Étude des substrats cérébraux associés au traitement sémantique dans le vieillissement pathologique et normal

Introduction : Les patients atteints de la variante sémantique de l'aphasie primaire progressive (vsAPP) et de trouble neurocognitif majeur dû à la maladie d'Alzheimer (MA) ont des déficits langagiers qui nuisent à leur qualité de vie. Ces déficits sont notamment liés à une atteinte du traitement de la signification des mots ou sémantique. Les thérapies actuelles, telles que les thérapies de rééducation du langage et la pharmacothérapie, ont une efficacité limitée pour améliorer les habiletés langagières chez les personnes atteintes de vsAPP et de MA. Une des raisons pouvant contribuer aux limites de l'efficacité de ces thérapies est qu'ils ne ciblent pas de façon spécifique les substrats cérébraux liés à l'atteinte du traitement sémantique. Or, ces substrats cérébraux ont besoin d'être mieux définis. Plusieurs mesures liées à l'anatomie, à l'activité électrophysiologique et à la modulation de l'activité cérébrale permettent d'étudier les substrats cérébraux associés au traitement sémantique. En ce qui a trait à l'anatomie, il est possible de mesurer le volume de matière grise du cerveau. Comme mesures de l'activité électrophysiologique, on note le potentiel évoqué N400 et la puissance des oscillations au repos. La modulation de l'activité cérébrale permet, pour sa part, d'explorer des liens de causalité entre des processus cognitifs et des réseaux cérébraux. Différentes techniques permettent d'obtenir ces mesures, telles la morphométrie cérébrale, l'électroencéphalographie (EEG) et la stimulation transcrânienne à courant continu (STCC). Objectif : L'objectif général de cette thèse est d'étudier les substrats cérébraux associés au traitement sémantique, au cours du vieillissement, afin de contribuer au développement d'approches thérapeutiques pour améliorer le langage dans le vieillissement pathologique. Hypothèse : L'anatomie et l'activité électrophysiologique cérébrale sont associées au traitement sémantique dans le vieillissement pathologique et normal, et la modulation de l'activité cérébrale permet d'explorer des liens de causalité entre le traitement sémantique et des régions cérébrales. Méthode : Pour atteindre notre objectif, nous avons effectué 4 études. L'étude 1 a pour but d'identifier les régions du cerveau dont le volume de matière grise est lié aux habiletés en lecture de mots, laquelle implique un traitement sémantique, chez des patients atteints de vsAPP et de MA et des aînés sains à l'aide de la morphométrie cérébrale. L'étude 2 a pour but d'étudier le traitement sémantique via le comportement et le potentiel évoqué N400 dans la MA et le vieillissement normal, par le biais d'une revue systématique. L'étude 3 a pour but d'étudier l'activité cérébrale associée au traitement sémantique chez des aînés sains en comparaison à celle de jeunes adultes avec l'EEG. L'étude 4 a pour but d'identifier les régions du cerveau auxquelles la STCC peut être appliquée pour moduler le traitement sémantique par le biais d'une revue de littérature. Résultats : L'étude 1 a révélé que le volume de matière grise du lobe temporal antérieur gauche est associé au nombre d'erreurs commises lors de la lecture de mots, qui implique un traitement sémantique. L'étude 2 a révélé des différences dans le potentiel évoqué N400 entre les personnes atteintes de MA et les aînés sains, ainsi qu'entre ces derniers et les adultes plus jeunes. L'étude 3 a révélé que, malgré un comportement similaire entre les aînés et les jeunes, l'activité électrophysiologique cérébrale associée au traitement sémantique diffère entre les groupes d'âge. L'étude 4 a révélé que la STCC appliquée à des régions des cortex frontal, temporal et pariétal peut moduler le traitement sémantique chez des adultes en santé. Conclusion : Des mesures de l'anatomie et de l'activité électrophysiologique, dont le volume de matière grise du lobe temporal du cerveau et le potentiel évoqué N400, sont associés au traitement sémantique dans le vieillissement pathologique et normal. Les mesures de la modulation de l'activité cérébrale renforcent le rôle de régions cérébrales temporales, frontales et pariétales dans le traitement sémantique. Ces études fournissent des pistes quant aux régions cérébrales qui pourraient être ciblées pour améliorer le traitement sémantique dans le vieillissement pathologique, tel que par l'utilisation de techniques de neuromodulation non-invasive.Introduction: Patients with the semantic variant of primary progressive aphasia (svPPA) and with Alzheimer's disease (AD) show language impairments that affect their quality of life. One of the main sources of language impairment in these populations is that they present with abnormal processing of the meaning of words (semantic processing deficits). Treatment options currently available, namely pharmacotherapy and language therapy, have limited effectiveness to improve language abilities in these patients. It is possible that a therapy that would directly target the neural substrates involved in semantic processing, unlike currently available therapies, could have a positive impact on language abilities. However, these neural substrates are not that well characterized. Neural substrates of semantic processing can be studied via different anatomical and electrophysiological brain measures, or through neuromodulation of brain activity. To study the structural brain anatomy and electrophysiological brain activity, one can measure respectively gray matter volume and the N400 event-related potential. The measurement of the effects of neuromodulation further allows to explore causal links between cognitive processes and targeted brain regions. Different techniques enable to collect these measures, such as voxel-based morphometry (VBM), electroencephalography (EEG) and transcranial direct current stimulation (tDCS). Objective: The main objective of this thesis is to study the brain substrates related to semantic processing in aging in order to contribute to the development of treatments aiming at improving language abilities. Hypothesis: Anatomical and electrophysiological brain measures are associated with semantic processing in pathological and healthy aging, and neuromodulation allows to explore causal links between semantic processing and brain regions. Methods: To achieve our objective, we conducted 4 studies. Study 1 aims at identifying the brain regions in which gray matter volume is associated with whole-word reading (which implies semantic processing) in patients with svPPA or AD and healthy elderly adults using VBM. Study 2 aims at investigating the N400 event-related potential, associated with semantic processing, in AD and healthy aging through a systematic review. Study 3 aims at investigating the electrophysiological brain activity associated with semantic processing in healthy elderly adults in comparison to young adults using EEG. Study 4 aims at identifying the brain regions that could be targeted with tDCS to modulate semantic processing through a literature review. Results: Study 1 revealed that gray matter volume of the left anterior temporal lobe is associated with the number of errors in whole-word reading, which implies semantic processing. Study 2 revealed differences in the N400 event-related potential between patients with AD and healthy elderly adults, as well as between healthy elderly and younger adults. Study 3 revealed that, despite a similar behavioral performance between elderly and younger adults, some of the electrophysiological activity patterns associated with semantic processing differed between the two age groups. Study 4 revealed that tDCS delivered over the frontal, temporal and parietal cortices can modulate semantic processing in healthy adults. Conclusion: Anatomical and electrophysiological brain measures, including gray matter volume and the N400 event-related potential, are associated with semantic processing in pathological and healthy aging. Neuromodulation measures strengthen the role of temporal, frontal and parietal brain regions in semantic processing. These studies outline brain regions that could be targeted with non-invasive neuromodulation techniques to improve semantic processing in pathological aging

