The Structural and functional organization of the language network in non- or minimally verbal autism spectrum disorders
Language impairment forms a broader spectrum in humans than current diagnostic labels such as specific language impairment suggest. This thesis is about language capacities at the neglected bottom end of severity across this spectrum, with a focus on non- or minimally verbal children and adults with...
| Autor: | |
|---|---|
| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2022 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/674212 |
| Acceso en línea: | http://hdl.handle.net/10803/674212 |
| Access Level: | acceso abierto |
| Palabra clave: | Autism spectrum disorders Language impairment 81 |
| Sumario: | Language impairment forms a broader spectrum in humans than current diagnostic labels such as specific language impairment suggest. This thesis is about language capacities at the neglected bottom end of severity across this spectrum, with a focus on non- or minimally verbal children and adults with autism (nvASD). Despite fundamental challenges that this population poses in terms of investigating affected individuals, language impairment at this level also provides opportunities for illuminating aspects of the neural basis of language through their absence. Currently, insights from fMRI are unavailable. In this context, this thesis sets out firstly to reconceptualize the landscape of language impairment with a view to integrating language impairment of this kind. It then provides the first neuropsychological profiling of this population from a lifetime perspective. The remainder of the thesis is devoted to a first exploration using fMRI of the intrinsic functional connectivity (FC) of whole brain and language networks in nvASD, and of responses to auditory verbal stimuli, mapped against resting state auditory components, in order to probe deeper into the functionality of language regions. Structural connectivity and microstructure of language tracts was also assessed. The final chapter expands the view to a comparative case study of language capacities at a similarly severe end, yet in the absence of ASD. Overall, results of the neuropsychological profiling revealed an apparent glass ceiling of language capacities in this population at any age, with generally correlated levels of productive and receptive language, despite some variation in nonverbal IQ. In FC, despite surprising maintenance of intrinsic coupling of language regions as reflective of very early language endowment in humans generally, a crucial difference emerged within the hierarchy of auditory language processing between the superior and middle temporal gyri. In stimulus-driven auditory processing, I found a generally manifest leftlateralized language network at a group level, overlapping to different degrees with an auditory network as revealed by independent component analysis. The structural connectivity analysis revealed anomalous right-lateralization of the arcuate fasciculus, expanding previous volumetric findings at a microstructural level. Unlike in nvASD, the non-ASD comparative cases were revealing by showing more profound across both anatomical and functional organization of the brain, which were meaningful in relation to behavioural measures. Overall, these new results expand our vision of language impairment in nvASD and beyond, revealing that, to a large extent, and despite the uniform absence of phrase speech, it is not the existence of the neural infrastructure of language itself, but its functional tuning, which is aberrant in this population. This raises essential questions about this neural infrastructure, as well as informing the need to investigate conditions of minimal language at other levels |
|---|