- About
-
The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
provided by the
Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
Search results
Showing 81 to 90 of 138 (0.082 seconds)| 81 |
The effect of body posture on cognitive performance: a question of sleep qualityMühlhan, Markus, Marxen, Michael, Landsiedel, Julia, Malberg, Hagen, Zaunseder, Sebastian 14 July 2014 (has links) (PDF)
Nearly all functional magnetic resonance imaging (fMRI) studies are conducted in the supine body posture, which has been discussed as a potential confounder of such examinations. The literature suggests that cognitive functions, such as problem solving or perception, differ between supine and upright postures. However, the effect of posture on many cognitive functions is still unknown. Therefore, the aim of the present study was to investigate the effects of body posture (supine vs. sitting) on one of the most frequently used paradigms in the cognitive sciences: the N-back working memory paradigm. Twenty-two subjects were investigated in a randomized within-subject design. Subjects performed the N-back task on two consecutive days in either the supine or the upright posture. Subjective sleep quality and chronic stress were recorded as covariates. Furthermore, changes in mood dimensions and heart rate variability (HRV) were assessed during the experiment. Results indicate that the quality of sleep strongly affects reaction times when subjects performed a working memory task in a supine posture. These effects, however, could not be observed in the sitting position. The findings can be explained by HRV parameters that indicated differences in autonomic regulation in the upright vs. the supine posture. The finding is of particular relevance for fMRI group comparisons when group differences in sleep quality cannot be ruled out.
|
| 82 |
Fear Processing in Dental Phobia during Crossmodal Symptom Provocation: An fMRI StudyHilbert, Kevin, Evens, Ricarda, Maslowski, Nina Isabel, Wittchen, Hans-Ulrich, Lüken, Ulrike 09 July 2014 (has links) (PDF)
While previous studies successfully identified the core neural substrates of the animal subtype of specific phobia, only few and inconsistent research is available for dental phobia. These findings might partly relate to the fact that, typically, visual stimuli were employed. The current study aimed to investigate the influence of stimulus modality on neural fear processing in dental phobia. Thirteen dental phobics (DP) and thirteen healthy controls (HC) attended a block-design functional magnetic resonance imaging (fMRI) symptom provocation paradigm encompassing both visual and auditory stimuli. Drill sounds and matched neutral sinus tones served as auditory stimuli and dentist scenes and matched neutral videos as visual stimuli. Group comparisons showed increased activation in the insula, anterior cingulate cortex, orbitofrontal cortex, and thalamus in DP compared to HC during auditory but not visual stimulation. On the contrary, no differential autonomic reactions were observed in DP. Present results are largely comparable to brain areas identified in animal phobia, but also point towards a potential downregulation of autonomic outflow by neural fear circuits in this disorder. Findings enlarge our knowledge about neural correlates of dental phobia and may help to understand the neural underpinnings of the clinical and physiological characteristics of the disorder.
|
| 83 |
Stimulationsintensitäten in kognitiven ParadigmenKaminski, Jakob 02 December 2015 (has links) (PDF)
Die transkranielle Magnetstimulation (TMS) ist zu einer essentiellen Untersuchungsmethode der Neurowissenschaften geworden. Sie ermöglicht es, mittels eines kurzen, starken Magnetfeldes, Neuronen im Gehirn anzuregen und kurzfristig deren Aktivität zu modulieren. Diese Effekte sind allerdings nur bei Stimulation des motorischen Kortexes als motorisch evozierte Potentiale (MEP) an peripheren Muskeln direkt messbar. Hier lässt sich auch eine individuelle Reizschwelle (engl. motorthreshold, MT) bestimmen, die sich allerdings von Proband zu Proband stark unterscheidet. Bei Stimulation außerhalb des motorischen Kortexes, bei der durch Änderung der Aktivität einer umschriebenen Neuronengruppe, behaviorale Effekte erzeugt werden sollen, existiert ein solches direktes Maß der neuronalen Erregbarkeit nicht, weshalb häufig die Stimulationsintensität an die individuelle MT angepasst wird. Die vorliegenden Arbeit stellt, diese Anpassung der Intensität in Frage. Hierzu erhielten Probanden vor der Durchführung eines kognitiven Tests über einer mittels funktioneller Magnetresonanztomographie (fMRT) ermittelten Region des präfrontalen Kortex eine Stimulation. Die Intensität wurde hierbei einmal an die MT angepasst und einmal nicht. Erstmals konnte mittels einer Korrelationsanalyse gezeigt werden, dass es einen Zusammenhang zwischen der Sensitivität des präfrontalen Kortexes und der des Motorkortexes gibt. Dieser Zusammenhang kann zur nachträglichen Korrektur der behavioralen Daten genutzt werden, da die MT die zwischen den Probanden bestehenden relativen Unterschiede erklärt.
