Vicariances : la flexibilité du vivant

Les processus vicariants différentiels proposés par Maurice Reuchlin en 1978 se caractérisent par le fait que face à un problème donné, chaque individu disposerait de plusieurs processus redondants. L’évocabilité de chacun de ces processus serait variable d’un individu à l’autre, mais aussi et surtout d’une situation à l’autre. Après les avoir décrits et positionnés dans le cadre des travaux contemporains, leur dynamique, liée à la variabilité intra-individuelle, est développée à partir d’exemples empruntés aux comportements spatiaux, à la neuropathologie et au développement cognitif. Dans une perspective évolutionniste, la convergence entre les vicariances et les théories neutralistes est rappelée.Vicarious processes were defined by Maurice Reuchlin in 1978. They are characterised by two main properties: 1) the redundancy, each personn has at their disposal several processes to handle a given problem, and 2) idiosyncratic evocability, as for a given individual some of these processes, and especially situations, are more easily evoked than others. These processes are described and placed in the context of contemporary work, and their dynamics, which are associated with intra-individual differences, are then developed using examples borrowed from spatial orientation, neuropathology and cognitive development. Finally, from an evolutionist perspective, vicariousness is positioned in the frame of neutralism theory

Mechanism of HIV-1 Tat RNA translation and its activation by the Tat protein

<p>Abstract</p> <p>Background</p> <p>The human immunodeficiency virus type 1 (HIV-1) Tat protein is a major viral transactivator required for HIV-1 replication. In the nucleus Tat greatly stimulates the synthesis of full-length transcripts from the HIV-1 promoter by causing efficient transcriptional elongation. Tat induces elongation by directly interacting with the bulge of the transactivation response (TAR) RNA, a hairpin-loop located at the 5'-end of all nascent viral transcripts, and by recruiting cellular transcriptional co-activators. In the cytoplasm, Tat is thought to act as a translational activator of HIV-1 mRNAs. Thus, Tat plays a central role in the regulation of HIV-1 gene expression both at the level of mRNA and protein synthesis. The requirement of Tat in these processes poses an essential question on how sufficient amounts of Tat can be made early on in HIV-1 infected cells to sustain its own synthesis. To address this issue we studied translation of the Tat mRNA <it>in vitro </it>and in human cells using recombinant monocistronic and dicistronic RNAs containing the 5' untranslated region (5'-UTR) of Tat RNA.</p> <p>Results</p> <p>This study shows that the Tat mRNA can be efficiently translated both <it>in vitro </it>and in cells. Furthermore, our data suggest that translation initiation from the Tat mRNA probably occurs by a internal ribosome entry site (IRES) mechanism. Finally, we show that Tat protein can strongly stimulate translation from its cognate mRNA in a TAR dependent fashion.</p> <p>Conclusion</p> <p>These results indicate that Tat mRNA translation is efficient and benefits from a feedback stimulation by the Tat protein. This translational control mechanism would ensure that minute amounts of Tat mRNA are sufficient to generate enough Tat protein required to stimulate HIV-1 replication.</p

Lentiviral RNAs can use different mechanisms for translation initiation

Abstract The full-length genomic RNA of lentiviruses can be translated to produce proteins and incorporated as genomic RNA in the viral particle. Interestingly, both functions are driven by the genomic 5 -UTR (5 -untranslated region), which harbours structural RNA motifs for the replication cycle of the virus. Recent work has shown that this RNA architecture also functions as an IRES (internal ribosome entry site) in HIV-1 and -2, and in SIV (simian immunodeficiency virus). In addition, the IRES extends to the gag coding region for all these viruses and this leads to the synthesis of shorter isoforms of the Gag polyprotein from downstream initiation codons. In the present study, we have investigated how different members of the lentivirus family (namely HIV-1 and -2, and SIV) can initiate protein synthesis by distinct mechanisms. For this, we have used the competitive reticulocyte lysate that we have recently described. Our results show that HIV-1 is able to drive the synthesis of the Gag polyprotein both by a classical cap-dependent mechanism and an IRES, whereas HIV-2 and SIV appear to use exclusively an IRES mechanism

Long Lasting Egocentric Disorientation Induced by Normal Sensori-Motor Spatial Interaction

Perception of the cardinal directions of the body, right-left, up-down, ahead-behind, which appears so absolute and fundamental to the organisation of behaviour can in fact, be modified. Perhaps unsurprisingly, it has been shown that prolonged distorted perception of the orientation of body axes can be a consequence of disordered sensori-motor signals, including long-term prismatic adaptation and lesions of the central nervous system. We report the novel and surprising finding that a long-lasting distortion of perception of personal space can also be induced by an ecological pointing task without the artifice of distorting normal sensori-motor relationships.Twelve right-handed healthy adults performed the task of pointing with their arms, without vision, to indicate their subjective 'straight ahead', a task often used to assess the Egocentric Reference. This was performed before, immediately, and one day after a second task intended to 'modulate' perception of spatial direction. The 'modulating' task lasted 5 minutes and consisted of asking participants to point with the right finger to targets that appeared only in one (right or left) half of a computer screen. Estimates of the 'straight-ahead' during pre-test were accurate (inferior to 0.3 degrees deviation). Significantly, up to one day after performing the modulating task, the subjective 'straight-ahead' was deviated (by approximately 3.2 degrees) to the same side to which subjects had pointed to targets.These results reveal that the perception of directional axes for behaviour is readily influenced by interactions with the environment that involve no artificial distortion of normal sensori-motor-spatial relationships and does not necessarily conform to the cardinal directions as defined by the anatomy of orthostatic posture. We thus suggest that perceived space is a dynamic construction directly dependent upon our past experience about the direction and/or the localisation of our sensori-motor spatial interaction with environment

