Deficits in Spontaneous Cognition as an Early Marker of Alzheimer’s Disease

Abstract

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. Glossary Alzheimer's disease (AD): A progressive and irreversible neurodegenerative disease, affecting primarily older population, which is characterized by significant impairments in episodic memory and other cognitive abilities, leading to a loss of functional independence. Default mode network (DMN): A widely distributed functional network along the brain's midline that is important for self-referential information processing. It is characterized by high activations when people are engaged in processing internal thoughts and deactivations when individuals perform attentionally demanding experimental tasks. Intrusive memories: Memories that repeatedly intrude upon consciousness, often against one's will, are hard to control, and may disrupt one's ongoing activities. Although they can be sometimes about positive events, they are predominantly negative and disturbing, and constitute a core symptom of the Post-Traumatic Stress Disorder. Involuntary autobiographical memories: Memories of past events that pop into mind without any deliberate intention to recall anything, often when a person is engaged in some mundane everyday activities (e.g., driving, brushing teeth) and in response to easily identifiable triggers. They may refer to positive, negative, or completely neutral events such as remembering one's first romantic kiss, failing an exam, or buying food in a supermarket. Involuntary (or spontaneous) future thinking: Involves mental representations about the future, which may come to mind unintended (unexpectedly) while being engaged in other habitual activities, and in response to irrelevant stimuli in the environment. They can refer to planned events (e.g., buying a train ticket tomorrow), plausible future events (e.g., a trip to Japan) or hypothetical scenarios and wishful thinking (e.g., winning the lottery). Involuntary semantic memories: Fragments of semantic knowledge (e.g., someone's name, image of Big Ben, or a familiar song) that pop into mind unexpectedly, without any 5 accompanying contextual information (e.g., memory of when we last heard the song). Research on mind-pops has focussed mainly on 'earworms'-when a song or a tune gets stuck in one's mind and repeatedl...

The effects of aging and an episodic specificity induction on spontaneous task-unrelated thought

“…A recent meta-analysis found a reduced frequency of spontaneous thoughts in older compared to younger adults but identified methodological moderators suggesting that this effect may be partially due to the experimental paradigms most commonly used [ 8 ]. This is in line with a recent review of the effects of healthy and pathological aging on spontaneous thoughts that suggests that the decrease in spontaneous thoughts in healthy aging is absent when the experimental conditions include meaningful cues that activate the spontaneous retrieval route [ 9 ]. The impact of aging on qualitative aspects of spontaneous thoughts, in particular episodic specificity, has been much less explored.…”

Out of the blue: understanding abrupt and wayward transitions in thought using probability and predictive processing

“…Their development and wide-spread adoption could, however, be a crucial stepping stone towards reaching a place of clearer understanding about the origins of spontaneous thoughts. Given the enormous role that spontaneous thought plays in individual mental health outcomes [5,60] and societal wellbeing more broadly, reaching that place is of great importance.…”

A closer look at the timecourse of mind wandering: Pupillary responses and behaviour

“…Participants completed a modified version of the computer-based vigilance task with cue-words, which was originally developed by Schlagman and Kvavilashvili [22]. As detailed in Kvavilashvili et al [21] this paradigm has been extensively used to investigate different types of spontaneous cognitions, including involuntary autobiographical memories [38][39][40][41][42][43][44][45] involuntary thoughts about the past and future [46][47][48], and spontaneous mind wandering [12,13,19,20]. The task used in the present study consisted of 1020 trials, presented in fixed order, each lasting 2 s. A white fixation point (0.2 deg diameter) was always shown at screen center.…”