Trusting versus monitoring: an experiment of endogenous institutional choices

We investigate the problem of deciding between trusting and monitoring, and how this decision affects subsequent behavior, using a laboratory experiment where subjects choose between the Ultimatum and the Yes-No Game. Despite the similarity of the two games in Ultimatum Games responders monitor the allocation proposal, while in Yes-No games responders react without monitoring, i.e. have to rely on trust. We permit either the proposer or responder to make the game choice and analyze how both roles choose between trusting and monitoring, what the ensuing effects of their choices are, and how they vary depending on who has chosen the game. We, also, experimentally vary the cost of monitoring and the responder’s conflict payoff. Since monitoring is usually costly, the amount to share in Yes-No Games (YNG) can exceed that in Ultimatum Games (UG). Regarding the conflict payoff, it can be positive or negative with the former rendering Yes-No interaction a social dilemma. According to our results, proposers (responders) opt for trusting significantly more (less) often than for monitoring. Average offers are higher in Ultimatum than in Yes-No games, but neither UG nor YNG offers depend on who has chosen between games

Azamacrocyclic Ca2+ Sensitive Contrast Agents for MR Imaging

As calcium plays an important role in regulating a great variety of neuronal processes, many efforts are already made to generate gadolinium complexes that can act as a calcium-sensors in MRI.1 We developed a series of the DO3A-based macrocyclic and bismacrocyclic gadolinium chelates, bearing phosphonate groups as an additional coordination sites. These complexes are hypothesized to change the MRI contrast dynamically with Ca2+ concentration. Different lengths of the phosphonate side chains are exploited for fine-tuning the sensitivity of the agent to calcium ion concentration

Smart MRI Agents Sensing Extracellular Calcium Fluctuations

Functional Magnetic Resonance Imaging (fMRI) is currently the main tool used for the study of function and dysfunction of the human brain. The current mainstay of fMRI, the so-called Blood-Oxygen-Level-Dependent (BOLD) contrast, capitalizes on the detection of changes in cerebral blood flow, volume and oxygenation, but cannot directly report neural activity, as it suffers from poor spatiotemporal resolution and specificity compared to the actual neural events. An alternative methodology could be that relying on the responsive, ‘smart’ contrast agents whose relaxivity depends on the concentration of substances directly related to neuronal activity. Ca2+ is an excellent marker closely linked to brain activation and is preferred target for various imaging methods. We report two Gd3+ chelates linked to a modified EGTA moiety that have a relaxivity response to extracellular Ca2+ fluctuations in the brain. The proton relaxivity of both Gd3+ complexes is sensitive to the variation of Ca2+ concentration. They are selective to Ca2+ with respect to the main competitor cation Mg2+. Upon interaction with Ca2+, the complexes exhibit high and reversible relaxivity changes; the relaxivity response of one complex upon addition of Ca2+ exceeds 80. Moreover, the relaxivity changes remain remarkable (>50) even in the medium mimicking the brain extracellular fluid, exhibiting a ~10 relaxivity change in the physiologically relevant Ca2+ concentration range (changes induced during the neural activity). These agents have great potential to be applied as functional MR markers and be used for the visualization of the neural processes. They can substantially increase the specificity and spatial resolution of the MR-detected signals and open new perspectives in fMRI

Trusting versus monitoring: an experiment of endogenous institutional choices

We investigate the problem of deciding between trusting and monitoring, and how this decision affects subsequent behavior, using a laboratory experiment where subjects choose between the Ultimatum and the Yes-No Game. Despite the similarity of the two games in Ultimatum Games responders monitor the allocation proposal, while in Yes-No games responders react without monitoring, i.e. have to rely on trust. We permit either the proposer or responder to make the game choice and analyze how both roles choose between trusting and monitoring, what the ensuing effects of their choices are, and how they vary depending on who has chosen the game. We, also, experimentally vary the cost of monitoring and the responder’s conflict payoff. Since monitoring is usually costly, the amount to share in Yes-No Games (YNG) can exceed that in Ultimatum Games (UG). Regarding the conflict payoff, it can be positive or negative with the former rendering Yes-No interaction a social dilemma. According to our results, proposers (responders) opt for trusting significantly more (less) often than for monitoring. Average offers are higher in Ultimatum than in Yes-No games, but neither UG nor YNG offers depend on who has chosen between games

Sampling Order Optimization for contrast preservation in accelerated prospective 3D MRI

