Abstract
Categorical verbal fluency tests (CFT) are commonly used to assess the integrity of semantic memory in individuals with brain damage. Persons with Dementia of the Alzheimer’s Type display a reduced output on CFT, and a similar pattern has been reported in persons with amnesic Mild Cognitive Impairment (aMCI). The aims of the present study were to assess whether the semantic relations between lexical entries produced on a categorical fluency test were different between healthy persons and those with aMCI, and whether this difference was more pronounced in individuals who converted to dementia during a 3-year follow-up period.MethodsWe recruited 34 individuals with aMCI and 29 matched healthy persons. During the follow-up period, 10 individuals converted to Dementia (aMCI-conv). Two measures assessing semantic relations between consecutively produced word pairs (Path length and Extended Gloss Overlap) were obtained from the Wordnet database.ResultsThe number of word pairs analyzed among the healthy participants (HP) and persons with aMCI were 498 (birds: 262; pieces of furniture: 236) and 395 (birds: 174; pieces of furniture: 221), respectively. Path length was lower in aMCI-conv than in HP (p = 0.035), but no differences were found between stable aMCI and HP, and between aMCI-stable and aMCI-conv. The ANOVA for lexical entries belonging to the “birds” category showed a significant effect of group (F = 5.630; p = 0.004); the post hoc analysis showed a significant difference between HP and aMCI-conv (p = 0.003). The “pieces of furniture” category was significantly affected by group (F = 4.107; p = 0.017); the post hoc test showed significant differences between aMCI-conv and healthy individuals (p = 0.049), and between aMCI-conv and stable aMCI (p = 0.001).DiscussionIndividuals with aMCI who convert to dementia show a deterioration in the semantic relations between lexical entries, produced on a CFT. This phenomenon may be interpreted as a marker of a very early disruption of semantic memory.
Highlights
Verbal fluency tasks are traditionally used in the assessment of patients with dementia, with Alzheimer’s disease
The aims of the present study were: (a) to compare measures of semantic relations obtained from a Categorical verbal fluency tests (CFT) between healthy participants (HP) and individuals with an amnesic form of Mild Cognitive impairment (MCI), in particular in patients who progressed to dementia, and (b) to verify the possibility of identifying word clusters using measures of semantic relations obtained from Wordnet, and to compare the number of such clusters observed in HP and individuals with aMCI
The two groups did not differ in terms of age (|t| = 0.591; p = 0.557) and education (|t| = 0.368; p = 0.715) but, as expected, the mean score obtained by individuals with aMCI on MMSE was significantly lower than that obtained by HP (|t| = 7.386; p < 0.001)
Summary
Verbal fluency tasks are traditionally used in the assessment of patients with dementia, with Alzheimer’s disease. The most common versions of verbal fluency tests consist of the production of words in a limited amount of time starting with a given letter (phonological verbal fluency tasks) or within a semantic category (categorical verbal fluency tasks) (Strauss et al, 2006; Lezak, 2012). Both tasks produce the same kind of score (the number of words per unit of time), but are based on quite different mechanisms. We have previously reported that individuals with MCI display an increased level of typicality of words produced in a CFT test, and that individuals producing highly typical words are more prone to developing dementia during the follow-up period (Vita et al, 2014)
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