This assay has some advantages over the ethanol self-administration assay: (1) the ethanol concentration that the flies experience can be controlled by the experimenter and (2) the ethanol stimulus is removed during the test, allowing measurement of the rewarding value of the drug rather than immediate preference for the drug.
Impulsive choice in the context of delay discounting involves an increased preference for immediate rewards over more long-term advantageous, but delayed, outcomes (Ainslie 1975).
Although not completely consistent [ 4, 5], the majority of studies suggest that ADHD is associated with delayed aversion, an abnormal preference for immediate rather than delayed reinforcement, as well as a greater behavioral sensitivity to reinforcement contingencies, which is generally accompanied by lower psychophysiological reactivity (see [ 6] for review).
Other studies of this at-risk population have shown both a greater hedonic impact of reward outcomes generally (Mason et al., 2012 a ) as well as a preference for immediate over delayed-but-superior rewards (Mason et al., 2012 b ), as indexed by an event-related potential originating from the ventral frontostriatal pathway (Carlson et al., 2011).
In a recent study in European starlings, Sturnus vulgaris (Bateson, Brilot, Gillespie, Monaghan, & Nettle, 2015), we found that birds that had experienced more developmental telomere attrition (an integrative measure of developmental stress) had a stronger preference for immediate over delayed rewards as adults.
It is also possible that frequent media multitasking instead, or also, "trains the brain" to have a higher preference for immediate rewards due to habituation to the immediately gratifying nature of media multitasking.
It's no coincidence that we love our smart wireless devices: Humans are a notoriously impatient species, born with a preference for immediate rewards.
The results of Study 2 provide evidence that HMMs have a higher preference for immediate gratification than LMMs.
Those who have higher discounting rates (i.e., who discount future rewards more and, therefore, have a higher preference for immediate gratification) are thought to be more impulsive and to have less self-control (e.g., MacKillop et al., 2011).
The NAcb is also implicated in impulsivity measured in delay discounting tasks and rats that are impulsive in the 5CSRTT show an increased preference for small immediate over larger delayed rewards.
