Neurocognitive mechanisms of delay discounting

Delay discounting has been defined as a dimension of impulsivity, and specifically, as the degree to which future events fail to influence current decisions. Humans and animals typically prefer more immediate rewards over delayed rewards; the trade-off is termed ‘intertemporal choice’. This thesis investigates specific mechanisms of hyperbolic delay discounting. This trait is known to be associated with detrimental life outcomes, of which some have argued it represents a transdiagnostic measure.

Addressing the challenge of the “black box” of delay discounting (Rubinstein, 2003), there was some support for a valuation-based process (J. Peters & Büchel, 2011) based on aberrant time estimation ability as reported in Chapters 2 and 3. These findings could explain differences in delay discounting to some extent. However, based on effect size, the neurophysiology of decision making (conflict monitoring) appears to be far more critical in delay discounting decisions, as seen in Chapter 5. While counterintuitive, this suggests that a more significant part of individual differences in delay discounting behavior can be found post-decision rather than pre-decision. Such a process is instrumental for learning and adaptation (Yeung & Summerfield, 2012), which was explicitly reflected in the characteristics of low impulsive individuals after immediate reward choices.

This thesis may contribute to a better understanding of impulsive behavior in general and tobacco smoking addiction specifically. Our studies may hopefully lead to better treatment options to counter the negative life consequences of hyperbolic discounting. These may include behavioral (aimed at time estimation and decreasing impatience), neurophysiological (e.g., through theta burst stimulation), and ultimately psychopharmacological interventions, insofar as the findings of this thesis may inspire further research into the role of specific neurotransmitters, which may include norepinephrine as well as dopamine.