Early ontogeny is a time of rapid anatomical and behavioral development in most organisms. The degree of synchrony between form and function during this period, and the concomitant performance consequences, can strongly impact individual survival. Understanding the development of feeding during early ontogeny is important because nutrient acquisition universally influences organismal biology. A one-year, longitudinal feeding study was conducted for two elasmobranch species that were selected for their disparate morphology, behavior, and habitat: the whitespotted bambooshark Chiloscyllium plagiosum and the leopard shark Triakis semifasciata. To quantify changes in cranial morphology, external attributes of the feeding apparatus were measured weekly. Additionally, specimens were dissected to examine trends in the growth of select muscles and the volume of the buccal cavity. To quantify feeding behavior, individuals were observed weekly using high-speed digital cameras as they consumed various food types. Suction performance was evaluated using particle image velocimetry and direct measurements of suction pressure. The cranial morphology of C. plagiosum exhibited primarily isometric growth while the cranial morphology of T. semifasciata was dominated by allometric growth. Allometric increases were noted in the cross-sectional area of every muscle examined in both species, though the primary hyoid depressor, the coracohyoideus, hypertrophied to a greater degree in C. plagiosum. Although intra-individual differences throughout ontogeny complicated comparison, modulation in response to food attributes was clearly evident in T. semifasciata but broadly absent in C. plagiosum. Over ontogeny C. plagiosum generated allometrically greater suction while T. semifasciata generated relatively less. The shape of the parcel of water ingested during feeding did not change over ontogeny in either species. The capacity to perform diverse feeding behaviors throughout ontogeny is not constrained in T. semifasciata but tends to be stereotyped and accompanied by enhanced performance in C. plagiosum. A functionally generalized feeding apparatus and repertoire may benefit T. semifasciata by allowing the use of diverse feeding behaviors in variable environments, such as estuaries, over ontogeny. Morphological and behavioral conservation of the feeding apparatus throughout ontogeny, however, may allow C. plagiosum to exploit taxonomically varied crevice-dwelling reef organisms using a single specialized behavior.

The heterogeneous, chronic, and proliferating aspect of attention deficit hyperactivity disorder (ADHD) and comorbidities covers heritability, cognitive, emotional, motor, and everyday behavioral domains that place individuals presenting the condition at some considerable disadvantage. Disruption of "typical developmental trajectories" in the manifestation of gene-environment interactive predispositions implies that ADHD children and adolescents may continue to perform at defective levels as adults with regard to academic achievement, occupational enterprises, and interpersonal relationships, despite the promise of pharmacotherapeutic treatments. Physical exercise provides a plethora of beneficial effects against stress, anxiety, depression, negative affect and behavior, poor impulse control, and compulsive behavior concomitant with improved executive functioning, working memory and positive affect, as well as improved conditions for relatives and care-givers. Brain-derived neurotrophic factor, an essential element in normal brain development that promotes health-associated behaviors and quality-of-life, though reduced in ADHD, is increased markedly by the intervention of regular physical exercise. Functional, regional, and biomarker deficits, as well as hypothalamic-pituitary-adrenal disruptions, have been improved through regular and carefully applied exercise programs. In view of the complications involving ADHD with co-morbidities, such as obesity, the influence of regular physical exercise has not been found negligible. Physical exercise bestows a propensity for eventual manifestation of "redifferentiated" developmental trajectories that may equip ADHD adults with a prognosis that is more adaptive functionally, independent of the applications of other therapeutic agents and treatments.

