The influence of dopamine on semantic activation in Parkinson's disease: Evidence from a multipriming task

Research has suggested that semantic processing deficits in Parkinson's disease (PD) are related to striatal dopamine deficiency. As an investigation of the influence of dopamine on semantic activation in PD, 7 participants with PD performed a lexical-decision task when on and off levodopa medication. Seven healthy controls matched to the participants with PD in terms of sex, age, and education also participated in the study. By use of a multipriming paradigm, whereby 2 prime words were presented prior to the target word, semantic priming effects were measured across stimulus onset asynchronies (SOAs) of 250 Ins and 1,200 Ins. The results revealed a similar pattern of priming across SOAs for the control group and the PD participants on medication. In contrast, within-group comparisons revealed that automatic semantic activation was compromised in PD participants when off medication. The implications of these results for the neuromodulatory influence of dopamine on semantic processing in PD are discussed.

Goal orientation, ability and task performance: A moderated analysis

Achievement goal orientation represents an individual's general approach to an achievement situation, and has important implications for how individuals react to novel, challenging tasks. However, theorists such as Yeo and Neal (2004) have suggested that the effects of goal orientation may emerge over time. Bell and Kozlowski (2002) have further argued that these effects may be moderated by individual ability. The current study tested the dynamic effects of a new 2x2 model of goal orientation (mastery/performance x approach/avoidance) on performance on a simulated air traffic control (ATC) task, as moderated by dynamic spatial ability. One hundred and one first-year participants completed a self-report goal orientation measure and computerbased dynamic spatial ability test and performed 30 trials of an ATC task. Hypotheses were tested using a two-level hierarchical linear model. Mastery-approach orientation was positively related to task performance, although no interaction with ability was observed. Performance-avoidance orientation was negatively related to task performance; this association was weaker at high levels of ability. Theoretical and practical implications will be discussed.

ESCOLHAS E DECISÕES: ESTUDO DO PROCESSO PARTICIPATIVO EM ORGANIZAÇÕES DA ECONOMIA SOLIDÁRIA

As últimas décadas, no caso brasileiro, foram marcadas pela predominância da estabilidade econômica e desregulamentação estatal no campo da economia, desconsiderando o impacto na vida das pessoas. Quebras e falências são constatadas como resultado desse processo. Aos trabalhadores surge a oportunidade, com muito esforço, de modelos alternativos nas relações de trabalho. Aparece nesse contexto, o novo discurso da Economia Solidária que preza por práticas autogestionadas. As Empresas Recuperadas são enquadradas dentro desse novo discurso. Entretanto, nas Empresas Recuperadas e nos empreendimentos da Economia Solidária, o espaço fértil proporcionado no campo da subjetividade enfrenta um dilema objetivo. Em sua batalha pela sobrevivência e sustentação, a organização deverá adotar práticas burocráticas e poderá desencantar o espaço da participação. Resulta disso, um dilema entre a objetividade, que a gestão demanda, e a subjetividade que o discurso da Economia Solidária exige. Nessa dissertação, propõe-se que a participação permite um efeito psicológico na medida em que assegura uma inter-relação contínua entre o funcionamento das instituições e as qualidades e atitudes das pessoas que atuam em seu interior. Escolhas e decisões, dessa forma, se colocam como processo que compõe a categoria da participação. Como os trabalhadores das Organizações da Economia Solidária participam do processo de escolhas e decisões em um sistema coletivo e cooperativo de trabalho? Essa é a pergunta central desta pesquisa, que tem por objetivo analisar o processo de escolhas e decisões em organizações da Economia Solidária. Nesse intuito realizou-se um estudo de caso por meio da metodologia da pesquisa-ação de uma empresa recuperada no interior de São Paulo. A pesquisa-ação é um tipo de pesquisa social, com base empírica, que é concebida e realizada em estreita associação com uma ação ou resolução de um problema. Esse problema, no contexto do estudo de caso, foi a concepção de um processo de formação de funcionários para futuros cooperados. A trajetória da discussão foi realizada com acompanhamento de um Grupo Tarefa composto por membros (celetistas e cooperados) da organização. A análise dos resultados foi construída a partir da fundamentação teórica convergindo em três categorias, que compõe o processo de participação, dentro de uma organização da Economia Solidária: Eu comigo (EUCMG), Eu com o(s) outro(s) (EUCOU) e Eu na Organização (EUORG). Os resultados mostram que a Empresa estudada não pode ser considerada como autogestionada e está fundamentada em práticas elitizadas. Há poucas práticas coletivas e se divide em classes internas (chão-defábrica e staff). Contudo, reconhece-se um grande esforço para chegar a uma nova prática de gestão coletiva. A participação se dá dentro de aspectos formais (assembléia) com predominância de assuntos burocráticos que não passaram por apropriação coletiva em sua construção. A educatividade ilumina o caminho processual, rompendo com visões finalísticas e alcançando uma sustentabilidade para a organização.(AU)

