Selective Coupling between Theta Phase and Neocortical Fast Gamma Oscillations during REM-Sleep in Mice

TORT, A. B. L. ; SCHEFFER-TEIXEIRA, R ; Souza, B.C. ; DRAGUHN, A. ; BRANKACK, J. . Theta-associated high-frequency oscillations (110-160 Hz) in the hippocampus and neocortex. Progress in Neurobiology , v. 100, p. 1-14, 2013.

Calcium oscillations

Changes in cellular calcium concentration control a wide range of physiological processes, from the subsecond release of synaptic neurotransmitters, to the regulation of gene expression over months or years. Calcium can also trigger cell death through both apoptosis and necrosis, and so the regulation of cellular calcium concentration must be tightly controlled through the concerted action of pumps, channels and buffers that transport calcium into and out of the cell cytoplasm. A hallmark of cellular calcium signalling is its spatiotemporal complexity: stimulation of cells by a hormone or neurotransmitter leads to oscillations in cytoplasmic calcium concentration that can vary markedly in time course, amplitude, frequency, and spatial range. In this chapter we review some of the biological roles of calcium, the experimental characterisation of complex dynamic changes in calcium concentration, and attempts to explain this complexity using computational models. We consider the "toolkit" of cellular proteins which influence calcium concentration, describe mechanistic models of key elements of the toolkit, and fit these into the framework of whole cell models of calcium oscillations and waves. Finally, we will touch on recent efforts to use stochastic modelling to elucidate elementary calcium signal events, and how these may evolve into global signals.

Increase in Hippocampal Theta Oscillations during Spatial Decision Making

The processing of spatial and mnemonic information is believed to depend on hippocampal theta oscillations (5–12 Hz). However, in rats both the power and the frequency of the theta rhythm are modulated by locomotor activity, which is a major confounding factor when estimating its cognitive correlates. Previous studies have suggested that hippocampal theta oscillations support decision-making processes. In this study, we investigated to what extent spatial decision making modulates hippocampal theta oscillations when controlling for variations in locomotion speed. We recorded local field potentials from the CA1 region of rats while animals had to choose one arm to enter for reward (goal) in a four-arm radial maze. We observed prominent theta oscillations during the decision-making period of the task, which occurred in the center of the maze before animals deliberately ran through an arm toward goal location. In speed-controlled analyses, theta power and frequency were higher during the decision period when compared to either an intertrial delay period (also at the maze center), or to the period of running toward goal location. In addition, theta activity was higher during decision periods preceding correct choices than during decision periods preceding incorrect choices. Altogether, our data support a cognitive function for the hippocampal theta rhythm in spatial decision making

Slow Oscillations in the Mouse Hippocampus Entrained by Nasal Respiration

Different types of network oscillations occur in different behavioral, cognitive, or vigilance states. The rodent hippocampus expresses prominentoscillations atfrequencies between 4 and 12Hz,which are superimposed by phase-coupledoscillations (30 –100Hz).These patterns entrain multineuronal activity over large distances and have been implicated in sensory information processing and memory formation. Here we report a new type of oscillation at near- frequencies (2– 4 Hz) in the hippocampus of urethane-anesthetized mice. The rhythm is highly coherent with nasal respiration and with rhythmic field potentials in the olfactory bulb: hence, we called it hippocampal respiration-induced oscillations. Despite the similarity in frequency range, several features distinguish this pattern from locally generatedoscillations: hippocampal respiration-induced oscillations have a unique laminar amplitude profile, are resistant to atropine, couple differentlytooscillations, and are abolished when nasal airflow is bypassed bytracheotomy. Hippocampal neurons are entrained by both the respiration-induced rhythm and concurrent oscillations, suggesting a direct interaction between endogenous activity in the hippocampus and nasal respiratory inputs. Our results demonstrate that nasal respiration strongly modulates hippocampal network activity in mice, providing a long-range synchronizing signal between olfactory and hippocampal networks.

