Deficits in Spontaneous Cognition as an Early Marker of Alzheimer’s Disease
In the absence of pharmacological cure, finding the most sensitive early cognitive markers of Alzheimer’s disease (AD) is becoming increasingly important. In this paper, we review evidence showing that brain mechanisms of spontaneous, but stimulus-dependent, cognition overlap with key hubs of the default mode network (DMN), which become compromised by amyloid pathology years before the clinical symptoms of AD. This leads to the formulation of a novel hypothesis, which predicts that spontaneous, but stimulus-dependent conscious retrieval processes, generally intact in healthy ageing, will be particularly compromised in people at the earliest stages of AD. Initial evidence for this hypothesis is presented across diverse experimental paradigms (e.g., prospective memory, mind-wandering), and new avenues for research in this area are outlined.