Introduction
Impulse control disorders are characterized by repetitive behaviors and impaired inhibition of these behaviors. Important defining criteria for these disorders include:

• The failure to resist an impulse to perform some act that is harmful to the individual or others;
• An increasing sense of arousal or tension prior to committing or engaging in the act;
• An experience of either pleasure, gratification, or release of tension at the time of committing the act.

In addition, there is usually a pattern of engaging in the abnormal behavior in spite of adverse consequences (e.g., criminal charges, impairment of normal functioning, etc.). The Diagnostic and Statistical Manual of Psychiatric Disorders (DSM-IV) include the following impulse control disorders: pathological gambling, trichotillomania, kleptomania, pyromania, and intermittent explosive disorder. Compulsive-impulsive Internet usage disorder, compulsive-impulsive sexual behaviors, compulsive-impulsive skin picking, and compulsive-impulsive shopping are also regarded as impulse control disorders by many experts.

Pathological gambling
Pathological gambling is characterized by recurrent and maladaptive patterns of gambling behavior that significantly disrupts the patient’s functioning in the personal, familial, or vocational spheres. Studies suggest that the prevalence of pathological gambling is between 1% and 3% of the adult population, and a meta-analysis estimated that 86% of the population of the USA are recreational gamblers. The disorder usually starts during adolescence with a prevalence of approximately 4-7% in this population. The disorder is currently more common in men than in women. Individuals with pathological gambling have been found to have high incidences of various psychiatric disorders, including depression, bipolar, anxiety and substance use disorders.

Trichotillomania
Individuals with trichotillomania describe an overwhelming urge to pluck out specific hairs; when they do so, the anxiety is momentarily relieved but is quickly replaced by another compulsive urge to pluck and even greater anxiety. Estimates from surveys suggest that 1.5% of males and 3.4% of females endorse clinically significant hair pulling, with .6% endorsing all diagnostic criteria of trichotillomania. Persons with trichotillomania recognize the behavior as senseless, undesirable and performed in response to increasing anxiety, with resultant tension relief. The compulsive hair pulling often affects the individual’s ability to maintain close relationships, to interact socially, and to manage tasks in the home.

Pyromania
In pyromania there is impulsive, repetitive, deliberate fire setting without external reward (e.g., arson for money, revenge, as a political act). There are very few sample studies of firesetting, which is understandable since it is illegal and thus likely to be kept secret. The majority of epidemiological studies have focused on pyromania in childhood and adolescence and have reported the prevalence to be between 2.4% and 3.5%. Some evidence indicate that adolescent boys may be at higher risk for firesetting than adolescent girls. This is an important problem: 60% of all fires in large U.S. cities are lit by individuals between 11 years and 18 years. Experts believe that there is a close link between firesetting and aggression and between firesetting and antisocial behavior.

Intermittent explosive disorder is characterized by recurrent episodes of aggressive behavior that is out of proportion to psychosocial stressors and/or provocation and that is not better accounted by another mental disorder, comorbid medical conditions, or the physiologic effects of a pharmacologic agent or other substance with psychotropic properties. It has been suggested that there are 1.4 million individuals with current intermittent explosive disorder in the U.S. and 10 million with lifetime intermittent explosive disorder.

Kleptomania is a disorder in which the individual impulsively steals even though there is no need to do so (i.e., the individual has money to pay for the stolen items or does not need the stolen goods). Kleptomania is characterized by an anxiety-driven urge to perform an act that is pleasurable in the moment but causes significant distress and dysfunction. The prevalence of kleptomania in the U.S. is unknown but has been estimated at 6 per 1000 people. Kleptomania is thought to account for 5% of shoplifting in the U.S. Kleptomanic behavior carries serious legal consequences: approximately 2 million Americans are charged with shoplifting annually. If kleptomania accounts for 5% of these, this translates into 100,000 arrests.

