Does Cocaine Increase the Threat of HIV?
Impulse Control, Cocaine Use and the Transmission and Progression of HIV
Half of HIV positive individuals in the U.S. admit to substance abuse at some point in the previous year. Cocaine is of particular concern because it is associated with an increased likelihood of behaviors associated with HIV transmission and disease progression, including unprotected sexual intercourse and non-adherence to HIV medications. Specifically, cocaine use is linked to higher viral loads, declines in CD4 count, and increases in AIDS-related illnesses.
Dr. Christina Meade, an amfAR grantee in the department of psychiatry and behavioral sciences at Duke University, employed an advanced brain imaging technique in an attempt to define the impact of cocaine dependence on the executive network of brain signaling pathways associated with high-level, complex problem-solving. Dr. Meade and colleagues describe their work in the June 30 issue of the journal Psychiatry Research: Neuroimaging. They recruited 39 HIV-positive adults on antiretroviral therapy who were either active users, past users, or had no history of substance use and presented participants with "delayed discounting" tasks. These tasks allow researchers to measure impulsiveness based upon the relationship between the delay of a reward and its perceived value. Greater impulsivity is reflected by preferences for smaller but immediate rewards over larger but delayed rewards. Rational decision-making is central to the task's outcome.
As each subject selected among reward options, brain activity was assessed by functional magnetic resonance imaging, fMRI. Confronted with hard as opposed to easy choices, active drug users had much smaller increases in brain activity in specific regions of the brain known to be involved in decision making. These physical changes were consistent with prior behavioral studies documenting that individuals who use drugs, particularly stimulants such as cocaine and crystal meth, are more cognitively impulsive than healthy controls or former drug users, scoring poorer in assessments of flexibility in thinking, memory, and complex decision-making. These brain activity differences also make sense on a molecular level since both cocaine and crystal meth affect nerve receptors, known as dopamine D2, believed to be critical in reward-based behaviors. In contrast to current cocaine users, past users showed a more complex pattern of brain activity. Given easy choices, they performed similarly to drug-naive subjects, but for hard choices they showed deficits characteristic of active cocaine users.
Meade and associates note that the areas affected by cocaine are also structures disrupted by HIV infection itself. They postulate that these deficits in activity in the executive regions of the brain in active, HIV-positive cocaine users contribute to impulsive decision making, leading to riskier behaviors associated with HIV transmission and disease progression. They also suggest following cocaine users through rehab and recovery to examine the long-term consequences of prior drug use.
Dr. Laurence is amfAR's senior scientific consultant.
This article was provided by amfAR, The Foundation for AIDS Research. Visit amfAR's website to find out more about their activities and publications.
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