Semantic inhibition and dementia severity in Alzheimer's disease

Background: Semantic inhibition is often found to be impaired in Alzheimer's disease (AD). The sentence completion task (Hayling test) was used to investigate whether it would be useful for differentiating mild AD from moderate AD. Method: Latency responses and error scores in the automatic and inhibition parts of the test were registered in these two groups of patients and in a group of healthy older participants. The types of errors were also analysed. Group differences were analysed by ANOVA. In addition, relationships with other neuropsychological tests were reported. Results: Participants with moderate AD performed worse than controls in both the automatic and inhibition sections, whereas participants with mild AD exhibited impaired performance in the inhibition part, but not in the automatic part. Differences between the groups with mild and moderate AD appeared only in the error scores in the inhibition part, specifically type 3 errors. Error scores in the inhibition part correlated with performance in verbal fluency and working memory tests. Conclusions: The Hayling task may be a useful tool for investigating control of inhibition in different stages of AD because different patterns of responses were observed.