Lesion analysis of language production deficits in aphasia

Abstract

Background: Three aspects of language production are impaired to different degrees in individuals with post-stroke aphasia: ability to repeat words and nonwords, name pictures, and produce sentences. These impairments often persist into the chronic stages, and the neuroanatomical distribution of lesions associated with chronicity of each of these impairments is incompletely understood.

Aims: The primary objective of this study was to investigate the lesion correlates of picture naming, sentence production, and nonword repetition deficits in the same participant group because most prior lesion studies have mapped single language impairments. The broader goal of this study was to investigate the extent and degree of overlap and uniqueness among lesions resulting in these deficits in order to advance the current understanding of functional subdivision of neuroanatomical regions involved in language production.

Methods & Procedures: In this study, lesion-symptom mapping was used to determine if specific cortical regions are associated with nonword repetition, picture naming, and sentence production scores. Structural brain images and behavioural performance of 31 individuals with post-stroke left hemisphere lesions and a diagnosis of aphasia were used in the lesion analysis.

Outcomes & Results: Each impairment was associated with mostly unique, but a few shared lesions. Overall, sentence and repetition deficits were associated with left anterior perisylvian lesions, including the pars opercularis and triangularis of the inferior frontal lobe, anterior superior temporal gyrus, anterior portions of the supramarginal gyrus, the putamen, and anterior portions of the insula. In contrast, impaired picture naming was associated with posterior perisylvian lesions including major portions of the inferior parietal lobe and middle temporal gyrus. The distribution of lesions in the insula was consistent with this antero-posterior perisylvian gradient. Significant voxels in the posterior planum temporale were associated with a combination of all three deficits.

Conclusions: These findings emphasise the participation of each perisylvian region in multiple linguistic functions, suggesting a many(functions)-to-many(networks) framework while also identifying functional subdivisions within each region.

Keywords:

• Aphasia
• Lesion analysis
• Sentence production
• Repetition
• Inferior frontal gyrus
• Superior temporal gyrus
• Insula
• Planum temporale.

Notes

¹ We use the term processing to generally refer to input processes, while processes involved in computing language output are referred to as production or encoding.

² The overall cluster size for SMG was small relative to other lesion clusters, and therefore one cannot rule out the possibility of this being a false positive finding, given that correction for multiple comparisons was not used in this study.

³ The PT is a triangular region in the Sylvian fissure, bounded anteriorly by the Heschls gyri and continuing posteriorly into the parieto-temporal operculum and SMG (Griffiths & Warren, 2002; Shapleske, Rossel, Woodruff, & David, 1999). The PT is considered by some researchers to be part of Wernicke’s area (Binder, Frost, Hammeke, Rao, & Cox, 1996; Wise et al., 2001).

⁴ For example, the insula is more susceptible to middle cerebral artery strokes (Ay, Arsava, Koroshetz, & Sorensen, 2008). But this was not the case in our patient sample (see Table 2).