The role of texture amplitude in shape from shading: evidence from a haptic matching task

The pattern of illumination on an undulating surface can be used to infer its 3-D form (shape from shading). But the recovery of shape would be invalid if the shading actually arose from reflectance variation. When a corrugated surface is painted with an albedo texture, the variation in local mean luminance (LM) due to shading is accompanied by a similar modulation in texture amplitude (AM). This is not so for reflectance variation, nor for roughly textured surfaces. We used a haptic matching technique to show that modulations of texture amplitude play a role in the interpretation of shape from shading. Observers were shown plaid stimuli comprising LM and AM combined in-phase (LM+AM) on one oblique and in anti-phase (LM-AM) on the other. Stimuli were presented via a modified ReachIN workstation allowing the co-registration of visual and haptic stimuli. In the first experiment, observers were asked to adjust the phase of a haptic surface, which had the same orientation as the LM+AM combination, until its peak in depth aligned with the visually perceived peak. The resulting alignments were consistent with the use of a lighting-from-above prior. In the second experiment, observers were asked to adjust the amplitude of the haptic surface to match that of the visually perceived surface. Observers chose relatively large amplitude settings when the haptic surface was oriented and phase-aligned with the LM+AM cue. When the haptic surface was aligned with the LM-AM cue, amplitude settings were close to zero. Thus the LM/AM phase relation is a significant visual depth cue, and is used to discriminate between shading and reflectance variations. [Supported by the Engineering and Physical Sciences Research Council, EPSRC].

