Biomedical subjects

Markus Raab

Publications and source records attributed to Markus Raab.

10 recordsLinked to original sources

PubMed2006

Why you think milan is larger than modena: neural correlates of the recognition heuristic.

When ranking two alternatives by some criteria and only one of the alternatives is recognized, participants overwhelmingly adopt the strategy, termed the recognition heuristic (RH), of choosing the recognized alternative. Understanding the neural correlates underlying decisions that follow the RH could help determine whether people make judgments about the RH's applicability or simply choose the recognized alternative. We measured brain activity by using functional magnetic resonance imaging while participants indicated which of two cities they thought was larger (Experiment 1) or which city they recognized (Experiment 2). In Experiment 1, increased activation was observed within the anterior frontomedian cortex (aFMC), precuneus, and retrosplenial cortex when participants followed the RH compared to when they did not. Experiment 2 revealed that RH decisional processes cannot be reduced to recognition memory processes. As the aFMC has previously been associated with self-referential judgments, we conclude that RH decisional processes involve an assessment about the applicability of the RH.

Adult↗

PubMed2005

Analyzing a complex visuomotor tracking task with brain-electrical event related potentials.

Non-invasive techniques such as neuroimaging and event-related potential (ERP) methods have dramatically enhanced our understanding of the human brain. According to the requirements of the applied method, it is useful to simplify tasks for methodological reasons. In the present study we tested whether ERP measures are also suitable for analyzing complex tasks. In order to do this, we developed an analysis strategy based on the post hoc analysis of the behavioural data. We applied this method to a pursuit-tracking task of 25 s trial duration, consisting of repeated and non-repeated waveforms, where subjects had to track a target cross with a mouse-controlled cursor cross. An EEG was recorded from 62 channels. Response-locked ERPs were computed for two types of error correction: the correction of errors induced externally by the change of target direction and of internal errors generated by the subject itself. We found several ERP components that could be assigned to different feedback and feedforward controlled processing steps in the frontoparietal circuitry underlying visuomotor control, such as movement planning, movement execution (motor potential), reafferent activity, visuospatial analysis, and attentional (P300) processes. Our results support newer models that propose a role for the posterior parietal cortex in integrating multimodal sensory information. In addition, fast (about 180 ms and probably facilitated by anticipation) and slow (about 230-260 ms) error corrections could be differentiated by the time course of ERP activity. Our results show that complex (motor) tasks can be investigated with ERPs. This opens fruitful perspectives for future research on motor control in an ecological setting.

Adult↗

PubMed2005

Improving the 'how' and 'what' decisions of elite table tennis players.

Training methods in sport usually focus on improving either technical or tactical aspects of performance, ignoring the fact that successful performance requires the athlete to simultaneously decide what movement to perform and how it should be executed. Young elite table tennis players were trained, in a first phase, to improve their forehand and backhand movements and, in a second phase, to make a tactical switch between forehand and backhand movements. Half of the players took part in behavioral training focusing on how to perform the required movements, whereas half received additional video feedback about their technical and tactical performance (decision training). The results indicate that improvements of how decisions (techniques) and what decisions (tactics) can occur as a consequence of combining technical and tactical training. These results were stable in delayed Post-test analyses of competitive matches. It was concluded that a combination of both technical and tactical training is beneficial to elite table tennis performers, particularly during early seasonal training programs.

Child↗

PubMed2005

Motion as input: a functional explanation of movement effects on cognitive processes.

Motion is often thought of as the result of perceptual and higher cognitive processes. Although this idea has been investigated in myriad ways, the understanding of how movements tune cognitive processes is still in its infancy. The present study examined the nonaffective tuning of movements (arm extension and arm flexion) on heuristic and systematic processes. In a departure from recent cognitive tuning models, a model was derived that defines the tuning effect based on the movement goal and not on the movement position. In the experiment, participants moved toward an extension or flexion position with a movement goal which connected the movement with either an avoidance or an approach function. Analysis indicated that cognitive tuning is a product of the movement goal rather than the movement position. Implications for models of motor control as well as for cognitive tuning models are presented.

Adult↗

PubMed2004

Individual differences of action orientation for risktaking in sports.

