Untitled

Abstract

Background: Research on the genetic basis for impulsivity has revealed an array of ambiguous findings. This may be a result of limitations to self-report assessments of impulsivity. Behavioral measures that assess more narrowly defined aspects of impulsivity may clarify genetic influences. This study examined the relationship between possession of the DRD2 TaqI A and DRD4 48 bp VNTR genetic polymorphisms and performance on a behavioral measure of impulsivity, the delay discounting task (DDT), and three traditional self-report measures.

High temporal discounters overvalue immediate rewards rather than undervalue future rewards: An event-related brain potential study

“…The delay periods ranged across 11 values, from 1 week to 25 years: 1 week, 2 weeks, 2 months, 6 months, 1 year, 2 years, 5 years, 10 years, 15 years, 20 years, and 25 years. The immediate monetary rewards ranged from $0.10 to $100 Canadian, with 29 possible amounts (see Eisenberg et al, 2007, for the details). For example, a typical question was "Would you prefer $45 today or $100 in 5 years?"…”

“…The DDT was modeled after that of Eisenberg et al (2007) and Rachlin et al (1991) using MATLAB (The Mathworks, Natick, MA). Each participant was presented with a series of choices between two hypothetical amounts of money, one consisting of $100 available sometime in the future, and the other equal to or less than $100 available immediately.…”

“…Furthermore, the population response of dopamine neurons to conditioned stimuli decreased as a function of reward delay according to a function that was best described by a hyperbolic curve. Consonant with these findings, a genetics study involving human participants suggested that individual differences in the midbrain dopamine system may underlie idiosyncratic discounting rates (Eisenberg et al, 2007). Specifically, individuals with steeper discount rates were found to have genetic polymorphisms coding for the expression of D2 (TaqI A) and D4 (VNTR) dopamine receptors that, according to the researchers, influence the balance of processing between the striatal systems involved in reward salience and the frontal systems involved in deliberative control.…”

Variation in the <i>DRD2</i> gene affects impulsivity in intertemporal choice

“…In the present study, we selected two SNPs in the DRD2 gene: C957T (rs6277) [37] and TaqI A (rs1800497) [38], which were suggested to influence impulsivity as measured with delay discounting tasks. These SNPs were genotyped at the Human SNP-Typing Center (University of Tokyo, Tokyo, Japan) by using the DigiTag2 assay [49,50], which is designed for multiplex SNP typing.…”

“…As for DRD2 gene polymorphisms, C957T was suggested to be associated with dysfunctional impulsivity [37]. DRD2 TaqI A polymorphism was also suggested to influence impulsivity as measured with a delay discounting task [38], and had a significant association with severe substance dependence [39].…”