Purpose/Introduction: At ultra-short TE and TR, macromolecule quantification becomes extremely important [1, 2], because of shorter relaxation times and thus lower saturation, these molecules contribute greatly to the spectrum. Measuring the MMs and including them as a single baseline might not be enough because of regional and relaxation time differences between the different macromolecule components [1, 2]. In this work, we measured and modelled individual macromolecule components at 9.4T. We then used our proposed MM model to highlight the necessity of parametrizing the individual macromolecule components for ultra-short TE and TR MRSI measurements. Subjects and Methods: 8 healthy subjects were scanned on a 9.4T Siemens whole-body human scanner. Metabolite-nulled data using DIR [1] were acquired and used to model the MM baseline. The T1 of these metabolites in gray and white matter were estimated using variable flip angle method on MRSI datasets acquired at 4 different flip angles with a TR of 500 ms. High resolution (3.25mm 9 3.25mm 9 10 mm) ultra-short TE 1H FID MRSI [3–6] data with two different TRs of 300 ms and 500 ms were also collected. These data were fitted using LCMODEL [7] with three different MM baseline models (‘‘no MM’’, ‘‘measured MM’’ as an average single-component MM baseline model, and our proposed multi-component ‘‘modelled MM’’ shown in Figure 1a). Results: Figure 1 shows our proposed MM model along with the estimated T1 values. Figure 2 shows the metabolite maps resulting from fitting the datasets acquired at TR = 300 ms with 3 different models for 2 different volunteers. Figure 3 shows a boxplot of how much the metabolite concentrations are overestimated when different models are used. The difference between the two different TRs are due to saturation effects that have not been corrected for. However, the figure highlights how using different MM models on each TR can account for the macromolecule saturation effects. Discussion/Conclusion: Figure 1 shows that there are regional and relaxation time differences between individual macromolecule components that cause metabolite concentrations to differ from the no MM model to various degrees (as shown in Figure 2). Figure 3 further shows that if a single MM baseline is used in fitting, depending on the TR, the concentration of metabolite will be underestimated to varying degrees, since different macromolecule components relax at different rates. Also, due to regional differences, the overestimation degree varies between white and gray matter. The only way to account for all of this is to use a parametrized MM model like the one we have proposed

MRI sensing based on the displacement of paramagnetic ions from chelated complexes

We introduce a mechanism for ion sensing by MRI in which analytes compete with paramagnetic ions for binding to polydentate chelating agents. Displacement of the paramagnetic ions results in alteration of solvent interaction parameters and consequent changes in relaxivity and MRI contrast. The MRI changes can be tuned by the choice of chelator. As an example, we show that calcium-dependent displacement of Mn[superscript 2+] ions bound to EGTA and BAPTA results in a T[subscript 1]-weighted MRI signal increase, whereas displacement from calmodulin results in a signal decrease. The changes are ion selective and can be explained using relaxivity theory. The ratio of T[subscript 2] to T[subscript 1] relaxivity is also calcium-dependent, indicating the feasibility of “ratiometric” analyte detection, independent of the probe concentration. Measurement of paramagnetic ion displacement effects could be used to determine analyte ion concentrations with spatial resolution in opaque specimens.National Institutes of Health (U.S.) (grant DP2-OD2441)National Institutes of Health (U.S.) (grant R01-GM65519)McGovern Institute for Brain Research at MIT. Neurotechnology (MINT) Progra

Copper complexes as a source of redox active MRI contrast agents

The study reports an advance in designing copper-based redox sensing MRI contrast agents. Although the data demonstrate that copper(II) complexes are not able to compete with lanthanoids species in terms of contrast, the redox-dependent switch between diamagnetic copper(I) and paramagnetic copper(II) yields a novel redox-sensitive contrast moiety with potential for reversibility

Ion-sensitive Gd(III)-chelates as "smart" MRI contrast agents

Magnetic Resonance Imaging (MRI) is very important tool in clinical diagnostics and biological research, being often superior to other imaging techniques available today as it provides high resolution 3D images of the body and living tissues. The use of contrast agents e. g. Gd(III)-chelates enhances the MR signal and thus improves the quality of obtained images. The development of bioactivated, responsive or smart MR probes is one of the most exciting aspects of current contrast agent research. Their use would enable tracking of numerous biological processes and could potentially provide extremely improtant information in the desease diagnostics and the brain research. Careful design and appropriate synthetic modifications allow for the incorporation of various sensor moieties to DO3A, a widely used percursor for the preparation of these ‘intelligent' probes. Organometallic Gd(III)-chelates thus obtained response to a desired target such as ions or enzymes and alter their magnetic properties changing the relaxation times of the nuclei in surrounding water molecules. For instance, incorporation of the pH sensitive group such as prosphonates on the optimal distance from the lanthanide metal leads to the pH-responsive agent. Similary, coupling of EGTA-, BAPTA- or EDTA-modified Ca(II) chelators results in the Ca(II)-sensitive contrast agents. These agents could potentially be used for the visualization of the neural processes as the pH or concentration of Ca(II) is changing during the neural activity. The development of such smart MR agents would revolutionize neuroimaging and allow the dynamic imaging of the brain function