The Addiction Process
In the “Impaired Response Inhibition and Salience Attribution” (iRISA) model, the Neuropsychoimaging of Addiction and Related Conditions (NARC) Program’s research emphasized the interaction between inhibitory control (e.g., willed-control over automatic processes, interruption of ongoing behavior) and reward processing (e.g., the experience of pleasure, attribution of relative reward value) in drug addiction, suggesting that inhibitory control would be especially impaired under conditions of high drug salience (Goldstein & Volkow, 2002; Goldstein & Volkow, 2011).
Using neuroimaging techniques and targeting blood oxygenation, blood flow, glucose metabolism, or neurochemistry, abnormalities in the functioning of the striato-thalamo-orbitofrontal circuit during acute drug intoxication, short-term and protracted withdrawal and during drug craving have been documented. This same circuit has been repeatedly implicated in salience attribution/reward processing and inhibitory control in animal and human (neurophysiology, lesion, neuroimaging) studies.
The brain circuits we focus on in iRISA are the mesolimbic and mesocortical dopamine pathways encompassing the dorsal and ventral striatum (caudate, putamen, nucleus accumbens), thalamus, amygdala and hippocampus, anterior cingulate, insula, and the orbitofrontal cortex. The core behaviors encompass intoxication, craving, drug bingeing, and relapse, as presented in the figure above.
Reward Processing in Cocaine Addiction
NARC has now reported differences between cocaine addicted individuals and healthy control subjects in the processing of monetary reward in several brain regions encompassing the lateral orbitofrontal cortex, ventromedial prefrontal cortex (PFC), and dorsal striatum (Goldstein et al., 2007; Konova et al., 2012). These brain abnormalities in reward processing were associated with measures of self-control and severity of drug use; correlations with dopamine receptor availability were also reported (Asensio et al., 2010). Some of these results have been validated with ERPs and vis-à-vis anatomical brain scans (see ERP page).
Practice Effects/Habituation in Cocaine Addiction
Results suggest a disruption in drug addiction of neural habituation to practice that possibly encompasses opponent anterior vs. posterior brain adaptation to the novelty of the experience: overly expeditious for the former but overly protracted for the latter.
Cocaine addicted individuals may therefore be predisposed to an increased challenge when required to maintain alertness as a task progresses, not able to optimally utilize a prematurely habituating PFC to compensate with an increased attribution of salience to a desired reward (Goldstein et al., 2007).
Visuospatial Processing and Working Memory in Cocaine Addiction
NARC also uses other tasks of attention and cognitive function (e.g., sustained visuospatial attention and verbal working memory) in cocaine addicted individuals. Here, findings provide evidence of a widespread functional disruption that may underlie compromises in sensory processing, attention and vigilance, and executive control in cocaine addicted individuals (Tomasi et al., 2007; Tomasi et al., 2007).
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