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<p>We investigated 1) how objects come to serve as landmarks in spatial memory and more specifically how they form part of an allocentric cognitive map and 2) how humans encode multiple connected spatial environments. In both sets of experiments, participants performing a virtual driving task incidentally learned the layout of a town and locations of objects or stores in that town. Their spatial memory and recognition memory for the objects or stores were subsequently tested. To assess whether the objects were encoded allocentrically, we developed a new measurement, pointing consistency. We found that when participants had more limited experience of the environment spatial memory for objects at navigationally relevant locations was more consistent across tested viewpoints than for objects at navigationally less relevant locations. When participants’ attention was focused on the appearance of objects, the navigational relevance effect was eliminated, whereas when their attention was focused on the objects’ locations, this effect was enhanced, supporting the hypothesis that when objects are processed in the service of navigation, rather than merely being viewed as objects, they engage qualitatively distinct attentional systems and are incorporated into an allocentric spatial representation. The results were consistent with evidence from the neuroimaging literature that when objects are relevant to navigation, they not only engage the ventral “object processing stream”, but also the dorsal stream and medial temporal lobe memory system classically associated with allocentric spatial memory. Moreover, in the connected environments, our data were more consistent with the formation of local maps, regardless of whether the neighborhoods were learned together or separately. Only when all visible distinctions between neighborhoods were removed did people behave as if they formed one integrated map. These data are broadly consistent with evidence from rodent hippocampal place cell recordings in connected boxes, and with hierarchical models of spatial coding.</p> / Doctor of Philosophy (PhD)

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Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

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La navigation et les modes de déplacement intéressent la communauté scientifique depuis maintenant près d'un demi siècle. Cependant, l’augmentation de l’incidence des troubles dégénératifs du système nerveux central chez l’homme rend plus prégnante la nécessité de compréhension de la navigation et de l’influence du temps sur celle-ci. S'il est connu chez l'homme comme chez le rongeur que l'avancée en âge affecte les capacités à se déplacer dans de vastes environnements, peu de données sont disponibles quant aux processus cognitifs impliqués dans ce type de comportement et leurs éventuelles modulations avec l'âge. La définition des stratégies utilisées, l’incidence respective des mécanismes allocentriques et égocentriques, la capacité de mise en œuvre d’une stratégie au moment demandé, lors d’un rappel à court ou à long délai, l’influence du temps qui passe sont autant de questions que nous avons abordées dans ce travail de thèse. Afin d’effectuer ces études, nous avons développé des tâches en environnements virtuels modélisés sur ordinateur et utilisé des tests neuropsychologiques nécessitant la mobilisation des compétences visuo-spatiales. Dans une première étude utilisant une épreuve de localisation spatiale, les résultats obtenus mettent en évidence chez les personnes âgées, une altération des aptitudes lors de la mise en œuvre d’une stratégie allocentrique, sans atteinte des performances égocentriques. La deuxième étude utilisant une version virtuelle du test de la piscine de Morris reconnu comme une tâche allocentrique chez le rongeur, conforte ces données. De façon similaire dans les deux études, les personnes âgées présentent une altération de la sélection et de l’exécution de la stratégie de déplacement qui s’avère optimale pour résoudre la tâche spatiale. Nous avons également mis en évidence une difficulté, chez ces mêmes participants, à utiliser une représentation mentale globale de l’espace, sans toutefois qu’il soit possible de distinguer si l’origine de cette difficulté vient d’une altération de la formation ou de la récupération de cette « carte cognitive ». Le temps pourrait également jouer son rôle de par le délai entre l'acquisition d'une information spatiale et le moment où il est nécessaire de l’utiliser à nouveau. En étudiant l’effet du délai sur la trace mnésique spatiale, nous avons observé que les sujets jeunes utilisant de façon prédominante une stratégie allocentrique voyaient leurs performances diminuer lors d’un rappel après quatre semaines alors que celles des sujets âgés restaient inchangées. Ceci soulève bien entendu la question