Close-in planets around giant stars: lack of hot-Jupiters and prevalence of multiplanetary systems

Extrasolar planets abound in almost any possible configuration. However, until five years ago, there was a lack of planets orbiting closer than 0.5 au to giant or subgiant stars. Since then, recent detections have started to populated this regime by confirming 13 planetary systems. We discuss the properties of these systems in terms of their formation and evolution off the main sequence. Interestingly, we find that 70.0 ± 6.6% of the planets in this regime are inner components of multiplanetary systems. This value is 4.2σ higher than for main-sequence hosts, which we find to be 42.4 ± 0.1%. The properties of the known planets seem to indicate that the closest-in planets (a< 0.06 au) to main-sequence stars are massive (i.e., hot Jupiters) and isolated and that they are subsequently engulfed by their host as it evolves to the red giant branch, leaving only the predominant population of multiplanetary systems in orbits 0.06

Sloshing and slamming oscillations in collapsible channel flow

We consider laminar high-Reynolds-number flow through a finite-length planar channel, where a portion of one wall is replaced by a thin massless elastic membrane that is held under longitudinal tension T and subject to an external pressure distribution. The flow is driven by a fixed pressure drop along the full length of the channel. We investigate the global stability of two-dimensional Poiseuille flow using a method of matched local eigenfunction expansions, which is compared to direct numerical simulations. We trace the neutral stability curve of the primary oscillatory instability of the system, illustrating a transition from high-frequency ‘sloshing’ oscillations at high T to vigorous ‘slamming’ motion at low T . Small-amplitude sloshing at high T can be captured using a low-order eigenmode truncation involving four surface-based modes in the compliant segment of the channel coupled to Womersley flow in the rigid segments. At lower tensions, we show that hydrodynamic modes contribute increasingly to the global instability and we demonstrate a change in the mechanism of energy transfer from the mean flow, with viscous effects being destabilising. Simulations of finite-amplitude oscillations at low T reveal a generic slamming motion, in which the the flexible membrane is drawn close to the opposite rigid wall before rapidly recovering. A simple model is used to demonstrate how fluid inertia in the downstream rigid channel segment, coupled to membrane curvature downstream of the moving constriction, together control slamming dynamics.

NONLINEAR EFFECTS IN MAGNETIC GARNET FILMS AND NONRECIPROCAL OPTICAL BLOCH OSCILLATIONS IN WAVEGUIDE ARRAYS

This dissertation presents detailed experimental and theoretical investigations of nonlinear and nonreciprocal effects in magnetic garnet films. The dissertation thus comprises two major sections. The first section concentrates on the study of a new class of nonlinear magneto-optic thin film materials possessing strong higher order magnetic susceptibility for nonlinear optical applications. The focus was on enlarging the nonlinear performance of ferrite garnet films by strain generation and compositional gradients in the sputter-deposition growth of these films. Under this project several bismuth-substituted yttrium iron garnet (Bi,Y) 3 (Fe,Ga)5 O12(acronym as Bi:YIG) films have been sputter-deposited over gadolinium gallium garnet (Gd 3 Ga5 O12 ) substrates and characterized for their nonlinear optical response. One of the important findings of this work is that lattice mismatch strain drives the second harmonic (SH) signal in the Bi:YIG films, in agreement with theoretical predictions; whereas micro-strain was found not to correlate significantly with SH signal at the micro-strain levels present in these films. This study also elaborates on the role of the film's constitutive elements and their concentration gradients in nonlinear response of the films. Ultrahigh sensitivity delivered by second harmonic generation provides a new exciting tool for studying magnetized surfaces and buried interfaces, making this work important from both a fundamental and application point of view. The second part of the dissertation addresses an important technological need; namely the development of an on-chip optical isolator for use in photonic integrated circuits. It is based on two related novel effects, nonreciprocal and unidirectional optical Bloch oscillations (BOs), recently proposed and developed by Professor Miguel Levy and myself. This dissertation work has established a comprehensive theoretical background for the implementation of these effects in magneto-optic waveguide arrays. The model systems we developed consist of photonic lattices in the form of one-dimensional waveguide arrays where an optical force is introduced into the array through geometrical design turning the beam sideways. Laterally displaced photons are periodically returned to a central guide by photonic crystal action. The effect leads to a novel oscillatory optical phenomenon that can be magnetically controlled and rendered unidirectional. An on-chip optical isolator was designed based on the unidirectionality of the magneto-opticBloch oscillatory motion. The proposed device delivers an isolation ratio as high as 36 dB that remains above 30 dB in a 0.7 nm wavelength bandwidth, at the telecommunication wavelength 1.55 μm. Slight modifications in isolator design allow one to achieve an even more impressive isolation ratio ~ 55 dB, but at the expense of smaller bandwidth. Moreover, the device allows multifunctionality, such as optical switching with a simultaneous isolation function, well suited for photonic integrated circuits.

