Effects of slow oscillatory transcranial direct current stimulation (so-tDCS) on sleep-dependent memory consolidation

Hintergrund: Es gibt zunehmende Evidenz, dass Schlaf eine aktive Rolle in der Gedächtniskonsolidierung spielt. Insbesondere wird in diesem Zusammenhang die Bedeutung langsamer Oszillationen (< 1 Hz) für die schlafbezogenen Gedächtniskonsolidierungsprozesse diskutiert. In einer wegweisenden Studie, in der eine langsam oszillierende transkranielle Gleichstromstimulation (so-tDCS) appliziert wurde, konnte bei jungen Probanden eine erfolgreiche exogene Manipulation dieser langsamen Oszillationen sowie eine Verbesserung des deklarativen Gedächtnisses beobachtet werden. Spätere Studien, die mit ähnlicher Methodik durchgeführt wurden, zeigten jedoch widersprüchliche Ergebnisse. Die Wirksamkeit dieser neuromodulatorischen Technik wird deshalb in Frage gestellt. Ziel: In dieser Studie wurde untersucht, ob mittels so-tDCS spezifische neurale Oszillationen während des Schlafes moduliert werden können und das deklarative Gedächtnis gesteigert werden kann. Das Ziel war es, die Ergebnisse der Pionierstudie an gesunden jungen Probanden zu replizieren. Dazu wurde ein leicht modifiziertes Stimulationsprotokoll verwendet, welches zuvor an älteren Probanden angewandt wurde. Methoden: In einem doppelblinden, placebo-kontrollierten Laborexperiment mit randomisiertem Crossover-Design wurde der Effekt von bifrontal applizierter anodaler so-tDCS (Frequenz 0,75 Hz) während des Schlafstadium 2 (N2) des Non-REM Schlafes auf die Ergebnisse eines Wortpaar-Assoziationstests und einer Finger-Tapping-Aufgabe an 23 gesunden Probanden (Mittelwert ± Standardabweichung: 23.2 ± 1.9 Jahre; 13 Frauen) überprüft. Stimulationseffekte wurden für Schlafstadien, die Schlafspindeldichte und die EEG-Power analysiert. Weiterhin wurde der Einfluss der so-tDCS auf die deklarative und prozedurale Gedächtniskonsolidierung überprüft. Ergebnisse: Weder auf Verhaltens-, noch auf physiologischer Ebene wurden signifikante Stimulationseffekte beobachtet. Unter beiden Stimulationsbedingungen verbesserte sich die Gedächtnisleistung über Nacht bei der prozeduralen Aufgabe, während sie sich bei der deklarativen Aufgabe verschlechterte. Hatten die Probanden jedoch zusätzliche Lernmöglichkeiten, verringerte dies die Abnahme der deklarativen Gedächtnisleistung. Unabhängig von der Stimulation kam es zu einer Abnahme der schnellen parietalen Spindeldichte von der Baseline (vor Stimulation) zu den stimulationsfreien Intervallen, während bei der langsamen frontalen Spindeldichte kein signifikanter Unterschied auftrat. Schlussfolgerungen: Die vorliegende Studie konnte die Ergebnisse der Pionierstudie nicht reproduzieren. Unsere Ergebnisse stimmen jedoch mit einer früheren Studie überein, die das gleiche Stimulationsprotokoll bei älteren Probanden verwendete. Das Ausmaß der nächtlichen Konsolidierung von deklarativen Gedächtnisinhalten war davon abhängig, ob es eine Möglichkeit zur Wiederholung der Lerninhalte gab. Die Standardisierung des Studienprotokolls und eine Berücksichtigung individueller Variabilität sind essentiell für so-tDCS Studien.Background: There is growing evidence that sleep plays an active role in memory consolidation. Specially, there are indications that slow oscillations (< 1 Hz) might be involved in sleep-dependent memory consolidation processes. Employing slow oscillatory transcranial direct current stimulation (so-tDCS) during slow-wave sleep, a pioneer study reported a successful exogenous manipulation of slow oscillations accompanied by an enhancement of declarative memory in young participants. However, subsequent studies using similar methodologies yielded contradictory results questioning the effectiveness of this neuromodulatory technique. Aim: This study attempted to modulate specific neural oscillations during sleep and boost declarative memory using so-tDCS with the aim to replicate the findings of a seminal study in young healthy adults, using a slightly modified stimulation protocol previously implemented in elderly participants. Methods: The effect of anodal so-tDCS applied bifrontally (frequency 0.75 Hz) during non-rapid eye movement (NREM) stage 2 sleep (N2) was assessed on a word-pair task and a sequential finger tapping task in 23 healthy participants (mean ± Sd: 23.2 ± 1.9 years; 13 women) in a double-blind, placebo controlled, counterbalanced, randomized crossover design. Stimulation effects were analyzed on sleep stages, sleep spindle densities, and EEG power, as well as on declarative and procedural memory performances. Results: No significant stimulation effects were observed neither on the behavioral performance nor at the physiological level. Under both stimulation conditions, overnight retention raised in the procedural task and declined in the declarative task. However, when participants had additional learning opportunities, the decline in declarative memory performance diminished. Regardless of stimulation, fast parietal spindle densities decreased from baseline (prior to stimulation) to stimulation-free intervals, while slow frontal spindle density showed no significant changes. Conclusion: The present study failed to replicate the results of the pioneer study in this field. However, our findings are in line with a previous study that used the same stimulation protocol in elderly participants. Overnight retention performances in declarative memory were dependent on re-encoding opportunities. Finally, it should be noted that protocol standardization and variability control are essential in so-tDCS studies

Transferências federais a entidades privadas sem fins lucrativos (1999-2010)

