Brain imaging helps in the search for impulsivity.
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.
The cause and effect conundrum
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.
Brain differences in impulsive people
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.
Interestingly, these changes to the brain also correlated well with the individual's self-reported tendency to act on impulse and went hand in hand with an increase in alcohol, caffeine and tobacco use.
The study was led by psychologist Avram Holmes, who says:
"The findings allow us to have a better understanding of how normal variation in brain anatomy in the general population might bias both temperamental characteristics and health behaviors, including substance abuse."
The key benefit of this particular study is that the individuals involved were healthy and not addicted substance users. This means that the differences in brain anatomy are not a consequence of a history of abuse or mental illness.
The results dovetail neatly with previous findings. An earlier study found subtle volume changes in similar regions of the cortex in the brains of impulsive adolescents. Similarly, another study showed that these reductions in cortical thickness could predict the severity of ADHD (attention deficit hyperactivity disorder) symptoms; another still correlated cortical thickness in the frontal and posterior cingulate regions to traits such as harm avoidance, reward dependence and persistence.
The importance of interpersonal differences in neuroanatomy is still a fledgling area of research. Holmes plans to continue investigating anatomical changes and their potential influence on psychiatric well-being and other negative health outcomes.
Medical News Today previously covered research claiming to have found "alcoholism neurons" in the brain.