Incidence of debris discs around FGK stars in the solar neighbourhood

Context. Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their counterparts in the solar system are the asteroid and Edgeworth-Kuiper belts. Aims. The aim of this paper is to provide robust numbers for the incidence of debris discs around FGK stars in the solar neighbourhood. Methods. The full sample of 177 FGK stars with d ≤ 20 pc proposed for the DUst around NEarby Stars (DUNES) survey is presented. Herschel/PACS observations at 100 and 160 μm were obtained, and were complemented in some cases with data at 70 μm and at 250, 350, and 500 μm SPIRE photometry. The 123 objects observed by the DUNES collaboration were presented in a previous paper. The remaining 54 stars, shared with the Disc Emission via a Bias-free Reconnaissance in IR and Sub-mm (DEBRIS) consortium and observed by them, and the combined full sample are studied in this paper. The incidence of debris discs per spectral type is analysed and put into context together with other parameters of the sample, like metallicity, rotation and activity, and age. Results. The subsample of 105 stars with d ≤ 15 pc containing 23 F, 33 G, and 49 K stars is complete for F stars, almost complete for G stars, and contains a substantial number of K stars from which we draw solid conclusions on objects of this spectral type. The incidence rates of debris discs per spectral type are 0.26^+0.21_-0.14 (6 objects with excesses out of 23 F stars), 0.21^+0.17_-0.11 (7 out of 33 G stars), and 0.20^+0.14_-0.09 (10 out of 49 K stars); the fraction for all three spectral types together is 0.22^+0.08_-0.07 (23 out of 105 stars). The uncertainties correspond to a 95% confidence level. The medians of the upper limits of L_dust/L_∗ for each spectral type are 7.8 × 10^-7 (F), 1.4 × 10^-6 (G), and 2.2 × 10^-6 (K); the lowest values are around 4.0 × 10^-7. The incidence of debris discs is similar for active (young) and inactive (old) stars. The fractional luminosity tends to drop with increasing age, as expected from collisional erosion of the debris belts.

Long-period oscillations in GPS Up time series. Study over the European/Mediterranean area

The surface of the Earth is subjected to vertical deformations caused by geophysical and geological processes which can be monitored by Global Positioning System (GPS) observations. The purpose of this work is to investigate GPS height time series to identify interannual signals affecting the Earth’s surface over the European and Mediterranean area, during the period 2001-2019. Thirty-six homogeneously distributed GPS stations were selected from the online dataset made available by the Nevada Geodetic Laboratory (NGL) on the basis of the length and quality of the data series. The Principal Component Analysis (PCA) is the technique applied to extract the main patterns of the space and time variability of the GPS Up coordinate. The time series were studied by means of a frequency analysis using a periodogram and the real-valued Morlet wavelet. The periodogram is used to identify the dominant frequencies and the spectral density of the investigated signals; the second one is applied to identify the signals in the time domain and the relevant periodicities. This study has identified, over European and Mediterranean area, the presence of interannual non-linear signals with a period of 2-to-4 years, possibly related to atmospheric and hydrological loading displacements and to climate phenomena, such as El Niño Southern Oscillation (ENSO). A clear signal with a period of about six years is present in the vertical component of the GPS time series, likely explainable by the gravitational coupling between the Earth’s mantle and the inner core. Moreover, signals with a period in the order of 8-9 years, might be explained by mantle-inner core gravity coupling and the cycle of the lunar perigee, and a signal of 18.6 years, likely associated to lunar nodal cycle, were identified through the wavelet spectrum. However, these last two signals need further confirmation because the present length of the GPS time series is still too short when compared to the periods involved.

