Neurocognitive signatures of phonemic sequencing in expert backward speakers

Despite its prolific growth, neurolinguistic research on phonemic sequencing has largely neglected the study of individuals with highly developed skills in this domain. To bridge this gap, we report multidimensional signatures of two experts in backward speech, that is, the capacity to produce utterances by reversing the order of phonemes while retaining their identity. Our approach included behavioral assessments of backward and forward speech alongside neuroimaging measures of voxel-based morphometry, diffusion tensor imaging, and resting-state functional connectivity. Relative to controls, both backward speakers exhibited behavioral advantages for reversing words and sentences of varying complexity, irrespective of working memory skills. These patterns were accompanied by increased grey matter volume, higher mean diffusivity, and enhanced functional connectivity along dorsal and ventral stream regions mediating phonological and other linguistic operations, with complementary support of areas subserving associative-visual and domain-general processes. Still, the specific loci of these neural patterns differed between both subjects, suggesting individual variability in the correlates of expert backward speech. Taken together, our results offer new vistas on the domain of phonemic sequencing, while illuminating neuroplastic patterns underlying extraordinary language abilities

From dysfunctional to extraordinary verbal repetition abilities: clinical implications and neural features

Three cases are presented to index the hypothesis that mitigated echolalia emerges from overreliance on the dorsal language stream, through the arcuate fasciculus, when the ventral stream is damaged; whereas conduite d’approche ensues when the ventral stream attempts to compensate a dorsal damage. The role of the right hemisphere and other alternative pathways in both cerebral hemispheres in the successful compensation of brain injury is also discussed. Further, Study 2 reconceptualizes different types of echolalia within a continuous of severity and communication capacity. To accomplish this new instantiation, it is proposed that different types of echolalia may be associated to failure in distinctive linguistic and non-linguistic cognitive functions. Recommendations for its evaluation and treatment are provided, suggesting that echolalia interfering with functional communication should be treated. Further, complementing the previous one, Study 3 reports a comprehensive single case study exploring response to treatment, and behavioral and neuroimaging features of a person with mitigated echolalia associated to a chronic fluent aphasia. Findings from such case include a reduction of mitigated echolalia after two weeks of intensive aphasia therapy as well as the maintenance of these gains with memantine alone for at least 6 months. Importantly, reduction of mitigated echolalia instances in response to treatment speeded up the time needed to complete comprehension tasks. Neuroimaging results, although indirectly, suggested that mitigated echolalia may be supported by the activity of the remaining components of the left dorsal stream and compensatory right hemisphere recruitment. Additionally, to further explore the neural and cognitive mechanisms involved in verbal repetition in a model of language expertise, Study 4 tackles cognitive features and neural correlates of verbal expertise in two healthy adult subjects displaying an extraordinary ability to orally reverse language, a condition referred to as backward speech. Results suggest that phonological expertise, as shown in backward speech, involves reshaping (or pre-existent differences) of cortical areas and tracts relevant for auditory-motor integration and semantic processing. Greater functional coupling between critical language areas and domain-general and high-order visual areas may further support reversing processes. Lastly, Study 5 presents a systematic review of the literature aimed to examine sex differences in the prevalence of repetition deficits in persons with post-stroke aphasia. Results show that the proportion of females in the group of aphasia characterized by repetition deficits (i.e., conduction aphasia) is lower than the expected by the prevalence of stroke among them. It is suggested that sex-related differences in the volume of areas of the right hemisphere homologues to the ones subserving repetition in the left hemisphere may be at the base of this difference. This finding poses sex as a relevant variable to account for variance in repetition abilities, and as a relevant factor to consider in future studies of language acquisition, maturation, and relearning promoted by aphasia therapy. Fecha de lectura de Tesis Doctoral: 16 de diciembre 2019Verbal repetition and audio-visual imitation stand as crucial functions for the acquisition and maturation of language in childhood, language learning in adulthood, and a major resource for language recovery after brain damage. Although modern neuroimaging techniques have allowed the identification of the brain areas involved in repetition tasks in healthy subjects, many clinical and neural aspects of this linguistic function are still overlooked in persons with aphasia and in emerging models of language expertise. Therefore, the present dissertation aims to explore cognitive correlates and neural features of verbal repetition from different perspectives including models of dysfunctional repetition (i.e., people with aphasia) and language expertise (i.e., healthy backward speakers). Generally, this thesis explores the potential of the dorsal and ventral components of the neural network supporting verbal repetition to assume, under certain circumstances (e.g., brain damage or extraordinary abilities), non-canonical functions. Further, this dissertation addresses clinical issues of some aphasic symptoms characterized by uncontrolled repetition (i.e., echolalia), as well as reviews sex as a source of variability in verbal repetition outcomes after brain damage. This dissertation includes five studies that are part of this dissertation. First, it reviews the mechanisms involved in dysfunctional repetition, especially in two repetitive verbal behaviors named conduite d’approche and mitigated echolalia (Study 1) and addresses clinical issues of the last one (Study 2 and 3). In this regard, Study 1 proposes that in the context of aphasia these symptoms (i.e., conduite d’approche and mitigated echolalia) may represent active attempts of verbal communication, rather than inconsequential repetitive verbal behaviors resulting from maladaptive neural changes

