Frontoparietal cortical activity of methamphetamine‐dependent and comparison subjects performing a delay discounting task

Abstract

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.

Human Ecstasy Use is Associated with Increased Cortical Excitability: An fMRI Study

“…Although METH effects on a simple visual fMRI paradigm have not been previously reported to our knowledge, several studies of brain activation during cognitive paradigms in METH-dependent individuals have found a mixed pattern of activation, similar to that observed in MDMA users, when compared with control subjects during a facial affect matching task (Payer et al, 2008) and a delay discounting task (Monterosso et al, 2007;Hoffman et al, 2008).…”

Morphometric Correlation of Impulsivity in Medial Prefrontal Cortex

“…So far, certain anatomical studies seemed to endorse this association between DLPFC and impulsivity level (Bjork et al 2009), while others do not (Boes et al 2009;Matsuo et al 2009). In support of the former, there are also fMRI (Monterosso et al 2007;McClure et al 2004) and neurophysiological experiments conducted either with repetitive transcranial magnetic stimulation (rTMS) or transcranial direct current stimulation (Fecteau et al 2007;Koch et al 2005;van't Wout et al 2005). By applying rTMS to the right DLPFC in young healthy subjects, we were able to temporarily affect impulsivity level as measured by the DDT (Cho et al 2010).…”

Hypothetical and Real Choice Differentially Activate Common Valuation Areas

“…In many experiments in psychology and neuroscience, it is common to elicit hypothetical choices or ask hypothetical questions that cannot be actually implemented for practical reasons. Typical examples include experiments for very high stakes, payments with long delays, unusual highly controlled social events, or morally charged consequences (Greene et al, 2001(Greene et al, , 2004Delgado et al, 2005;Hariri et al, 2006;Monterosso et al, 2007;Takahashi et al, 2009). Generalizing claims about neural processing in these hypothetical choice tasks to real choice rests heavily on the assumption that neural processes engaged in the two kinds of decisions are highly overlapping.…”