Tense, aspect and modality in first and second language

Time after time… and aspect and mood. Over the last twenty five years, the study of time, aspect and - to a lesser extent - mood acquisition has enjoyed increasing popularity and a constant widening of its scope. In such a teeming field, what can be the contribution of this book? We believe that it is unique in several respects. First, this volume encompasses studies from different theoretical frameworks: functionalism vs generativism or function-based vs form-based approaches. It also brings together various sub-fields (first and second language acquisition, child and adult acquisition, bilingualism) that tend to evolve in parallel rather than learn from each other. A further originality is that it focuses on a wide range of typologically different languages, and features less studied languages such as Korean and Bulgarian. Finally, the book gathers some well-established scholars, young researchers, and even research students, in a rich inter-generational exchange, that ensures the survival but also the renewal and the refreshment of the discipline. The book at a glance The first part of the volume is devoted to the study of child language acquisition in monolingual, impaired and bilingual acquisition, while the second part focuses on adult learners. In this section, we will provide an overview of each chapter. The first study by Aviya Hacohen explores the acquisition of compositional telicity in Hebrew L1. Her psycholinguistic approach contributes valuable data to refine theoretical accounts. Through an innovating methodology, she gathers information from adults and children on the influence of definiteness, number, and the mass vs countable distinction on the constitution of a telic interpretation of the verb phrase. She notices that the notion of definiteness is mastered by children as young as 10, while the mass/count distinction does not appear before 10;7. However, this does not entail an adult-like use of telicity. She therefore concludes that beyond definiteness and noun type, pragmatics may play an important role in the derivation of Hebrew compositional telicity. For the second chapter we move from a Semitic language to a Slavic one. Milena Kuehnast focuses on the acquisition of negative imperatives in Bulgarian, a form that presents the specificity of being grammatical only with the imperfective form of the verb. The study examines how 40 Bulgarian children distributed in two age-groups (15 between 2;11-3;11, and 25 between 4;00 and 5;00) develop with respect to the acquisition of imperfective viewpoints, and the use of imperfective morphology. It shows an evolution in the recourse to expression of force in the use of negative imperatives, as well as the influence of morphological complexity on the successful production of forms. With Yi-An Lin’s study, we concentrate both on another type of informant and of framework. Indeed, he studies the production of children suffering from Specific Language Impairment (SLI), a developmental language disorder the causes of which exclude cognitive impairment, psycho-emotional disturbance, and motor-articulatory disorders. Using the Leonard corpus in CLAN, Lin aims to test two competing accounts of SLI (the Agreement and Tense Omission Model [ATOM] and his own Phonetic Form Deficit Model [PFDM]) that conflicts on the role attributed to spellout in the impairment. Spellout is the point at which the Computational System for Human Language (CHL) passes over the most recently derived part of the derivation to the interface components, Phonetic Form (PF) and Logical Form (LF). ATOM claims that SLI sufferers have a deficit in their syntactic representation while PFDM suggests that the problem only occurs at the spellout level. After studying the corpus from the point of view of tense / agreement marking, case marking, argument-movement and auxiliary inversion, Lin finds further support for his model. Olga Gupol, Susan Rohstein and Sharon Armon-Lotem’s chapter offers a welcome bridge between child language acquisition and multilingualism. Their study explores the influence of intensive exposure to L2 Hebrew on the development of L1 Russian tense and aspect morphology through an elicited narrative. Their informants are 40 Russian-Hebrew sequential bilingual children distributed in two age groups 4;0 – 4;11 and 7;0 - 8;0. They come to the conclusion that bilingual children anchor their narratives in perfective like monolinguals. However, while aware of grammatical aspect, bilinguals lack the full form-function mapping and tend to overgeneralize the imperfective on the principles of simplicity (as imperfective are the least morphologically marked forms), universality (as it covers more functions) and interference. Rafael Salaberry opens the second section on foreign language learners. In his contribution, he reflects on the difficulty L2 learners of Spanish encounter when it comes to distinguishing between iterativity (conveyed with the use of the preterite) and habituality (expressed through the imperfect). He examines in turn the theoretical views that see, on the one hand, habituality as part of grammatical knowledge and iterativity as pragmatic knowledge, and on the other hand both habituality and iterativity as grammatical knowledge. He comes to the conclusion that the use of preterite as a default past tense marker may explain the impoverished system of aspectual distinctions, not only at beginners but also at advanced levels, which may indicate that the system is differentially represented among L1 and L2 speakers. Acquiring the vast array of functions conveyed by a form is therefore no mean feat, as confirmed by the next study. Based on the prototype theory, Kathleen Bardovi-Harlig’s chapter focuses on the development of the progressive in L2 English. It opens with an overview of the functions of the progressive in English. Then, a review of acquisition research on the progressive in English and other languages is provided. The bulk of the chapter reports on a longitudinal study of 16 learners of L2 English and shows how their use of the progressive expands from the prototypical uses of process and continuousness to the less prototypical uses of repetition and future. The study concludes that the progressive spreads in interlanguage in accordance with prototype accounts. However, it suggests additional stages, not predicted by the Aspect Hypothesis, in the development from activities and accomplishments at least for the meaning of repeatedness. A similar theoretical framework is adopted in the following chapter, but it deals with a lesser studied language. Hyun-Jin Kim revisits the claims of the Aspect Hypothesis in relation to the acquisition of L2 Korean by two L1 English learners. Inspired by studies on L2 Japanese, she focuses on the emergence and spread of the past / perfective marker ¬–ess- and the progressive – ko iss- in the interlanguage of her informants throughout their third and fourth semesters of study. The data collected through six sessions of conversational interviews and picture description tasks seem to support the Aspect Hypothesis. Indeed learners show a strong association between past tense and accomplishments / achievements at the start and a gradual extension to other types; a limited use of past / perfective marker with states and an affinity of progressive with activities / accomplishments and later achievements. In addition, - ko iss– moves from progressive to resultative in the specific category of Korean verbs meaning wear / carry. While the previous contributions focus on function, Evgeniya Sergeeva and Jean-Pierre Chevrot’s is interested in form. The authors explore the acquisition of verbal morphology in L2 French by 30 instructed native speakers of Russian distributed in a low and high levels. They use an elicitation task for verbs with different models of stem alternation and study how token frequency and base forms influence stem selection. The analysis shows that frequency affects correct production, especially among learners with high proficiency. As for substitution errors, it appears that forms with a simple structure are systematically more frequent than the target form they replace. When a complex form serves as a substitute, it is more frequent only when it is replacing another complex form. As regards the use of base forms, the 3rd person singular of the present – and to some extent the infinitive – play this role in the corpus. The authors therefore conclude that the processing of surface forms can be influenced positively or negatively by the frequency of the target forms and of other competing stems, and by the proximity of the target stem to a base form. Finally, Martin Howard’s contribution takes up the challenge of focusing on the poorer relation of the TAM system. On the basis of L2 French data obtained through sociolinguistic interviews, he studies the expression of futurity, conditional and subjunctive in three groups of university learners with classroom teaching only (two or three years of university teaching) or with a mixture of classroom teaching and naturalistic exposure (2 years at University + 1 year abroad). An analysis of relative frequencies leads him to suggest a continuum of use going from futurate present to conditional with past hypothetic conditional clauses in si, which needs to be confirmed by further studies. Acknowledgements The present volume was inspired by the conference Acquisition of Tense – Aspect – Mood in First and Second Language held on 9th and 10th February 2008 at Aston University (Birmingham, UK) where over 40 delegates from four continents and over a dozen countries met for lively and enjoyable discussions. This collection of papers was double peer-reviewed by an international scientific committee made of Kathleen Bardovi-Harlig (Indiana University), Christine Bozier (Lund Universitet), Alex Housen (Vrije Universiteit Brussel), Martin Howard (University College Cork), Florence Myles (Newcastle University), Urszula Paprocka (Catholic University of Lublin), †Clive Perdue (Université Paris 8), Michel Pierrard (Vrije Universiteit Brussel), Rafael Salaberry (University of Texas at Austin), Suzanne Schlyter (Lund Universitet), Richard Towell (Salford University), and Daniel Véronique (Université d’Aix-en-Provence). We are very much indebted to that scientific committee for their insightful input at each step of the project. We are also thankful for the financial support of the Association for French Language Studies through its workshop grant, and to the Aston Modern Languages Research Foundation for funding the proofreading of the manuscript.