Brain structural predispositions for music and language processing

[eng] It has been shown that music and language training can elicit plastic changes on brain structure and function bringing along behavioural benefits. For instance, musicians have been reported to have better auditory discrimination including pitch and speech-in-noise perception, motor-synchronization, verbal memory and general IQ than individuals without formal musical background. Also, bilinguals have shown higher executive function and attention-related abilities than monolinguals. Furthermore, altered functional and structural connectivity can be tracked to brain areas related to the activities most frequently performed by both musicians (instrumentalists and singers) and linguistic experts (such as bilinguals or professional phoneticians). While research in the last decade has devoted important effort to the study of brain plasticity, only a few investigations have addressed the connection between the initial functional or structural properties of brain networks related to auditory-motor function and subsequent language or musical training. Indeed, brain structural markers such as grey matter volume/density or white-matter diffusivity measurements from diffusion tensor imaging (DTI) data, as well as functional measurements from task- related activity or resting-state data from magnetic resonance imaging (MRI) or electroenceplhalography (EEG) have been demonstrated to correlate with consecutive performance and learning in the auditory-motor domain. The main goal of the present dissertation was twofold: we aimed to further the existing knowledge regarding brain plasticity elicited during putative sensitive periods and after long-term music practice, and to explore the white-matter pathways that predict linguistic or musical skills at baseline . Our secondary goals were to confirm previous findings regarding the brain structures involved in music and language processing, as well as to provide evidence of the benefits of usingstructural measurements and correlational analyses between imaging and behavioural data to study inter-individual differences. Study I focused on the comparison between professional pianists and non- musicians observing a complex pattern of increases and decreases in grey matter volume. In comparison to non-musician individuals, pianists showed greater grey matter volume in areas related to motor skill and the automatization of learned movements, as well as reinforcement learning and emotional processing. On the other hand, regions associated to sensorimotor control, score reading and auditory and musical perception presented a reduction in grey matter volume. Study II explored the relationship between white-matter structural properties of the arcuate fasciculus (AF) and the performance of native German speakers in a foreign- language (Hindi) sentence and word imitation task. We found that a greater left lateralization of the AF volume predicted performance on the imitation task. This result was confirmed by using not only a manual deterministic approach but also an automatic atlas-based fibre-reconstruction method, which in addition pointed out to a specific region in the anterior half of the left AF as the most related to imitation ability. Study III aimed to investigate whether the white-matter structural connectivity of the pathways previously described as targets for plasticity mechanisms in professional musicians predicted musical abilities in non-musicians. We observed that the white- matter microstructural organization of the right hemisphere pathways involved in motor-control (corticospinal tract) and auditory-motor transformations (AF) correlated with the performance of non-musician individuals during the initial stages of rhythmic and melodic learning. The present work confirmed the involvement of several brain structures previously described to display plastic effects associated to music and language training in the first stages of audio-motor learning. Furthermore, they challenge previous views regarding music-induced plasticity by showing that expertise is not always or uniquely correlated with increases in brain tissue. This raises the question of the role of efficiency mechanisms derived from professional-like practice. Most importantly, the results from these three studies converge in showing that a prediction-feedback-feedforward loop for auditory-motor processing may be crucially involved in both musical and language learning and skills. We thus suggest that brain auditory-motor systems previously described as participating in native language processing (cortical areas of the dorsal route for language processing and the AF that connects them) may also be recruited during exposure to new linguistic or musical material, being refined after sustained music practice.