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

  • Autores: María José Torres Prioris
  • Directores de la Tesis: Marcelo L. Berthier Torres (dir. tes.), María Guadalupe Dávila Arias (codir. tes.)
  • Lectura: En la Universidad de Málaga ( España ) en 2019
  • Idioma: español
  • Tribunal Calificador de la Tesis: Matti Laine (presid.), Javier García Orza (secret.), Lucia Vaquero Zamora (voc.)
  • Materias:
  • Enlaces
    • Tesis en acceso abierto en: RIUMA
  • Resumen
    • Verbal 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.

      Five studies that are part of this dissertation. Study 1 reviews the neural mechanisms involved in two repetitive verbal behaviors named conduite d’approche and mitigated echolalia. In this regard, 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. 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.

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