May the contact lens force be with you

FULL TEXT: Like many people one of my favourite pastimes over the holiday season is to watch the great movies that are offered on the television channels and new releases in the movie theatres or catching up on those DVDs that you have been wanting to watch all year. Recently we had the new ‘Star Wars’ movie, ‘The Force Awakens’, which is reckoned to become the highest grossing movie of all time, and the latest offering from James Bond, ‘Spectre’ (which included, for the car aficionados amongst you, the gorgeous new Aston Martin DB10). It is always amusing to see how vision correction or eye injury is dealt with by movie makers. Spy movies and science fiction movies have a freehand to design aliens with multiples eyes on stalks or retina scanning door locks or goggles that can see through walls. Eye surgery is usually shown in some kind of day case simplified laser treatment that gives instant results, apart from the great scene in the original ‘Terminator’ movie where Arnold Schwarzenegger's android character encounters an injury to one eye and then proceeds to remove the humanoid covering to this mechanical eye over a bathroom sink. I suppose it is much more difficult to try and include contact lenses in such movies. Although you may recall the film ‘Charlie's Angels’, which did have a scene where one of the Angels wore a contact lens that had a retinal image imprinted on it so she could by-pass a retinal scan door lock and an Eddy Murphy spy movie ‘I-Spy’, where he wore contact lenses that had electronic gadgetry that allowed whatever he was looking at to be beamed back to someone else, a kind of remote video camera device. Maybe we aren’t quite there in terms of devices available but these things are probably not the behest of science fiction anymore as the technology does exist to put these things together. The technology to incorporate electronics into contact lenses is being developed and I am sure we will be reporting on it in the near future. In the meantime we can continue to enjoy the unrealistic scenes of eye swapping as in the film ‘Minority Report’ (with Tom Cruise). Much more closely to home, than in a galaxy far far away, in this issue you can find articles on topics much nearer to the closer future. More and more optometrists in the UK are becoming registered for therapeutic work as independent prescribers and the number is likely to rise in the near future. These practitioners will be interested in the review paper by Michael Doughty, who is a member of the CLAE editorial panel (soon to be renamed the Jedi Council!), on prescribing drugs as part of the management of chronic meibomian gland dysfunction. Contact lenses play an active role in myopia control and orthokeratology has been used not only to help provide refractive correction but also in the retardation of myopia. In this issue there are three articles related to this topic. Firstly, an excellent paper looking at the link between higher spherical equivalent refractive errors and the association with slower axial elongation. Secondly, a paper that discusses the effectiveness and safety of overnight orthokeratology with high-permeability lens material. Finally, a paper that looks at the stabilisation of early adult-onset myopia. Whilst we are always eager for new and exciting developments in contact lenses and related instrumentation in this issue of CLAE there is a demonstration of a novel and practical use of a smartphone to assisted anterior segment imaging and suggestions of this may be used in telemedicine. It is not hard to imagine someone taking an image remotely and transmitting that back to a central diagnostic centre with the relevant expertise housed in one place where the information can be interpreted and instruction given back to the remote site. Back to ‘Star Wars’ and you will recall in the film ‘The Phantom Menace’ when Qui-Gon Jinn first meets Anakin Skywalker on Tatooine he takes a sample of his blood and sends a scan of it back to Obi-Wan Kenobi to send for analysis and they find that the boy has the highest midichlorian count ever seen. On behalf of the CLAE Editorial board (or Jedi Council) and the BCLA Council (the Senate of the Republic) we wish for you a great 2016 and ‘may the contact lens force be with you’. Or let me put that another way ‘the CLAE Editorial Board and BCLA Council, on behalf of, a great 2016, we wish for you!’

