Associations between lesion size, lesion location and aphasia in acute stroke

Abstract

Background: The localization and organization of language has been an ongoing research interest ever since the early findings of Paul Broca. The emergence of neuroimaging the past 20 years has given us new insights on the anatomical and structural organization of the brain. Lesion studies on patients with aphasia can provide knowledge on where and how specific language functions are organized in the brain. Aims: The primary objective of the study was to investigate the relationships between aphasia severity, aphasic symptoms, lesion location and lesion volume in patients with left hemispheric stroke in the acute phase (within one week post-stroke). Using a voxelbased lesion-symptom mapping method (VLSM), we hypothesized that lesions associated with speech comprehension deficits mainly would involve regions within the posterior superior and middle temporal lobe, and lesions associated with speech production deficits would mainly be associated to the inferior frontal areas of the left hemisphere. Methods & procedures: Findings from diffusion-weighted magnetic resonance imaging (DWI-MRI) and patients’ scores from the Norwegian Basic Aphasia Assessment (NBAA) were used to investigate our research questions. We did a whole group analysis of descriptive statistics, lesion localization and lesion volume. We thereafter divided the patients into two groups based on their median scores on the NBAA, one high comprehension group and one low comprehension group. We used VLSM to investigate the associations between the patients’ lesions and the results from the NBAA. Outcomes & Results:Lesion volume was significantly associated with all subtest from the NBAA. Our initial analysis of the whole group showed that difficulties in naming was associated with lesions within the rolandic operculum. We also found that difficulties in repetition was associated with lesions within the rolandic operculum, and in addition, the superior temporal gyrus. In the group of patients with high comprehension scores lesions within Broca’s area, insula, the superior temporal gyrus (STG) and Heschl’s gyrus were found to be associated with difficulties with overall aphasia severity,repetition, naming, and reading out loud from the NBAA. Conclusions: Lesion volume is strongly associated with aphasia severity in the acute stages of stroke. Further, lesions within Broca’s area, the insula, the STG and Heschl’s gyrus were found to be crucial areas in language comprehension and production. This confirms current views that speech and language processes depend on the integrity of the entire network comprising both cortical structures and their interconnected fibre tracts.