of Chronic Fatigue Syndrome
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Year: 2019 Publisher: Leuven KU Leuven. Faculteit Geneeskunde

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Background: Chronic fatigue syndrome (CFS) remains the subject of controversy because of its unknown etiology and pathophysiology. The disease is characterized by a wide range of symptoms, most importantly extreme fatigue. Although the etiology of CFS is unknown, studies show evidence for central nervous system (CNS) and/or immune system abnormalities. Together with the common co-morbidity of gastrointestinal symptoms, recent research in CFS focuses on the putative involvement of the gut microbiota, acting through the gut-brain axis. More specifically, perturbation of the intestinal microbial community (i.e. dysbiosis) in CFS might lead to gastrointestinal discomfort, peripheral inflammation and neuroinflammation. This systematic review summarizes published microbiome studies in CFS patients to explore the hypothesis for a role of the gut microbiota in the etiology and pathophysiology of CFS. Methods: A literature search was conducted using the electronic databases PubMed, Embase, Web of Science and Google Scholar. After applying the specific search terms, all articles were screened on title and abstract. The included studies were assessed for methodological quality using the Critical Appraisal Skills Programme (CASP) checklist. Data pooling was prevented due to poor quality of and variability between the studies. Results: Nine articles were included in the analysis. All studies but one recorded significant alterations of the gut microbiota in the CFS cohort in comparison to healthy controls. However, the results appeared to be inconsistent and difficult to interpret. The main reason for these conflicting results is the poor quality of the included studies, due to the lack of statistical power, emerging from small sample sizes. Conclusion: There is insufficient evidence to confirm a link between dysbiosis and the etiology and pathophysiology of CFS. Future research should focus on proper sample size and study design, i.e. longitudinal studies, to define causality and to control for confounding factors within the study population.

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Dissertation
The pleasure of absent danger : Subjective, physiological and neural correlates of threat omission relief
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Year: 2023 Publisher: Leuven KU Leuven. Faculteit Psychologie en Pedagogische Wetenschappen

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Dissertation
Cardiac Vagal Tone as a Mediating Variable between Personality and Pain Outcome
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Year: 2012 Publisher: Leuven K.U.Leuven. Faculteit Psychologie en Pedagogische Wetenschappen

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Dissertation
Symptom Referral in Patients with Globus

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Background. Globus is the uncomfortable feeling of a lump in the throat. Although a lot of research has been done on the subject, the etiology remains unclear. Chen et al. (2009) suggested visceral hypersensitivity and aberrant symptom referral as a possible cause. Aim. To assess differences in perception thresholds and symptom location during repeated esophageal and UES balloon distension in subjects with and without globus.Methods. 44 globus patients and 25 healthy controls participated. Perception and discomfort thresholds were assessed using stepwise isobaric esophageal balloon distensions (2mmHg/30sec). The barostat balloon was located in the UES and in the esophageal body 10 cm below the UES. Both tests were repeated, with the second measurement immediately following the first. Location of perception was indicated on a body map. A mixed procedure, two-way ANOVA, was used to analyze the data. Results. Patients showed more proximal discomfort during the second esophageal distension in comparison the first distension (1.62 cm vs. 2.39 cm above the xyphoid, p=0.0030), whereas controls showed no significant changes. Patients showed lower discomfort thresholds at second distension (sensitization, from 21.41 mmHg vs. 17.19 mmHg, p<.0001) whereas controls did not show any significant changes. Combined, this indicates that the lower the discomfort thresholds, the higher patients perceive the sensation of discomfort, as confirmed by mixed regression analysis. Conclusion. Globus patients perceive the sensation evoked by repeated esophageal balloon distension significantly higher than healthy control. In addition, patients show lowered discomfort thresholds during the second compared to the first distension sequence, whereas controls show no significant changes. We can conclude that the globus patients are characterized by sensitization upon repeated esophageal distension, corresponding with increased height of symptom perception.

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Dissertation
What did Pavlov's dogs hear? : Perceptual alterations through conditioning and their pathogenic potential in chronic pain
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Year: 2016 Publisher: Leuven KU Leuven. Faculteit Psychologie en Pedagogische Wetenschappen

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The effect of stress on subsequent fear acquisition and extinction in men.
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Year: 2022 Publisher: Leuven KU Leuven. Faculteit Geneeskunde