Shared cognitive processes underlying past and future thinking:the impact of imagery and concurrent task demands on event specificity

Recent literature has argued that whereas remembering the past and imagining the future make use of shared cognitive substrates, simulating future events places heavier demands on executive resources. These propositions were explored in 3 experiments comparing the impact of imagery and concurrent task demands on speed and accuracy of past event retrieval and future event simulation. Results provide support for the suggestion that both past and future episodes can be constructed through 2 mechanisms: a noneffortful "direct" pathway and a controlled, effortful "generative" pathway. However, limited evidence emerged for the suggestion that simulating of future, compared with retrieving past, episodes places heavier demands on executive resources; only under certain conditions did it emerge as a more error prone and lengthier process. The findings are discussed in terms of how retrieval and simulation make use of the same cognitive substrates in subtly different ways. © 2011 American Psychological Association.

Association between the oxytocin receptor (OXTR) gene and mesolimbic responses to rewards.

BACKGROUND: There has been significant progress in identifying genes that confer risk for autism spectrum disorders (ASDs). However, the heterogeneity of symptom presentation in ASDs impedes the detection of ASD risk genes. One approach to understanding genetic influences on ASD symptom expression is to evaluate relations between variants of ASD candidate genes and neural endophenotypes in unaffected samples. Allelic variations in the oxytocin receptor (OXTR) gene confer small but significant risk for ASDs for which the underlying mechanisms may involve associations between variability in oxytocin signaling pathways and neural response to rewards. The purpose of this preliminary study was to investigate the influence of allelic variability in the OXTR gene on neural responses to monetary rewards in healthy adults using functional magnetic resonance imaging (fMRI). METHODS: The moderating effects of three single nucleotide polymorphisms (SNPs) (rs1042778, rs2268493 and rs237887) of the OXTR gene on mesolimbic responses to rewards were evaluated using a monetary incentive delay fMRI task. RESULTS: T homozygotes of the rs2268493 SNP demonstrated relatively decreased activation in mesolimbic reward circuitry (including the nucleus accumbens, amygdala, insula, thalamus and prefrontal cortical regions) during the anticipation of rewards but not during the outcome phase of the task. Allelic variation of the rs1042778 and rs237887 SNPs did not moderate mesolimbic activation during either reward anticipation or outcomes. CONCLUSIONS: This preliminary study suggests that the OXTR SNP rs2268493, which has been previously identified as an ASD risk gene, moderates mesolimbic responses during reward anticipation. Given previous findings of decreased mesolimbic activation during reward anticipation in ASD, the present results suggest that OXTR may confer ASD risk via influences on the neural systems that support reward anticipation.

