The neuroscience of impulse and addiction

IMPULSIVITY, sensation-seeking and substance abuse have long been linked. Although individuals who abuse drugs are known to act impulsively and have subtly different neuroanatomy, it is not clear whether these changes are the cause or the effect of the abuse. A new study investigates these links further. Everyone has a level of impulsivity in their character; we are all points along a scale.
Some of us consistently act on a whim, whereas others rarely make decisions without deep consideration. As a personality trait, impulsivity is often connected to a predisposition for drug abuse. Studies have shown that adolescents who experiment with recreational drugs are more likely to have lower levels of self-control.
Scientists have also noted subtle neuroanatomical changes in the brains of those who are, or have been, addicted to drugs. To muddy the waters further, there seems to be a genetic component to impulsive, sensation-seeking behavior and substance abuse. This interplay between behavior, genetics and neuroanatomy is a long way from being fully understood. The job of teasing apart the chicken and the egg is a gargantuan task; did the difference in brain structure cause the recreational drug use, or did the recreational drug use change the brain structures?
Drug abuse is known to affect brain anatomy over time, so working out how much of that change occurred since the drug abuse took hold would necessitate having access to comprehensive brain scans taken prior to the addiction. A new study, carried out by a joint effort between Yale University in Connecticut, Harvard University in Massachusetts and the Massachusetts General Hospital, peels back another layer of the mystery. The team investigated the neuroanatomy of 1,234 males and females with no history of substance dependence or psychiatric disorders.
The participants filled out a suite of questionnaires assessing personality traits with a particular interest in sensation-seeking and impulsivity; the questions delved into the individual’s desire for intense or novel experiences, along with alcohol, caffeine and tobacco usage. For each individual, the researchers took magnetic resonance imaging (MRI) scans, in order to chart various aspects of their neuroanatomy.
The results from the scans, published in The Journal of Neuroscience, showed that individuals with a naturally impulsive character were more likely to have a thinner cortex (decreased gray matter) in brain regions associated with decision-making and self-control. These changes were most marked in two areas of the brain considered to be important in regulating emotions and behavior: the middle frontal gyrus and the anterior cingulate. The latter of these two regions is known to play a role in decision-making, empathy and impulse control, among other functions.

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