Cocaine addicts may have brain deficits

Cocaine addicts may have brain deficits that predispose them to drug abuse, and abusing drugs appears to make matters worse, U.S. researchers said on Wednesday.
They said images of cocaine addicts' brains reveal abnormalities in the cerebral cortex -- the brain's outer surface -- and these changes relate to dysfunction in areas responsible for attention and decision-making."These data point to a mixture of both drug effects and predisposition underlying the structural alterations we observed," said Dr. Hans Breiter of Massachusetts General Hospital, whose research appears in the journal Neuron.Breiter and colleagues compared magnetic resonance images, or MRIs, of 20 cocaine addicts with 20 carefully matched volunteers to map out cocaine-related differences in the brain.Compared to their healthy counterparts, cocaine addicts had far less overall volume in the cortex, the outer layer that helps plan, execute and control behavior. These differences were especially pronounced in areas regulating reward, attention and decision-making.They also noticed that while the healthy volunteers tended to have thicker areas in some frontal regions on the right side of the brain, this was reversed in the addicts. And overall, the addicts had less variation in the thickness of their cortex.
Differences in the right and left side of the brain are important because they typically suggest a genetic cause, Breiter said.The researchers also found changes in the cingulate -- another reward center -- that appeared to correspond with the length of cocaine use but not nicotine or alcohol use, suggesting that these changes were the result of long-term cocaine exposure."Human studies have shown differences in how addicts make judgments and decisions, but it is not well understood how these differences relate to alterations in the structure of the brains of addicts," Breiter said in a statement.New research findings suggest that structural abnormalities in the brains of cocaine addicts are related in part to drug use and in part to a predisposition toward addiction. The research, published by Cell Press in the 9th October issue of the journal Neuron, maps the topography of the addicted brain and provides new insight into the effect of cocaine on neural systems mediating cognition and motivation.'Human studies have shown differences in how addicts make judgements and decisions, but it is not well understood how these differences relate to alterations in the structure of the brains of addicts. Claims have been made that cocaine, potentially in connection with alcohol or other drugs, may be toxic to brain cells. We sought evidence supporting a hypothesis that brain thickness is reduced in some brain regions in addicts, is related to altered decision-making and cognition, and might to some limited degree, be connected to their exposure to cocaine,' explains senior study author Dr Hans Breiter from Massachusetts General Hospital.Dr Breiter and colleagues found that brain regions involved with regulation of attention and reward, specifically the dorsolateral prefrontal cortex (DLPFC) and insular cortices, were significantly thinner in cocaine addicts when compared with matched controls. Behavioural tests revealed that the thinner cortex was associated with restrictions in preference-based judgement and decision-making, and with less accurate effortful attention. A general reduction in the level of preference and in the range of decisions reflecting these preferences can be considered an example of a fundamental feature of addiction - the loss of interest in many things outside of drug use.Some cortical thickness differences were associated with years of drug use, but the researchers also observed differences in the symmetry of DLPFC thickness between control subjects and cocaine addicts that suggested predisposition to drug abuse. 'In human and animal studies, differences in the structure of the right and left sides of the brain are important for many behaviours, and when these normal differences in brain structure are altered, there may be a genetic basis for the change. We found an altered right/left relationship in a part of the frontal cortex that was also associated with altered judgement and decision-making in addicts. We further found that the overall brain thickness in the cocaine addicts was more uniform across the brain, which is quite different from what is observed in non-drug users. These differences did not correlate with any drug use measure. Together, this set of findings point to predisposing factors being a potential contributing factor to the addiction,' explains Dr Breiter.In total, these observations provide evidence that cortical thickness abnormalities associated with cocaine addiction may be a reflection of both drug use and a preexisting inclination to drug abuse. 'A fundamental component of addiction may involve adaptations and/or developmental predispositions involving brain regions necessary for judgement and decision-making regarding complex rewards and attention towards goal-objects. Addiction thus may represent a complex phenotype with multiple effects necessary for compulsive drug use, and the resulting restriction in the range of behaviours they show,' concludes Dr Breiter.