Abstract
The capacity for subjective time in humans encompasses the perception of time’s unfolding from moment to moment, as well as the ability to traverse larger temporal expanses of past- and future-oriented thought via mental time travel. Disruption in time perception can result in maladaptive outcomes—from the innocuous lapse in timing that leads to a burnt piece of toast, to the grievous miscalculation that produces a traffic accident—while disruption to mental time travel can impact core functions from planning appointments to making long-term decisions. Mounting evidence suggests that disturbances to both time perception and mental time travel are prominent in dementia syndromes. Given that such disruptions can have severe consequences for independent functioning in everyday life, here we aim to provide a comprehensive exposition of subjective timing dysfunction in dementia, with a view to informing the management of such disturbances. We consider the neurocognitive mechanisms underpinning changes to both time perception and mental time travel across different dementia disorders. Moreover, we explicate the functional implications of altered subjective timing by reference to two key and representative adaptive capacities: prospective memory and intertemporal decision-making. Overall, our review sheds light on the transdiagnostic implications of subjective timing disturbances in dementia and highlights the high variability in performance across clinical syndromes and functional domains.
Highlights
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We have explored how neurodegeneration influences the cognitive profile of time perception and mental time travel, using Alzheimer’s disease (AD) and frontotemporal dementia (FTD) as representative conditions to explicate the mechanisms and consequences of impairment
We hope that this narrative review will serve simultaneously as an overview of basic science questions around neurodegeneration-related changes to these vital human timing capacities, as well as a tool for scientists and clinicians seeking insight into the subjective time disruptions displayed by their patients
Summary
In terms of neural architecture, the capacity for mental time travel relies on the integrity of a core network that overlaps closely with the default mode network of the brain [49]. It has been suggested that the vmPFC initiates the construction of mental scenes by coordinating the assimilation of perceptual details from neocortical sites [55]; activation of anterior midline regions might reflect self-referential processing across subjective time [59]. Lateral parietal activation— in the angular gyrus—has recently been suggested to reflect the multimodal integration of sensory–perceptual details into a contextually rich layer [67], which is overlaid onto the core memory supplied by the hippocampus [68]. Lateral temporal lobe involvement likely provides the requisite semantic knowledge to scaffold the constructed event, into which episodic details can be assimilated [40,69]. From this brief summary, the complexity of the neurocognitive architecture of mental time travel should be evident. We consider how this complexity renders subjective timing vulnerable in the context of neurodegenerative disorders
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