Dynamic causal modelling shows a prominent role of local inhibition in alpha power modulation in higher visual cortex

During resting-state EEG recordings, alpha activity is more prominent over the posterior cortex in eyes-closed (EC) conditions compared to eyes-open (EO). In this study, we characterized the difference in spectra between EO and EC conditions using dynamic causal modelling. Specifically, we investigated the role of intrinsic and extrinsic connectivity-within the visual cortex-in generating EC-EO alpha power differences over posterior electrodes. The primary visual cortex (V1) and the bilateral middle temporal visual areas (V5) were equipped with bidirectional extrinsic connections using a canonical microcircuit. The states of four intrinsically coupled subpopulations-within each occipital source-were also modelled. Using Bayesian model selection, we tested whether modulations of the intrinsic connections in V1, V5 or extrinsic connections (or a combination thereof) provided the best evidence for the data. In addition, using parametric empirical Bayes (PEB), we estimated group averages under the winning model. Bayesian model selection showed that the winning model contained both extrinsic connectivity modulations, as well as intrinsic connectivity modulations in all sources. The PEB analysis revealed increased extrinsic connectivity during EC. Overall, we found a reduction in the inhibitory intrinsic connections during EC. The results suggest that the intrinsic modulations in V5 played the most important role in producing EC-EO alpha differences, suggesting an intrinsic disinhibition in higher order visual cortex, during EC resting state.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for spatially resolved trace analysis of early-medieval archaeological iron finds

The suitability of laser ablation ICP-MS for minor and trace analysis of archaeological iron finds, produced by a direct reduction process in a 'bloomery' furnace, is reported. The analysis of elemental impurities in the iron can provide useful archaeometallurgical information on the production process and the provenance of the iron. Since, even after refinement, the iron resulting from this process may contain many inclusions (slag, charcoal, holes, etc.), a method should be used with sufficient spatial resolution to preclude the inclusions from the analysis. The ablation parameters are selected such that ablation craters of approx. 100 microm in diameter are obtained. The method is validated with low alloy steel and cast iron standard reference materials and by a comparative analysis with electron probe microanalysis (EPMA). The precision is limited mainly by the homogeneity of the iron, rather than by instrumental reproducibility. The advantages and drawbacks of the method are briefly compared with EPMA. Preliminary results from the analysis of archaeological iron samples from excavations at Develier-Courtetelle (Canton Jura, CH), Neftenbach (Canton Zurich, CH), Wartau (Canton St Gallen, CH) and Mont Chemin (Canton Valais, CH) are given.

Inductively coupled plasma mass spectrometry: a versatile tool for a variety of different tasks

In a laboratory that is working in many different fields, a systematic approach is needed to decide efficiently how a given analytical task should be handled. Four typical examples are presented to show how ICP-MS may be used to solve client's problems. The examples are: the identification of lead projectiles, the determination of total and leachable fractions of impurities in a polymer (PVDF), used for manufacturing components of ultrapure water distribution systems, the authentication of antique silver alloys, and the determination of rare earth elements in geological materials. These examples demonstrate not only typical challenges for the instruments and the analysts handling them, but also ways to reach a satisfactory solution within a reasonable amount of time.