Examining Brain Differences in Siblings That Contribute to Addiction

Recent studies have shown that there are certain brain function differences in those who use stimulant drugs when compared with controls that do not use drugs. The studies have often focused on the fronto-striatal systems of the brain that are responsible for functions of self-control.

A new study examined the thought that brain structure related to self-control may be inherited and increases the likelihood of becoming dependent on stimulants (Ersche et al., 2012). The team used drug-dependent participants, along with their siblings to study the differences in brain structure and function.

The researchers included 50 biological sibling pairs in their analysis. In each sibling pair, there was one sibling who met criteria for dependence on amphetamines or cocaine, while the other sibling was required to have no history of any substance addiction, except tobacco use. In addition, the researchers recruited another 50 participants who were non-drug dependent controls who were similar in age and intelligence quotient as the pairs with drug-dependence.

The participants were required to perform a task that focused on pressing a button repeatedly unless they were notified not to do so with an auditory indicator. The task was intended to assess inhibitory control by measuring how long it took the participant to react to the signal and stop pressing the button. The measure from this test is called the stop-signal reaction time (SSRT) and may predict the development of substance abuse among some participants.

The participants were also examined using magnetic resonance brain scans. These gave the researchers a way to measure and compare the quality of the white matter fiber tracts and measure the volume of gray matter in the brain of each individual.

The results of the study show that drug-dependent individuals and their siblings, who had no record of drug addiction, exhibited longer SSRTs when compared with the controls. This result shows that there may be an inherited impairment in inhibitory control.

In addition, the pairs of biological siblings showed less white matter integrity when compared with the controls. A lesser white matter integrity was also associated with longer SSRTs in the inhibitory control exercise. This association indicates that white matter integrity may be a marker for poor levels of inhibitory control, which is also a predictor of stimulant drug dependence.

There were also several other areas of the brain’s gray matter noted to be smaller in the brains of the biological siblings when compared with the controls. These areas included the basal ganglia, orbitofrontal cortex, medial temporal lobe and the putamen.

The authors of the study note that several limitations must be considered related to the study, including the recruiting of participants from treatment centers. The study does not provide information about a possible association between treatment history and brain structure. In addition, the study does not attempt to offer information about addictions other than stimulant addiction.