Semantic processing in connected speech at a uniformly early stage of autopsy-confirmed Alzheimer's disease.
OBJECTIVE
The aim of the present study was to quantify the semantic content of connected speech produced by patients at a uniformly early stage of pathologically proven Alzheimer's disease (AD). A secondary aim was to establish whether semantic units were reduced globally, or whether there was a disproportionate reduction of specific classes of information.


METHODS
Discourse samples were obtained from 18 AD patients and 18 matched controls, all pathologically confirmed. Semantic unit identification was scored overall and for four subclasses: subjects, locations, objects, and actions. Idea density and efficiency were calculated.


RESULTS
AD transcripts showed significantly reduced units overall, particularly actions and subjects, as well as reduced efficiency. Total semantic units and a combination of subject-, location-, and object-related units ("noun" units) correlated with the Expression subscore on the Cambridge Cognitive Examination (CAMCOG). Subject related units correlated with the CAMCOG Abstract Thinking scale. Logistic regression analyses confirmed that all measures that were lower in AD than controls were predictive of group membership. An exploratory comparison between units expressed mainly using nouns and those mainly using verbs showed that the latter was the stronger of these two predictors.


CONCLUSIONS
The present study adds a lexico-semantic dimension to the linguistic profile based on discourse analysis in typical AD, recently described by the same authors. 2012, 83(11): 1056-1062). The suggestion of differential importance of verb and noun use in the present study may be related to the reduction in syntactic complexity that was reported, using the same set of discourse samples, in the earlier study.
Stroke and Dementia Research Centre, St George’s, University of London, London, United Kingdom.
Samrah
S
Ahmed
Celeste A
CA
de Jager
Anne-Marie
AM
Haigh
Peter
P
Garrard
D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000150:complications* / Q000175:diagnosis; D001344:Autopsy; D016022:Case-Control Studies; D003072:Cognition Disorders / Q000209:etiology; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D009483:Neuropsychological Tests; D011237:Predictive Value of Tests; D011569:Psychiatric Status Rating Scales; D012660:Semantics; D013064:Speech Disorders / Q000209:etiology*