Différence de sensibilité de 12 tests verbaux à quatre catégories socio-économiques

Ohlmann Théophile. Différence de sensibilité de 12 tests verbaux à quatre catégories socio-économiques. In: Bulletin de psychologie, tome 32 n°340, 1979. L'intelligence. pp. 487-500

Contraintes situationnelles et plasticité individuelle : compétences des systèmes vicariants

Les contraintes situationnelles Au sein d'une espèce donnée, l'ampleur des différences observables entre les individus est régulée de manière non linéaire par les contraintes situationnelles. En effet, le modèle darwinien traditionnel suppose qu'en fonction de caractères adaptatifs positifs, un tri sévère s'effectue au niveau même de la population des individus. En cas de fortes contraintes, les différences sont alors réduites et la population semble obéir à une loi générale. Baldwin (1896) e..

Dépendance-indépendance à l'égard du champ et inégalité des estimations visuelle et tactile de longueurs

Summary Some subjects display considerable intermodal variability for certain perceptual activities. It was hypothesised that this variability is associated with cognitive style, specifically with field dependence-independence. Eighteen subjects, males and females aged 7 years 6 months, estimated the length of rods both visually and tactually. As predicted, field dependence was associated with greater differences between the tactual and the visual estimations. Moreover, only among the field dependent subjecls did this difference increase as a function of the length of the rod. Subjects' cognitive styles were manifested particulary in the way the tactual exploration was mode, a factor accounting for the differences in performance.Résumé Certains sujets présentent une forte variabilité intermodale de certaines activités perceptives. On vérifie l'hypothèse selon laquelle cette dispersion serait associée, en partie, à un style cognitif : la dépendance à l'égard du champ. 18 sujets, garçons et filles, âgés de 7 ans 6 mois ont estimé des longueurs de baguettes en modalité tactile et visuelle. Les sujets les plus dépendants à l'égard du champ sont ceux qui présentent les plus grands écarts entre leurs estimations visuelles et tactiles. Cet écart croît avec la longueur des baguettes chez les dépendants alors qu'il est constant chez les indépendants. Le style cognitif du sujet se manifeste en particulier par des procédures qui rendraient compte des différences de performances.Ohlmann Théophile. Dépendance-indépendance à l'égard du champ et inégalité des estimations visuelle et tactile de longueurs. In: L'année psychologique. 1981 vol. 81, n°1. pp. 7-21

Effet d'un contexte visuel incliné : vers une explication en termes d'inclinaison du plan médian apparent

Summary: Towards an alternative hypothesis for the rod-and-frame effect. Adjusting a rod to the gravitational vertical in the presence of a large square or rectangular tilted frame leads to a significant deviation towards the orientation of the frame. According to the «vectiorial hypothesis», the tilted frame produces a self-tilt illusion in the observer, in a direction opposite to that of the frame. This self-tilt illusion is similar, by analogy, to the self-motion induced by rotating peripheral displays. A compensatory process, engaged in response to the illusory body tilt induced by the tilted frame, would explain the deviation ofthe subjective vertical towards the direction of the frame. However, although widely held, there is little direct evidence supporting this hypothesis. Moreover, other empirical observations support an alternative possibility that the frame effect, like the Dietzel-Roelofs effect, could arise because of a tilt of the apparent median plane of the observer towards the frame. This hypothesis may be referred as «the apparent-median-plane-tilt hypothesis». The aim of this paper is threefold. First, we describe a number of different hypotheses about the frame effect. We focus on two : the vectional hypothesis and the apparent-median-plane-tilt hypothesis. Second, we attempt to explore the generality of the vectional hypothesis and third, we try to distinguish between the vectional hypothesis and the apparent-median-plane-tilt hypothesis. Key words : rod-and-frame effect, perception of verticality, apparent median-plane.Résumé L'effet-cadre traduit l'influence de l'inclinaison d'une configuration visuelle rectangulaire ou carrée sur la perception de la verticale. Cet effet est mis en évidence, le plus souvent, lors de la passation du test de la baguette et du cadre, épreuve plus communément appelée Rod and Frame Test ou RFT. Plusieurs explications de ce phénomène ont été proposées mais l'hypothèse vec-tionnelle est celle qui, depuis les années soixante-dix, rallie incontestablement le plus grand nombre de chercheurs. Dans ce contexte, les déviations de la verticale subjective seraient, par analogie à la vection optocinétique, la conséquence d'une illusion d'inclinaison du corps en sens inverse du cadre. Cette proposition souffre toutefois d'une absence de preuves directes attestant l'existence, au RFT, d'un processus vectionnel de nature optostatique. Un certain nombre d'éléments plaident plutôt en faveur d'une hypothèse minoritaire selon laquelle l'effet-cadre, similaire à l'effet Dietzel-Roelofs, résulterait de l'inclinaison subjective du plan médian apparent dans le sens du cadre. L'objectif est ici d'examiner les principales hypothèses explicatives de l'effet-cadre, de présenter les limites de l'hypothèse vectionnelle et d'apporter les éléments permettant de montrer tout l'intérêt de l'hypothèse d'inclinaison du plan médian apparent. Mots-clés : effet-cadre, perception de la verticale, plan médian apparent.Luyat Marion, Ohlmann Théophile. Effet d'un contexte visuel incliné : vers une explication en termes d'inclinaison du plan médian apparent. In: L'année psychologique. 1997 vol. 97, n°2. pp. 267-292