The role of the left anterior temporal lobe for unpredictable and complex mappings in word reading

The anterior temporal lobes (ATLs) have been consistently associated with semantic processing which, in turn, has a key role in reading aloud single words. This study aimed to investigate (1) the reading abilities in patients with the semantic variant of primary progressive aphasia (svPPA), and (2) the relationship between gray matter (GM) volume of the left ATL and word reading performance using voxel-based morphometry (VBM). Three groups of participants (svPPA, Alzheimer’s Disease, AD and healthy elderly adults) performed a reading task with exception words, regular words and pseudowords, along with a structural magnetic resonance imaging scan. For exception words, the svPPA group had a lower accuracy and a greater number of regularization errors as compared to the control groups of healthy participants and AD patients. Similarly, for regular words, svPPA patients had a lower accuracy in comparison with AD patients, and a greater number of errors related to complex orthography-to-phonology mappings (OPM) in comparison to both control groups. VBM analyses revealed that GM volume of the left ATL was associated with the number of regularization errors. Also, GM volume of the left lateral ATL was associated with the number of errors with complex OPM during regular word reading. Our results suggest that the left ATL might play a role in the reading of exception words, in accordance with its role in semantic processing. Results further support the involvement of the left lateral ATL in combinatorial processes, including the integration of semantic and phonological information, for both exception and regular words

Are musical activities associated with enhanced speech perception in noise in adults? A systematic review and meta-analysis

The ability to process speech in noise (SPiN) declines with age, with a detrimental impact on life quality. Music-making activities such as singing and playing a musical instrument have raised interest as potential prevention strategies for SPiN perception decline because of their positive impact on several brain system, especially the auditory system, which is critical for SPiN. However, the literature on the effect of musicianship on SPiN performance has yielded mixed results. By critically assessing the existing literature with a systematic review and a meta-analysis, we aim to provide a comprehensive portrait of the relationship between music-making activities and SPiN in different experimental conditions. 38/49 articles, most focusing on young adults, were included in the quantitative analysis. The results show a positive relationship between music-making activities and SPiN, with the strongest effects found in the most challenging listening conditions, and little to no effect in less challenging situations. This pattern of results supports the notion of a relative advantage for musicians on SPiN performance and clarify the scope of this effect. However, further studies, especially with older adults, using adequate randomization methods, are needed to extend the present conclusions and assess the potential for musical activities to be used to mitigate SPiN decline in seniors