Cette thèse s’inscrit dans le courant des études portant sur la relation langage-cognition enL2. L’objectif principal est d’analyser la conceptualisation spatiale dans une tâchenarrative orale (Frog story) chez plusieurs groupes d’apprenants qui se distinguent a) pourleur L1 (anglais, français, italien), b) pour leur L2 (italien, français) et c) pour leur niveaude compétence en L2 (intermédiaire vs. avancé). Pour ce faire, nous adoptons uneméthodologie impliquant des comparaisons successives entre les récits de groupes natifs etnon natifs ayant accompli la même tâche, afin de comprendre de quelle manière lesapprenants se rapprochent de la LC et s’ils sont influencés par leur L1 lors du discoursspatial en L2.L’analyse des récits natifs confirme les différences intertypologiques entre les languesverb-framed, français et italien, et satellite-framed, l’anglais (Talmy 1985). Néanmoins,une variation intra-typologique entre l’italien et le français est attestée: seul l’italienexploite des constructions satellitaires.Quant aux productions en L2, les apprenants, surtout les intermédiaires, traitent la tâche defaçon minimale (traitement prototypique, Watorek 1996) en exprimant essentiellement latrajectoire, qui représente la composante de base dans la tâche demandée. Au niveauintermédiaire, il n’y a pas de traces d’influence de la L1 sur la conceptualisation spatiale enL2, qui est, en revanche, attestée chez les apprenants anglophones avancés de l’italien L2 àtravers l’emploi de constructions satellitaires. L’existence de structures similaires dans laLS et la LC et l’évidence positive dans l’input semblent favoriser le transfert conceptuel enL2. / This thesis intervenes in the line of studies about the relation between language andcognition in L2. The main objective is to analyze spatial conceptualization in an oralnarrative task (Frog story) by several groups of learners who differ for a) their L1 (English,French, Italian), b) their L2 (Italian, French) and c) their L2 proficiency level (intermediatevs. advanced). In order to do this, we adopt a methodology that implies successivecomparisons between the productions performed by different native and non-native groupsaccomplishing the same task. The aim is to distinguish to what extent learners get closer tothe TL and if they are influenced by their L1 during the spatial production in L2.The L1 results confirm the intertypological differences between verb-framed, Italian andFrench, and satellite-framed languages, English (Talmy 1985, 2000). Nevertheless, anintratypological variation between Italian and French is attested: only Italian makes use ofsatellite constructions.As for L2 productions, learners, especially the intermediate ones, provide a minimalresponse to the task (traitement prototypique, Watorek 1996) by encoding mainly Path, thebasic component of the task. At the intermediate level, there are no traces of the influenceof the L1 on spatial conceptualization in L2, instead attested by advanced English learnersof Italian L2 through the use of satellite constructions. The existence of similar structure inthe SL and TL and the positive evidence in the input seem to favour conceptual transfertfrom L1 to L2.

Ce travail de recherche s’inscrit dans le domaine de la phonétique clinique et relève plus particulièrement de l’intelligibilité de la parole d’enfants sourds implantés cochléaires et d’enfants normo-entendants. L’intérêt de cette thèse réside dans la comparaison des productions d’enfants sourds implantés cochléaires et d’enfants normo-entendants, appariés en âge chronologique. Nous analysons des paramètres segmentaux et suprasegmentaux en production, tels que les voyelles du français standard et les consonnes fricatives /f, s, ʃ/, l’étude du débit de parole, l’intelligibilité de mots monosyllabiques auprès d’auditeurs naïfs, ou encore l’intelligibilité de la parole semi-spontanée. Nous nous intéressons également à la façon dont les productions des enfants implantés cochléaires sont perçues par un jury d’auditeurs naïfs (n=10 ; moyenne d’âge 37 ans). Le but premier de ce travail est de mettre en avant les différences ou similitudes majeures entre nos deux groupes en fonction de l’âge chronologique des enfants mais également en fonction du recul à l’implant, du suivi rééducatif et du mode de communication. Les enfants sourds porteurs d’un implant cochléaire présentent une qualité de la voix et de la parole comparable à celle d’enfants normo-entendants de même âge chronologique, mais non similaire puisque des différences acoustiques, segmentales et supra-segmentales ont été mises en avant. Il pourrait être intéressant d’étendre cette observation aux enfants implantés précocement. / This research task falls under the field of clinical phonetics and more particularly raises of the intelligibility of the word of deaf children with cochlear implant and normal-hearing children. The interest of this thesis lies in the comparison of the productions of deaf children with cochlear implant and normal-hearing children, paired in chronological age. We analyze segmental and suprasegmental parameters in production, such as the vowels of standard French and the fricative consonants /f, S, ʃ/, the study of the speech rate of word, the comprehensibility of monosyllabic words with naive listeners, or still the comprehensibility of the semi-spontaneous word. We are also interested in the way in which the productions of the established children cochléaires are perceived by a jury of naive listeners (n=10; average age 37 years). The primary purpose of this work is to highlight the major differences or similarities between the two groups based on the chronological age of the children but also on the age back to the cochlear implant, the rehabilitative monitoring and communication mode. Deaf children with cochlear implants present a quality of the voice and word comparable with that of normal-hearing children of the same chronological age, but non similar age since differences acoustic, segmental and suprasegmental were put ahead. It might be interesting to extend this observation to early implanted children.