Compulsive-impulsive Internet usage disorder, also referred as Internet addiction or problematic Internet use, has been proposed as an explanation for uncontrollable and damaging use of the Internet, and has only recently begun to appear in the psychiatric literature. People with problematic Internet use often report increasing amounts of time- spent web surfing, gambling, shopping or exploring pornographic sites. Others report spending time in chat rooms or corresponding by email. Frequently these people develop a preoccupation with the Internet, a need for escape to the Internet and increasing irritability when trying to cut back their Internet use. For some individuals, their excessive Internet use may be entirely accounted for by another disorder such as pathological gambling or compulsive-impulsive sexual behaviors. However, much remains unknown about the overlap among various mental disorders with excessive computer use. Even if new research satisfactorily demonstrates that the prevalence of computer addiction is relatively stable and robust, epidemiologists also must establish that this phenomenon represents a unique construct. As with pathological gambling, questions about comorbid conditions and the need for exclusion criteria also exist with excessive computer use. It has been suggested that there is a link between depression and pathological Internet use but acknowledged that it is unclear whether depression is the cause or the effect of excessive computer use.

Compulsive-impulsive sexual behaviors include repetitive sexual acts and compulsive sexual thoughts. The individual feels compelled or driven to perform the behavior, which may or may not cause subjective distress. The behavior may interfere with several aspects of the patient’s life, causing social or occupational impairment, or legal and financial consequences. C-ISBs involve a broad range of paraphilic or non-paraphilic symptoms. Paraphilic compulsive-impulsive sexual behaviors involve unconventional sexual behaviors in which there is a disturbance in the object of sexual gratification or in the expression of sexual gratification (e.g., exhibitionism, voyeurism). Non-paraphilic compulsive-impulsive sexual behaviors involve conventional sexual behaviors that have become excessive or uncontrolled. Investigations reported prevalence estimates of compulsive-impulsive sexual behaviors ranging from 5% to 6% of the U.S. population.

Compulsive-impulsive shopping, also referred as compulsive buying, is characterized by maladaptive preoccupations or impulses to buy or shop that are experienced as irresistible, intrusive and/or senseless, accompanied by frequent episodes of buying items that are not needed and/or that cost more than can be afforded. Frequently, these patients engage in these behaviors for longer periods of time than intended, and they experience distress and significant impairment in social and occupational performance. A recent study on compulsive-impulsive shopping disorder estimated the prevalence of this disorder to be between 2% and 8% of the general adult population in the U.S.; 80% to 95% of those affected are female. Onset occurs in the late teens or early twenties, and the disorder is generally chronic.

Compulsive-impulsive skin picking
Patients with compulsive-impulsive skin picking frequently present to dermatologists, and it has been estimated that about 2% of dermatology clinic patients may suffer from this condition. Prevalence in the general population or in psychiatric clinics is unknown. Skin picking is often not a transient behavior but may persist with a waxing and waning lifetime course. It should be considered pathological when it becomes habitual, chronic and extensive, leading to significant distress, dysfunction or disfigurement. The majority of patients with compulsive-impulsive skin picking are women.

Neurobiology
The human brain is wired with natural checks and balances that control emotions, but breakdowns in this regulatory system appear to dramatically heighten risk of impulsive behavior. Impulsive behavior may be related to the interplay between several distinct brain regions, namely the orbital frontal cortex, the anterior cingulate cortex, and the amygdala. The orbital frontal cortex plays a crucial role in constraining impulsive outbursts, while the anterior cingulate cortex recruits other brain regions in the response to a stimulus or conflict. The amygdala, a tiny but highly influential portion of the brain, is involved in the production of a fear response and other emotions.
Over the past several years, case reports and series have noted the onset of pathological gambling in patients with Parkinson disease treated with levodopa (Larodopa) and dopamine agonists. The case reports have named dopamine receptor agonists as the likely culprits, but the role of levodopa has been unclear and the possibility that the symptom is a manifestation of Parkinson’s disease itself has been posited. The idea that pathologic gambling can be precipitated by drug therapy challenges conventional views about complex behaviors and the effects that drugs can have.