253 research outputs found
The Role of Dopamine in Anticipatory Pursuit Eye Movements: Insights from Genetic Polymorphisms in Healthy Adults
There is a long history of eye movement research in patients with psychiatric diseases for which dysfunctions of neurotransmission are considered to be the major pathologic mechanism. However, neuromodulation of oculomotor control is still hardly understood. We aimed to investigate in particular the impact of dopamine on smooth pursuit eye movements. Systematic variability in dopaminergic transmission due to genetic polymorphisms in healthy subjects offers a noninvasive opportunity to determine functional associations. We measured smooth pursuit in 110 healthy subjects genotyped for two well-documented polymorphisms, the COMT Val158Met polymorphism and the SLC6A3 3´-UTR-VNTR polymorphism. Pursuit paradigms were chosen to particularly assess the ability of the pursuit system to initiate tracking when target motion onset is blanked, reflecting the impact of extraretinal signals. In contrast, when following a fully visible target sensory, retinal signals are available. Our results highlight the crucial functional role of dopamine for anticipatory, but not for sensory-driven, pursuit processes. We found the COMT Val158Met polymorphism specifically associated with anticipatory pursuit parameters, emphasizing the dominant impact of prefrontal dopamine activity on complex oculomotor control. In contrast, modulation of striatal dopamine activity by the SLC6A3 3´-UTR-VNTR polymorphism had no significant functional effect. Though often neglected so far, individual differences in healthy subjects provide a promising approach to uncovering functional mechanisms and can be used as a bridge to understanding deficits in patients
Erste Nachweise von Bergmolchen (Ichthyosaura alpestris) im sachsenanhaltischen Fläming
In den Jahren 2009 und 2010 wurde das Büro Öko & Plan – Landschaftsplanung Dr. Simon durch das Landesamt für Umweltschutz Sachsen-Anhalt (LAU), Fachbereich Naturschutz, beauftragt, Untersuchungen zur Erfassung von Amphibien- und Reptilien-Arten der Anhänge II und IV der FFH Richtlinie sowohl in FFH-Gebieten als auch auf weiteren Flächen mit hohem Naturschutzwert im Nordosten Sachsen-Anhalts (rechtselbischer Teil) durchzuführen. Im Rahmen dieser Tätigkeit gelang Ralf Hennig am 02.07.2009 der Erstnachweis von Bergmolchen in einer Fahrspur nördlich Göritz inmitten eines Kiefernforstes im Hochfläming in Sachsen-Anhalt
Transient Experimental and 3D-FSI Investigation of Flapper Valve Dynamics for Refrigerant Compressors
The design of the valves for refrigerant compressors has a distinct influence on the efficiency of the refrigeration cycle. In order to predict the valve behavior for compressor optimization, flow characteristics and valve system dynamics are key factors. State of the art valve model approaches have to date ignored the retainer deflection and the influence of contact effects on fluid-structure interaction behavior. With this fact in mind, experimental valve lift investigations by means of laser vibrometry measurements were performed. In order to determine dynamic flapper valve characteristics, oscillation frequency analyses and numerical natural frequency analyses for free oscillation of the flapper valve were carried out. Additionally this paper presents an extended three-dimensional numerical discharge valve model containing a fully-coupled fluid-structure interaction (FSI) approach. The two-way mechanical coupling is carried out by a commercial CFD code combined with a commercial FEA package. The numerical results are validated using the presented experimental transient results and compared to a lumped 1D valve model. The numerical 3D-FSI results show good agreement with the experimental results and allow for further investigations of multiphysics phenomena such as adhesive effects on the flapper valve
Условия формирования пласта Ю[2] Вынгапуровского месторождения Западно-Сибирского нефтегазоносного бассейна
Practical considerations for in vivo MRI with higher dimensional spatial encoding
Object: This work seeks to examine practical aspects of in vivo imaging when spatial encoding is performed with three or more encoding channels for a 2D image. Materials and methods: The recently developed 4-Dimensional Radial In/Out (4D-RIO) trajectory is compared in simulations to an alternative higher-order encoding scheme referred to as O-space imaging. Direct comparison of local k-space representations leads to the proposal of a modification to the O-space imaging trajectory based on a scheme of prephasing to improve the reconstructed image quality. Data were collected using a 4D-RIO acquisition in vivo in the human brain and several image reconstructions were compared, exploiting the property that the dense encoding matrix, after a 1D or 2D Fourier transform, can be approximated by a sparse matrix by discarding entries below a chosen magnitude. Results: The proposed prephasing scheme for the O-space trajectory shows a marked improvement in quality in the simulated image reconstruction. In experiments, 4D-RIO data acquired in vivo in the human brain can be reconstructed to a reasonable quality using only 5% of the encoding matrix—massively reducing computer memory requirements for a practical reconstruction. Conclusion: Trajectory design and reconstruction techniques such as these may prove especially useful when extending generalized higher-order encoding methods to 3D image
Time Scales of Auditory Habituation in the Amygdala and Cerebral Cortex
Habituation is a fundamental form of learning manifested by a decrement of neuronal responses to repeated sensory stimulation. In addition, habituation is also known to occur on the behavioral level, manifested by reduced emotional reactions to repeatedly presented affective stimuli. It is, however, not clear which brain areas show a decline in activity during repeated sensory stimulation on the same time scale as reduced valence and arousal experience and whether these areas can be delineated from other brain areas with habituation effects on faster or slower time scales. These questions were addressed using functional magnetic resonance imaging acquired during repeated stimulation with piano melodies. The magnitude of functional responses in the laterobasal amygdala and in related cortical areas and that of valence and arousal ratings, given after each music presentation, declined in parallel over the experiment. In contrast to this long-term habituation (43 min), short-term decreases occurring within seconds were found in the primary auditory cortex. Sustained responses that remained throughout the whole investigated time period were detected in the ventrolateral prefrontal cortex extending to the dorsal part of the anterior insular cortex. These findings identify an amygdalocortical network that forms the potential basis of affective habituation in human
Multidirectional flow analysis by cardiovascular magnetic resonance in aneurysm development following repair of aortic coarctation
Aneurysm formation is a life-threatening complication after operative therapy in coarctation. The identification of patients at risk for the development of such secondary pathologies is of high interest and requires a detailed understanding of the link between vascular malformation and altered hemodynamics. The routine morphometric follow-up by magnetic resonance angiography is a well-established technique. However, the intrinsic sensitivity of magnetic resonance (MR) towards motion offers the possibility to additionally investigate hemodynamic consequences of morphological changes of the aorta
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