de la différence d’encodage des informations entre les sujets jeunes et âgés, avec un versant plus détaillé chez les sujets jeunes, mais surtout s’intègre au sein du débat actuel sur l’existence d’une modification de la trace mnésique qui pourrait selon la théorie des traces multiples de la consolidation, évoluer vers un souvenir plus schématisé avec le délai. Les résultats d’une dernière étude dans laquelle nous manipulons le contexte environnemental de la piscine virtuelle de Morris, amène des arguments en faveur d’une « schématisation » du souvenir au cours de la consolidation, en mettant en évidence une absence de discrimination par les participants, d’un changement des repères spatiaux lors d’un rappel de l’information après six semaines de délai. Toutes ces données sont discutées dans le cadre du débat actuel de la consolidation, notamment sur la contribution de l’hippocampe dans le stockage et le rappel des informations anciennes. A la lumière de nos données, nous proposons une vue intégrative du fonctionnement de l’interface hippocampo-corticale lors des rappels après un court et long délai, en fonction de l’âge. / While the detrimental effects of human aging on cognitive functions are well documented, how normal aging affects spatial memory processing and the organization of recent and long-term memories remains unclear. What are the cognitive strategies used when confronted to spatial navigation in large environments? How are the selection and use of these strategies affected by aging? How are recent and long-term remote memories organized as a function of aging during systems-level consolidation? These are the questions we sought to address during the course of this Ph.D. thesis by developing a series of virtual environments aimed at assessing spatial navigation and memory performance in young adults and aged participants. In a first series of experiments, participants were tested for object location memory in a virtual environment (a medieval castle) that enabled shifts in spatial viewpoints between study and test. Aged participants exhibited poor performance relative to young adults only in the shifted view conditions, thus providing strong evidence for a decline in allocentric, but not egocentric, spatial memory. In contrast to young adults, aged participants exhibited difficulties in processing efficiently distal cues of the environment and were less prone to adopt allocentric strategies. Manipulations of the spatial layout of the environment led us to the conclusion that aging seems to preferentially interfere with the capacity to form or use mental representations built upon all pieces of the environmental features which typically, are never in full view in real world large-scale environments. In a second set of experiments, participants were tested in an ecologically-relevant virtual version of the Morris water maze which mimics that classically used in rodents. Aged participants performed more poorly compared to middle-aged and young adults and formed a more schematic spatial memory. They favoured a directional single cue-based strategy to locate the hidden platform contrasting with young adults who formed complex geometrical relationships between distal cues of the environment. A neuropsychological test battery confirmed that binding of unrelated items and abilities to mentally manipulate information were two processes involved in solving the water maze task. Thus, upon acquisition, aged participants had difficulties in forming experientially detailed cognitive maps and in binding unrelated features of the environment into a cohesive spatial memory, possibly indicative of altered hippocampal-frontal circuitry. We next proceeded to examine the organization of spatial memory as a function of time. Long-term memory assessed 4 weeks after acquisition revealed that performance decreased more rapidly in young adults compared to elderly participants, suggesting that the passage of time differentially affects the content of spatial memory, richly detailed spatial memories being more vulnerable to decay than schematic ones. This concept of memory transformation (i.e. memories are not stored in the cortex in their original form) was supported by findings of a last experiment in which we provide evidence that participants failed in detecting changes in the spatial layout of the pool as memories matured over time. All these findings are discussed in the context of the current debate about the concept of memory consolidation which opposes the standard model of memory consolidation to the multiple trace theory, two views which make different predictions about the contribution of the hippocampus to remote memory storage and retrieval. In light of our own findings, we attempt to propose an integrative view of the functioning of the hippocampal-cortical interface during recent and remote memory retrieval as a function of normal aging.