Semantic Processing in Healthy Aging and Alzheimer’s Disease: A Systematic Review of the N400 Differences

Semantic deficits are common in individuals with Alzheimer’s disease (AD). These deficits notably impact the ability to understand words. In healthy aging, semantic knowledge increases but semantic processing (i.e., the ability to use this knowledge) may be impaired. This systematic review aimed to investigate semantic processing in healthy aging and AD through behavioral responses and the N400 brain event-related potential. The results of the quantitative and qualitative analyses suggested an overall decrease in accuracy and increase in response times in healthy elderly as compared to young adults, as well as in individuals with AD as compared to age-matched controls. The influence of semantic association, as measured by N400 effect amplitudes, appears smaller in healthy aging and even more so in AD patients. Thus, semantic processing differences may occur in both healthy and pathological aging. The establishment of norms of healthy aging for these outcomes that vary between normal and pathological aging could eventually help early detection of AD

Vocal health and vocal health knowledge among occupational voice users in the Province of Quebec

Voice disorders are frequent among occupational voice users such as teachers. Although these disorders can have serious personal and professional consequences, they are not often recognized as occupational diseases and little attention is paid to their prevention. This study aimed to provide a portrait of the self-reported vocal health and vocal health knowledge of occupational voice users in Quebec, Canada, and to identify risk factors associated with voice disorder symptoms. We conducted an online survey targeting occupational voice users in the province of Quebec, Canada, with a focus on those involved in teaching or training. The final sample, after excluding incomplete surveys, included 808 respondents (665 women, M = 41.5 ± 10.4 years old). The survey responses were analyzed using descriptive and inferential statistics. Results indicated that 9.8% of the respondents had a history of a diagnosed voice disorder and 68.8% of the respondents experienced at least one voice symptom on a regular basis. Ordinal logistic regressions showed that several personal and environmental factors are associated with an increased risk of developing voice disorders symptoms: being a woman, suffering from a breathing disorder, allergies, acid reflux and/or hearing impairment, having less work experience, working with elementary school children and/or with continuous or speech noise in the background. Most of the respondents (94.6%) had never received information regarding voice disorders during their academic training and less than half of them (47.7%) knew which professionals can treat voice disorders. These findings highlight the need for formal vocal health education among both occupational voice users and their employers to improve prevention and treatment for voice disorders in an at-risk population

Characterizing emotional Stroop interference in posttraumatic stress disorder, major depression and anxiety disorders: A systematic review and meta-analysis

<div><p>Background</p><p>Posttraumatic stress disorder is a debilitating psychiatric disorder characterized by symptoms of intrusive re-experiencing of trauma, avoidance and hyper-arousal. Diagnosis and treatment of PTSD is further complicated by concurrently occurring disorders, the most frequent being major depressive disorder and anxiety disorders. Previous research highlights that attentional processing in posttraumatic stress disorder is associated with substantial interference by emotional stimuli, a phenomenon also observed in these concurrently occurring psychiatric disorders. However, the diagnosis-relevance of this interference remains elusive. Here, we investigated the emotional Stroop interference for diagnosis-related stimuli, generally negative stimuli, and generally positive stimuli in posttraumatic stress disorder, major depressive disorder and anxiety disorders.</p><p>Methods</p><p>We performed a systematic database search in PubMed (Medline), Cochrane Library and PsycINFO on emotional Stroop performance in individuals with a diagnosis of posttraumatic stress disorder, major depressive disorder or anxiety disorders separately. Mean effect sizes, standard errors and confidence intervals were estimated for each clinical group and healthy control group comparison using random effect models.</p><p>Results</p><p>As compared to healthy control group, the posttraumatic stress disorder group displayed greater interference by diagnosis-related stimuli and positive stimuli but not for generally negative stimuli. The major depressive disorder and anxiety disorders groups showed greater interference by diagnosis-related and negative stimuli, but not by positive stimuli. The age and sex had no significant impact on interference.</p><p>Conclusions</p><p>These findings highlight the importance of diagnosis-relevant information on attentional processing in all three clinical populations, posttraumatic stress disorder, major depressive disorder and anxiety disorders. Further, the impact of generally negative stimuli but not generally positive stimuli in major depressive disorder and anxiety disorders indicate impaired attentional bias for mood-congruent stimuli but not for general stimuli. Finally, it remains to be studied whether the influence of generally positive stimuli in posttraumatic stress disorder indicate that positive stimuli are perceived as PTSD related.</p></div