Functional changes in the cortical semantic network in amnestic mild cognitive impairment
Article [Accepted Manuscript]
Is part of
Neuropsychology ; vol. 32, no. 4, pp. 417-435.Publisher(s)
American Psychological AssociationAuthor(s)
Abstract(s)
Semantic memory impairment has been documented in older individuals with amnestic
Mild cognitive impairment (aMCI), who are at risk of developing Alzheimer’s disease (AD), yet
little is known about the neural basis of this breakdown. The main objective of this study was to
investigate the brain mechanisms associated with semantic performance in patients with aMCI.
Method: A group of aMCI patients and a group of healthy older controls carried out a semantic
categorization task while their brain activity was recorded using magnetoencephalography (MEG).
During the task, participants were shown famous faces and had to determine whether each famous
person matched a given occupation. The main hypotheses were that: (i) semantic processing should
be compromised for aMCI patients, and (ii) these deficits should be associated with cortical
dysfunctions within specific areas of the semantic network. Results: Behavioural results showed
that aMCI participants were significantly slower and less accurate than control participants at the
semantic task, corroborating previous reports. Additionally, relative to controls, a significant
pattern of hyperactivation was found in the aMCI group within specific regions of the semantic
network, including the right anterior temporal lobe and inferior prefrontal cortex. Conclusions:
Abnormal functional activation within key areas of the semantic network suggests that it is
compromised early in the disease process. Moreover, this pattern of increased activation in aMCI
was positively associated with grey matter integrity in specific areas, but was not associated with
any specific pattern of atrophy, suggesting that functional hyperactivation may precede atrophy of
the semantic network in aMCI.
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