Malgré la multiplicité des études démontrant le comportement fascinant des animaux dans leur milieu naturel, quelques domaines de recherches demeurent difficiles à aborder. Ainsi, l’étude de certains aspects cognitifs nécessite un certain contrôle sur l’environnement afin de dissocier les influences écologiques et sociales de l’implication cognitive ; par exemple la cognition spatiale incluant la mémoire spatiale, les mécanismes d’orientation spatiale, ainsi que leur implication dans la navigation, tel que par la planification. L’étude de la cognition spatiale des chimpanzés sauvages s’est déroulée dans le Parc national de Taï, une forêt tropicale dense où les ressources potentielles sont abondantes et réparties sur un territoire de 25 km², avec une visibilité d’environ 30 mètres. De plus, les chimpanzés vivent dans une société du type fission-fusion, impliquant de multiples relations sociales. Toutefois, l’enregistrement précis de la position et des activités des chimpanzés, ainsi qu’une carte botanique précise, nous a permis de dissocier les effets écologiques, sociaux et cognitifs afin de mieux comprendre les relations entre ces différents facteurs. Par cette étude, nous montrons que les chimpanzés ont développé un mécanisme permettant une navigation précise grâce à une carte Euclidienne contenant des informations sur la direction et la distances vers des ressources connues. Ce mécanisme est extrêmement adapté et efficace par la connaissance précise de la localisation de milliers de ressources dans leur habitat. Ces capacités permettent d’augmenter leur efficacité en sélectionnant les ressources les plus productives, en les planifiant à l’avance et, de manière plus avancée, en planifiant le parcours le plus court à travers ces différentes ressources durant la journée lorsque la pression sociale requière une meilleure précision dans le choix des ressources. Ces découvertes illustrent d’abord les capacités extraordinaires des chimpanzés, et deuxièmement que les aspects cognitifs peuvent être expliqués dans le milieu naturel des animaux. / Whereas numerous studies demonstrated fascinating behaviour of animals in their natural habitat, some important areas of research were difficult to tackle in the field. This is the case of many studies on cognitive aspects that required controlled environment to dissociate ecological and social influence from cognition. One of these important areas of research is the spatial cognition including spatial memory, spatial orientation mechanisms and the practical use of these abilities to travel efficiently, such as planning skills. This study on spatial cognition in wild chimpanzees took place in Taï National Park, a tropical dense forest where potential food resources are highly abundant in their 25 km² territory, and the visibility is approximately 30 meters. Adding to this complexity, chimpanzees live in a fission-fusion society, maintaining relationships with each other. Nevertheless, with a precise recording of chimpanzee’s location and activities and a precise botanic map of the territory, we were able to dissociate the ecological, social and cognitive effects and understand some relationships between these factors. Here, we showed that wild chimpanzees developed a precise mechanism to navigate efficiently in their large area using a Euclidean map containing accurate information about direction and distance to the known resources. This mechanism is highly adapted and efficient as the chimpanzees have a precise knowledge of the resources location in their area, remembering the location of thousand trees location. These highly developed abilities allowed them to increase their efficiency by selecting the most productive resources, planning them in advanced and on a higher level to plan the shortest path through these major resources during the day when the social pressure induce a higher precision in resource selection. These findings highlight first the outstanding spatial abilities of wild chimpanzees and second that cognition can be better explained in animals’ natural complex environment. / Trotz zahlreicher Studien, die das faszinierende Verhalten von Wildtieren in ihrer natürlichen Umwelt dokumentieren, bleiben einige Studienfelder schwer erfassbar. So ist zum Beispiel bei der Erforschung von bestimmten kognitiven Aspekten die Rücksichtnahme auf den Umweltfaktor erforderlich, damit Umwelt- und Sozialeinfluss von den kognitiven Faktoren unterschieden werden können. Zu diesen Untersuchungsfeldern gehört die Raumkognition, welche das