Executive functions in patients with Alzheimer's disease, type 2 diabetes mellitus patients and cognitively healthy older adults

Objectives: The present study investigated whether the performance on executive function tasks of patients with type 2 diabetes mellitus (T2DM) is as impaired as that of Alzheimer's disease (AD) patients and to compare their performance with that of a group of cognitively healthy older adults. We also investigated whether glycosylated hemoglobin levels (HbA1c, a measure of glucose regulation) are related to performance on executive control tasks. Methods: Three groups of participants (AD, T2DM, and healthy older adults) completed medical and psychological evaluations and performed a series of computerized tasks, including processing speed (simple and choice reaction time) tasks, verbal and visuospatial working memory (WM) updating (n-back) tasks, and the Wisconsin Card Sorting Test (WCST), to assess processing speed and executive functioning. Results: As expected, the results showed that AD patients performed significantly worse than the healthy older adult group in all tasks. Executive functions deteriorated in the two groups of patients but more in the AD group. The T2DM group differed from healthy older controls but not from AD patients in the percentage of perseverations and the percentage of perseverative errors (WCST). Conclusions: These findings revealed working memory (updating and maintenance) and executive control declines in the T2DM compared to healthy older controls but smaller than that suffered by the AD patients. The impairment of executive processing of T2DM patients despite the glycosylated hemoglobin control suggests that these patients are at risk of developing AD. (C) 2016 Elsevier Inc. All rights reserved.