Alpha oscillations index the functionality and the plastic changes of the visual system

Alpha oscillations are linked to visual awareness and to the periodical sampling of visual information, suggesting that alpha rhythm reflect an index of the functionality of the posterior cortices, and hence of the visual system. Therefore, the present work described a series of studies investigating alpha oscillations as a biomarker of the functionality and the plastic modifications of the visual system in response to lesions to the visual cortices or to external stimulations. The studies presented in chapter 5 and 6 showed that posterior lesions alter alpha oscillations in hemianopic patients, with reduced alpha reactivity at the eyes opening and decreased alpha functional connectivity, especially in right-lesioned hemianopics, with concurrent dysfunctions in the theta range, suggesting a specialization of the right hemisphere in orchestrating alpha oscillations and coordinating complex interplays among different brain rhythms. The study presented in chapter 7 investigated a mechanism of rhythmical attentional sampling of visual information in healthy participants, showing that perceptual performance is influenced by a rhythmical mechanism of attentional allocation, occurring at lower-alpha frequencies (i.e., 7 Hz), when a single spatial location is monitored, and at lower frequencies (i.e., 5 Hz), when attention is allocated to two spatial locations. Moreover, the right hemisphere seemed to have a dominance in this rhythmical attentional sampling, distributing attentional resources to the entire visual field. Finally, the study presented in chapter 8 showed that prolonged visual entrainment induce long-term modulations of resting-state alpha activity in healthy participants, suggesting that persistent modifications in the functionality of the visual system are possible. Altogheter, these findings show that functional processes and plastic changes of the visual system are reflected in alpha oscillatory patterns. Therefore, investigating and promoting alpha oscillations may contribute to the development of rehabilitative protocols to ameliorate the functionality of the visual system, in brain lesioned patients.

Ecological responses of Western Palearctic avian species to late Quaternary climate oscillations

This PhD thesis explores the ecological responses of bird species to glacial-interglacial transitions during the late Quaternary in the Western Palearctic, using multiple approaches and at different scales, enhancing the importance of the bird fossil record and quantitative methods to elucidate biotic trends in relation to long-term climate changes. The taxonomic and taphonomic analyses of the avian fossil assemblages from four Italian Middle and Upper Pleistocene sedimentary successions (Grotta del Cavallo, Grotta di Fumane, Grotta di Castelcivita, and Grotta di Uluzzo C) allowed us to reconstruct local-scale patterns in birds’ response to climate changes. These bird assemblages are characterized by the presence of temperate species and by the occasional presence of cold-dwelling species during glacials, related to range shifts. These local patterns are supported by those identified at the continental scale. In this respect, I mapped the present-day and LGM climatic envelopes of species with different climatic requirements. The results show a substantial stability in the range of temperate species and pronounced changes in the range of cold-dwelling species, supported by their fossil records. Therefore, the responses to climate oscillations are highly related to the thermal niches of investigated species. I also clarified the dynamics of the presence of boreal and arctic bird species in Mediterranean Europe, due to southern range shifts, during the glacial phases. After a reassessment of the reliability of the existing fossil evidence, I show that this phenomenon is not as common as previously thought, with important implications for the paleoclimatic and paleoenvironmental significance of the targeted species. I have also been able to explore the potential of multivariate and rarefaction methods in the analyses of avian fossils from Grotta del Cavallo. These approaches helped to delineate the main drivers of taphonomic damages and the dynamics of species diversity in relation to climate-driven paleoenvironmental changes.

Unveiling the unknown of cool stars with high-resolution spectroscopy

Cool giant and supergiant stars are among the brightest populations in any stellar system and they are easily observable out to large distances, especially at infrared wavelengths. These stars also dominate the integrated light of star clusters in a wide range of ages, making them powerful tracers of stellar populations in more distant galaxies. High-resolution near-IR spectroscopy is a key tool for quantitatively investigating their kinematic, evolutionary and chemical properties. However, the systematic exploration and calibration of the NIR spectral diagnostics to study these cool stellar populations based on high-resolution spectroscopy is still in its pioneering stage. Any effort to make progress in the field is innovative and of impact on stellar archaeology and stellar evolution. This PhD project takes the challenge of exploring that new parameter space and characterizing the physical properties, the chemical content and the kinematics of cool giants and supergiants in selected disc fields and clusters of our Galaxy, with the ultimate goal of tracing their past and recent star formation and chemical enrichment history. By using optical HARPS-N and near-infrared GIANO-B high-resolution stellar spectra in the context of the large program SPA-Stellar Population Astrophysics: the detailed, age-resolved chemistry of the Milky Way disk” (PI L. Origlia), an extensive study of Arcturus, a standard calibrator for red giant stars, has been performed. New diagnostics of stellar parameters as well as optimal linelists for chemical analysis have been provided. Then, such diagnostics have been used to determine evolutionary properties, detailed chemical abundances of almost 30 different elements and mixing processes of a homogeneous sample of red supergiant stars in the Perseus complex.

