Objective A new method to classify individuals as “responders” to task-activated cerebral blood flow velocity (CBFv) has recently been developed. This study investigated whether CBFv response rate to task-activation is affected by Alzheimer’s disease (AD) and mild cognitive impairment (MCI). Approach The 95th thresholds for cross correlation peak function and variance ratio were derived from 270 unstimulated, healthy hemispheres, and were used to classify the presence of a response to task activation. Thresholds were applied to five cognitive tasks (attention, verbal fluency, language, visuospatial, memory) in CBFv data from 30 healthy older adults (HC), 35 AD and 22 MCI participants. Cumulative response rate (CRR) was calculated from the sum of responses across five tasks, for both hemispheres. Area under the curve (AUC) was derived from receiver operating characteristic (ROC) curve analysis. Main Results The number of responders differed significantly between tasks (p<0.005) and diagnostic groups (p=0.011). On post-hoc tests there were more responders in the visuospatial (79-90%) compared to fluency (45-80%), language (50-77%), and memory (44-70%) tasks bilaterally, and responders were greater in the HC (70%) compared to AD (41%) and MCI (23%) groups to at least eight out of ten tasks. At an optimal threshold of 7.5 out of 10 responses, the AUC-ROC distinguished HC from AD and MCI with a; sensitivity 66% and specificity 70% (AUC=0.72). Significance Using a novel method to classify responders to cognitive task-activation, HC demonstrated a higher CRR than those with MCI or AD, and a threshold of <8 responses distinguished healthy ageing from dementia.
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