Neuronal adaptation effects in decision making

Recently, there has been an increased interest on the neural mechanisms underlying perceptual decision making. However, the effect of neuronal adaptation in this context has not yet been studied. We begin our study by investigating how adaptation can bias perceptual decisions. We considered behavioral data from an experiment on high-level adaptation-related aftereffects in a perceptual decision task with ambiguous stimuli on humans. To understand the driving force behind the perceptual decision process, a biologically inspired cortical network model was used. Two theoretical scenarios arose for explaining the perceptual switch from the category of the adaptor stimulus to the opposite, nonadapted one. One is noise-driven transition due to the probabilistic spike times of neurons and the other is adaptation-driven transition due to afterhyperpolarization currents. With increasing levels of neural adaptation, the system shifts from a noise-driven to an adaptation-driven modus. The behavioral results show that the underlying model is not just a bistable model, as usual in the decision-making modeling literature, but that neuronal adaptation is high and therefore the working point of the model is in the oscillatory regime. Using the same model parameters, we studied the effect of neural adaptation in a perceptual decision-making task where the same ambiguous stimulus was presented with and without a preceding adaptor stimulus. We find that for different levels of sensory evidence favoring one of the two interpretations of the ambiguous stimulus, higher levels of neural adaptation lead to quicker decisions contributing to a speed–accuracy trade off.

The neuronal basis of attention: rate versus synchronization modulation

Extensive theoretical and experimental work on the neuronal correlates of visual attention raises two hypotheses about the underlying mechanisms. The first hypothesis, named biased competition, originates from experimental single-cell recordings that have shown that attention upmodulates the firing rates of the neurons encoding the attended features and downregulates the firing rates of the neurons encoding the unattended features. Furthermore, attentional modulation of firing rates increases along the visual pathway. The other, newer hypothesis assigns synchronization a crucial role in the attentional process. It stems from experiments that have shown that attention modulates gamma-frequency synchronization. In this paper, we study the coexistence of the two phenomena using a theoretical framework. We find that the two effects can vary independently of each other and across layers. Therefore, the two phenomena are not concomitant. However, we show that there is an advantage in the processing of information if rate modulation is accompanied by gamma modulation, namely that reaction times are shorter, implying behavioral relevance for gamma synchronization.

The control of microtubule stability in vitro and in transfected cells by MAP1B and SCG10.

In neurons, the regulation of microtubules plays an important role for neurite outgrowth, axonal elongation, and growth cone steering. SCG10 family proteins are the only known neuronal proteins that have a strong destabilizing effect, are highly enriched in growth cones and are thought to play an important role during axonal elongation. MAP1B, a microtubule-stabilizing protein, is found in growth cones as well, therefore it was important to test their effect on microtubules in the presence of both proteins. We used recombinant proteins in microtubule assembly assays and in transfected COS-7 cells to analyze their combined effects in vitro and in living cells, respectively. Individually, both proteins showed their expected activities in microtubule stabilization and destruction respectively. In MAP1B/SCG10 double-transfected cells, MAP1B could not protect microtubules from SCG10-induced disassembly in most cells, in particular not in cells that contained high levels of SCG10. This suggests that SCG10 is more potent to destabilize microtubules than MAP1B to rescue them. In microtubule assembly assays, MAP1B promoted microtubule formation at a ratio of 1 MAP1B per 70 tubulin dimers while a ratio of 1 SCG10 per two tubulin dimers was needed to destroy microtubules. In addition to its known binding to tubulin dimers, SCG10 binds also to purified microtubules in growth cones of dorsal root ganglion neurons in culture. In conclusion, neuronal microtubules are regulated by antagonistic effects of MAP1B and SCG10 and a fine tuning of the balance of these proteins may be critical for the regulation of microtubule dynamics in growth cones.

Culture marked: racist epithets in translations of Mark Twain's Adventures of Huckleberry Finn

Aquest projecte analitza com s’ha plasmat el terme cultural nigger a dues traduccions al castellà de la novel•la Adventures of Huckleberry Finn de Mark Twain, amb l’objectiu d’estudiar de quina manera poden adaptar-se els elements culturals en una traducció. En primer lloc, s’ofereix la contextualització del terme original al text i a la cultura d’origen, seguida de la descripció del terme traduït en el context de la cultura d’arribada. A continuació, mitjançant l’anàlisi comparativa del mecanisme retòric de la repetició i d’elements com ara determinants, adjectius i complements, emprats tant a l’obra original com a les dues traduccions estudiades, aquest projecte pretén demostrar que la conservació dels esmentats recursos estilístics a la traducció pot facilitar la comprensió de les connotacions del marcador cultural nigger i de la seva funció temàtica al text d’arribada.

Epidermal growth factor and bovine growth hormone stimulate differentiation and myelination of brain cell aggregates in culture.

