Anderson, Storm Harvey; (2025) Post stroke anomia: Co-occurring impairments, Lesion sites, and the Anomaly of Pure Anomia. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Word finding difficulties (anomia) are widely reported as the most common and pervasive aphasic impairment after stroke. The overarching goal of this thesis was to better understand the cognitive and physiological causes of post-stroke anomia, using behavioural data and T1 MRI neuroimaging data from the PLORAS database. Experiment 1 found that, contrary to expectation, (i) the incidence of anomia was not greater than the incidence of comprehension impairments; (ii) severe anomia strongly predicted co-occurring repetition and/or comprehension impairments, (iii) the absence of anomia reliably predicted that repetition and comprehension impairments will be mild, (iv) mild anomia was inconsistently associated with repetition and comprehension impairments because a subset of patients with mild anomia have selective (i.e. pure) anomia. Experiment 2 focused on patients with pure anomia, comparing their naming accuracy and errors to 299 neurotypical controls. Two subtypes of pure anomia were identified with impairments in: transitioning from semantic-to-phonological processing, and post-semantic phonological processing. Critically, over half of the cohort could not be subtyped because their naming was indistinguishable from the controls. Experiment 3 built on Experiment 2 by analysing wider language abilities, patient-reported speech measures and MRI brain imaging. This identified (i) three more subtypes of pure anomia including: impaired speech initiation, low pre-stroke naming abilities, and unclear aetiology; (ii) that pure anomia typically emerges from more generalised aphasia and (iii) heterogeneity in the associated lesion sites. Experiment 4 identified three neural signatures for pure anomia which were subsequently validated in their association with anomia in a larger sample of patients with non-pure anomia or no anomia. In addition, Experiment 4 identified lesions that were either rarely observed (n=3) or rarely associated with anomia (n=1). Collectively, these findings have novel implications for understanding, predicting and treating anomia recovery after stroke, and offer methodological procedures that can be used to study other language functions.

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