Subjective cognitive decline and cerebral-cognitive reserve in late age

Abstract

Determining the boundaries of the norm and pathology of mental aging is an urgent scientific task. We have formulated a hypothesis about the presence of a transitional period within the cognitive continuum, which represents a borderline between normality and cognitive disorder; such a transitional state is subjective cognitive decline. The outcome of this period depends on the interaction between disease factors and protective factors, one of which is cognitive reserve. The purposeof this review is to systematize the current data in the field of research on subjective cognitive decline and protective factors that prevent its transformation into cognitive disorder. Materials and methods of researchA systematic review of scientific studies was conducted. The search was conducted using PubMed using the keywords: “subjective cognitive decline”, “subjective cognitive impairment”, “cerebral reserve”, “cognitive reserve”, “Alzheimer's disease”. The review includes an analysis of 126 full-text literature sources. The significance of cerebral-cognitive reserve at various stages of AD and the diagnostic boundaries of the concepts “Preclinical conditions of AD” and “Subjective cognitive decline” are analyzed. ConclusionsThe analysis of scientific literature has shown the absence of clear terminological and diagnostic boundaries regarding the definition of the preclinical stage of the disease and compensatory mechanisms that deter the breakthrough of the disease into clinical level. At each stage of Alzheimer's disease there is an interaction between destructive and protective processes. The reserve plays a protective role; it delays the onset of clinical manifestations of Alzheimer's disease. The subjective cognitive decline is a transitional stage from a phenomenological cognitive norm to a clinically manifested pathology. As Alzheimer's disease progresses, there is a transition from the protective role of the reserve to its compensatory function. The defense mechanisms underlying the reserve concept are partially controllable, which makes it possible to build strategies for correcting cellular homeostasis, brain functions, behavioral and cognitive patterns.