[spa] Estudios previos muestran que la formación musical y lingüística provoca cambios plásticos en las estructuras y funciones cerebrales, acompañándose también de beneficios conductuales. Por ejemplo, se ha descrito que los músicos poseen mejores habilidades de discriminación auditiva (incluyendo la percepción tonal y la discriminación del habla en un ambiente ruidoso), una mayor capacidad de sincronización motora, así como mejor memoria verbal y coeficiente intelectual general en comparación con personas sin formación musical. Paralelamente, los bilingües muestran mejores funciones ejecutivas y habilidades relacionadas con la atención en comparación con individuos monolingües. Además, las alteraciones en la conectividad cerebral funcional y estructural pueden ser rastreadas estudiando las áreas cerebrales relacionadas con las actividades más utilizadas por músicos (instrumentistas y cantantes) y expertos lingüísticos (como bilingües o fonetistas profesionales). Pese a que en la última década se han dedicado esfuerzos importantes en el campo de la investigación sobre la plasticidad cerebral, sólo unos pocos estudios han tratado de investigar la conexión entre las propiedades iniciales del cerebro, en cuanto a las funciones y estructuras que se relacionan con las funciones auditivo-motoras, y el posterior aprendizaje musical o del lenguaje. Sin embargo, los marcadores estructurales cerebrales, tales como volumen/densidad de materia gris o medidas de difusividad en la sustancia blanca a partir de datos de imagen del tensor de difusión, así como medidas funcionales de la actividad relacionada con una tarea o datos de resting-state (estado de reposo) obtenidos por resonancia magnética o electroencefalografía, han demostrado que pueden correlacionar con el rendimiento y el aprendizaje en el dominio auditivo- motor. En la presente tesis pretendíamos ampliar nuestro conocimiento en cuanto a la plasticidad cerebral obtenida durante los supuestos “períodos sensibles” y después de la práctica musical mantenida en el tiempo, por un lado, y explorar las vías de sustancia blanca que pueden predecir habilidades lingüísticas o musicales al inicio del aprendizaje, por otro lado. Como objetivos secundarios, queríamos confirmar resultados previos con respecto a las estructuras cerebrales involucradas en el procesamiento de la música y el lenguaje, así como apoyar el uso de mediciones estructurales y enfoques correlacionales (entre datos de neuroimagen y conductuales) para estudiar las diferencias inter- individuales. El Estudio I se centró en la comparación entre pianistas profesionales y no músicos, observando un complejo patrón de aumentos y disminuciones en el volumen de materia gris. En comparación con los individuos no músicos, los pianistas mostraron mayor volumen de sustancia gris en áreas relacionadas con la habilidad motora y la automatización de movimientos aprendidos, así como el aprendizaje a través del refuerzo y el procesamiento emocional, mientras que las regiones asociadas al control sensoriomotor, lectura de partituras y percepción auditiva y musical presentaron una reducción del volumen de materia gris. El Estudio II exploró la relación entre las propiedades estructurales de la materia blanca del fascículo arqueado (AF por sus siglas en inglés) y el rendimiento de hablantes nativos de alemán en una tarea de imitación de frases y palabras en una lengua extranjera (hindi). Encontramos que una mayor lateralización del volumen de AF hacia la izquierda predecía el desempeño en la tarea de imitación. Este resultado se confirmó utilizando no sólo un enfoque determinístico-manual sino también una reconstrucción automática (basada en atlas anatómicos) de las fibras de sustancia blanca que, además, señalaba una región específica en la mitad anterior del AF izquierdo como la más relacionada con las capacidades de imitación. El Estudio III tenía como objetivo investigar si la conectividad estructural de vías de sustancia blanca anteriormente descritas como dianas para los mecanismos de plasticidad en músicos profesionales, podría predecir las habilidades musicales en los no músicos. Se observó que la organización micro-estructural de la materia blanca en el hemisferio derecho en vías involucradas en el control motor (tracto corticoespinal) y en transformaciones auditivo-motoras (AF) correlacionaba con el desempeño de individuos no músicos en las etapas iniciales del aprendizaje rítmico y melódico. El presente trabajo ha confirmado la implicación en las primeras etapas del aprendizaje audio-motor de varias estructuras cerebrales que previamente habían mostrado efectos plásticos asociados al aprendizaje musical y del lenguaje. Además, estos resultados desafían las opiniones anteriores sobre la plasticidad inducida por la experiencia musical al demostrar que la experiencia no se correlaciona siempre ni únicamente con un aumento del tejido cerebral, y planteando así preguntas sobre los mecanismos de eficiencia derivados de la práctica musical a nivel profesional. Más importante aún es que los resultados de estos tres estudios convergen mostrando que un bucle de predicción–retroalimentación (feedback)–alimentación directa (feedforward) para el procesamiento auditivo-motor puede estar implicado de manera crucial tanto en el aprendizaje musical como en el aprendizaje de idiomas. Por tanto, sugerimos que los sistemas auditivo-motrices del cerebro, que previamente se habían descrito como participantes en el procesamiento del lenguaje nativo (áreas corticales involucradas en la vía dorsal para el procesamiento del lenguaje, y el AF, que las conecta) también pueden ser reclutados durante la exposición a material lingüístico o musical nuevo, siendo refinado tras años de práctica musical activ

