Neural dynamics underlying successful auditory short-term memory performance

Listeners often operate in complex acoustic environments, consisting of many concurrent sounds. Accurately encoding and maintaining such auditory objects in short-term memory is crucial for communication and scene analysis. Yet, the neural underpinnings of successful auditory short-term memory (ASTM) performance are currently not well understood. To elucidate this issue, we presented a novel, challenging auditory delayed match-to-sample task while recording MEG. Human participants listened to ‘scenes’ comprising three concurrent tone pip streams. The task was to indicate, after a delay, whether a probe stream was present in the just-heard scene. We present three key findings: First, behavioural performance revealed faster responses in correct versus incorrect trials as well as in ‘probe present’ versus ‘probe absent’ trials, consistent with ASTM search. Second, successful compared with unsuccessful ASTM performance was associated with a significant enhancement of event-related fields and oscillatory activity in the theta, alpha and beta frequency ranges. This extends previous findings of an overall increase of persistent activity during short-term memory performance. Third, using distributed source modelling, we found these effects to be confined mostly to sensory areas during encoding, presumably related to ASTM contents per se. Parietal and frontal sources then became relevant during the maintenance stage, indicating that effective STM operation also relies on ongoing inhibitory processes suppressing task-irrelevant information. In summary, our results deliver a detailed account of the neural patterns that differentiate successful from unsuccessful ASTM performance in the context of a complex, multi-object auditory scene

Thermal expansion and de-hydroxylation of phengite micas

Phengite samples (2M 1 and 3T politypes) and a synthetic end-member muscovite specimen were studied by in situ high-temperature synchrotron radiation X-ray diffraction. The measured volume thermal expansion of 2M 1 phengite ( 48 36.6 7 10 126 K 121) was systematically greater than of the 3T polytype ( 4833.3 7 10 126 K 121). A positive linear correlation between the average thermal expansion on (001) plane and the mean tetrahedral rotation angle at ambient condition is proposed on the ground of new measurements and literature data. Dehydroxylation processes were observed in 2M 1, starting at 1,000 K in 3T at 800 and 945 K in synthetic muscovite. Rietveld refinements allowed a determination of structural variations upon heating of phengite samples and their dehydroxylate phases. The phengite structure expands by regularizing the tetrahedral sheet and by reducing the bond length differences between the outer and inner coordination shell of the interlayer site. The dehydroxylate phase derived from 2M 1 is characterized by fivefold polyhedra in the low temperature form as a consequence of two OH groups reacting to form H2O + O (residual). The dehydroxylate exhibits an increase of the cation\u2013cation distances along the M\u2013Or\u2013M bonds with respect to low-temperature phengite structures. For the 3T phase, we were unable to achieve completion of dehydroxylation. The refined structural model of the dehydroxylate phase shows two hydroxyl sites, but at a short distance from one another. This result suggests that the dehydroxylation reaction did not proceed to completion

Low-pressure ferroelastic phase transition in rutile-type AX2 minerals: cassiterite (SnO2), pyrolusite (MnO2) and sellaite (MgF2)

The structural behaviour of cassiterite (SnO2), pyrolusite (MnO2) and sellaite (MgF2), i.e. AX2-minerals, has been investigated at room temperature by in situ high-pressure single-crystal diffraction, up to 14 GPa, using a diamond anvil cell. Such minerals undergo a ferroelastic phase transition, from rutile-like structure (SG: P42/mnm) to CaCl2-like structure (SG: Pnnm), at ≈ 10.25, 4.05 and 4.80 GPa, respectively. The structural evolution under pressure has been described by the trends of some structure parameters that are other than zero in the region of the low-symmetry phase’s stability. In particular, three tilting-angles (ω, ω′, ABS) and the metric distortion of the cation-centred octahedron (quantified via the difference between apical-anion and equatorial-anion distances Δ|Xax−Xeq|) are used to express the atoms’ readjustment, i.e. relaxation, taking place in the CaCl2-like structures under pressure. The crystallographic investigation presented is complemented with an analysis of the energy involved in the phase transition using the Landau formalism and adopting the following definition for the order parameter: Q = η11–η22, ηij being the spontaneous strain tensor. The dependence of ω, ω′, ABS and Δ|Xax−Xeq| on Q allows determination of a correlation between geometrical deformation parameter and energy. Lastly, the relaxation mechanisms that exploits ω, ω′, ABS and Δ|Xax−Xeq| may be related to the ionic degree of bonding, the latter modelled via quantum mechanics and Bader theory. Sellaite, the mineral exhibiting the highest degree of ionic bonding among those investigated, tends to accomplish relaxation through pure rotation of the octahedron, rather than a metric distortion (Δ|Xax−Xeq|), which would shorten inter-atomic distances thus increasing repulsion between anions

