Cocaine is a highly stimulating drug that achieves its effects by altering the normal brain levels of an important chemical called dopamine. Because of the way it works on the brain and the rest of the central nervous system, the drug presents a serious risk for the onset of physical dependence and addiction. However, not all people who use cocaine will develop these problems. In 2011, British researchers uncovered significant evidence that indicates that many people who develop cocaine addictions have pre-existing abnormalities in a part of the brain called the basal ganglia. Still, no one can predict in advance which users will or will not become addicted to cocaine. Cocaine and Its Effects All cocaine comes from leaves of the coca plant, which grows both naturally and under human cultivation in various highland areas of South America. In its powdered, dissolvable form, the drug is known as cocaine hydrochloride; makers of cheaper crack cocaine \u201crocks\u201d strip away the hydrochloride portion of the drug through a chemical process that involves the use of common baking soda. Whatever its form or method of delivery (injection, smoking, or nasal inhalation), the drug rapidly increases the brain\u2019s dopamine supply. Dopamine plays a critical role in a portion of the brain called the limbic system, which triggers pleasurable sensations in response to certain actions and behaviors. When levels of this chemical rise, feelings of pleasure generated in the limbic system increase; in turn, this increase creates a rewarding feedback loop that reinforces the likelihood of future participation in the action or behavior in question. Physical dependence on cocaine (or any other common drug of abuse) occurs when the brain starts to treat its altered dopamine levels as the normal or default situation. When dopamine levels fall below this new normal, withdrawal symptoms kick in, and the severity of these symptoms typically gives the user a strong incentive for continued drug intake. Addiction occurs when this incentive becomes compulsive and the user makes obtaining and consuming cocaine (or other drugs) the focal point of his or her daily existence. The Role of the Basal Ganglia Basal ganglia is the collective term for a group of brain structures that sit above and around the limbic system. Initially, scientists believed that the singular purpose of these structures was the control of various types of body movement. However, according to a 2008 report in Neurology Today, researchers now have a fuller understanding of the basal ganglia. In addition to their role in movement control, they link closely with an advanced part of the brain called the neocortex and help us perform higher mental functions such as learning and memory formation. Crucially, the basal ganglia also play a significant role in creating the pleasurable, dopamine-related rewards that were previously only associated with the main structures of the limbic system. Pre-Existing Basal Ganglia Differences In a study reported in 2011 in the journal Brain, researchers from Cambridge University in Great Britain examined the basal ganglia in a large group of known cocaine users. They discovered that, when compared to people in the study who didn\u2019t use cocaine, all members of this group had abnormally enlarged basal ganglia. However, the same amount of enlargement appeared in new cocaine users and long-term, habitual users. According to the researchers conducting the study, this uniform degree of change indicates that basal ganglia enlargement existed before any cocaine use occurred; in other words, cocaine users in the study had pre-existing abnormalities in their basal ganglia. The researchers concluded further that these abnormalities may indicate a built-in sensitivity to cocaine\u2019s effects, and therefore may help explain why some cocaine users become addicted while others don\u2019t. A Complex Picture While basal ganglia enlargement and other inborn or genetic factors may help lay the foundation for addiction to cocaine or other drugs, the overall picture for dependence and addiction is much more complex, doctors at the University of Massachusetts Medical School explain. Other factors that operate in combination with (or instead of) genetic tendencies include an individual\u2019s family environment, social environment, personality traits, exposure to drug-related peer pressure, exposure to emotional and\/or physical trauma, exposure to stress, and susceptibility to impulsive behavior. Because of the virtually limitless potential for interaction among these variables, no one can predict in advance who will become addicted to cocaine or other drugs of abuse. On average, approximately 10 percent of all drug experimenters will eventually develop an addiction to their drug of choice.