Abstract
The pursuit of relating the location of neural damage to the pattern of acquired language and general cognitive deficits post-stroke stems back to the 19th century behavioural neurology. While spatial specificity has improved dramatically over time, from the large areas of damage specified by post-mortem investigation to the millimetre precision of modern MRI, there is an underlying issue that is rarely addressed, which relates to the fact that damage to a given area of the brain is not random but constrained by the brain’s vasculature. Accordingly, the aim of this study was to uncover the statistical structure underlying the lesion profile in chronic aphasia post-stroke. By applying varimax-rotated principal component analysis to the lesions of 70 patients with chronic post-stroke aphasia, we identified 17 interpretable clusters, largely reflecting the vascular supply of middle cerebral artery sub-branches and other sources of individual variation in vascular supply as shown in classical angiography studies. This vascular parcellation produced smaller displacement error in simulated lesion–symptom analysis compared with individual voxels and Brodmann regions. A second principal component analysis of the patients’ detailed neuropsychological data revealed a four-factor solution reflecting phonological, semantic, executive-demand and speech fluency abilities. As a preliminary exploration, stepwise regression was used to relate behavioural factor scores to the lesion principal components. Phonological ability was related to two components, which covered the posterior temporal region including the posterior segment of the arcuate fasciculus, and the inferior frontal gyrus. Three components were linked to semantic ability and were located in the white matter underlying the anterior temporal lobe, the supramarginal gyrus and angular gyrus. Executive-demand related to two components covering the dorsal edge of the middle cerebral artery territory, while speech fluency was linked to two components that were located in the middle frontal gyrus, precentral gyrus and subcortical regions (putamen and thalamus). Future studies can explore in formal terms the utility of these principal component analysis-derived lesion components for relating post-stroke lesions and symptoms.
Highlights
Investigators used post mortem dissections to provide insight into which brain areas were related to different behaviours/functions
The maximum number of participants who had a lesion in any one voxel was 56 (MNI co-ordinates -38, -9, 24; anatomy of peak: anterior segment of arcuate fasciculus)
We describe the location of each cluster in relation to anatomy using the HarvardOxford and natbrainlab atlases
Summary
Investigators used post mortem dissections to provide insight into which brain areas were related to different behaviours/functions. A subsequent development allowed the general area of damage to be explored, in vivo: one consequence of the tragic World Wars was that, for soldiers who survived missile head injuries, the trajectory of the missile could be determined (by entry/exit points). This allowed researchers to infer the location of damage and determine the effects on behaviour in greater detail This engineering technology has been combined with advances in analytical techniques (Bates et al, 2003; Tyler, Marslen-Wilson, & Stamatakis, 2005) resulting in increasingly sophisticated, detailed lesion-symptom mapping (though subject to significant challenges: cf. Mah et al, 2014) and the evaluation of lesion-based prediction models
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