New indicators of star cluster dynamical evolution

This thesis presents a study of globular clusters (GCs), based on analysis of Monte Carlo simulations of globular clusters (GCs) with the aim to define new empirical parameters measurable from observations and able to trace the different phases of their dynamical evolution history. During their long term dynamical evolution, due to mass segregation and and dynamical friction, massive stars transfer kinetic energy to lower-mass objects, causing them to sink toward the cluster center. This continuous transfer of kinetic energy from the core to the outskirts triggers the runaway contraction of the core, known as "core collapse" (CC), followed by episodes of expansion and contraction called gravothermal oscillations. Clearly, such an internal dynamical evolution corresponds to significant variations also of the structure of the system. Determining the dynamical age of a cluster can be challenging as it depends on various internal and external properties. The traditional classification of GCs as CC or post-CC systems relies on detecting a steep power-law cusp in the central density profile, which may not always be reliable due to post-CC oscillations or other processes. In this thesis, based on the normalized cumulative radial distribution (nCRD) within a fraction of the half-mass radius is analyzed, and three diagnostics (A5, P5, and S2.5) are defined. These diagnostics show sensitivity to dynamical evolution and can distinguish pre-CC clusters from post-CC clusters.The analysis performed using multiple simulations with different initial conditions, including varying binary fractions and the presence of dark remnants showed the time variations of the diagnostics follow distinct patterns depending on the binary fraction and the retention or ejection of black holes. This analysis is extended to a larger set of simulations matching the observed properties of Galactic GCs, and the parameters show a potential to distinguish the dynamical stages of the observed clusters as well.

Combined Analysis Of νμ Disappearance And νμ→νe Appearance In Minos Using Accelerator And Atmospheric Neutrinos.

We report on a new analysis of neutrino oscillations in MINOS using the complete set of accelerator and atmospheric data. The analysis combines the ν(μ) disappearance and ν(e) appearance data using the three-flavor formalism. We measure |Δm(32)(2)| = [2.28-2.46] × 10(-3) eV(2) (68% C.L.) and sin(2)θ(23) = 0.35-0.65 (90% C.L.) in the normal hierarchy, and |Δm(32)(2)| = [2.32-2.53] × 10(-3) eV(2) (68% C.L.) and sin(2)θ(23) = 0.34-0.67 (90% C.L.) in the inverted hierarchy. The data also constrain δ(CP), the θ(23} octant degeneracy and the mass hierarchy; we disfavor 36% (11%) of this three-parameter space at 68% (90%) C.L.

Visual Navigation In The Neotropical Ant Odontomachus Hastatus (formicidae, Ponerinae), A Predominantly Nocturnal, Canopy-dwelling Predator Of The Atlantic Rainforest.

The arboreal ant Odontomachus hastatus nests among roots of epiphytic bromeliads in the sandy forest at Cardoso Island (Brazil). Crepuscular and nocturnal foragers travel up to 8m to search for arthropod prey in the canopy, where silhouettes of leaves and branches potentially provide directional information. We investigated the relevance of visual cues (canopy, horizon patterns) during navigation in O. hastatus. Laboratory experiments using a captive ant colony and a round foraging arena revealed that an artificial canopy pattern above the ants and horizon visual marks are effective orientation cues for homing O. hastatus. On the other hand, foragers that were only given a tridimensional landmark (cylinder) or chemical marks were unable to home correctly. Navigation by visual cues in O. hastatus is in accordance with other diurnal arboreal ants. Nocturnal luminosity (moon, stars) is apparently sufficient to produce contrasting silhouettes from the canopy and surrounding vegetation, thus providing orientation cues. Contrary to the plain floor of the round arena, chemical cues may be important for marking bifurcated arboreal routes. This experimental demonstration of the use of visual cues by a predominantly nocturnal arboreal ant provides important information for comparative studies on the evolution of spatial orientation behavior in ants. This article is part of a Special Issue entitled: Neotropical Behaviour.