Mécanismes psychophysiques et neuronaux de la compensation dynamique de multiples champs de force : facilitation et anticipation liée à des indices de couleur

Dans cette thèse, nous abordons le contrôle moteur du mouvement du coude à travers deux approches expérimentales : une première étude psychophysique a été effectuée chez les sujets humains, et une seconde implique des enregistrements neurophysiologiques chez le singe. Nous avons recensé plusieurs aspects non résolus jusqu’à présent dans l’apprentissage moteur, particulièrement concernant l’interférence survenant lors de l’adaptation à deux ou plusieurs champs de force anti-corrélés. Nous avons conçu un paradigme où des stimuli de couleur aident les sujets à prédire la nature du champ de force externe actuel avant qu’ils ne l’expérimentent physiquement durant des mouvements d’atteinte. Ces connaissances contextuelles faciliteraient l’adaptation à des champs de forces en diminuant l’interférence. Selon le modèle computationnel de l’apprentissage moteur MOSAIC (MOdular Selection And Identification model for Control), les stimuli de couleur aident les sujets à former « un modèle interne » de chaque champ de forces, à s’en rappeler et à faire la transition entre deux champs de force différents, sans interférence. Dans l’expérience psychophysique, quatre groupes de sujets humains ont exécuté des mouvements de flexion/extension du coude contre deux champs de forces. Chaque force visqueuse était associée à une couleur de l’écran de l’ordinateur et les deux forces étaient anti-corrélées : une force résistante (Vr) a été associée à la couleur rouge de l’écran et l’autre, assistante (Va), à la couleur verte de l’écran. Les deux premiers groupes de sujets étaient des groupes témoins : la couleur de l’écran changeait à chaque bloc de 4 essais, tandis que le champ de force ne changeait pas. Les sujets du groupe témoin Va ne rencontraient que la force assistante Va et les sujets du groupe témoin Vr performaient leurs mouvements uniquement contre une force résistante Vr. Ainsi, dans ces deux groupes témoins, les stimuli de couleur n’étaient pas pertinents pour adapter le mouvement et les sujets ne s’adaptaient qu’à une seule force (Va ou Vr). Dans les deux groupes expérimentaux, cependant, les sujets expérimentaient deux champs de forces différents dans les différents blocs d’essais (4 par bloc), associés à ces couleurs. Dans le premier groupe expérimental (groupe « indice certain », IC), la relation entre le champ de force et le stimulus (couleur de l’écran) était constante. La couleur rouge signalait toujours la force Vr tandis que la force Va était signalée par la couleur verte. L’adaptation aux deux forces anti-corrélées pour le groupe IC s’est avérée significative au cours des 10 jours d’entraînement et leurs mouvements étaient presque aussi bien ajustés que ceux des deux groupes témoins qui n’avaient expérimenté qu’une seule des deux forces. De plus, les sujets du groupe IC ont rapidement démontré des changements adaptatifs prédictifs dans leurs sorties motrices à chaque changement de couleur de l’écran, et ceci même durant leur première journée d’entraînement. Ceci démontre qu’ils pouvaient utiliser les stimuli de couleur afin de se rappeler de la commande motrice adéquate. Dans le deuxième groupe expérimental, la couleur de l’écran changeait régulièrement de vert à rouge à chaque transition de blocs d’essais, mais le changement des champs de forces était randomisé par rapport aux changements de couleur (groupe « indice-incertain », II). Ces sujets ont pris plus de temps à s’adapter aux champs de forces que les 3 autres groupes et ne pouvaient pas utiliser les stimuli de couleurs, qui n’étaient pas fiables puisque non systématiquement reliés aux champs de forces, pour faire des changements prédictifs dans leurs sorties motrices. Toutefois, tous les sujets de ce groupe ont développé une stratégie ingénieuse leur permettant d’émettre une réponse motrice « par défaut » afin de palper ou de sentir le type de la force qu’ils allaient rencontrer dans le premier essai de chaque bloc, à chaque changement de couleur. En effet, ils utilisaient la rétroaction proprioceptive liée à la nature du champ de force afin de prédire la sortie motrice appropriée pour les essais qui suivent, jusqu’au prochain changement de couleur d’écran qui signifiait la possibilité de changement de force. Cette stratégie était efficace puisque la force demeurait la même dans chaque bloc, pendant lequel la couleur de l’écran restait inchangée. Cette étude a démontré que les sujets du groupe II étaient capables d’utiliser les stimuli de couleur pour extraire des informations implicites et explicites nécessaires à la réalisation des mouvements, et qu’ils pouvaient utiliser ces informations pour diminuer l’interférence