Role of Executive Functions in the Conversion from Mild Cognitive Impairment to Dementia

Abstract

Background: Recent research pointed to executive dysfunction as a potential early predictor of the progression of mild cognitive impairment (MCI) to dementia in Alzheimer’s clinical syndrome (ACS). Such cognitive impairments account for functional impairments in instrumental activities of daily living (IADL). Objective: The present study analyzes the contributions of executive functions to predict MCI–dementia progression in ACS. Methods: We assessed 145 participants, 51 cognitively unimpaired and 94 MCI. The latter were divided using the traditional, memory-based MCI classification (single domain amnestic, multidomain amnestic, and non-amnestic). Eight tests assessing executive functions were administered at baseline and at 1-year follow-up, together with cognitive screening tools and IADL measures. MCI patients were reclassified based on the outcomes from a K-mean cluster analysis which identified three groups. A simple lineal regression model was used to examine whether the classification based on executive functioning could more accurately predict progression to dementia a year later. Results: Clusters based on executive function deficits explained a significant proportion of the variance linked to MCI–dementia conversion, even after controlling for the severity of MCI at baseline (F(1, 68) = 116.25, p = 0.000, R2 = 0.63). Classical memory-based MCI classification failed to predict such a conversion (F(1, 68) = 5.09, p = 0.955, R2 = 0.07). Switching, categories generation, and planning were the executive functions that best distinguished between MCI converters and stable. Conclusion: MCI with a dysexecutive phenotype significantly predicts conversion to dementia in ACS a year later. Switching abilities and verbal fluency (categories) must be evaluated in MCI patients to assess risk of future dementia.

Higher-Level Executive Functions in Mild Cognitive Impairment: A Systematic Review

“…Thirteen studies used "CLOX-1" or "Clock Drawing Test (CDT)" [51; 78, 79, 84, 85, 89, 95, 100, 102, 108, 110, 111, 112]; two studies used the "Wisconsin Card Sorting Test -Computer Version (WCST -CV)" [76][77]; ten studies used the "Tower of London (TOL)" [23,28,41,49,68,69,86,87,90,91], six studies used "Zoo Map Test" [24,48,59,93,94,106], two studies used "Tower of Hanoi (TOH)" [31,103]; one study used "Raven's Coloured Progressive Matrices (RCPM)" [21]; one study used "Tower Test (D-KEFS)" [66]; one study used "Groton Maze Learning Test" [83]; one study used "Trail Making Test (B-A)" [109]; one study used "Porteus Maze Test" [109]; one study used "Verbal Fluency Test (fruits and animals version)" [109]; one study used "Action Program Test" [48]; and one study used "Key search Test" [48].…”

“…One study [48] performed three tests to assess planning ability and observed a worse performance in MCI in only two of them (Action Program Test and Zoo Map Test). The remaining twenty-one studies reported poor performance in MCI than healthy subjects [28,31,41,49,59,66,68,69,76,77,83,84,85,89,92,93,94,95,108,109].…”

“…Three studies used the "Zoo Map Test" [59,93,94]. Sanders et al, [93] highlighted higher total errors in MCI than healthy controls.…”

“…Sanders et al, [93] highlighted higher total errors in MCI than healthy controls. Junquera et al, [59] analyzed the differences between healthy subjects, aMCI, naMCI, and aMCI multiple domains: aMCI multiple domains showed lower planning than healthy elderly and aMCI single domain, while naMCI subjects showed a poor planning ability than healthy elderly. Sanders et al, [93] observed decreased planning ability in MCI compared to healthy elderly.…”

Ventral Tegmental Area Disconnection Contributes Two Years Early to Correctly Classify Patients Converted to Alzheimer’s Disease: Implications for Treatment

“…Even within the a-MCI classification, some people convert to AD in a short time while other patients remain stable for longer intervals, and providing patients and their carers with informative prognosis is extremely challenging. Previous studies based on different types of biomarkers have identified some genetic [4,5], cognitive [6,7], environmental [8][9][10][11][12], and neuroimaging predictors [13][14][15][16] of conversion to dementia. Degeneration in the cholinergic system, whose neurons are located in the basal forebrain and project to the hippocampus and frontal and cingulate cortices, is associated with memory dysfunctions and behavioural symptoms in patients with AD [17][18][19].…”