Regional amyloid‐β is linked to disruptions in connected speech in amnestic mild cognitive impairment

Abstract

AbstractBackgroundSpeech changes in amnesic mild cognitive impairment (aMCI) are potential markers for the early detection of Alzheimer disease (AD). However, few studies investigate the relationship between speech and amyloid‐β burden. The focus of this study was to examine the relationship between the linguistic features and the distribution of amyloid‐β load in aMCI.MethodThis study recruited 25 aMCI patients (52% female, aged 70‐85 years) and 25 healthy elders (44% female, aged 68‐80 years) from the memory clinic of Cardinal Tian Hospital in Taiwan. All participants received [18F] florbetaben PET and standardized cognitive tests. Amyloid‐β load using a standardized uptake value ratio (SUVr) was estimated from 5 cortical regions (parietal, frontal, cingulate, temporal, and occipital). Spontaneous speech was recorded using the picture description task (three Taiwanese culture‐related pictures) and transcribed verbatim. Linguistic features were extracted, including lexical richness (total words, unique words, type‐token‐ratio, lexical density, and frequency), syntactic complexity (mean length of utterance/sentence, ratio of verbs/pronouns/passive sentence), and speech fluency (ratio of long pauses/ fillers).ResultEighteen subjects with high amyloid burden (SUVr > 1.21) progressed (defined as CDR‐SB change≧1) within 1 year. We performed linear regression analyses between linguistic features (dependent variables, separate models) and amyloid‐β load in brain regions. Analyses were adjusted for age and education. The data revealed that a high amyloid‐β burden in the frontal region was associated with fewer unique words, less lexical density, and an increased proportion of long pauses and fillers. Reduced passive sentence, short mean length of utterance and lower scores on episodic memory tests related to increased amyloid‐β burden in the parietal region.ConclusionLexical richness and speech fluency was associated with amyloid‐β burden in the frontal region, indicating that voluntary lexical retrieval may require the additional recruitment of frontal lobe. Less syntactic complexity related to increased amyloid‐β burden in the parietal region. In conclusion, regional amyloid‐β is linked to subtle spontaneous speech deficits in aMCI.