Phasic changes in eye’s pupil diameter have been repeatedly observed during cognitive, emotional and behavioral activity in mammals. Although pupil diameter is known to be associated with noradrenergic firing in the pontine Locus Coeruleus (LC), thus far the causal chain coupling spontaneous pupil dynamics to specific cortical brain networks remains unknown. In the present study, we acquired steady-state blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) data combined with eye-tracking pupillometry from fifteen healthy subjects that were trained to maintain a constant attentional load. Regression analysis revealed widespread visual and sensorimotor BOLD-fMRI deactivations correlated with pupil diameter. Furthermore, we found BOLD-fMRI activations correlated with pupil diameter change rate within a set of brain regions known to be implicated in selective attention, salience, error-detection and decision-making. These regions included LC, thalamus, posterior cingulate cortex (PCC), dorsal anterior cingulate and paracingulate cortex (dACC/PaCC), orbitofrontal cortex (OFC), and right anterior insular cortex (rAIC). Granger-causality analysis performed on these regions yielded a complex pattern of interdependence, wherein LC and pupil dynamics were far apart in the network and separated by several cortical stages. Functional connectivity (FC) analysis revealed the ubiquitous presence of the superior frontal gyrus (SFG) in the networks identified by the brain regions correlated to the pupil diameter change rate. No significant correlations were observed between pupil dynamics, regional activation and behavioral performance. Based on the involved brain regions, we speculate that pupil dynamics reflects brain processing implicated in changes between self- and environment-directed awareness.

We have studied local structure of ${\text{IrTe}}_2$ by Ir $L$ ${}_3$-edge extended x-ray absorption fine structure (EXAFS) measurements as a function of temperature to investigate origin of the observed structural phase transition at $T_s\sim 270$ K. The EXAFS results show an appearance of longer Ir-Te bond length ($\Delta R\sim 0.05$ Å) at $T<T_s$. We have found Ir-Ir dimerization, characterized by distinct Ir-Ir bond lengths ($\Delta R\sim 0.13$ Å), existing both above and below $T_s$. The results suggest that the phase transition in IrTe${}_2$ should be an order-disorder-like transition of Ir-Ir dimers assisted by Ir-Te bond correlations, thus indicating important role of the interaction between the Ir $5d$ and Te $5p$ orbitals in this transition.

The effect of Ru substitution on the local structure of layered SmFe${}_{1-x}$Ru${}_x$AsO${}_{0.85}$F${}_{0.15}$ superconductor has been studied by As $K$- and Sm $L_3$-edge x-ray-absorption spectroscopy. The extended x-ray-absorption fine-structure measurements reveal distinct Fe-As and Ru-As bond lengths in the Ru substituted samples with the latter being $\sim$0.03 Å longer. Local disorder induced by the Ru substitution is mainly confined to the FeAs layer while the SmO spacer layer sustains a relative order, consistent with the x-ray-absorption near-edge structure spectra. The results suggest that, in addition to the order/disorder in the active FeAs layer, its coupling to the rare-earth–oxygen spacer layer needs to be considered for describing the electronic properties of these layered superconductors.