The goal of this article is to explain empirical risk-taking behavior in sports from an individual cognitive modeling perspective. A basketball task was used in which participants viewed four video options that varied in the degree of associated risk. The participants were independently classified by scores on the Questionnaire for Assessing Prospective Action Orientation and State Orientation in Success, Failure, and Planning Situations as action-oriented or state-oriented decision makers. The results of the experiment show that action-oriented players shoot faster and more often to the basket and that state-oriented players prefer to pass to a playmaker more often. Four versions of a computational model of decision making, Decision Field Theory, were compared to evaluate whether behavioral differences depend on the focus of attention, the initial preferences, threshold values, or an approach-avoidance interpretation of the task. Different starting preferences explained individual choices and decision times most accurately. Risk taking in basketball shooting behavior can be best explained by different preferences for starting values for risky and safe options caused by different levels of action orientation.

Adult↗

PubMed2002

In vitro effects of cyclosporin A on the expression of adhesion molecules on human umbilical vein endothelial cells.

BACKGROUND: Among the different factors playing crucial roles in endothelial cell activation, cytokines such as interleukin-1 (IL-1), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) have been reported to demonstrate profound effects on this cell type. It has been shown that the increased release of IFN-alpha/gamma and TNF-alpha causes structural and functional modulations of the endothelial cell. These cytokines participate in the recruitment and activation of the immune system. CsA is an immunosuppressive drug that is necessary at high levels in human recipients of vascularised xenografts. This drug could contribute to a prolonged graft survival by modulation of endothelial cell activation. METHODS: The present study deals with the effects of cyclosporin A on adhesion molecule expression (i.e. ICAM-1, VCAM-1, E-selectin, P-selectin, PECAM-1 and the L-selectin ligand CD 34) on the surface of cytokine stimulated HUVECs. The in vitro model described herein mimics the stimulation of endothelial cells by cytokines as seen during inflammatory processes after transplantation. Therefore, HUVECs were activated either with TNF-alpha, IL-1beta or with a cytokine mixture consisting of those stimulants present at an elevated level in sera of patients during allograft rejection (i.e. IL-1beta, IL-2, IL-4, IL-6, IL-10, TNF-alpha and IFN-gamma). RESULTS: The results obtained show that the immunosuppression of CsA is not only achieved by inhibiting lymphocyte proliferation, but also by decreasing the expression of adhesion molecules on endothelial cells, which are the first target of the cellular rejection process. CONCLUSION: Co-incubation of stimulated endothelial cells with a final CsA concentration of 5 microg/ml revealed a significant down-regulating influence on the surface expression of E-selectin and VCAM-1.

Adjuvants, Immunologic↗

PubMed2002

Influence of mycophenolic acid on inosine 5'-monophosphate dehydrogenase activity in human peripheral blood mononuclear cells.

BACKGROUND: Inosine 5'-monophosphate dehydrogenase (IMPDH) catalyses the oxidation of inosine 5'-monophosphate (IMP) to xanthosine 5'-monophosphate (XMP). Thus, this enzyme plays an important role in the rate-limiting step of the de novo guanine nucleotide biosynthesis, making it a potent target for immunosuppressive drugs. Mycophenolic acid (MPA) is the most potent and specific inhibitor of IMPDH. METHOD: IMPDH activity is determined via evaluation of XMP formation and the inhibitory influence of MPA in human peripheral blood mononuclear cells (PBMCs) is assessed by means of high-performance liquid chromatography (HPLC). For this objective, we have optimised a method based on solvent-generated ion exchange chromatography by cautiously varying mobile phase parameters. RESULTS: The optimised method renders it possible to separate 18 analytes in 54 min in a single isocratic experiment and to measure the IMPDH activity in the lysate of human PBMCs in dependence on incubation time, substrate, co-substrate and inhibitor concentrations. In this way, we have determined the Michaelis-Menten constants K(M) and V(max) for IMP and beta-NAD+ and the inhibitor constant K(i) for MPA. CONCLUSIONS: The chromatographic method presented in this report allows a rapid, reliable and reproducible quantification of IMPDH activity in PBMCs and therefore represents an attractive tool for the pharmacodynamic monitoring of the effects of MPA in patients under immunosuppressive therapy.