目的：基於初診斷乳癌患者的心理沮喪反應存在個別差異性之假設，本研究旨在探討乳癌患者的心理沮喪發展軌跡及其與資源變化、因應風格之間的關係，並採用動態性的壓力調適觀點來說明影響個體間發展差異與個人內變化之因素。三個主要的目的為（1）初診斷乳癌患者是否具有不同的心理沮喪發展軌跡？（2）隨時序變化的資源變化與因應風格可否區辨不同的軌跡組別；以及（3）不同軌跡組別的資源變化與因應風格對其心理沮喪之影響是否不同？ 方法： 本研究採用貫時性的研究設計，共收錄200名初診斷乳癌患者。患者於診斷後的手術前一天進行評估，並於術後一個月、術後四個月、術後七個月及術後一年進行後續的追蹤。每一點的心理沮喪分數採用中文的醫院版焦慮與憂鬱量表（HADS）來測量，追蹤時間點的資源變化與癌症因應風格之分數，分別是以修編的資源改變量表（資源流失與資源獲得）與台灣版癌症心理調適量表（Mini-MAC）進行評估。 結果：潛在類別成長模式的結果顯示，相較於過去的研究，心理沮喪的變化軌跡可區辨出「韌性組」、「復原組」、「晚發組」及「慢性組」。潛在成長曲線模式的分析顯示，相較於其他三組，「韌性組」的壓力因應特性為：診斷之後維持在低資源流失、較低的初始AP，以及較低的CA成長率；相較於「韌性組」，「復原組」還具有下降較慢的FS；「晚發組」與「慢性組」又比前兩組具有更高的初始HH與較高的AP成長率，而「慢性組」比起其他三組在診斷初期具有最高的資源流失、最高的HH以及最低的FS。階層線性模式的分析顯示，四組之中的資源流失與因應風格皆可預測心理沮喪，作用的差異之處主要出現在「慢性組」的資源獲得與CA具有減緩心理沮喪之效果，以及各組之內的預測因子不同。 結論：本研究支持罹癌後的壓力反應具有個別差異性，並且指出乳癌患者的心理沮喪反應具有四種不同的發展型態。本研究也強調於連續變化的向度中考量不同的心理沮喪發展軌跡及其相關的壓力調適因子亦具有時序變化之重要性。有關的理論與實務意涵將於後作進一步地討論。 / Objectives: This study assumed the psychological distress of newly-diagnosed breast cancer (BC) patients existed the entities of the individual difference, so this study examined distinct development trajectories of psychological distress amongst BC patients and their relationship with resource changes and coping styles, and adopted a dynamic stress-coping perspective to shed light on the factors that contribute to the diversity of inter-individual development and intra-individual change. The three major purposes were (1) to determine if there are distinct development trajectories of psychological distress amongst newly-diagnosis BC patients; (2) to test whether time-varying resource changes and coping styles can distinguish the trajectory groups; (3) to explore whether the effect of time-varying resource changes and coping styles on psychological distress differ within each trajectories group. Methods: A longitudinal reasarch study of 200 newly-diagnosed BC patients was recruited and participants were assessed at the day before surgery, and again at the 1-month, 4-month, 7-month and 1-year post-surgery follow-ups. Psychological distress was measured at the five time-points using the Chinese version of Hospital Anxiety and Depression Scale (HADS). Resource changes and cancer-specific coping were assessed at all follow-ups using the revised Resource Change Scale and the the Chinese version of Mini-MAC Scale, respectively. Results: Latent Class Growth Analysis (LCGA) identified four latent classes of BC patients with distinct developmental trajectories of psychological distress - resilience, recovery, late onset and chronic dysfunction. Latent Growth Curve Model (LGM) revealed that the stress-coping properties of the resilience group featured a stabilized lower level of resource loss after diagnosis, a lower level of initial AP-coping and a lower growth rate of CA-coping when compared with the others. The recovery group was more likely to have a lower decrease of FS-coping than the resilience group. Moreover, the late onset group and the chronic dysfunction group were more likely to have a higher level of initial HH-coping and a higher increase in AP-coping, and the chronic dysfunction group was characterized by the highest level of initial resource loss and HH-coping, and the lowest level of initial FS-coping compared with the other groups. The Hierarchical Linear Model (HLM) indicated that resource loss and use of coping styles could significantly predict levels of psychological distress in each trajectory group. The major differences that appeared were in the positive effect of resource gain and use of CA-coping on decreasing distress symptoms amongst people in the chronic dysfunction group, as well as in the different predictors that were found in each trajectory group. Conclusions: The present study shows that there are individual differences in cancer-specific stress responses and outlines four different developmental patterns of psychological distress amongst newly-diagnosed Taiwanese BC patients. This study also stressed the importance of considering time-serial continuity of distinct developmental trajectories with regards to psychological distress as well as the related stress-coping factors which also varies with time. Further theoretical and practical implications are discussed in depth in the content of the study.