On the crystal chemistry and elastic behavior of a phlogopite 3T

The crystal chemistry and the elastic behavior under isothermal conditions up to 9 GPa of a natural, and extremely rare, 3T-phlogopite from Traversella (Valchiusella, Turin, Western Alps) [(K0. 99Na0.05Ba0.01)(Mg2.60Al0.20Fe0.212+)[Si2.71Al1.29O10](OH)2, space group P3112, with a = 5.3167(4), c = 30.440(2) \uc5, and V = 745.16(9) \uc53] have been investigated by electron microprobe analysis in wavelength dispersion mode, single-crystal X-ray diffraction at 100 K, and in situ high-pressure synchrotron radiation powder diffraction (at room temperature) with a diamond anvil cell. The single-crystal refinement confirms the general structure features expected for trioctahedral micas, with the inter-layer site partially occupied by potassium and sodium, iron almost homogeneously distributed over the three independent octahedral sites, and the average bond distances of the two unique tetrahedra suggesting a disordered Si/Al-distribution (i. e., \u3008T1-O\u3009\u303 1.658 and \u3008T2-O\u3009\u303 1.656 \uc5). The location of the H-site confirms the orientation of the O-H vector nearly perpendicular to (0001). The refinement converged with R1(F) = 0.0382, 846 unique reflections with FO > 4\u3c3(FO) and 61 refined parameters, and not significant residuals in the final difference-Fourier map of the electron density (+0.77/-0.37 e-/\uc53). The high-pressure experiments showed no phase transition within the pressure range investigated. The P-V data were fitted with a Murnaghan (M-EoS) and a third-order Birch-Murnaghan equation of state (BM-EoS), yielding: (1) M-EoS, V0 = 747.0(3) \uc53, KT0 = 44.5(24) GPa, and K\u2032 = 8.0(9); (2) BM-EoS, V0 = 747.0(3) \uc53, KT0 = 42.8(29) GPa, and K\u2032 = 9.9(17). A comparison between the elastic behavior in response to pressure observed in 1M- and 3T-phlogopite is made

Phlogopite-pargasite coexistence in an oxygen reduced spinel-peridotite ambient

The occurrence of phlogopite and amphibole in mantle ultramafic rocks is widely accepted as the modal effect of metasomatism in the upper mantle. However, their simultaneous formation during metasomatic events and the related sub-solidus equilibrium with the peridotite has not been extensively studied. In this work, we discuss the geochemical conditions at which the pargasite-phlogopite assemblage becomes stable, through the investigation of two mantle xenoliths from Mount Leura (Victoria State, Australia) that bear phlogopite and the phlogopite + amphibole (pargasite) pair disseminated in a harzburgite matrix. Combining a mineralogical study and thermodynamic modelling, we predict that the P\u2013T locus of the equilibrium reaction pargasite + forsterite = Na-phlogopite + 2 diopside + spinel, over the range 1.3\u20133.0 GPa/540\u20131500\ua0K, yields a negative Clapeyron slope of -0.003 GPa K\u20131 (on average). The intersection of the P\u2013T locus of supposed equilibrium with the new mantle geotherm calculated in this work allowed us to state that the Mount Leura xenoliths achieved equilibrium at 2.3 GPa /1190\ua0K, that represents a plausible depth of ~ 70\ua0km. Metasomatic K-Na-OH rich fluids stabilize hydrous phases. This has been modelled by the following equilibrium equation: 2 (K,Na)-phlogopite + forsterite = 7/2 enstatite + spinel + fluid (components: Na2O,K2O,H2O). Using quantum-mechanics, semi-empirical potentials, lattice dynamics and observed thermo-elastic data, we concluded that K-Na-OH rich fluids are not effective metasomatic agents to convey alkali species across the upper mantle, as the fluids are highly reactive with the ultramafic system and favour the rapid formation of phlogopite and amphibole. In addition, oxygen fugacity estimates of the Mount Leura mantle xenoliths [\u394(FMQ) = \u20131.97 \ub1 0.35; \u20131.83 \ub1 0.36] indicate a more reducing mantle environment than what is expected from the occurrence of phlogopite and amphibole in spinel-bearing peridotites. This is accounted for by our model of full molecular dissociation of the fluid and incorporation of the O-H-K-Na species into (OH)-K-Na-bearing mineral phases (phlogopite and amphibole), that leads to a peridotite metasomatized ambient characterized by reduced oxygen fugacity