Exploring the ventral language pathways of the brain through bilingualism: a Tractography study

The focus of the present PhD thesis is to compare the brain correlates associated to bimodal bilingualism with respect to unimodal bilingualism. The overarching aim is to identify which are the common neuronal substrates between signed and spoken languages, with respect to the neural substrates that are specific for each linguistic modality, i.e., signed versus spoken. This is a relevant issue as it allows to better explore (i) to what extent and for which function the two language modalities might interact; (ii) for which function they might interfere, and (iii) whether the two language modalities are supported by independent neuronal systems. In addition, this project explores the organization of the bilingual brain in a broader view, assessing whether the neural structures underlying the first language (L1) can be separated from structures mainly devoted at handling the second language (L2). Measures of diffusion magnetic resonance imaging tractography will be assessed in a group of unimodal bilinguals of Italian (L1) and English (L2) and in a group of bimodal bilinguals of Italian (L1) and Italian Sign Language (L2), with variable level of proficiency in the second language. Together with the tract-specific measures, both demographical and behavioral data will be collected in order to assess the level of performance for both L1 and L2. Tract-specific data will be correlated with behavioral data, revealing how the degree of expertise with signed or spoken language and the relative modality are capable of shaping the neural circuitry at the service of specific linguistic functions

The neuroanatomical hallmarks of chronic tinnitus in comorbidity with pure-tone hearing loss