|
| 84 |
MR-tomographische Bestimmung der zerebrovaskulären Reservekapazität bei Probanden und Patienten mittels BOLD-Kontrast / Non-invasive measurement of cerebrovascular reserve capacity in healthy adults and patients using BOLD fMRI at 3 TeslaRühlmann, Johanna 25 October 2011 (has links)
No description available.
|
| 85 |
Magnetresonanztomographische Untersuchung der Hirnnerven- Anatomie unter Verwendung von Volumensequenzen bei 3 Tesla / Cranial nerve anatomy using volume-sequences at 3 TeslaBrüggemann, Anne-Kathrin 02 November 2010 (has links)
No description available.
|
| 86 |
Enhanced Sympathetic Arousal in Response to fMRI Scanning Correlates with Task Induced Activations and DeactivationsMühlhan, Markus, Lüken, Ulrike, Siegert, Jens, Wittchen, Hans-Ulrich, Smolka, Michael N., Kirschbaum, Clemens 22 January 2014 (has links) (PDF)
It has been repeatedly shown that functional magnetic resonance imaging (fMRI) triggers distress and neuroendocrine response systems. Prior studies have revealed that sympathetic arousal increases, particularly at the beginning of the examination. Against this background it appears likely that those stress reactions during the scanning procedure may influence task performance and neural correlates. However, the question how sympathetic arousal elicited by the scanning procedure itself may act as a potential confounder of fMRI data remains unresolved today. Thirty-seven scanner naive healthy subjects performed a simple cued target detection task. Levels of salivary alpha amylase (sAA), as a biomarker for sympathetic activity, were assessed in samples obtained at several time points during the lab visit. SAA increased two times, immediately prior to scanning and at the end of the scanning procedure. Neural activation related to motor preparation and timing as well as task performance was positively correlated with the first increase. Furthermore, the first sAA increase was associated with task induced deactivation (TID) in frontal and parietal regions. However, these effects were restricted to the first part of the experiment. Consequently, this bias of scanner related sympathetic activation should be considered in future fMRI investigations. It is of particular importance for pharmacological investigations studying adrenergic agents and the comparison of groups with different stress vulnerabilities like patients and controls or adolescents and adults.
|
| 87 |
The Impact of Genome-Wide Supported Schizophrenia Risk Variants in the Neurogranin Gene on Brain Structure and FunctionWalton, Esther, Geisler, Daniel, Hass, Johannes, Liu, Jingyu, Turner, Jessica, Yendiki, Anastasia, Smolka, Michael N., Ho, Beng-Choon, Manoach, Dara S., Gollub, Randy L., Rößner, Veit, Calhoun, Vince D., Ehrlich, Stefan 06 February 2014 (has links) (PDF)
The neural mechanisms underlying genetic risk for schizophrenia, a highly heritable psychiatric condition, are still under investigation. New schizophrenia risk genes discovered through genome-wide association studies (GWAS), such as neurogranin (NRGN), can be used to identify these mechanisms. In this study we examined the association of two common NRGN risk single nucleotide polymorphisms (SNPs) with functional and structural brain-based intermediate phenotypes for schizophrenia. We obtained structural, functional MRI and genotype data of 92 schizophrenia patients and 114 healthy volunteers from the multisite Mind Clinical Imaging Consortium study. Two schizophrenia-associated NRGN SNPs (rs12807809 and rs12541) were tested for association with working memory-elicited dorsolateral prefrontal cortex (DLPFC) activity and surface-wide cortical thickness. NRGN rs12541 risk allele homozygotes (TT) displayed increased working memory-related activity in several brain regions, including the left DLPFC, left insula, left somatosensory cortex and the cingulate cortex, when compared to non-risk allele carriers. NRGN rs12807809 non-risk allele (C) carriers showed reduced cortical gray matter thickness compared to risk allele homozygotes (TT) in an area comprising the right pericalcarine gyrus, the right cuneus, and the right lingual gyrus. Our study highlights the effects of schizophrenia risk variants in the NRGN gene on functional and structural brain-based intermediate phenotypes for schizophrenia. These results support recent GWAS findings and further implicate NRGN in the pathophysiology of schizophrenia by suggesting that genetic NRGN risk variants contribute to subtle changes in neural functioning and anatomy that can be quantified with neuroimaging methods.