Thèse de doctorat présentée en vue de l'obtention du doctorat en psychologie - recherche intervention, option neuropsychologie clinique (Ph.D). / Les cardiopathies congénitales, c’est-à-dire les anomalies de la structure du cœur ou des vaisseaux sanguins, constituent les malformations les plus fréquentes à la naissance. Considérant la prévalence des altérations cérébrales, des retards de développement et des déficits cognitifs qui leur sont associés, les cardiopathies congénitales sont reconnues comme une problématique de santé publique. Plusieurs questions méritent d’être étudiées pour mieux comprendre les conséquences neurodéveloppementales de ces malformations et identifier les mécanismes d’action qui en sont à l’origine. Dans ce contexte, la présente thèse vise à documenter le fonctionnement cérébral et le développement moteur et langagier des enfants présentant une cardiopathie congénitale complexe, ainsi qu’à identifier des facteurs de prévention et des pistes d’intervention pour améliorer leur pronostic neurodéveloppemental. Cette thèse est composée d’une revue de littérature et de quatre études empiriques. Le premier article avait pour objectif de recenser les principales données scientifiques disponibles dans la littérature, afin d’obtenir une vision intégrée des fonctions cognitives potentiellement affectées dans cette population et des facteurs qui en augmentent le risque. Le deuxième article visait à documenter les patrons de connectivité fonctionnelle des nourrissons de quatre mois ayant subi une chirurgie cardiaque correctrice, à l’aide de la spectroscopie proche infrarouge. Nos données de neuroimagerie révèlent une connectivité inférieure chez les participants avec malformation cardiaque comparativement aux contrôles, ce qui suggère la présence d’altérations du fonctionnement cérébral après la chirurgie cardiaque. Par ailleurs, nos résultats nous amènent à supposer que les régions frontales présenteraient un risque accru de dysfonctionnement, tandis que la connectivité fonctionnelle entre les régions temporales pourrait être préservée. L’objectif du troisième article était de décrire le développement de la motricité globale entre 4 et 24 mois dans cette population. Nos données révèlent une augmentation significative des performances motrices avec l’âge, et ce, particulièrement pour le groupe d’enfants ayant bénéficié d’interventions régulières en physiothérapie. Ceci suggère que l’intervention motrice pourrait améliorer le développement de la motricité globale chez les enfants à risque de retard moteur. Le quatrième article visait à décrire le développement du langage, entre 12 et 24 mois, chez les enfants présentant une cardiopathie congénitale complexe et à explorer les associations entre les habiletés de communication précoces et les capacités langagières futures. Les résultats de cette étude suggèrent une vulnérabilité spécifique des habiletés langagières expressives, comparativement aux compétences réceptives, et indiquent que les habiletés de communication gestuelle à 12 mois constituent un fort prédicteur du développement langagier futur. Enfin, le cinquième article avait pour objectif d’évaluer l’impact d’un programme développemental sur le fonctionnement moteur, cognitif et comportemental des enfants avec malformation cardiaque âgés de trois ans. Les résultats de cette étude suggèrent, pour la première fois, les potentiels bénéfices d’un tel programme sur le développement du vocabulaire réceptif et des compétences visuoconstructives. Ensemble, les résultats de cette thèse contribuent aux connaissances scientifiques sur le neurodéveloppement des enfants présentant une cardiopathie congénitale. Nos travaux permettent, en effet, de mieux comprendre le développement cognitif, moteur et langagier de ces enfants et fournissent des pistes concrètes pour une meilleure prévention des difficultés langagières et motrices dans cette population. Par ailleurs, ils soulignent la pertinence des études de neuroimagerie fonctionnelle pour comprendre les mécanismes d’action à l’origine de ces conséquences neurodéveloppementales, et ainsi, favoriser le développement de ces enfants. / Congenital heart disease, defined as a problem that affects the structure of the heart, constitutes the world’s most common birth defect. Given the prevalence of brain abnormalities, developmental delays and cognitive impairments associated