Tinnitus is one of the main hearing impairments often associated with pure-tone hearing loss, and typically manifested in the perception of phantom sounds. Nevertheless, tinnitus has traditionally been studied in isolation without necessarily considering auditory ghosting and hearing loss as part of the same syndrome. Hence, in the present neuroanatomical study, we attempted to pave the way toward a better understanding of the tinnitus syndrome, and compared two groups of almost perfectly matched individuals with (TIHL) and without (NTHL) pure-tone tinnitus, but both characterized by pure-tone hearing loss. The two groups were homogenized in terms of sample size, age, gender, handedness, education, and hearing loss. Furthermore, since the assessment of pure-tone hearing thresholds alone is not sufficient to describe the full spectrum of hearing abilities, the two groups were also harmonized for supra-threshold hearing estimates which were collected using temporal compression, frequency selectivity und speech-in-noise tasks. Regions-of-interest (ROI) analyses based on key brain structures identified in previous neuroimaging studies showed that the TIHL group exhibited increased cortical volume (CV) and surface area (CSA) of the right supramarginal gyrus and posterior planum temporale (PT) as well as CSA of the left middle-anterior part of the superior temporal sulcus (STS). The TIHL group also demonstrated larger volumes of the left amygdala and of the left head and body of the hippocampus. Notably, vertex-wise multiple linear regression analyses additionally brought to light that CSA of a specific cluster, which was located in the left middle-anterior part of the STS and overlapped with the one found to be significant in the between-group analyses, was positively associated with tinnitus distress level. Furthermore, distress also positively correlated with CSA of gray matter vertices in the right dorsal prefrontal cortex and the right posterior STS, whereas tinnitus duration was positively associated with CSA and CV of the right angular gyrus (AG) and posterior part of the STS. These results provide new insights into the critical gray matter architecture of the tinnitus syndrome matrix responsible for the emergence, maintenance and distress of auditory phantom sensations

Experience Dependent Plasticity over short and long timescales

The brain is constantly changing. Genetically specified developmental pathways interact with extrinsic factors including illness, injury and learning to shape the brain. This thesis presents two projects on experience dependent plasticity over different timescales. Exerting its effect across years, deafness provides a model of long term crossmodal plasticity. In the first part of this thesis I ask how deafness affects the thalamus. Diffusion weighted imaging was used to segment the thalamus and with probabilistic tractography, thalamo-cortical connections were traced. Microstructural properties of visual and frontal thalamic segmentations, thalamo-cortical tracts throughout the brain, apart from the temporal thalamo-cortical tract were altered. The neuroanatomical sequelae of deafness are evident throughout the brain. Deaf people have enhanced peripheral vision, facilitating a protective orienting mechanism when hearing cannot be relied upon. Widefield population receptive field (pRF) modeling with fMRI was completed to examine the functional and structural properties of primary visual cortex. Deaf participants had enlarged pRF profiles and thinner cortex in peripheral visual regions, again emphasizing plasticity across many years. In the second part I examine plasticity over the course of days. Visuomotor transformations translate visual input to motor actions, and its neural instantiation might change with training. We used a pattern component model on fMRI data to reveal a gradient of visual to motor information from occipital to parietal to motor cortex. Strikingly, we observed motor coding in visual cortex and visual coding in motor cortex. More tentatively, our results suggest that during sensorimotor skill learning there is decreased dependence on visual cortex as motor cortex learns the novel visuomotor mapping. In summary, I show crossmodal processing and plasticity in regions previously considered not to exhibit these properties, both in long- and short-term plasticity. This work emphasizes the contribution that computational neuroimaging can provide to the field of experience dependent plasticity

Changing our brains and minds: exploring the effects of individual differences in bilingual language experience on brain structure, function, and cognition

Current research suggests that bilingualism affects both the structure of the brain and several cognitive processes. However, few studies have specifically examined effects of individual differences in bilingual language use on domain-general control processes and their neural correlates. This thesis project assesses the hypothesis that specific language use factors within the bilingual experience will alter neural activity and plasticity in regions implicated in language/executive control. Three studies are run. The first study is longitudinal, examining effects of long-term linguistic immersion on neural plasticity in highly proficient non-native (L2) speakers of English. Data from this study shows adaptations in brain structure related to increased efficiency of language processing and control and modulated by the length of L2 use prior to the study. The second and third studies are cross-sectional, examining effects of specific language use factors on 1) neural structure and intrinsic functional connectivity and 2) performance and neural activation patterns on executive function tasks. Factors related to duration of L2 use correlate to neurocognitive adaptations suggesting increased efficiency in language control. Factors related to extent of L2 use correlate to neurocognitive adaptations suggesting increased language control demands. Considered together, the data suggest that the brain constantly strives to be maximally effective and efficient in language processing control, which in turn affects domain-general cognitive processes. Crucially, the data highlight the necessity of considering specific, individual language experiences in assessing neurocognitive effects of bilingualism

