Global ETD Search

1	Cerebral Perfusion and Metabolism during Experimental Extracorporeal Circulation Jonsson, Ove January 2011 (has links) Neurologic injuries are major causes of mortality and morbidity after cardiac surgery. This thesis aimed to investigate cerebral metabolism and perfusion abnormalities in pigs during hypothermic circulatory arrest, selective antegrade cerebral perfusion (SACP) and extracorporeal circulation following progressive venous stasis. Hypothermic circulatory arrest induced a metabolic pattern consistent with overt ischaemia, which was absent following SACP. In contrast, metabolism during SACP was influenced by the perfusate temperature, where a colder perfusate (20 °C) preserved cellular metabolism and membrane integrity better than a warmer perfusate (28 °C). The minimum SACP flow required to maintain metabolism during hypothermia at 20 °C was investigated with magnetic resonance imaging, protein S100β, near infrared spectroscopy and microdialysis. The findings suggested an ischaemic threshold close to 6 ml/kg/min in the present models. Furthermore, regional differences in perfusion with a hemispheric distribution were apparent at all flow levels and differed from earlier studies where the differences were uniform and followed a neuranatomical pattern. Venus stasis following superior vena cava congestion produced measurable signs of impaired cerebral perfusion and patterns of cerebral ischaemia were evident in individual animals. As venous pressure increased, the mean arterial pressure stayed more or less unchanged, generating reduced cerebral perfusion pressure and consequently an increased risk of ischaemia, which may impair cerebral perfusion, especially in cases of compromised arterial flow during extracorporeal circulation. In conclusion, cerebral metabolism and perfusion are influenced by temperature, SACP flow levels and venous congestion. In clinical practice, the regional differences in perfusion during SACP may be of pathogenic importance in focal cerebral ischaemia. Furthermore, the reduced superior vena cava cannula flow may pass undetected during bicaval cardiopulmonary bypass if the superior vena cava flow is not specifically monitored. cerebral perfusion Experimental brain research Experimentell hjärnforskning
2	Train your brain : updating, transfer, and neural changes / Träning av hjärnan : uppdatering, transfer effekter, och neurala förändringar Dahlin, Erika January 2009 (has links) An initial aim of this thesis was to determine whether training of a specific executive function (updating) produces improvements in performance on trained and transfer tasks, and whether the effects are maintained over time. Neural systems underlying training and transfer effects were also investigated and one question considered is whether transfer depends on general or specific neural overlap between training and transfer tasks. An additional aim was to identify how individual differences in executive functioning are mapped to functional brain changes. In Study I, significant training-related changes in performance on the letter memory criterion task were found in both young and older adults after 5 weeks of updating training. Transfer to a 3-back test of updating was also demonstrated in the young adults. Functional Magnetic Resonance Imaging (fMRI) revealed overlapping activity in letter memory and 3-back tasks in fronto-parietal areas and striatum pre-training, and a joint training-related activity increase for the tasks in a striatal region. No transfer was observed to a task (Stroop) that engaged fronto-parietal areas, but not the striatal region and updating per se. Moreover, age-related striatal changes imposed constraints on transfer. In Study II, additional transfer tasks and a test of long-term maintenance were included. Results revealed that training-related gains in performance were maintained 18 months post-training in both young and older adults, whereas transfer effects were limited to tasks requiring updating and restricted to young participants. In Study III, analyses of brain activity and performance during n-back (1/2/3-back) were executed. This task enables manipulation of executive demand, which permits examination of how individual differences in executive functioning can be mapped to functional brain changes. Relative to a young high- performing group, capacity constraints in executive functioning were apparent between 1–2-back for the elderly participants and between 2–3-back for a young low-performing group. Capacity constraints in neural activity followed this pattern by showing a monotonically increasing response in the parietal cortex and the thalamus for young high performers, whereas activity levelled off at 1-back for elderly performers and at 2-back for young low performers. The response in the dorsal frontal cortex followed a similar pattern. Together, these findings indicate that fronto-parietal as well as sub-cortical areas are important for individual differences in executive functioning, training of updating and transfer effects. cognitive training executive functioning transfer fMRI brain system young adults elderly practice neural correlates individual differences Experimental brain research Experimentell hjärnforskning Cognitive science Kognitionsforskning
3	Positron Emission Tomography (PET) Studies in Anxiety Disorders Michelgård Palmquist, Åsa January 2010 (has links) Anxiety disorders are very common and the primary feature is abnormal or inappropriate anxiety. Fear and anxiety is often mediated by the amygdala, a brain structure rich in substance P (SP) and neurokinin 1 (NK1) receptors. To learn more about how the human amygdala is modulated by fear and anxiety in event-triggered anxiety disorders and to investigate if the SP/NK1 receptor system is affected, regional cerebral blood flow (rCBF) ([15O]-water; Study I and II) and the SP/NK1 receptor system ([11C]GR205171; Study III and IV) were studied with positron emission tomography (PET). In Study I we investigated the neural correlates of affective startle modulation in persons with specific phobia by measuring rCBF during exposure to fearful and non-fearful pictures, paired and unpaired with acoustic startle stimuli. Fear-potentiated startle was associated with activation of the affective part of the anterior cingulate cortex and the left amygdaloid–hippocampal area. In Study II short-term drug treatment effects on rCBF in patients diagnosed with social phobia was evaluated, comparing the NK1 receptor antagonist GR205171 to the selective serotonin reuptake inhibitor citalopram and placebo. Social anxiety and neural activity in the medial temporal lobe including the amygdala was significantly reduced by both drugs but not placebo. In Study III we investigated if activity in the SP/NK1 receptor system in the amygdala would be affected by fear provocation in individuals with specific snake or spider phobia. Fear provocation was associated with a decreased uptake of the NK1 antagonist [11C]GR205171 in the amygdala, possibly explained by an increase in endogenous SP release occupying the NK1 receptors. Study IV was conducted to explore the resting state NK1 receptor availability in PTSD patients as compared to healthy controls. Increased resting state binding of the tracer [11C]GR205171 in the amygdala of patients with PTSD suggested an increased amount of available receptors. In summary, fear and fear-potentiated startle modulates the human amygdala, possibly through the SP/NK1 receptor system. Positron emission tomography PET amygdala fear anxiety anxiety disorders specific phobia social phobia posttraumatic stress disorder PTSD regional cerebral blood flow rCBF substance P SP neurokinin 1 receptor NK1 GR205171 STAI-S Psychiatry Psykiatri Neurobiology Neurobiologi Neuroscience Neurovetenskap Experimental brain research Experimentell hjärnforskning Molecular neurobiology Molekylär neurobiologi Radiation biology Strålningsbiologi Neurobiology Neurobiologi Neurobiology Neurobiologi

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