Temporal cognition: subjective time and its connection with memory in frontotemporal dementia

Abstract

Although ubiquitous and central to everyday life, how humans apprehend, experience, and mentally navigate time remains poorly understood. This thesis aimed to explore subjective time in healthy ageing, as well as pathological ageing, frontotemporal dementia (FTD), namely, behavioural-variant frontotemporal dementia (bvFTD), semantic dementia (SD) and progressive nonfluent aphasia (PNFA), to determine profiles and neural correlates of subjective time in older adults and dementia syndromes, and to reveal how subjective time alterations potentially relate to everyday memory impairments across syndromes.

Employing multiple time perception tasks, Chapters 3 and 4 reveal compromised subjective time in healthy ageing and bvFTD but intact performance in language variants of FTD (a combination of SD and PNFA). Time perception in FTD relates to grey matter density decrease in predominantly frontoinsular brain regions and the basal ganglia (i.e., putamen and caudate), as well as decreased functional connectivity of the frontoparietal network and salience network. Furthermore, Chapter 5 demonstrates past- and future-oriented memory disturbances in both Alzheimer’s disease (AD) and bvFTD, rather than SD and PNFA, with neuroimaging analyses suggesting the role of the orbitofrontal cortex in everyday memory across past and future contexts in dementia. Taken together, these findings provide novel insights on the complex nature of time perception across healthy ageing and pathological ageing, with the potential to inform the characterisation and management of FTD.