Bovine growth hormone (bGH) and epidermal growth factor (EGF) increased the activity of ornithine decarboxylase (ODC) in brain cell aggregates cultured in a serum-free chemically defined medium. ODC is considered as a marker of cell growth and differentiation. The effect of bGH and EGF on myelination was investigated by measuring two myelin markers, 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) and myelin basic protein (MBP). EGF treatment at days 2 and 5 caused a dose-dependent increase of both myelin markers at culture day 12. This increase could still be observed at culture day 19, indicating a prolonged action of EGF. The continual presence of bGH in the culture medium produced a large accumulation of MBP at day 19. This effect was dose-dependent and required the presence of triiodothyronine (T3). In contrast, the effect of bGH on CNP activity did not require the presence of T3. This is the first report showing a direct effect of bGH on CNS myelination in vitro and of EGF on both MBP accumulation and ODC activity.

Determination of Transmembrane Water Fluxes in Neurons Elicited by Glutamate Ionotropic Receptors and by the Cotransporters KCC2 and NKCC1: A Digital Holographic Microscopy Study.

Digital holographic microscopy (DHM) is a noninvasive optical imaging technique that provides quantitative phase images of living cells. In a recent study, we showed that the quantitative monitoring of the phase signal by DHM was a simple label-free method to study the effects of glutamate on neuronal optical responses (Pavillon et al., 2010). Here, we refine these observations and show that glutamate produces the following three distinct optical responses in mouse primary cortical neurons in culture, predominantly mediated by NMDA receptors: biphasic, reversible decrease (RD) and irreversible decrease (ID) responses. The shape and amplitude of the optical signal were not associated with a particular cellular phenotype but reflected the physiopathological status of neurons linked to the degree of NMDA activity. Thus, the biphasic, RD, and ID responses indicated, respectively, a low-level, a high-level, and an "excitotoxic" level of NMDA activation. Moreover, furosemide and bumetanide, two inhibitors of sodium-coupled and/or potassium-coupled chloride movement strongly modified the phase shift, suggesting an involvement of two neuronal cotransporters, NKCC1 (Na-K-Cl) and KCC2 (K-Cl) in the genesis of the optical signal. This observation is of particular interest since it shows that DHM is the first imaging technique able to monitor dynamically and in situ the activity of these cotransporters during physiological and/or pathological neuronal conditions.

Inhibitory effects of (2S, 3S)-3-[3-[4-(trifluoromethyl)benzoylamino]benzyloxy]aspartate (TFB-TBOA) on the astrocytic sodium responses to glutamate.

Astrocytes are responsible for the majority of the clearance of extracellular glutamate released during neuronal activity. dl-threo-beta-benzyloxyaspartate (TBOA) is extensively used as inhibitor of glutamate transport activity, but suffers from relatively low affinity for the transporter. Here, we characterized the effects of (2S, 3S)-3-[3-[4-(trifluoromethyl)benzoylamino]benzyloxy]aspartate (TFB-TBOA), a recently developed inhibitor of the glutamate transporter on mouse cortical astrocytes in primary culture. The glial Na(+)-glutamate transport system is very efficient and its activation by glutamate causes rapid intracellular Na(+) concentration (Na(+)(i)) changes that enable real time monitoring of transporter activity. Na(+)(i) was monitored by fluorescence microscopy in single astrocytes using the fluorescent Na(+)-sensitive probe sodium-binding benzofuran isophtalate. When applied alone, TFB-TBOA, at a concentration of 1 muM, caused small alterations of Na(+)(i). TFB-TBOA inhibited the Na(+)(i) response evoked by 200 muM glutamate in a concentration-dependent manner with IC(50) value of 43+/-9 nM, as measured on the amplitude of the Na(+)(i) response. The maximum inhibition of glutamate-evoked Na(+)(i) increase by TFB-TBOA was >80%, but was only partly reversible. The residual response persisted in the presence of the AMPA/kainate receptor antagonist CNQX. TFB-TBOA also efficiently inhibited Na(+)(i) elevations caused by the application of d-aspartate, a transporter substrate that does not activate non-NMDA ionotropic receptors. TFB-TBOA was found not to influence the membrane properties of cultured cortical neurons recorded in whole-cell patch clamp. Thus, TFB-TBOA, with its high potency and its apparent lack of neuronal effects, appears to be one of the most useful pharmacological tools available so far for studying glial glutamate transporters.

