On 25 January 2018 Dr Lachlan Tiffen was admitted to the degree of Doctor of Philosophy with his thesis successfully examined and completed with minimal changes required. Lachlan thesis, Individual Difference in Substance Use and Emotion, integrated a wide body of research from Jaak Panksepp’s affective neuroscience model of discrete emotions, the self-medication hypothesis, and personality.
The guiding research question was ‘why do some people transition to harmful substance use while others do not’. The thesis centred on translating substance related knowledge from affective neuroscience, through a discrete emotion systems model (Panksepp, 1998), to clinical psychology nomenclature. The framework came from Self Medication Hypothesis (SMH; Khantzian, 1997) propositions that the foundation of addiction vulnerability was dysfunctional self-regulation manifest in personality, which had psychopharmacological specificity.
The research program contained three studies, each exploring one of three aspects of emotion enquiry; subjective experience, behaviour and physiology (Mauss, Levenson, McCarter, Wilhelm & Gross, 2005) in relation to substance involvement risk. Study 1 examined subjective experience of personality, temperament, emotional regulation and parenting. Study 1 identified emotion related constructs that significantly correlated to and regressions models that could predict significant variability in participants’ involvement with various substances. Study 2 piloted a behavioural categorisation of International Affective Picture System (IAPS; Lang, Bradley & Cuthbert, 2008) stimuli. Study 2 produced image sets representing one neutral and seven discrete emotions providing preliminary support for dual, discrete and dimensional, models of emotion. Study 3 used these image sets to elicit electrodermal activity in a pilot experiment exploring links between participant substance involvement and psychophysiological response to emotional stimuli. Study 3 indicated some differentiation of electrodermal activity components between various substance types, however, results were tentative.
The research program evidence recommends separate analysis by gender and specific substances in future addiction research. It also provided evidence supporting reconceptualised SMH propositions. Although the translation of affective neuroscience through personality required refinement, other individual difference constructs that related to substance use offer interesting avenues for further investigation. This was the real legacy of the thesis; providing unique insights built on diverse, but interrelated foundations to act as guidance for future research into this most insidious and elusive problem for society.
Congratulations Dr Tiffen!
(Primary Supervisor Miles Bore, Co-Supervisor Frances Martin)