with these defects, congenital heart diseases are recognized as a public health issue. Several questions remain to be investigated for a better understanding of the resulting neurodevelopmental complications, and to identify its specific mechanisms of action. This thesis aims to document the brain function and the development of motor and language skills of young children with complex congenital heart disease, and to identify preventive factors and avenues of intervention to improve their neurodevelopmental issue. This thesis includes a literature review and four empirical studies. The first article aimed to review the current knowledge, to get an overall view of cognitive disabilities that result from a congenital heart disease and the clinical factors that increase this risk. The goal of the second article was to investigate brain functional connectivity in 4-month-old infants with repaired congenital heart disease, using near-infrared spectroscopy. This neuroimaging study reveals reduced connectivity strength in infants with congenital heart disease compared to healthy controls, which suggests that alterations of brain functional connectivity persist after corrective cardiac surgery. Furthermore, our data lead us to hypothesize that functional connectivity in homologous temporal regions might be preserved in patients with congenital heart defect, while connectivity involving frontal regions might be at increased risk for dysfunction. The third study aimed to document the gross motor development in children with complex congenital heart disease aged 4 to 24 months. Our data revealed an increase in gross motor scores with age, and this, particularly for children who received regular motor intervention sessions. These results suggest that physical therapy may help to improve gross motor skills in children at risk of motor delay. The aim of the fourth article was to describe the language development, from 12 to 24 months of age, in children born with a heart disease, and to explore the relationship between early language performances and future language skills. The results of this study suggest that language impairments prominently affect expressive skills, rather than receptive skills, and indicate that early communicative gestures constitute a strong predictor of later language skills. Finally, the goal of the fifth article was to assess the impacts of a neurocardiac developmental follow-up program on motor, cognitive and behavioral functioning of 3-year-old children with congenital heart defect. This study suggests, for the first time, the potential benefits of such program on language receptive and visuospatial skills. This thesis significantly contributes to the scientific knowledge on neurodevelopment of children born with a congenital heart disease. The results of our studies allow a better description of the cognitive, motor and language development in this population, and provide interesting avenues for a better prevention of language and motor impairments. Furthermore, these results underline the relevance of functional neuroimaging studies for the understanding of mechanisms that result in neurodevelopmental disabilities and, therefore, the improvement of these children’s development.

研究目的：欲瞭解自閉症類疾患兒童，橫跨幼兒期、學齡前期至學齡期的自閉症狀發展軌跡，探究當中是否存有不同的發展軌跡，並檢視不同發展軌跡的群體在認知功能與適應行為隨時間的變化型態是否有差異，以及不同群體在早期的社會溝通能力或療育經驗上是否有差異。 方法：本研究有37名自閉症類與24位非自閉症類受試者納入分析，共測量三次：時間點一平均生理年齡為2歲半、時間點二為4歲、時間點三為8歲半。於三個時間點皆以自閉症診斷觀察量表評估自閉症狀嚴重度、以及穆林發展量表或魏氏兒童智力量表第四版評估認知功能，在時間點二與時間點三以文蘭適應行為量表第二版評估適應行為；另外，在時間點一以台灣版兩歲期自閉症篩檢工具評估社會溝通能力，以及在時間點一至時間點二之間，以電話訪問的方式紀錄兒童每週參與療育的時數。 結果：由階層式集群分析結果顯示，社交情感嚴重度校正分數可將自閉症類與非自閉症類兒童分群，並於自閉症類兒童中可再分為維持高嚴重度組與退步組。兩組自閉症類兒童於學齡時期在社交情感症狀皆呈現嚴重度明顯上升的趨勢，在認知功能與適應行為隨時間的變化型態相似，不過維持高嚴重度組在認知功能與適應行為有較低的分數（但未達統計顯著）。此外，兩組自閉症類兒童於時間點一的意圖溝通能力即有差異，不過僅共享式注意力可預測日後社交情感症狀發展軌跡之分群。 總結：由結果可見自閉症狀維持高嚴重度組，於認知功能與適應行為有較明顯缺損，推論自閉症類兒童的自閉症狀嚴重度與認知功能及適應行為並非完全獨立的變項。兩組自閉症類兒童於學齡期症狀嚴重度上升，而此趨勢在退步組兒童更為明顯。雖然本研究並未發現早期療育經驗對於社交情感症狀發展的影響，不過共享式注意力對於日後社交情感症狀有預測力。進一步討論此結果在理論與臨床實務上的應用。 / Purposes: the purpose of the study was to plot longitudinal developmental trajectories of autism symptom severity in the children with autism spectrum disorders (ASDs) from toddler age to school age. And to examine whether these different trajectories are associated with the cognitive function, adaptive behavior, early social communication skill, and early intervention experience. Methods: Thirty-seven children with ASDs and 24 children with developmental delay participated at time 1 (mean chronological age was 2.5 years old), and then followed at time 2 (mean chronological age was 4 years old) and time 3 (mean chronological age was 8.5 years old). The study assessed the autism symptom severity by ADOS and cognitive function by MSEL or WISC-Ⅳ at three time points; adaptive behavior by VABS-II at time 2 and time 3; and early social communication skills by T-STAT at time 1 and also used telephone interviews to record participants’ weekly intervention hours during time 1 to time 2. Results: In hierarchical cluster analysis, social affect calibrated severity score (CSS) could discriminate ASDs and Non-ASDs groups, also could divided ASDs into two groups, called persistent high and worsening groups. The social affect symptom severity increased at school age in both groups. On the other hand, the change of cognitive function and adaptive behavior with time showed similar pattern in the two groups. However, participants in the persistent high group have relatively lower scores of cognitive function and adaptive behavior, although did not rearch statistically significant. Furthermore, two ASDs groups at toddler showed difference in intention communication skills; however, only joint attention could predict social affect trajectory subgrouping. Conclusions: In summery, the study showed that persistent high group has more cognitive and adaptive function impairments than the worsening group in the children with ASDs. It seemed that the autistic symptom are not entirely independent with cognitive function and adaptive behavior. Moreover, the symptom severity increased at school age in both the persistent high and the worsening groups, and this trend was more significant in the worsening group. Additionally, the experience of early intervention showed no significant effects on developmental trajectories of social affect symptom; however, the joint attention was found to be an index to predict the development of social affect symptom in ASDs groups. The theoretical and clinical implications were discussed.

La majorité des personnes utilisatrices de drogues par injection (PUDI) contracteront le virus de l’hépatite C (VHC), les mettant à risque accru de complications hépatiques graves et parfois mortelles. Les comportements les plus risqués pour l’acquisition du VHC incluent le partage de matériel d’injection et l’injection à haute fréquence. Un facteur jusqu’ici négligé dans l’évaluation du risque de VHC est l’aspect dynamique de l’injection, c.-à-d. la manière dont elle varie dans le temps, incluant l’effet des périodes sans injection et celui des changements dans la fréquence d’injection. On reconnaît également l’effet délétère que l’instabilité résidentielle peut avoir sur le risque de VHC, bien que les mécanismes sous-jacents soient mal compris. Cette thèse s’intéresse à l’effet des variations temporelles de l’injection sur le risque de VHC, et à la manière dont la fréquence d’injection évolue en concomitance avec les conditions résidentielles dans le temps, afin d’aider au développement de nouvelles stratégies de prévention du VHC. Les données ont été recueillies entre mars 2011 et juin 2016 dans la Hepatitis Cohort, une cohorte de PUDI suivies trimestriellement à Montréal, au Québec. Une première analyse a évalué l’effet des périodes sans injection de trois mois ou moins sur le risque de VHC sur 916 personnes-années de suivi, par régression de Cox (N=372). Celle-ci suggère que les PUDI présentant des périodes sans injection courtes (3/3 mois sans injection) et sporadiques (1/3 ou 2/3 mois sans injection) sont respectivement 76% et 44% moins à risque de VHC que celles s’injectant de manière persistante (0/3 mois sans injection). Une deuxième analyse a utilisé la modélisation de trajectoires fondée sur le groupement pour identifier cinq types distincts de trajectoires de fréquence d’injection suivies sur une année, lesquels ont ensuite été comparés en termes d’incidence du VHC sur des périodes de suivi allant de 71 à 355 personnes-années (N=386). Les résultats suggèrent que les PUDI dont la fréquence reste élevée (injection fréquente) ou change dans le temps (croissante, décroissante) sont à plus haut risque de VHC que celles s’injectant à basse fréquence (sporadique, peu fréquente). Une dernière analyse a identifié trois types de trajectoires