Étude de la neuroplasticité en contexte de surdité par l’analyse de la matière blanche

Thèse de doctorat présentée en vue de l'obtention du doctorat en psychologie - recherche intervention, option neuropsychologie clinique (Ph.D)La privation sensorielle représente un excellent cadre pour l’étude de la neuroplasticité puisqu’elle permet de mieux comprendre l’impact de l’expérience sensorielle sur la structure et le fonctionnement du cerveau. En contexte de privation auditive, de nombreuses études de neuroimagerie fonctionnelle ont mis en évidence le recrutement des aires auditives pour le traitement visuel et tactile. Toutefois, les mécanismes qui sous-tendent ce transfert intermodal d’informations sensorielles ne sont toujours pas clairs. De plus, la surdité est une privation sensorielle qui permet particulièrement l’étude de l’expérience langagière sur les circuits neuronaux impliqués dans le traitement du langage. En effet, certaines personnes sourdes acquerront le langage oral alors que d’autres apprendront plutôt la langue des signes, une modalité de communication entièrement visuospatiale et motrice. Cependant, malgré la découverte de différences fonctionnelles dans le traitement et la production de la langue des signes comparée à la langue orale, peu d’études ont investigué la structure des faisceaux langagiers chez les personnes sourdes. Conséquemment, cette thèse doctorale vise à approfondir notre compréhension du phénomène de neuroplasticité du cerveau grâce à l’exploration de l’architecture de la matière blanche des systèmes sensoriels et du système langagier en contexte de surdité. Dans l’article 1, nous avons utilisé l’approche de la théorie des graphes pour décrire le réseau de connexions de matière blanche qui relient les aires sensorielles et associatives entre elles et au cerveau entier en contexte de surdité. L’analyse des caractéristiques globales des graphes révèle que le réseau des personnes sourdes semble conservé des propriétés d’intégration et de ségrégation similaires à celui des personnes entendantes. Au niveau des caractéristiques locales, les analyses bayésiennes ont offert un support modéré à l’hypothèse d’une centralité plus élevée dans certaines aires visuelles et associatives chez les personnes sourdes comparées aux personnes entendantes. Finalement, une corrélation significative a été établie entre le degré de sévérité et la centralité d’une région visuelle. Ainsi, nos résultats suggèrent d’abord que qu’un même réseau structurel puisse sous-tendre différents circuits de traitement sensoriel. Au niveau local, notre étude supporte, dans une certaine mesure, l’hypothèse d’une neuroplasticité intramodale compensatoire dépendante de l’usage augmentée des habiletés visuelles et visuospatiales sur lesquelles les personnes sourdes s’appuient au quotidien. Finalement, cet article a mis en lumière l’importance de considérer les caractéristiques de la surdité dans les études de la neuroplasticité. Dans l’article 2, nous avons étudié l’impact de la privation sensorielle auditive et de l’expérience langagière sur les faisceaux de matière blanche composant le système langagier. Nous avons d’abord procédé à une analyse des composantes principales qui nous a permis de créer deux nouvelles mesures liées à 1) la caractéristique d’entrave à la diffusion, et à 2) la complexité du tissu de matière blanche. Nous avons retrouvé une augmentation de la complexité des fibres au sein des voies dorsales du système langagier chez les personnes sourdes utilisant la langue des signes. Nous proposons que cela puisse soutenir l’usage d’articulateurs (doigts, mains, bras) plus larges et spatialement complexes. Cet article a mis en évidence l’importance de l’étude de l’expérience langagière en contexte de surdité pour une meilleure compréhension des mécanismes de neuroplasticité structurelle. Globalement, ces travaux nous permettent une meilleure appréciation de la structure du réseau de matière blanche qui supporte le traitement sensoriel et langagier en contexte de privation auditive. Cette thèse doctorale s’inscrit de façon intéressante au sein des théories modernes des mécanismes sous-tendant la neuroplasticité fonctionnelle. Elle fait également démonstration claire de la pertinence de l’étude de la matière blanche dans l’investigation des habiletés neuroplastiques du cerveau.Sensory deprivation represents an excellent setting for the study of neuroplasticity since it allows for a better understanding of the impact of sensory experience on brain structure and function. In the context of auditory deprivation, numerous functional neuroimaging studies have demonstrated the recruitment of auditory areas for visual and tactile processing. However, the mechanisms underlying this intermodal transfer of sensory information are still unclear. Moreover, deafness is a sensory deprivation that particularly allows the study of language experience on the neural circuits involved in language processing. Indeed, some deaf people will acquire oral language while others will learn sign language, an entirely visuospatial and motor communication modality. However, despite the discovery of functional differences in the processing and production of sign language compared to oral language, few studies have investigated the structure of language bundles in deaf individuals. Consequently, this doctoral thesis aims to further our understanding of the phenomenon of brain neuroplasticity by exploring the white matter architecture of sensory and language systems in the context of deafness. In article 1, we used a graph theory approach to describe the network of white matter connections that link sensory and associative areas to each other and to the whole brain in the context of deafness. Analysis of the global characteristics of the graphs reveals that the network of deaf individuals appears to retain similar integration and segregation properties to that of hearing individuals. At the level of local features, Bayesian analyses offered moderate support to the hypothesis of higher centrality in certain visual and associative areas in deaf people compared to hearing people. Finally, a significant correlation was found between the degree of severity and the centrality of a visual area. Thus, our results first suggest that the same structural network may underlie different sensory processing circuits. At the local level, our study supports, to some extent, the hypothesis of compensatory intramodal neuroplasticity dependent on the augmented use of visual and visuospatial skills on which deaf individuals rely in their daily lives. Finally, this article highlighted the importance of considering the characteristics of deafness in studies of neuroplasticity. In article 2, we investigated the impact of auditory sensory deprivation and language experience on the white matter bundles comprising the language system. We first performed a principal component analysis that allowed us to create two new measures related to 1) the diffusion hindrance feature, and 2) the complexity of the white matter tissue. We found an increase in fiber complexity within the dorsal pathways of the language system in deaf individuals using sign language. We propose that this may support the use of larger, spatially complex articulators (fingers, hands, arms). This paper has highlighted the importance of studying language experience in the context of deafness for a better understanding of structural neuroplasticity mechanisms. Overall, this work allows us to better appreciate the structure of the white matter network that supports sensory and language processing in the context of auditory deprivation. This doctoral thesis is an interesting addition to modern theories of the mechanisms underlying functional neuroplasticity. It also clearly demonstrates the relevance of the study of white matter in the investigation of neuroplastic abilities of the brain

