Abstract
Subjective Cognitive Decline (SCD) is possibly one of the earliest detectable signs of dementia, but we do not know which mental processes lead to elevated concern. In this narrative review, we will summarize the previous literature on the biomarkers and functional neuroanatomy of SCD. In order to extend upon the prevailing theory of SCD, compensatory hyperactivation, we will introduce a new model: the breakdown of homeostasis in the prediction error minimization system. A cognitive prediction error is a discrepancy between an implicit cognitive prediction and the corresponding outcome. Experiencing frequent prediction errors may be a primary source of elevated subjective concern. Our homeostasis breakdown model provides an explanation for the progression from both normal cognition to SCD and from SCD to advanced dementia stages.
Highlights
Subjective Cognitive Decline (SCD) refers to an individual’s perception that their cognitive performance has declined, despite having no significant objective cognitive impairment
We will provide a narrative review of the current literature for biomarkers, and the functional neuroanatomy associated with SCD
We have proposed a homeostatic prediction error model for understanding how the progression of neural system dysfunction can manifest as SCD. functional magnetic resonance imaging (fMRI) studies can help in validating that increases in error prediction, and conflict monitoring is central to the subjective perception of cognitive impairment
Summary
Subjective Cognitive Decline (SCD) refers to an individual’s perception that their cognitive performance has declined, despite having no significant objective cognitive impairment. Vogel and colleagues [7] found that amyloid status predicted future cognitive decline (on average, four years) among individuals with SCD. Brain atrophy and white matter hyperintensities have been reported in SCD, as seen in the early pre-clinical stages of AD progression. Whole-brain analysis by Verfaillie and colleagues [17] suggested that a steeper decline in cognition was associated with a thinner cortex of the temporal region and the frontal and occipital cortices in SCD. Increased amounts of white matter hyperintensities in widespread regions have been reported in SCD [18,19] These studies provide support for the idea that SCD may be an early transitional stage prior to the onset of dementia (i.e., MCI and AD), especially as seen with the perturbations in the memory systems
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