O estudo mapeia as transferências federais a entidades sem fins lucrativos realizadas entre 1999 e 2010 e analisa, política e tecnicamente, o sentido das parcerias entre a Administração Pública Federal e a sociedade civil

A Comparative Study of Signal Analysis Methods Applied in the Detection of Instantaneous Frequency

The smart grid concept is being applied more and more frequently and this is due to the need to integrate all the components that are part of power systems today, starting from generation units, storage systems, communications and connected loads. Non-linear and non-stationary signals have been obtained in this type of systems, which have high penetration of non-conventional energy sources (NCSRE) and non-linear loads. The power quality criterion has had to be adapted to the new conditions of the electrical systems and this has led to the need to search for new analysis methodologies for the acquired signals. In this article we present a review on non-linear and non-stationary signal analysis methods in electrical systems with high NCSRE penetration. To this end we explore the application of the Hilbert-Huang Transform (HHT), Wavelet Transform (WT) and Wigner-Ville Distribution (WVD), exposing each of the advantages and disadvantages of these methods. To validate the methodology, we have selected some synthetic signals that adequately describe the typical behaviors in these systems

Phase transitions in quantum crystals : on growth of magnetically ordered 3He and a search for supersolid 4He

Due to its rich magnetic phase diagram and its superfluidity, 3He is a very interesting system if magnetic effects on the crystal growth mechanisms want to be studied. Solid 3He orders magnetically into the U2D2 phase (an antiferromagnetic phase with two planes of spins pointing up and two planes of spins pointing down in sequence) when is cooled down to very low temperatures (below the N_el transition ~1mK). If the external magnetic field is increased above 450mT, the solid orders into a different magnetic phase, the so-called CNAF phase (a normal antiferromagnetic phase, but with the spins slightly tilted from their normal position with a significant magnetization). For first time a clear indication showing that external magnetic fields indeed affect the growth of the crystals was seen. Crystals in high magnetic fields grow almost ten times faster than crystals at zero magnetic field, which was completely unpredicted behavior. This results yield that the interface between the liquid and the solid and crystal lattice seem to couple strongly at high magnetic fields, while the coupling was weak at zero magnetic field.LEI Universiteit LeidenFOMLIO

Actinomicetos aislados del suelo del Jardín botánico de la Universidad Tecnológica de Pereira

Partiendo del  importante papel que desempeñan los microorganismos, especialmente las Rizobacterias denominadas Actinomicetos, en la salud y sostenibilidad del suelo, se realizó una identificación parcial de diferentes tipos de actinomicetos aislados del suelo del Jardín Botánico de la Universidad Tecnológica de Pereira (JBUTP), según género apoyándose en la Clave Taxonómica de Bergey, dando como resultado los siguientes posibles géneros: Nocardia, Actinopolyspora, Streptomyces, Thermonospora, Micromonospora, Actinobispora; presentándose en mayor porcentaje, los géneros Nocardia y Streptomyce

Actinomicetos aislados del suelo del Jardín botánico de la Universidad Tecnológica de Pereira

Partiendo del  importante papel que desempeñan los microorganismos, especialmente las Rizobacterias denominadas Actinomicetos, en la salud y sostenibilidad del suelo, se realizó una identificación parcial de diferentes tipos de actinomicetos aislados del suelo del Jardín Botánico de la Universidad Tecnológica de Pereira (JBUTP), según género apoyándose en la Clave Taxonómica de Bergey, dando como resultado los siguientes posibles géneros: Nocardia, Actinopolyspora, Streptomyces, Thermonospora, Micromonospora, Actinobispora; presentándose en mayor porcentaje, los géneros Nocardia y Streptomyce

Biodiversity and distribution of polar freshwater DNA viruses

Viruses constitute the most abundant biological entities and a large reservoir of genetic diversity on Earth. Despite the recent surge in their study, our knowledge on their actual biodiversity and distribution remains sparse. We report the first metagenomic analysis of Arctic freshwater viral DNA communities and a comparative analysis with other freshwater environments. Arctic viromes are dominated by unknown and single-stranded DNA viruses with no close relatives in the database. These unique viral DNA communities mostly relate to each other and present some minor genetic overlap with other environments studied, including an Arctic Ocean virome. Despite common environmental conditions in polar ecosystems, the Arctic and Antarctic DNA viromes differ at the fine-grain genetic level while sharing a similar taxonomic composition. The study uncovers some viral lineages with a bipolar distribution, suggesting a global dispersal capacity for viruses, and seemingly indicates that viruses do not follow the latitudinal diversity gradient known for macroorganisms. Our study sheds light into the global biogeography and connectivity of viral communities

A near-IR line of Mn I as a diagnostic tool of the average magnetic energy in the solar photosphere

We report on spectropolarimetric observations of a near-IR line of Mn I located at 15262.702 A whose intensity and polarization profiles are very sensitive to the presence of hyperfine structure. A theoretical investigation of the magnetic sensitivity of this line to the magnetic field uncovers several interesting properties. The most important one is that the presence of strong Paschen-Back perturbations due to the hyperfine structure produces an intensity line profile whose shape changes according to the absolute value of the magnetic field strength. A line ratio technique is developed from the intrinsic variations of the line profile. This line ratio technique is applied to spectropolarimetric observations of the quiet solar photosphere in order to explore the probability distribution function of the magnetic field strength. Particular attention is given to the quietest area of the observed field of view, which was encircled by an enhanced network region. A detailed theoretical investigation shows that the inferred distribution yields information on the average magnetic field strength and the spatial scale at which the magnetic field is organized. A first estimation gives ~250 G for the mean field strength and a tentative value of ~0.45" for the spatial scale at which the observed magnetic field is horizontally organized.Comment: 42 pages, 17 figures, accepted for publication in the Astrophysical Journal. Figures 1 and 9 are in JPG forma