Investigating the semantic control network and its structural decline in mild cognitive impairment and mild dementia
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2019-07-01
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en
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Abstract
Individuals with mild cognitive impairment (MCI) and mild dementia show pri-
marily episodic memory de cits, whereas some present with additional semantic
memory and executive dysfunction. Recently, we have come to better understand
control processes operating on semantic memory access which tailor automatic
spreading activation between highly related concepts to suit the current goal. Most
evidence on the brain network for semantic control comes from stroke-induced
lesions to perisylvian language areas, which led to a cortico-centric neuroanatomi-
cal model of semantic control. To investigate semantic control in MCI and mild
dementia as well as the role of the hippocampus and ventral language pathways
in the semantic control network, 9 individuals with MCI/mild dementia and 21
healthily aging controls performed a word-picture veri cation task and underwent
(di usion-weighted) magnetic resonance imaging. In the word-picture veri cation
task, participants indicated whether a word matched a subsequently presented
picture as quickly and accurately as possible. Congruent (\airplane" { picture:
airplane) and incongruent word-picture pairs were presented, the latter being
semantically related (\pilot" { picture: airplane) or unrelated (\knife" { picture:
airplane). In the related condition, more semantic control is needed. Both groups
showed a semantic interference e ect (increased RTs and errors in the related
vs. unrelated condition), whereas this e ect was disproportionally large in the
MCI/mild-dementia group with some individuals making errors in up to 58% of
the related word-picture pairs, suggesting semantic control dysfunction in some
cases of MCI and mild dementia. The semantic interference e ect was unrelated to
hippocampal volume and integrity of the inferior longitudinal fasciculus (ILF) but
related to white matter integrity of the inferior fronto-occipital fasciculus (IFOF)
and uncinate fasciculus (UF) in the healthily aging control group. However, this
relationship was in an unpredicted direction: those individuals with preserved
integrity in these tracts showed a larger semantic interference e ect. We propose
that higher white matter integrity might lead to representations with higher
delity with respect to semantic features, leading to enhanced competition in the
related condition. This hypothesis remains to be con rmed in future research.
The semantic interference e ect was not related to other neuropsychological test
scores in MCI/mild dementia assessed with a neuropsychological test battery, nor
to performance in a
anker task, rendering the word-picture veri cation task a
novel tool to understand semantic control de cits in the precursor of dementia.
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Faculteit der Sociale Wetenschappen