Raumgedächtnis, die Mechanismen der Raumorientierung sowie deren effizientes Nutzen durch die Schimpansen, z.B. durch ihre Fähigkeit zum Planen, einschließt. Die vorgestellte Studie über Raumkognition bei wild lebenden Schimpansen wurde im Nationalpark von Tai durchgeführt, das heißt, in einem dichten tropischen Wald, wo potentielle Ressourcen bei einer Sichtweite von ungefähr 30 Metern auf einem 25 qm großen Areal reichlich verteilt sind. Hinzu kommt, dass Schimpansen in einer Fission-Fusion Gesellschaftsstruktur leben, die vielfache soziale Beziehungen fördern. Jedoch, mit einer genauen Registrierung der räumlichen Lage und der Aktivitäten der Schimpansen und anhand einer präzisen botanischen Karte des Gebiets, konnten wir die Umwelt-, Sozial- und kognitiven Effekte gegeneinander abgrenzen und somit die zwischen diesen unterschiedlichen Faktoren bestehenden Beziehungen erfassen. In dieser Studie zeigen wir, dass Schimpansen einen besonderen Mechanismus zur Raumorientierung auf ihrem Gebiet entwickelt haben. Dabei verfügen sie über eine euklidische Mind-Karte mit präzisen Informationen über Richtungen und Entfernungen zu den bekannten Ressourcen. Durch ein genaues Wissen über die Verteilung der Nahrungsressourcen auf ihrem Gebiet ist dieser Mechanismus hoch effizient. Dank dieser Fähigkeiten werden Schimpansen immer effizienter, indem sie die ergiebigsten Ressourcen auswählen, dabei planende Fähigkeiten einsetzen und weiterhin indem sie an einem Tag die kürzeste Strecke zu den verschiedenen Ressourcen ausmachen, wenn der soziale Druck höchste Präzision in der Wahl der Nahrungsressourcen erfordert. Diese Erkenntnisse erhellen zuallererst die außergewöhnlichen Fähigkeiten der wild lebenden Schimpansen und beweisen, dass sich kognitive Mechanismen bei wild lebenden Tieren in ihrer natürlichen Umwelt besser erklären lassen.

No modelo dos multicomponentes da memória de trabalho o problema do armazenamento da ordem serial de eventos visuais e espaciais ainda é muito discutido. A literatura sugere que recursos do executivo central (o sistema de controle atencional da memória de trabalho) são utilizados para manter a representação da posição serial dos estímulos visuais e espaciais na memória. Mais precisamente, é proposto que a função executiva de atualização de informações esteja envolvida com este processo. Esta função promoveria a modificação contínua da representação mental conforme a entrada de novas informações no sistema cognitivo. Entretanto, não está esclarecido se ocorre uma dissociação visual e espacial no uso de recursos da função executiva de atualização de informações para o registro da ordem serial. O objetivo do presente estudo foi verificar o envolvimento da função executiva de atualização da informação na memória para a ordem de eventos visuais e espaciais. Os participantes foram estudantes universitários (n = 71) que realizaram as tarefas de memória delineadas segundo o paradigma de tarefas duplas. Neste procedimento as tarefas primárias de memória visual e espacial foram combinadas a tarefas secundárias executivas de tempo de reação de escolha (CRT) e tarefas que exigiam recursos de atualização da informação (tarefa de tempo de reação de escolha para um item anterior CRT-1). Na tarefa CRT o participante deveria julgar dois tons auditivos como sendo de alta ou baixa frequência. Na tarefa CRT-1 esta resposta deveria ser atrasada em um item, ou seja, a resposta ao estímulo n só deveria ser dada quando o estímulo n + 1 fosse apresentado. As tarefas secundárias eram realizadas durante a apresentação dos estímulos e no intervalo de retenção das tarefas primárias. No primeiro experimento a capacidade máxima de armazenamento espacial e visual (span) de cada participante foi estabelecida em sessão pré-teste, e no segundo experimento o participante memorizou sequências de três a sete itens. Os resultados mostraram que, de modo geral, o desempenho dos participantes nas tarefas primárias foi prejudicado mediante a interferência na função de atualização de informações. As semelhanças entre a memória serial visual e a memória serial espacial foram: curvas de posição serial caracterizadas por primazia e recência; predominância de erros de transposição de deslocamento em um item da posição correta; efeito prejudicial do aumento do tamanho da sequência; queda do desempenho quando recursos executivos são reduzidos, principalmente os designados a sustentar a função executiva de atualização da informação. As diferenças entre os dois tipos de representação serial em geral foram: menor