Motivation and timing: Clues for modeling the reward system

Abstract

There is growing evidence that a change in reward magnitude or value alters interval timing, indicating that motivation and timing are not independent processes as was previously believed. The present paper reviews several recent studies, as well as presenting some new evidence with further manipulations of reward value during training vs. testing on a peak procedure. The combined results cannot be accounted for by any of the current psychological timing theories. However, in examining the neural circuitry of the reward system, it is not surprising that motivation has an impact on timing because the motivation/valuation system directly interfaces with the timing system. A new approach is proposed for the development of the next generation of timing models, which utilizes knowledge of the neuroanatomy and neurophysiology of the reward system to guide the development of a neurocomputational model of the reward system. The initial foundation along with heuristics for proceeding with developing such a model is unveiled in an attempt to stimulate new theoretical approaches in the field.

Dissociations between interval timing and intertemporal choice following administration of fluoxetine, cocaine, or methamphetamine

“…The relationships among interval timing, associative learning, computational learning, temporal discounting, and decisions about options displaced through time are vastly understudied (Balsam et al, 2010; Galtress et al, 2012a,b; Jozefowiez and Machado, 2013; Jozefowiez et al, 2013; Ray and Bossaerts, 2011). At present, we have scant understanding of how much of the variation in impulsivity is due to differences in the manner in which the subject forms representations of the relevant time intervals and makes decisions based upon a comparison of these time values (cognitive model –Gallistel and Gibbon, 2001) versus the subject learning associations among the representations of these same time intervals and the relevant stimuli and responses – with the strength of these associations changing according to the principals of classical conditioning (associative model – Miller and Witnauer, 2012).…”

“…Time discrimination, especially as it relates to reward delivery, is obviously an important component of intertemporal choice (Galtress et al, 2012a,b; Kirkpatrick, 2013). In order for organisms to make appropriate decisions about options displaced through time, they must have an intact representation of the relevant time intervals.…”

“…The importance of DA projections to the striatum for value-based learning, temporal discounting, and control of impulsivity only underscores the linked nature of interval timing and reward (Asgari et al, 2006; Body et al, 2004, 2005, 2006, 2013; Ho, 1996; Kurti and Matell, 2011; MacDonald et al, 2012; Schultz et al, 1997; Wiener et al, 2008; Willuhn et al, 2010). Surprisingly, the relationship between hyperbolic discounting and timing remains almost wholly unstudied – but see Cui (2011) and Galtress et al (2012a, b) for recent initiatives. Our goal in the present experiment was to develop a novel version of the PI procedure using two different target durations (e.g., bi-peak procedure) in order to allow us to investigate the relationship between intertemporal choice and interval timing in rats (MacDonald and Meck, 2004, 2005, 2006; Matell et al, 2006; Meck et al, 2012a,b).…”

Interval timing under a behavioral microscope: Dissociating motivational and timing processes in fixed-interval performance

“…Such sensitivity is demonstrated by horizontal shifts in the peak-interval gradient and in the distribution of latencies (e.g., Belke & Christie-Fougere, 2006;Galtress & Kirkpatrick, 2009;Galtress et al, 2012;Ludvig et al, 2007;Plowright et al, 2000). Based on these effects, it has been theorized that motivation and timing processes are intimately connected and thus interact to produce overt behavior (Kirkpatrick, 2014).…”

“…Although previous studies have attempted to implement models embodying this notion Harris, 2015;Kirkpatrick, 2002), their implementation in FI schedules remains poorly characterized and has yet to be fully appreciated. Validation and implementation of fluctuation models in the analysis of FI performance would provide clarity on whether or not timing and motivation are related processes (Balcı, 2014;Balcı et al, 2010;Belke & Christie-Fougere, 2006;Galtress & Kirkpatrick, 2010;Galtress, Marshall, & Kirkpatrick, 2012;Kirkpatrick, 2014;Ludvig, Balcı, & Spetch, 2011;Ludvig, Conover, & Shizgal, 2007;Plowright, Church, Behnke, & Silverman, 2000;Sanabria, Thrailkill, & Killeen, 2009). Specifically, if motivation and timing are not dissociable, manipulations of motivation should influence performance in the timing state; if motivation and timing are dissociable, manipulations of motivation should influence performance only in the nontiming state.…”