Phlogopite-pargasite coexistence in an oxygen reduced spinel-peridotite ambient

The occurrence of phlogopite and amphibole in mantle ultramafic rocks is widely accepted as the modal effect of metasomatism in the upper mantle. However, their simultaneous formation during metasomatic events and the related sub-solidus equilibrium with the peridotite has not been extensively studied. In this work, we discuss the geochemical conditions at which the pargasite-phlogopite assemblage becomes stable, through the investigation of two mantle xenoliths from Mount Leura (Victoria State, Australia) that bear phlogopite and the phlogopite + amphibole (pargasite) pair disseminated in a harzburgite matrix. Combining a mineralogical study and thermodynamic modelling, we predict that the P–T locus of the equilibrium reaction pargasite + forsterite = Na-phlogopite + 2 diopside + spinel, over the range 1.3–3.0 GPa/540–1500 K, yields a negative Clapeyron slope of -0.003 GPa K–1 (on average). The intersection of the P–T locus of supposed equilibrium with the new mantle geotherm calculated in this work allowed us to state that the Mount Leura xenoliths achieved equilibrium at 2.3 GPa /1190 K, that represents a plausible depth of ~ 70 km. Metasomatic K-Na-OH rich fluids stabilize hydrous phases. This has been modelled by the following equilibrium equation: 2 (K,Na)-phlogopite + forsterite = 7/2 enstatite + spinel + fluid (components: Na2O,K2O,H2O). Using quantum-mechanics, semi-empirical potentials, lattice dynamics and observed thermo-elastic data, we concluded that K-Na-OH rich fluids are not effective metasomatic agents to convey alkali species across the upper mantle, as the fluids are highly reactive with the ultramafic system and favour the rapid formation of phlogopite and amphibole. In addition, oxygen fugacity estimates of the Mount Leura mantle xenoliths [Δ(FMQ) = –1.97 ± 0.35; –1.83 ± 0.36] indicate a more reducing mantle environment than what is expected from the occurrence of phlogopite and amphibole in spinel-bearing peridotites. This is accounted for by our model of full molecular dissociation of the fluid and incorporation of the O-H-K-Na species into (OH)-K-Na-bearing mineral phases (phlogopite and amphibole), that leads to a peridotite metasomatized ambient characterized by reduced oxygen fugacity

P-V and T-V Equations of State of natural biotite: An in-situ high-pressure and high-temperature powder diffraction study, combined with M\uf6ssbauer spectroscopy

The P-V and T-V equations of state of a natural biotite sample (Mg/Fe ratio 48 1) have been studied using in-situ high-pressure (0.0001\u9611 GPa) synchrotron radiation powder diffraction at the European Synchrotron Radiation Facilities (ESRF) in Grenoble, France, and in-situ high-temperature (298\u96610 K) laboratory X-ray powder diffraction. A third-order Birch-Murnaghan model [V0 = 498.7(1) \uc53, measured value] provides the following elastic parameters: K0 = 49(1) GPa, K\u2019 = 8.1(5). The volume thermal expansion is satisfactorily described by a constant value resulting in 37(2) 10\u966 K\u961. M\uf6ssbauer spectroscopy proves that REDOX reactions have occurred upon heating, presumably 2(OH\u96 + Fe2+) \u2192 2O2\u96 + 2Fe3+ + H2 \u2191 and/or 4Fe2+ + 2OH\u96 + O2 \u2192 4Fe3+ + 3O2\u96 + H2O. On the basis of the elastic and thermal parameters measured we have modeled the deformation contribution (Gdeform) to the Gibbs energy. The third-order Birch-Murnaghan model with V0 e xed at its experimental value and the model with re e ned V0 do not signi e cantly differ from one another in terms of Gdeform. A comparison based on Gdeform between biotite and phlogopite shows a better compliance to P of the former, though balanced in mineral reactions by a difference of molar volume, i.e., V0(biotite) > V0(phlogopite)