lors de l’adaptation aux forces anti-corrélées. Les résultats de cette première étude nous ont encouragés à étudier les mécanismes permettant aux sujets de se rappeler d’habiletés motrices multiples jumelées à des stimuli contextuels de couleur. Dans le cadre de notre deuxième étude, nos expériences ont été effectuées au niveau neuronal chez le singe. Notre but était alors d’élucider à quel point les neurones du cortex moteur primaire (M1) peuvent contribuer à la compensation d’un large éventail de différentes forces externes durant un mouvement de flexion/extension du coude. Par cette étude, nous avons testé l’hypothèse liée au modèle MOSAIC, selon laquelle il existe plusieurs modules contrôleurs dans le cervelet qui peuvent prédire chaque contexte et produire un signal de sortie motrice approprié pour un nombre restreint de conditions. Selon ce modèle, les neurones de M1 recevraient des entrées de la part de plusieurs contrôleurs cérébelleux spécialisés et montreraient ensuite une modulation appropriée de la réponse pour une large variété de conditions. Nous avons entraîné deux singes à adapter leurs mouvements de flexion/extension du coude dans le cadre de 5 champs de force différents : un champ nul ne présentant aucune perturbation, deux forces visqueuses anti-corrélées (assistante et résistante) qui dépendaient de la vitesse du mouvement et qui ressemblaient à celles utilisées dans notre étude psychophysique chez l’homme, une force élastique résistante qui dépendait de la position de l’articulation du coude et, finalement, un champ viscoélastique comportant une sommation linéaire de la force élastique et de la force visqueuse. Chaque champ de force était couplé à une couleur d’écran de l’ordinateur, donc nous avions un total de 5 couleurs différentes associées chacune à un champ de force (relation fixe). Les singes étaient bien adaptés aux 5 conditions de champs de forces et utilisaient les stimuli contextuels de couleur pour se rappeler de la sortie motrice appropriée au contexte de forces associé à chaque couleur, prédisant ainsi leur sortie motrice avant de sentir les effets du champ de force. Les enregistrements d’EMG ont permis d’éliminer la possibilité de co-contractions sous-tendant ces adaptations, étant donné que le patron des EMG était approprié pour compenser chaque condition de champ de force. En parallèle, les neurones de M1 ont montré des changements systématiques dans leurs activités, sur le plan unitaire et populationnel, dans chaque condition de champ de force, signalant les changements requis dans la direction, l’amplitude et le décours temporel de la sortie de force musculaire nécessaire pour compenser les 5 conditions de champs de force. Les changements dans le patron de réponse pour chaque champ de force étaient assez cohérents entre les divers neurones de M1, ce qui suggère que la plupart des neurones de M1 contribuent à la compensation de toutes les conditions de champs de force, conformément aux prédictions du modèle MOSAIC. Aussi, cette modulation de l’activité neuronale ne supporte pas l’hypothèse d’une organisation fortement modulaire de M1.

Flexible strategies for association analysis with genomic phenotypes

Thesis (Ph.D.)--University of Washington, 2016-08

A neuroimaging investigation of the association between aerobic fitness, hippocampal volume and memory performance in preadolescent children

Because children are becoming increasingly overweight, unhealthy and unfit, understanding the neurocognitive benefits of an active lifestyle in childhood has important public health and educational implications. Animal research has indicated that aerobic exercise is related to increased cell proliferation and survival in the hippocampus as well as enhanced hippocampal-dependent learning and memory. Recent evidence extends this relationship to elderly humans by suggesting that high aerobic fitness levels in older adults are associated with increased hippocampal volume and superior memory performance. The present study aimed to further extend the link between fitness, hippocampal volume, and memory to a sample of preadolescent children. To this end, magnetic resonance imaging was employed to investigate whether high- and low-fit 9- and 10-year-old children showed differences in hippocampal volume and if the differences were related to performance on an item and relational memory task. Relational but not item memory is primarily supported by the hippocampus. Consistent with predictions, high-fit children showed greater bilateral hippocampal volumes. Furthermore, hippocampal volume was positively associated with performance on the relational but not the item memory task. The findings are the first to suggest that aerobic fitness can impact the structure and function of the developing human brain.