Cognitive ageing is a highly complex and individualised process influenced by
underlying neurobiology and lifestyle factors, where the latter also influences
the former. Currently, the literature lacks clarity on factors influencing healthy
cognitive ageing, particularly concerning word-finding difficulties, which are a
primary challenge associated with ageing. This thesis aimed to investigate the
neurobiological and lifestyle contributions to word-finding in healthy ageing.

Chapter 2 reviewed the revisited Scaffolding Theory of Aging and Cognition
and Cognitive Reserve (CR) theory. Chapters 3 and 4 investigated the relationship between CR and word-finding across the lifespan and in Parkinson’s disease (PD). The findings revealed that education, occupation, and current lifestyle choices support word-finding in middle-aged but not in older adults or PD. Contrary to previous literature, CR did not have a positive impact in older adults or PD but did mitigate word-finding difficulties in middle age.

Chapter 4 investigated the link between action language and motor ability in PD.
We demonstrated a relationship between motor and word-finding ability in both
individuals with and without PD, suggesting a potential shared neuronal circuit.
Chapters 5 and 6 aimed to investigate the role of neural coherence in word-finding among younger and older adults using electroencephalography. Chapter 5 revealed a link between word-finding difficulties and functional brain networks, especially in the delta band. Finally, Chapter 6 demonstrated greater frontocentral phase coherence in older adults during action word comprehension, with greater frontocentral phase coherence being related to faster action word processing in both younger and older adults.

Overall, this thesis provided evidence for lifestyle contributions to word-finding
abilities in middle-aged but not in older adults. The findings also emphasised the significance of neurobiological factors, especially phase coherence, in maintaining word-finding abilities across the lifespan. The final chapter of this thesis will discuss implications, limitations, and suggestions for future research.