International nursing : cultivating a culture of empowerment

International nursing has been a growing phenomenon throughout the globe. International nurses have been found to be an asset to healthcare organizations and an important part of the health care team. However, growing concern for the plight of international nurses facing obstacles such as professional stagnation and exploitation has spurred the development of strategies to mitigate and ameliorate the experiences of nurses working abroad. In this respect, the purpose of this study was to explore the management-influenced factors and the nurse team-influenced factors that promote the empowerment of the international nurse in the health care setting. The methodology used in this study was a systemic review. After a rigorous search for relevant empirical studies using OVID database, eight empirical research studies were selected using systematic review methodology to collect, analyze and synthesize data. The selected eight empirical studies were then subjected to a content analysis. The results suggested that the empowerment of an international nurse is inseparable from the empowerment of the health care organization. Based on the findings in this study, strategies to promote international nurses were found to mirror strategies evidenced to empower the nursing organization. Some of the management-influenced factors which were found to facilitate empowerment included a diversity rich work culture, transformational leadership at the management level, and a responsibility to foster the values of the organization. The team-influenced factors which were found to contribute to the empowerment of the international nurse included a united mutually-interdependent nurse team, shared accountability among the members of the nurse team, and the building of trust in work relationships. To conlude, this study indicates that efforts to empower international nurses without considering the work culture and the organization as a whole are futile because empowerment cannot take place in an environment that lacks antecedent conditions. Strategies to empower the international nurse should not focus on the deficits and special needs of the international nurse, but should focus on the similarities and commonalities of the nursing body. Empowerment of the international nurse mean open honest communication, supportive work environment, and a firm policy to quell disruptive elements that threaten the organization's values, mission, and philosophy of care.

Guerre de Troie, guerres des cultures et guerres du Golfe : les usages de "l'Illiade" dans la culture écrite américaine contemporaine

Depuis 1990 et la fin de la Guerre Froide, les Etats-Unis d'Amérique sont devenus la première puissance mondiale, animée par l'idéal de défendre les valeurs occidentale et de répandre la démocratie dans le monde. Or, entre des racines identitaires gréco-romaines empruntées à l'Europe, et les guerres menées au Moyen-Orient contre différents ennemis, la « mission » de l'Amérique suscite critiques et interrogations, et le conflit est autant culturel que militaire. L'Iliade d'Homère au contenu guerrier, érigée par la tradition littéraire en oeuvre fondatrice de l'Occident, offre aux penseurs américains de tous horizons un outil de réflexion propre à éclairer ce présent si inconfortable. A travers l'étude d'un corpus tripartite inédit, ce travail se propose de questionner le rôle d'une oeuvre symbolique de l'Antiquité grecque dans le monde d'aujourd'hui, et débouche sur une réflexion plus large touchant au sens contemporain des études classiques et à la transmission du savoir au sein de la culture populaire. Dans un premier temps, elle examine des ouvrages ou articles à vocation scientifique, mais publiés pour la plupart hors du cadre académique, qui théorisent et expriment les enjeux des guerres des cultures américaines (« culture wars ») divisant conservateurs et libéraux sur la mission véritable d'une éducation libérale. Ces ouvrages se servent également de l'Iliade comme d'un miroir où se reflète les conflits modernes, afin d'atténuer le trouble contemporain en juxtaposant passé et présent. Dans un deuxième temps sont abordés les médias journalistiques et informatiques, à l'aide des résultats obtenus lors de recherches poussées, effectuées dans les archives informatiques des journaux publiés dans les capitales et villes majeures des cinquante Etats américains. De fascinantes comparaisons entre la guerre de Troie et la guerre en Irak y sont notamment construites. Le discours sur l'actualité se développe par le recours à l'Antiquité, et en tire de nombreuses « leçons » destinées au gouvernement américain et à tous les meneurs de guerres. Et dans un troisième temps, deux romans de science-fiction, Ilium (2003) et sa suite Olympos (2005), de Dan Simmons, fournissent un fascinant complément littéraire au reste du corpus. Imprégnés par les culture wars, ils transposent l'Iliade dans un lointain futur et expriment sous une forme nouvelle toutes les interrogations brûlantes qui, aujourd'hui particulièrement, animent une Amérique troublée tant par ses guerres que par la remise en question de son identité occidentale. Par cette réunion de trois domaines dissemblables, ce travail pose aussi de nombreuses questions épistémologiques sur la circulation de l'information, la transformation des savoirs, le flou des frontières entre les genres, la révolution que représente Internet, et la fragmentation progressive de la bulle académique. Il propose également de nombreuses perspectives d'ouverture permettant de poursuivre cette recherche. Car la réception contemporaine de l'Iliade - et de l'Antiquité en général - est un domaine riche et dynamique, qui présente l'avantage - ou l'inconvénient, c'est selon - d'être toujours d'actualité. L'inconfort du présent ne devrait pas empêcher son étude, car les résultats sont extrêmement révélateurs de la véritable relation qu'entretiennent les hommes d'aujourd'hui - et non plus seulement les savants - avec leur passé.