The Network Structure of Cognitive Impairment: From Subjective Cognitive Decline to Alzheimer's Disease

Abstract

It was proposed that a reorganization of the relationships between cognitive functions occurs in dementia, a vision that surpasses the idea of a mere decline of specific domains. The complexity of cognitive structure, as assessed by neuropsychological tests, can be captured by Exploratory Graph Analysis (EGA).EGA was applied to the neuropsychological assessment of people (humans) with Subjective Cognitive Decline (SCD), Mild Cognitive Impairment (MCI), and Alzheimer’s Disease (AD) (Total N=638). Both sexes were included.In AD, memory scores detach from the other cognitive functions and memory subdomains reduce their reciprocal relation. SCD showed a pattern of segregated neuropsychological domains, and MCI showed a noisy and less stable pattern.Results suggest that AD drives a reorganization of cognitive functions toward a less fractionated architecture compared to preclinical conditions. Cognitive functions show a reorganization that goes beyond the performance decline. Results also have clinical implications in test interpretations and usage.Significance StatementThe manuscript proposes an innovative vision for the study of the complex reorganization of cognition in people with dementia.We applied a sophisticated, reliable, cutting-edge statistical method (i.e., Exploratory Graph Analysis - EGA) to the neuropsychological evaluations of 638 patients classified into Subjective Cognitive Decline (N=155), Mild Cognitive Impairment (N=242) and Alzheimer’s Disease (N=241).Patients with Alzheimer’s Disease showed a simplified architecture as compared to subjects with Subjective Cognitive Decline. The MCI group resulted in sharing specific aspects with the SCD and others with the AD.Recognizing the complexity of the cognitive organization is fundamental for properly understanding cognitive impairment and stimulate the discussion about the interpretation of neuropsychological profiles from a more systemic point of view.