Impulsivity is a hallmark and common feature in various psychiatric disorders, including substance use disorder, attention deficit hyperactivity disorder (ADHD), conduct disorder, bipolar disorder, pathological gambling and personality disorders 
. Although impulsivity can be broadly defined as behavioral actions without adequate forethought, there is growing evidence that impulsivity is no unitary construct, but rather is dissociable into different aspects reflecting distinct underlying cognitive, emotional, and neural processes 
. Nonetheless, detailed research on the relationship between various aspects of impulsivity is still scarce.
Two widely recognized behavioral phenomena of impulsivity are impulsive choice and impulsive action. Impulsive choice
is oftentimes operationalized by impulsive decisions resulting from a distorted evaluation of delayed consequences of behavior and an increased preference for (smaller) immediate rewards over more beneficial delayed rewards. On the other hand, impulsive action
reflects the failure to inhibit an inappropriate response to prepotent stimuli 
In addition to self-report measures, impulsive choice and impulsive action can be assessed in different behavioral paradigms. Importantly, for most of these behavioral paradigms similar versions exist for humans and laboratory animals. In humans delay discounting paradigms are generally used to assess impulsive choice 
. To measure impulsive action, the go-no go task, stop signal task, Stroop task, or commission errors during a continuous performance task (CPT) are most often utilized in humans 
. Preclinical laboratory animal researchers have developed translational analogies of these neuropsychological tasks such as the delayed reward task (DRT) to study impulsive choice and the go-no go task, stop signal reaction time task and the five-choice serial reaction time task (5-CSRTT) to measure impulsive action (for review see 
). Translational, cross-species approaches combining clinical and preclinical data on impulsivity are particularly suited to deepen our understanding of the neurobiological mechanisms underlying impulsivity and the multidimensional nature thereof and may ultimately lead to improved treatment strategies for psychiatric disorders characterized by maladaptive impulsivity.
In recent years, both animal (for reviews see 
) and human (for reviews see 
) research has tremendously contributed to an increased understanding of the neurobiological mechanisms of impulsivity and has indicated that on a neurobiological level there is partial overlap in the neurotransmitter systems and brain regions modulating impulsive choice and impulsive action. In addition, the involvement of these forms of impulsivity in psychopathology, for example ADHD 
and drug dependence 
, show both overlap as well as dissociation.
Despite accumulating evidence further supporting the view that impulsivity is not a unitary construct, to date there is, especially in the preclinical animal literature, only limited data available on within-subject comparisons of various aspects of impulsivity. This approach is particularly suited to examine the multidimensional nature of impulsivity, because, in contrast to a between-subjects comparison, potential findings of separable aspects of impulsivity cannot be attributed to individual differences that might exist between subjects. Nonetheless, to date, most rodent work is conducted in separate groups each performing a single impulsivity paradigm and findings from the few rodent studies that have tested both impulsive action and choice in the same animals have been inconsistent: It has been demonstrated that animals showing high levels of impulsive action, also display steep discounting behavior 
, whereas such a relationship is not detected in other studies 
. In healthy volunteers, the studies that employed a within-subjects design have generally revealed separate factors for impulsive choice and impulsive action 
. The inconsistent findings in rodents and the limited number of studies using within-subject approaches warrant further investigation of the multidimensional nature of impulsivity in rodents and the translational value to human data.
The current study aimed to investigate the interrelationship between impulsive choice and impulsive action in a cross-species translational (rats and humans) design, using multiple assessments within the same subjects. To this aim, a cohort of rats was trained in the DRT and 5-CSRTT paradigm, the most often used behavioral laboratory measures for impulsive choice and impulsive action. In parallel, a cohort of healthy volunteers performed analogous impulsivity measures, namely a delay discounting task (DDT) for impulsive choice and immediate and delayed memory task (IMT/DMT, a modified CPT) for impulsive action. Additionally, to further delineate the interrelationship between aspects of impulsivity, human subjects completed the stop signal task (SST); one of the most frequently used paradigms for impulsive action in human studies, and the self-report Barratt Impulsiveness Scale (BIS-11). To extend previous neurobiological findings on the various aspects of impulsivity based on between-subject approaches, pharmacological challenges with the clinically relevant psychostimulant amphetamine (AMP) and the norepinephrine reuptake inhibitor atomoxetine (ATO) were conducted in the rodent experiment. Using this within-subjects, translational approach, we aimed to establish whether impulsive choice and impulsive action represent separate dissociable aspects or a unified construct of impulsivity in rats and humans.