|
| 88 |
Neurochirurgie – aktuelle und zukünftige Konzepte einer verbesserten operativen TherapieSchackert, Gabriele, Steinmeier, Ralf 26 February 2014 (has links) (PDF)
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
|
| 89 |
Enhanced Sympathetic Arousal in Response to fMRI Scanning Correlates with Task Induced Activations and DeactivationsMühlhan, Markus, Lüken, Ulrike, Siegert, Jens, Wittchen, Hans-Ulrich, Smolka, Michael N., Kirschbaum, Clemens 22 January 2014 (has links)
It has been repeatedly shown that functional magnetic resonance imaging (fMRI) triggers distress and neuroendocrine response systems. Prior studies have revealed that sympathetic arousal increases, particularly at the beginning of the examination. Against this background it appears likely that those stress reactions during the scanning procedure may influence task performance and neural correlates. However, the question how sympathetic arousal elicited by the scanning procedure itself may act as a potential confounder of fMRI data remains unresolved today. Thirty-seven scanner naive healthy subjects performed a simple cued target detection task. Levels of salivary alpha amylase (sAA), as a biomarker for sympathetic activity, were assessed in samples obtained at several time points during the lab visit. SAA increased two times, immediately prior to scanning and at the end of the scanning procedure. Neural activation related to motor preparation and timing as well as task performance was positively correlated with the first increase. Furthermore, the first sAA increase was associated with task induced deactivation (TID) in frontal and parietal regions. However, these effects were restricted to the first part of the experiment. Consequently, this bias of scanner related sympathetic activation should be considered in future fMRI investigations. It is of particular importance for pharmacological investigations studying adrenergic agents and the comparison of groups with different stress vulnerabilities like patients and controls or adolescents and adults.
|
| 90 |
Brain responses to odor mixtures with sub-threshold componentsHummel, Thomas, Olgun, Selda, Gerber, Johannes, Huchel, Ursula, Frasnelli, Johannes 06 February 2014 (has links)
Although most odorants we encounter in daily life are mixtures of several chemical substances, we still lack significant information on how we perceive and how the brain processes mixtures of odorants. We aimed to investigate the processing of odor mixtures using behavioral measures and functional magnetic resonance imaging (fMRI). The odor mixture contained a target odor (ambroxan) in a concentration at which it could be perceived by half of the subjects (sensitive group); the other half could not perceive the odor (insensitive group). In line with previous findings on multi-component odor mixtures, both groups of subjects were not able to distinguish a complex odor mixture containing or not containing the target odor. However, sensitive subjects had stronger activations than insensitive subjects in chemosensory processing areas such as the insula when exposed to the mixture containing the target odor. Furthermore, the sensitive group exhibited larger brain activations when presented with the odor mixture containing the target odor compared to the odor mixture without the target odor; this difference was smaller, though present for the insensitive group. In conclusion, we show that a target odor presented within a mixture of odors can influence brain activations although on a psychophysical level subjects are not able to distinguish the mixture with and without the target. On the practical side these results suggest that the addition of a certain compound to a mixture of odors may not be detected on a cognitive level; however, this additional odor may significantly change the cerebral processing of this mixture. In this context, FMRI offers unique possibilities to look at the subliminal effects of odors.
|
Page generated in 0.0889 seconds