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Impulse Inhibition and the Prefrontal Cortex
Phineas Gage is one of the most well-known and interesting case studies in the history of psychology. A rail worker from the early 19th Century, Gage was the victim of a serious workplace accident. During his blasting duties, a small iron rod went through his left eye and out of the top of his head.
Although Phineas was fortunate in that he survived the accident, his personality was irreparably damaged. There are many stories about how he displayed indiscriminate aggression and an inability to control impulses.
While generalizations from the case of Phineas Gage are controversial and generally considered to be unreliable, subsequent research has demonstrated a strong connection between impulse control and an area of the brain known as the prefrontal cortex - the area that was damaged in Gage's accident.
Whereas individuals with typical brain development are able to restrain themselves when they experience an urge to do something or act aggressively, damage to this area can often result in significant impairment of these faculties. One might roughly say that many desires and impulses are generated by the lower parts of the brain and are then sent up to the prefrontal cortex for further deliberation and consideration.
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The Role of Dopamine in Impulsivity Control
It is a common misconception that impulse control and other cognitive functions are "in" the neurotransmitters themselves. The situation is slightly more complex. Instead of being localized in the neurotransmitters, faculties such as impulsivity control are spread out through systems of neurons that cooperate in order to produce the higher-level effects we observe.
Neurotransmitters such as dopamine come into the picture when we look at how these systems propagate messages. Dopamine is one of the primary neurotransmitters which is used in the prefrontal cortex - especially in areas that are associated with impulse control. A good way to think about this might be: dopamine is the fuel or energy which powers certain brain circuits.
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Impulsivity Dopamine Treatment - Dopamine, Impulsivity and ADHD
Now we are in a position to better understand the relationship between dopamine levels, impulsive behavior and ADHD. There is a growing body of research which suggests that one of the primary underlying causes of ADHD symptoms is a deficiency in dopamine levels.
Given the considerations outlined above, this makes a lot of sense. If dopamine is used to "power" the circuits which are responsible for controlling impulses, then lower levels of dopamine will result in an impaired capacity for inhibition. Thus, individuals with dopamine deficiencies will be more likely to display many of the symptoms associated with ADHD than those who do not have this deficiency. This reasoning has lead researchers and clinicians to develop an impulsivity dopamine treatment.
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Medical Treatments for ADHD
Understanding this, it is now easy to see how clinicians use medications such as Ritalin and Vyvanse to treat impulsivity. While these drugs are stimulants, it is important to keep in mind exactly what they stimulate.
The majority of drugs that are used to treat ADHD work by causing neurons to release higher levels of dopamine. This means that while individuals are on the drug, their impulse control circuits are being given more "juice," and are thus able to perform their function more effectively. At the higher behavioral levels, this translates into much better management of impulsivity and other symptoms associated with predominantly hyperactive-impulsive types of attention-deficit/hyperactivity disorder.
These drugs may be thought of as an impulsivity dopamine treatment, as they essentially treat ADHD symptoms through indirectly administering dopamine to patients. The fundamental insight of this impulsivity dopamine treatment is that dopamine is the underlying cause of many of the symptoms of ADHD, and is therefore the most effective target for alleviating those symptoms.
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Harmon, Katherine. "Dopamine Determines Impulsive Behavior", http://www.scientificamerican.com/article.cfm?id=dopamine-impulsive-addiction.
Nauert, Rick. "Dopamine Influences ADHD", http://psychcentral.com/news/2007/08/07/dopamine-influences-adhd/1107.html.
Sternberg, Robert J. Cognitive Psychology: Fourth Edition. Thomson Wadsworth, 2006.
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"Phineas Gage CGI", By Roy Baty at en.wikipedia [Public domain], from Wikimedia Commons.