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The interaction between stress and fear conditioning serves as an illuminating model in the understanding of anxiety disorders. Previous work has shown that stress may change subsequent fear acquisition and extinction learning, likely through the stress hormone cortisol. However, variable effects have been described, ranging from facilitative, inhibitory, to null effects. In this article, we first performed a systematic review on the association of stress on subsequent fear acquisition and extinction learning in men. Then, we performed secondary analysis on an existing dataset comprising 133 men who underwent the Maastricht Acute Stress Test (MAST) prior to completing a fear acquisition and extinction task. We examined whether cortisol response trajectories derived from latent-class growth analysis (mild responders (n = 15), moderately-low responders (n = 46), moderately-high responders (n = 48), and hyper responders (n = 24)) could predict the rate of fear acquisition and/or extinction learning, as assessed by US expectancy ratings and skin conductance responses (SCRs). Our systematic review did not reveal a clear consensus pertaining to the association of stress on subsequent fear acquisition. For fear extinction, a negative association of stress exposure, and thus greater extinction resistance, was indicated. In our analysis, we found no significant associations between cortisol response trajectories in response to the MAST and subsequent fear acquisition. We did find an association with extinction learning as assessed by US expectancy ratings, suggesting better safety learning in participants with a hyper-responder cortisol trajectory participant. In addition, during extinction learning, higher overall SCRs were observed in these hyper-responders, indicating greater general arousal during extinction learning independent of stimulus type. These results demonstrate that cortisol responsiveness to a psychosocial stressor interferes with rate of extinction learning at the subjective level and promoted general arousal during this phase at the physiological level. As extinction learning is the theoretical model of exposure therapy, these findings could have clinical implications.

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Dissertation
Pharmacological and nutritional interventions to adapt gastrointestinal functions and improve functional gastrointestinal symptoms
Authors: --- --- ---
Year: 2020 Publisher: Leuven KU Leuven. Faculty of Medicine

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Functional dyspepsia (FD) and irritable bowel syndrome (IBS) are two common functional gastrointestinal disorders (FGIDs). Both conditions have a considerable impact on quality of life and presumably result from a heterogeneous and multifactorial pathophysiology with several factors suggested to be involved. To date, no reliable biomarker to accurately diagnose these FGIDs has been identified. Consequently, the diagnosis of FD and IBS is primarily based on symptom features, reflected in the Rome criteria. Due to the heterogeneity of both disorders in terms of pathophysiology and symptoms, correctly diagnosing the disorders and finding efficient treatment options to successfully improve symptoms has been proven challenging. Furthermore, the currently available therapies remain suboptimal, resulting in increased health care utilization, increasing health care costs, for both the patient and the society. The medical need for efficient and cost-efficient therapies for FD and IBS is high. As a result, the interest in non-pharmacological treatment options for FD and IBS has increased over the last decades. This doctoral thesis aims to investigate the effects of several therapeutic options (pharmacological and non-pharmacological) used to treat FD and IBS on the function of the GI tract and on gastrointestinal symptoms. Compounds investigated in relation to FD are (1) acotiamide, a first-in-class compound developed to treat FD, (2) the combination of peppermint oil and caraway oil and (3) rikkunshito, a Japanese Kampo herbal medicine to treat upper GI complaints. For IBS, the low-FODMAP diet is a frequently used treatment option to alleviate symptoms. Therefore, the effects of FODMAPs on upper GI motility and brain activation are studied in this PhD project.

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Dissertation
Stress axis (dys)function in irritable bowel syndrome: the subjective, cerebral and cerebellar responses to induced stress
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Year: 2022 Publisher: Leuven KU Leuven. Faculteit Geneeskunde

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Introduction Irritable bowel syndrome (IBS) and its comorbidities are thought to be associated with a dysfunction of the stress system. Tools like the Montreal Imaging Stress Task (MIST) and the Maastricht Acute Stress Test (MAST) have been developed to assess the response to experimental stress induction. The main aim of this pilot study is to investigate the effectiveness of these instruments in inducing stress in the population of IBS patients. Methods For both stress tasks, we included 9 patients diagnosed with irritable bowel syndrome according to the Rome IV criteria, regardless of the presence of any comorbidities. The MIST involved the performance of mental arithmetic in an MRI-scanner, with the temporary addition of stress provoking elements during the so-called ‘stress blocks’. During the MAST, stress was induced by alternating hand immersion trials in cold water and mental arithmetic, with a social evaluative component. The perceived stress during both tasks was assessed by means of short questionnaires and Visual Analogue Scales (VAS). Results Both the MIST and the MAST seemed to be effective in eliciting subjective stress. In our small patient samples, not all effect sizes were large enough to be significant, presumably partly due to the presence of anticipatory stress at the moment the first VAS in the MAST protocol was completed. Interestingly, the functional brain images primarily revealed stress-induced activation of the cerebellum, more specifically at the level of the left crus I and the right lobule VI. Discussion We can proceed using these tools for stress induction in the population of IBS patients, provided that subjective scores continue to be monitored. Furthermore, we suggest the addition of a baseline VAS in the MAST protocol, to reduce the effect of anticipatory stress. The interesting finding of cerebellar activation during stress supports existing hypotheses of an underestimated role for the cerebellum in the stress system and in the IBS pathophysiology.

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