de stabilité résidentielle suivies sur un an (persistance, déclin, amélioration; N=386), lesquels ont été évalués en association avec les trajectoires de fréquence d’injection suivies simultanément. Les résultats suggèrent qu’il existe un lien entre l’amélioration des conditions résidentielles et la diminution de la fréquence d’injection, mais aussi que la probabilité d’injection à fréquence croissante est plus élevée chez les PUDI maintenant des conditions résidentielles stables que celles chez qui elles s’améliorent. Collectivement, les résultats ont de nombreuses implications en termes de prévention du VHC. Cliniquement, l’instabilité de la fréquence d’injection semble être un facteur de risque à monitorer régulièrement. En termes de santé publique, les interventions favorisant l’engagement dans des périodes sans injection ou le maintien d’une basse fréquence d’injection pourraient être prometteuses. Enfin, les stratégies visant l’amélioration des conditions résidentielles pourraient éventuellement aider les PUDI à réduire leur fréquence d’injection, mais être insuffisantes pour maintenir celle-ci à basse fréquence une fois la stabilité atteinte. / The majority of people who inject drugs (PWID) will become infected with hepatitis C virus (HCV), placing them at risk of serious and sometimes fatal liver complications. Injecting behaviours with higher risk of HCV transmission include injecting equipment sharing and high frequency injecting. One factor that has been overlooked when assessing HCV acquisition risk is the dynamic aspect of drug injecting, i.e., how drug injecting varies over time, including the role of injecting cessation episodes and that of changes in injecting frequency. Moreover, there is growing recognition of the deleterious effect unstable housing can have on HCV acquisition risk, although the underlying mechanisms are not yet fully understood. This thesis examines how temporal variations in drug injecting relate to HCV acquisition risk and further explores how housing conditions and injecting frequency evolve together over time, for the purposes of contributing to the development of novel HCV prevention strategies. Data were collected between March 2011 and June 2016 in the Hepatitis Cohort, a prospective cohort study of PWID interviewed and tested for HCV infection at three-monthly intervals in Montréal, Québec. A first analysis examined the effect of injecting cessation episodes of three months or less on the risk of contracting HCV during 916 person-years of follow-up, using Cox regression (N=372). Results suggest that PWID with short injecting cessation episodes (3/3 months without injecting) or sporadic injecting cessation episodes (1/3 or 2/3 months without injecting) are 76% and 44% less at risk of contracting HCV than those with persistent injecting (0/3 months without injecting), respectively. A second analysis used group-based trajectory modeling to identify five distinct types of one-year injecting frequency trajectories and compared these in terms of HCV incidence over follow-up periods ranging from 71 to 355 person-years (N=386). Findings suggest that PWID injecting with consistently high frequencies (frequent) or time-varying frequencies (increasing, decreasing) are at greater HCV acquisition risk compared with those maintaining low injecting frequencies (sporadic, infrequent). Finally, a third analysis identified three types of one-year housing stability trajectories (sustained, declining, improving) and examined their associations with concomitant injecting frequency trajectories (N=386). Findings suggest an association between improving housing stability and decreasing injecting frequency, but also a higher probability of increasing injecting frequency among PWID who maintain housing stability compared to those that improve it. Collectively, these findings have numerous implications for HCV prevention. Clinically, instability in injecting frequency appears to be a risk factor that should be monitored regularly. From a public health perspective, interventions that promote engagement in injecting cessation episodes or maintenance of low injecting frequency may be promising. Finally, strategies aimed to improve housing stability may help PWID to decrease their injecting frequency but may not be sufficient to help them maintain low injecting frequencies once housing stability is achieved.