Impulsivity v1

The ability to respond quickly in a flexible and changing environment is advantageous in many settings (Dalley & Robbins, 2017). However, if such impulsive behaviours are chronically expressed they become maladaptive and salient to a number of brain disorders and damaging behaviours such as smoking and binge eating. Emerging evidence suggests that chronotype, which is an individual’s preference for waking and sleeping with morning types preferring to rise and go to bed early and evening-types preferring to go to bed late and rise late, is related to impulsivity. For example, Kang and colleagues (2015) observed a significant association between subjective trait impulsivity (as measured by the Barratt Impulsivity Scale (BIS 11, Patton, Stanford, & Barratt, 1995) and chronotype in healthy young adults (Kang et al., 2015). Similarly, Hwang et al., (2016) reported that morningness-eveningness was related to both impulsivity and anger (Hwang, Kang, Gwak, Park, & Lee, 2016). Limited data, therefore, point to a link between eveningness and impulsivity (Hwang et al., 2016; Kang et al., 2015). However, although self-report questionnaires are often structured according to different subtypes of impulsivity (e.g. the BIS includes measures of attentional, motor and non-planning impulsivity) impulsivity if often condensed to a single metric (Hwang et al., 2016; Kang et al., 2015). In addition, few studies have supplemented subjective outcomes with objective laboratory-based measures and related these to chronotype. One study, Berdynaj et al., (2016) found no difference between early/intermediate chronotypes and late chronotypes using a computer-based delay discounting task (Berdynaj et al., 2016). However, the modest sample size (n = 86) and the collapsing of early and intermediate chronotypes into a single group limits the interpretation these data (Berdynaj et al., 2016). The aim of the current study, therefore, is to extend previous findings (Berdynaj et al., 2016; Hwang et al., 2016; Kang et al., 2015) to include both subjective and objective metrics of impulsivity. Decisional impulsivity can be objectively measured using: 1) Delay discounting, which is the preference for small, immediate rewards versus larger but delayed rewards. An impulsive choice in a temporal discounting task is reflected as a preference for smaller, more-immediate outcomes and follows a delay-dependent hyperbolic function. And 2) The jumping to conclusions task (as measure of reflection impulsivity) which assays the tendency to make rapid decisions without adequate accumulation and consideration of the available evidence. Motor impulsivity can be assessed using the stop-signal reaction time (SSRT) which measures the ability to inhibit a response after it has been initiated (please see below for experimental details). Based on the extant literature, it is expected that later chronotype will be associated with increased self-report impulsivity. The proposed work also provides a unique opportunity to assess (in an exploratory manner) the relationship between chronotype and objective-measures of impulsivity.