Monterosso JR, Ainslie G, Xu J, Cordova X, Domier CP, London ED. Frontoparietal cortical activity of methamphetamine-dependent and comparison subjects performing a delay discounting task. Hum Brain Mapp 28: 383-393

Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, California 90024, USA.
Human Brain Mapping (Impact Factor: 5.97). 05/2007; 28(5):383-93. DOI: 10.1002/hbm.20281
Source: PubMed


Relative to individuals who do not have addictive disorders, drug abusers exhibit greater devaluation of rewards as a function of their delay ("delay discounting"). The present study sought to extend this finding to methamphetamine (MA) abusers and to help understand its neural basis. MA abusers (n = 12) and control subjects who did not use illicit drugs (n = 17) participated in tests of delay discounting with hypothetical money rewards. We then used a derived estimate of each individual's delay discounting to generate a functional magnetic resonance imaging probe task consisting of three conditions: "hard choices," requiring selections between "smaller, sooner" and "larger, later" alternatives that were similarly valued given the individual's delay discounting; "easy choices," in which alternatives differed dramatically in value; and a "no choice" control condition. MA abusers exhibited more delay discounting than control subjects (P < 0.05). Across groups, the "hard choice > no choice" contrast revealed significant effects in the ventrolateral prefrontal cortex, dorsolateral prefrontal cortex (DLPFC), dorsal anterior cingulate cortex, and areas surrounding the intraparietal sulcus (IPS). With group comparisons limited to these clusters, the "hard choice > easy choice" contrast indicated significant group differences in task-related activity within the left DLPFC and right IPS; qualitatively similar nonsignificant effects were present in the other clusters tested. Whereas control subjects showed less recruitment associated with easy than with hard choices, MA abusers generally did not. Correlational analysis did not indicate a relationship between this anomaly in frontoparietal recruitment and greater degree of delay discounting exhibited by MA abusers. Therefore, while apparent inefficiency of cortical processing related to decision-making in MA abusers may contribute to the neural basis of enhanced delay discounting by this population, other factors remain to be identified.

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    • "icult to state and require additional information on predicted future states . fMRI studies have investigated this issue by comparing tri - als in which preferences were difficult vs . when they were easily stated , and in these contrasts increased activity in brain regions encompassing the rTPJ is reported , in the right intraparietal sul - cus ( Monterosso et al . , 2007 ; Meade et al . , 2011 ) , inferior parietal cortex ( Stoeckel et al . , 2013 ) , and angular gyrus ( Hoffmann et al . , Frontiers in Neuroscience | www . frontiersin . org 5 March 2015 2008 ) . On the basis of these findings , it is reasonable to infer that when decision - making requires information about future affective states , inv"
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    • "The indifference points for a series of delays and rewards can be used to produce a discount curve, which typically describes the rate at which the value of a reward decreases as a function of increased time to reward receipt (Mazur, 1987; Mendez et al., 2010; Odum, 2011; Richards et al., 1997). Moreover, this method permits investigations of subjective " easy " versus " hard " choices by those trials that deviate more from an individual's indifference point (Amlung et al., 2014; Hoffman et al., 2008; Monterosso et al., 2007). Indifference points for a series of reward or delay-time choice options can be used to create a discount curve to reflect the rate at which the value of a reward decreases as a function of increased time to reward receipt. "
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    • "In line with previous reports, MA users displayed lower striatal D 2 /D 3 receptor availability (Volkow et al., 2001; Lee et al., 2009; Wang et al., 2012) and higher discount rates (Hoffman et al., 2006; Monterosso et al., 2007) than controls, on average. As hypothesized , discount rate was significantly negatively correlated with striatal D 2 /D 3 receptor availability in the combined sample and among MA users alone. "
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    ABSTRACT: Background: Individuals with substance use disorders typically exhibit a predilection toward instant gratification with apparent disregard for the future consequences of their actions. Indirect evidence suggests that low dopamine D2-type receptor availability in the striatum contributes to the propensity of these individuals to sacrifice long-term goals for short-term gain; however, this possibility has not been tested directly. We investigated whether striatal D2/D3 receptor availability is negatively correlated with preference for smaller, more immediate rewards over larger, delayed alternatives among research participants who met DSM-IV criteria for methamphetamine (MA) dependence. Methods: Fifty-four adults (n = 27 each: MA-dependent, non-user controls) completed the Kirby Monetary Choice Questionnaire, and underwent positron emission tomography (PET) scanning with [(18)F]fallypride. Results: MA users displayed steeper temporal discounting (p = 0.030) and lower striatal D2/D3 receptor availability (p < 0.001) than controls. Discount rate was negatively correlated with striatal D2/D3 receptor availability, with the relationship reaching statistical significance in the combined sample (r = -0.291, p = 0.016) and among MA users alone (r = -0.342, p = 0.041), but not among controls alone (r = -0.179, p = 0.185); the slopes did not differ significantly between MA users and controls (p = 0.5). Conclusions: These results provide the first direct evidence of a link between deficient D2/D3 receptor availability and steep temporal discounting. This finding fits with reports that low striatal D2/D3 receptor availability is associated with a higher risk of relapse among stimulant users, and may help to explain why some individuals choose to continue using drugs despite knowledge of their eventual negative consequences. Future research directions and therapeutic implications are discussed. © The Author 2015. Published by Oxford University Press on behalf of CINP.
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