capacidade e precisão na representação de itens na memória visual em comparação à espacial; a memória visual é mais susceptível ao aumento da quantidade de itens para retenção e para este tipo de armazenamento não há uma diferenciação clara entre os efeitos dos dois tipos de interferência executiva (CRT e CRT-1), como pôde ser determinado para a tarefa espacial. Conclui-se que recursos executivos de atualização da informação participam dos mecanismos envolvidos com o registro da ordem serial dos eventos visuais e espaciais de maneira integrada aos recursos específicos do armazenador visuoespacial. Sugere-se que a memória visual conta com um mecanismo de registro da ordem serial semelhante à memória espacial, sendo que as diferenças entre os dois padrões de desempenho são atribuídas às especificidades no registro da identidade dos itens, e não na manutenção da ordem serial dos mesmos. Implicações para a compreensão da interação funcional entre recursos de armazenamento e processamento da informação na memória de trabalho são discutidos. / In the multicomponent model of working memory is still unclear how the serial order of visual and spatial events is retained in memory. The literature suggests that the central executive resources (the attentional control system of working memory) are used to maintain the representation of serial position. More precisely, it is proposed that the executive function of updating information is involved with this process. This function makes continuous modification of mental representation to accommodate new information in the cognitive system. However, until now had not yet been determined whether there is a visual-spatial dissociation in use of executive function of updating information for the registration of serial order. The aim of this study was to investigate the involvement of the executive function of updating information in memory for the order of visual and spatial events. Participants were undergraduate students (n = 71) who performed memory tasks designed under the paradigm of dual-tasks. In this procedure the primary tasks of visual and spatial memory were combined with secondary executive tasks of choice reaction time (CRT) and tasks that occupied resources required to update the information (one-back choice reaction time CRT-1). In the CRT task the participant should judge two auditory tones as high or low frequency. In CRT-1 task this response should be delayed in one item, that is, the response to the n stimulus should only be given when the n + 1 stimulus was presented. The secondary tasks were performed during the presentation of the stimuli and the retention interval of the primary tasks. In the first experiment the capacity (span) to retain spatial and visual information was established in pre-test session, and in the second experiment the participants memorized sequences of three to seven items. The results showed that, overall, participants\' performance on primary tasks was impaired by interference on the updating information. The similarities between visual and spatial serial memory were: primacy and recency in serial position curves; most frequent serial position error of transposition in one item; detrimental effect of increasing the size of the sequence, performance impaired by the interference in the executive resources, especially those designed to support the executive function of updating information. The differences between the two types of serial representation, in general, were: smaller capacity and precision in the representation of visual items as compared to the spatial characteristics; the vulnerability of visual memory to the increasing the amount of items is bigger than in spatial memory, and for visual memory there is not a clear differentiation between the effects of two types of executive interference (CRT and CRT-1) as could be determined for the spatial task. We conclude that executive resources of updating information are part of the mechanisms involved in the registration of the serial order of visual and spatial events, and they work in an integrated manner to specific visuospatial resources. The data suggests that visual memory has a mechanism for registration of serial order like spatial memory, and the differences between the two patterns of performance are attributed to the maintenance of identity of the items, and not the maintenance of serial order. Implications for understanding the functional interaction between storage resources and processing of information in working memory are discussed.