A Meta-Analysis of Inhibitory-Control Deficits in Patients Diagnosed With Alzheimer's Dementia

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Objective: The authors conducted meta-analyses to determine the magnitude of performance impairments in patients diagnosed with Alzheimer’s dementia (AD) compared with healthy aging (HA) controls on eight tasks commonly used to measure inhibitory control. Method: Response time (RT) and error rates from a total of 64 studies were analyzed with random-effects models (overall effects) and mixed-effects models (moderator analyses). Results: Large differences between AD patients and HA controls emerged in the basic inhibition conditions of many of the tasks with AD patients often performing slower, overall d = 1.17, 95% CI [0.88–1.45], and making more errors, d = 0.83 [0.63–1.03]. However, comparably large differences were also present in performance on many of the baseline control-conditions, d = 1.01 [0.83–1.19] for RTs and d = 0.44 [0.19–0.69] for error rates. A standardized derived inhibition score (i.e., control-condition score - inhibition-condition score) suggested no significant mean group difference for RTs, d = −0.07 [−0.22–0.08], and only a small difference for errors, d = 0.24 [−0.12–0.60]. Effects systematically varied across tasks and with AD severity. Conclusions: Although the error rate results suggest a specific deterioration of inhibitory-control abilities in AD, further processes beyond inhibitory control (e.g., a general reduction in processing speed and other, task-specific attentional processes) appear to contribute to AD patients’ performance deficits observed on a variety of inhibitory-control tasks. Nonetheless, the inhibition conditions of many of these tasks well discriminate between AD patients and HA controls.

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