hide
Free keywords:
lesion-deficit analysis; VLSM; chronic aphasia; aphasia syndromes; linguistic modalities
Abstract:
One way to investigate the neuronal underpinnings of language competence is to correlate patholinguistic profiles of aphasic
patients to corresponding lesion sites. Constituting the beginnings of aphasiology and neurolinguistics over a century ago, this
approach has been revived and refined in the past decade by statistical approaches mapping continuous variables (providing
metrics that are not simply categorical) on voxel-wise lesion information (voxel-based lesion–symptom mapping). Here we
investigate whether and how voxel-based lesion–symptom mapping allows us to delineate specific lesion patterns for differ-
entially fine-grained clinical classifications. The latter encompass ‘classical’ syndrome-based approaches (e.g. Broca’s aphasia),
more symptom-oriented descriptions (e.g. agrammatism) and further refinement to linguistic sub-functions (e.g. lexico-semantic
deficits for inanimate versus animate items). From a large database of patients treated for aphasia of different aetiologies
(
n=
1167) a carefully selected group of 102 first ever ischaemic stroke patients with chronic aphasia (
;
12 months) were
included in a VLSM analysis. Specifically, we investigated how performance in the Aachen Aphasia Test—the standard clinical
test battery for chronic aphasia in German—relates to distinct brain lesions. The Aachen Aphasia Test evaluates aphasia on
different levels: a non-parametric discriminant procedure yields probabilities for the allocation to one of the four ‘standard’
syndromes (Broca, Wernicke, global and amnestic aphasia), whereas standardized subtests target linguistic modalities (e.g. repe-
tition), or even more specific symptoms (e.g. phoneme repetition). Because some subtests of the Aachen Aphasia Test (e.g. for
the linguistic level of lexico-semantics) rely on rather coarse and heterogeneous test items we complemented the analysis with a
number of more detailed clinically used tests in selected mostly mildly affected subgroups of patients. Our results indicate that:
(i) Aachen Aphasia Test-based syndrome allocation allows for an unexpectedly concise differentiation between ‘Broca’s’ and
‘Wernicke’s’ aphasia corresponding to non-overlapping anterior and posterior lesion sites; whereas (ii) analyses for modalities
and specific symptoms yielded more circumscribed but partially overlapping lesion foci, often cutting across the above syndrome
territories; and (iii) especially for lexico-semantic capacities more specialized clinical test-batteries are required to delineate
precise lesion patterns at this linguistic level. In sum this is the first report on a successful lesion-delineation of syndrome-based
aphasia classification highlighting the relevance of vascular distribution for the syndrome level while confirming and extending a
number of more linguistically motivated differentiations, based on clinically used tests. We consider such a comprehensive view
reaching from the syndrome to a fine-grained symptom-oriented assessment mandatory to converge neurolinguistic, patholin-
guistic and clinical-therapeutic knowledge on language-competence and impairment.