Chromatography, High Pressure Liquid↗

PubMed2002

Quantification of the influence of mycophenolic acid on the release of endothelial adhesion molecules.

BACKGROUND: Mycophenolic acid selectively inhibits inosine 5'-monophosphate dehydrogenase leading to a shortage of guanosine nucleotides. Since GTP is required for the synthesis of glycoproteins, this immunosuppressive drug also influences the production of several cell adhesion molecules. METHOD: Soluble endothelial cell adhesion molecules released into cell culture supernatants after an incubation period of 16 h are assessed via a standard ELISA procedure applying test kits for E-selectin, VCAM-1 and ICAM-1. RESULTS: Treatment with TNF-alpha leads to the induction of E-selectin and causes a significant increase in VCAM-1 and ICAM-1 content in the supernatant in relation to the level of unstimulated cells. Due to the inhibitory effects of MPA-applied either alone or in combination with cyclosporin A and prednisolone-sE-selectin is significantly reduced and sVCAM-1 is slightly but not significantly decreased, whereas sICAM-1 levels remain unchanged. CONCLUSIONS: We demonstrate that the influence of MPA on endothelial cell adhesion molecules can readily be determined via ELISA. The results indicate that the immunosuppression by MPA is also achieved by slightly reducing the expression and consequent release of E-selectin, a pivotal molecule in the first step of leucocyte-endothelial interactions.

Cell Adhesion Molecules↗

PubMed2002

Variation of adhesion molecule expression on human umbilical vein endothelial cells upon multiple cytokine application.

BACKGROUND: A variety of cytokines, mediators, activators, growth factors and other products are simultaneously released into circulation with the activation of the cellular immune system during rejection or infection. The secretion of these biochemical markers potentiates the immunological events associated with these processes. Among other things some cytokines demonstrate regulatory effects on the expression of endothelial cell adhesion molecules. METHOD: Endothelial cells are detached by trypsinisation and adhesion molecule expression is assessed by means of flow cytometry. Fluorescence-conjugated mouse monoclonal antibodies directed against VCAM-1, ICAM-1, PECAM-1, CD34, E- and P-selectin are used. RESULTS: The combined application of different cytokines synergistically evokes P-selectin expression after a chosen incubation period of 16 h, while under single cytokine treatment P-selectin induction is not observed. Co-stimulation with TNF-alpha and a second cytokine reduces its influence on E-selectin. IL-1 beta/IFN-gamma lead to E-selectin levels higher than those under treatment with one of the both alone. Concomitant incubation with all cytokines synergistically down-regulates PECAM-1 referred to each cytokine alone. CONCLUSION: Our investigations in some cases clearly demonstrate that the combination of a second cytokine with TNF-alpha, IL-1 beta or IFN-gamma can either synergistically or antagonistically modulate the expression of adhesion molecules on HUVECs.

Antigens, CD34↗

PubMed2002

Endothelial adhesion molecule expression in an in vitro model of inflammation.

BACKGROUND: Cytokines influence the expression of adhesion molecules and hence, regulate the passage of leucocytes from the blood to the site of inflammation causing leucocyte accumulation and the modulation of the nature and progression of inflammatory responses. They form a complex communication network causing results which are not determined by the effects of a single cytokine but especially by the interaction of several cytokines. METHOD: For the determination of adhesion molecule expression on the surface of enzymatically detached endothelial cells, flow cytometry is applied. Fluorescence-conjugated mouse monoclonal antibodies directed against VCAM-1, ICAM-1, PECAM-1, CD34, E- and P-selectin are used. RESULTS: We clearly demonstrate that ICAM-1, PECAM-1, P-selectin and CD34 are-in relation to an incubation cocktail containing solely TNF-alpha, IL-1beta and IFN-gamma-altered antagonistically by the supplementary addition of the inflammatory cytokines IL-2 and IL-6 as well as the anti-inflammatory cytokines IL-4 and IL-10, whereas VCAM-1 is synergistically enhanced under the same test conditions. CONCLUSION: The results of our in vitro investigations show that the effects of a single cytokine within a multi-component cytokine combination on endothelial adhesion molecule expression are strongly influenced by the nature of the other cytokines present in the combination tested.

Cell Adhesion Molecules↗