Tuesday June 21 2011
It's unclear if brain changes were caused by cocaine use
The Guardian reported that researchers have found that cocaine addiction is linked to “differences in key areas of grey matter affecting functions such as memory and attention”.
The study in question carried out brain scans and tests for impulsive and compulsive behaviour in 60 cocaine-dependent people and 60 healthy volunteers. It found that the cocaine-dependent individuals showed a reduction in the volumes of several areas of the brain, and increases in the volume in other areas. Differences in volume in certain areas appeared to be related to how long individuals had been using cocaine, and their levels of impulsivity and compulsivity.
One point to note is that a proportion of the cocaine-dependent people had other dependence problems, including nicotine dependence, and some also had alcohol dependence, cannabis dependence, or heroin dependence. These factors could also be related to the brain differences seen, rather than just the cocaine use.
This study increases what is known about the physical attributes of the brains of people who have cocaine dependency. However, it is not possible to say from this study whether the brain differences were present before cocaine use began or whether they are caused by cocaine use. As yet, it is not clear whether these findings will have direct implications for the diagnosis or treatment of cocaine addiction.
Where did the story come from?
The study was carried out by researchers from the University of Cambridge and GlaxoSmithKline, and was funded by GlaxoSmithKline. The study was published in the peer-reviewed medical journal Brain.
This research was reported in The Guardian, which covered the study well and included a quote from the study’s author, highlighting the fact that the study cannot tell us whether the cocaine use or the brain changes came first.
What kind of research was this?
This cross-sectional study looked at whether there were any differences between the brains of cocaine-dependent and healthy individuals, and whether these were related to levels of compulsivity and impulsivity.
Various studies have suggested links between addiction, brain changes, impulsivity and compulsivity. For example, people who are impulsive are thought to be more likely to change from being recreational cocaine users to compulsive users, and chronic cocaine use is thought to further increase impulsivity. Studies have also suggested that addiction changes the frontostriatal networks. These are nerve networks that connect the front part of the brain (the frontal lobes) with an area called the basal ganglia in the central part of the brain. These networks may influence impulsive and compulsive behaviour.
The researchers wanted to test whether increases in impulsivity and compulsivity in cocaine users would be associated with detectable changes in these frontostriatal areas of the brain.
This type of study can tell us whether there is an association between two factors, but cannot tell us which one came first. This means that it cannot be used to say that one factor may have caused the other.
What did the research involve?
The researchers enrolled 60 cocaine-dependent individuals and 60 healthy volunteers. They took MRI brain scans of these people and assessed their impulsivity and compulsivity, and determined whether these tests showed any differences between the groups.
To be eligible to participate, individuals had to be 18–50 years old and in good physical health. Anyone with a major medical or neurological illness, those who had ever had a psychotic illness or traumatic head injury, and those who could not have a brain scan were excluded. The cocaine-dependent participants met internationally accepted criteria for cocaine dependence, were actively using cocaine, and were not seeking treatment. The healthy control volunteers reported that they had no history of drug abuse and were not taking prescribed or illegal drugs regularly, and did not meet criteria for alcohol abuse or dependence. Urine samples were taken on the day of testing to ensure that the healthy controls were not taking illicit substances, and to assess whether the cocaine users were actively using cocaine.
The participants’ impulsivity and compulsivity were assessed using standard questionnaires and behavioural tasks. They were then given MRI brain scans to measure the volumes of certain areas of grey matter (the part of the brain containing the nerve cell bodies).
The researchers then compared the volumes of certain parts of the brain in the cocaine-dependent individuals and healthy controls. They then focused on any areas where they found differences, looking only in cocaine-dependent individuals, to see if grey matter volumes in these areas were related to differences in levels of impulsivity, compulsivity, or how long the person had been using cocaine.
What were the basic results?
The researchers found that the cocaine-dependent individuals had used the drug for an average of 10 years, starting at an average age of 21. The users had higher levels of impulsivity on the self-reported questionnaires than the healthy individuals, but not on the behavioural tests. They showed slower response time on these tests and problems with attention control.
The researchers found that the cocaine-dependent individuals had significantly different volumes of grey matter in several areas of the brain compared to healthy individuals. Most of these areas showed a reduction in volume in cocaine-dependent individuals, and the longer a person had been using cocaine, the greater the reduction in three areas of these areas (the orbitofrontal, cingulate and insular cortex). Some areas, known as the basal ganglia areas, showed an increase in the grey matter volume in cocaine-dependent individuals.
There were also differences in volume of certain brain areas between cocaine-dependent individuals with different levels of attention control or compulsive drug use. Cocaine-dependent individuals with less attention control had lower volume in the insular cortex but higher volume in the caudate nucleus. Cocaine-dependent individuals with more compulsive drug use had reduced volume in the orbitofrontal cortex.
How did the researchers interpret the results?
The researchers concluded that cocaine-dependent individuals had abnormalities in the structure of certain areas of the brain (corticostriatal systems). The changes in certain areas of the brain were related to differences in how long a person had been cocaine dependent, their level of inattention and the compulsiveness of their cocaine consumption.
This study has highlighted differences between the brains of individuals with cocaine dependency and healthy individuals. However, it is not possible to say from this study whether these brain differences were present before cocaine use began or whether they were caused by cocaine use. A prospective cohort study would be needed to determine which of these is the case. Other points to note include:
- There were differences between the cocaine-dependent and healthy groups other than cocaine use. For example, the cocaine users had higher depressive scores than the healthy people, and fewer years in formal education (11.5 compared to 12.3 years). Most of the cocaine users also had nicotine dependence (83%), some also had alcohol dependence (27%), cannabis dependence (18%) and heroin dependence (7%). These factors may also have been related to the brain differences seen, rather than just the cocaine use.
- The researchers note that impulsivity is a complex trait and that the measures they used would not have captured all aspects of it.
As yet, it is not clear whether these findings will have direct implications for the diagnosis or treatment of cocaine addiction.