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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/221221
Genetic and environmental modulators of neural encoding associated to speech processing and their relationship with auditory skills
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[eng] Individuals exhibit variability in auditory processing skills, including those related to musical or speech perception, which rely on an accurate neural representation of the spectro-temporal characteristics of the auditory signal. The Frequency-Following Response (FFR) is a neurological response originating mainly in the brainstem that synchronizes with incoming stimuli and serves as a tool to assess the tracking accuracy of the auditory system. FFR has been associated with problems in phonological awareness, reading alterations, and dyslexia. It has also been noted that this response is sensitive to environmental influences such as language experience, bilingualism, and musical training. In addition to studying environmental factors in auditory processing, genetic studies have helped to understand the contributions of genetic variants to individual differences observed in auditory skills. Twin studies have reported remarkable heritability for auditory processing, including pitch recognition, temporal processing, and dichotic word discrimination, among others. Molecular genetics approaches have investigated the association between genetic regions and behavioral phenotypes of auditory perception, such as music perception and beat synchronization. In the field of auditory responses measured by EEG, a study reported a significant association between the FFR and the serotonin uptake gene (SLC6A4), representing the only study relating an auditory electrophysiological response with a gene. While the study of auditory processing and perception has been focused on environmental factors or genetic contributions separately, studies that combine both approaches are scarce. Furthermore, studies that integrate measures at different levels, including genetic data, electrophysiological measures, and behavioral assessments of auditory processing in a iv single study, are non-existent. This thesis includes four studies that aim to explore the genetic and environmental factors contributing to auditory processing as reflected in the FFR. It also aims to investigate the relationship between FFR and functional assessments of audiological, musical and speech perception. A total of 129 young adults volunteered as participants in an experimental session that consisted of an FFR-EEG experiment, a saliva sample collection for genetic analyses, four behavioral tests to assess speech-in-noise (SIN) perception, reading skills, musical skills, and amplitude-modulation discrimination, in addition to a language proficiency questionnaire. Study I attempted at characterizing the relationship between the FFR and processing sounds in challenging environments. Its results revealed that background noise affects the FFR by enhancing the response to the F0 on one side and degrading the response to the formant and the neural transmission delay on the other side. Additionally, we correlated the FFR parameters with the performance in a SIN perception task, finding that only the response to the F1 to the vowel /a/ was correlated with SIN perception. In Study II, the auditory skills measured behaviorally were correlated with four components obtained by PCA from the FFR parameters to describe functional implications of the FFR. Only the F1 /o/ component was significantly correlated with the performance in reading skills and no other significant correlation was observed. When evaluating the relationship only between the behavioral measures, significant correlations were observed between SIN perception and reading skills. In Study III, we replicated the association between the promoter region of the SLC6A4 gene and the FFR response to the F0. Moreover, genome-wide analyses did not reveal significant associations after correcting for multiple comparisons, but suggestive probability values were found between FFR component and SNPs related to genes linked to different cognitive and behavioral assessments and v highly expressed in brain tissues. Based on the polygenic score analyses, we found a significant shared genetic etiology between SIN perception and ADHD. In Study IV, regarding the role of the age of bilingualism acquisition as a potential modulator of the neural response, we did not find a main effect of bilingualism across all FFR measures, nor with the behavioral assessments, indicating that by itself, this variable does not contribute to the observed differences. In summary, throughout this thesis, it was observed that the individual contribution of the different environmental and genetic effects studied has a relatively small effect size, thus highlighting the complexity underlying the in-depth study of auditory processing of sounds in our environment.
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PUDDU GALLARDO, Giannina. Genetic and environmental modulators of neural encoding associated to speech processing and their relationship with auditory skills. [consulta: 29 de novembre de 2025]. [Disponible a: https://hdl.handle.net/2445/221221]