Do informal caregivers of people with dementia mirror the cognitive deficits of their demented patients?:A pilot study

Recent research suggests that informal caregivers of people with dementia (ICs) experience more cognitive deficits than noncaregivers. The reason for this is not yet clear. Objective: to test the hypothesis that ICs ‘mirror' the cognitive deficits of the demented people they care for. Participants and methods: 105 adult ICs were asked to complete three neuropsychological tests: letter fluency, category fluency, and the logical memory test from the WMS-III. The ICs were grouped according to the diagnosis of their demented patients. One-sample ttests were conducted to investigate if the standardized mean scores (t-scores) of the ICs were different from normative data. A Bonferroni correction was used to correct for multiple comparisons. Results: 82 ICs cared for people with Alzheimer's dementia and 23 ICs cared for people with vascular dementia. Mean letter fluency score of the ICs of people with Alzheimer's dementia was significantly lower than the normative mean letter fluency score, p = .002. The other tests yielded no significant results. Conclusion: our data shows that ICs of Alzheimer patients have cognitive deficits on the letter fluency test. This test primarily measures executive functioning and it has been found to be sensitive to mild cognitive impairment in recent research. Our data tentatively suggests that ICs who care for Alzheimer patients also show signs of cognitive impairment but that it is too early to tell if this is cause for concern or not