An application of value-based decision-making (VBDM) to the study of addiction and recovery from it.

A body of theoretical and empirical work postulates that addiction arises from, and is maintained by, excessive valuation of substances relative to substance-free alternative reinforcers. Existing research, however, has largely focused on final choices that are made (Hardy et al., 2018) or temporally extended behavioural patterns over time (Tucker et al., 2021). Less is therefore known about how valuation processes affect the internal processes of decision-making that occur in the lead up to, and determine, discrete decisions that are made. This PhD aimed to address this important research gap. The first aim was to develop a novel value-based decision-making (VBDM) task that is methodologically appropriate to implement in addiction-related research and that can generate the behavioural data required to parameterise the internal processes of decision-making. The second aim was to empirically test predictions from recent conceptual accounts (Field, Heather, et al., 2020) by exploring whether decision parameters recovered from the VBDM task are sensitive to experimental manipulations of substance value (Chapters 4 and 5) and whether they characterise stable behaviour change and recovery from addiction (Chapters 6 and 7). Chapter 1 presented a narrative review that described in detail predictions derived from Field, Heather, et al. (2020). The sensitivity of VBDM tasks to minor alterations in trial wording was subsequently explored in Chapter 3, with the overall aim being to identify appropriate methodology that can be implemented in future addiction-related research. Chapters 4, 5, 6, and 7 then applied the VBDM task to the field of addiction. Findings demonstrated that the experimental manipulation of alcohol value, such that it was devalued (relative to valued), led to increases in evidence accumulation (EA) rates for soft drinks (Chapter 4) and that recovery from nicotine addiction was characterised by higher tobacco-related response thresholds (Chapter 7). As discussed in Chapter 8, the overall findings from this thesis offer partial support for the predictions derived from Field, Heather, et al. (2020) as the hypothesised alterations in VBDM decision parameters were not consistently observed among Chapters (see Chapters 5 and 6). By capitalising on methodological advances in the measurement of value-based choice, this research provides new insights into the internal processes that precede value-based decisions made about substances and substance-free alternatives, including how these may alter as a person changes their behaviour and recovers from addiction