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Impulse Control, Impulsivity, and Violence: Clinical Implications

Impulse Control, Impulsivity, and Violence: Clinical Implications

Disorders associated with violence and impulsivity/impulse dyscontrolTABLE: Disorders associated with violence and impulsivity/impulse dysc...

At some point in their life, most people are likely to have acted on impulses or reacted to provocations. This is accepted normal human behavior. However, in some cases it is pathological and some individuals behave this way habitually—as part of a pattern of behaviors that may have begun sometime in their youth. Although there are protean manifestations of these behaviors, ranging from suicidal gestures, substance abuse, risk taking, and antisocial behaviors, a subset of individuals are also aggressive and violent.

© Cartoonresource/shutterstock.com© Cartoonresource/shutterstock.com
The terms “impulsivity” and “disorders of impulse control” have customarily been used interchangeably. Yet there have been contrasting definitions in the literature. “Impulsivity” has been defined as a decreased sensitivity to negative consequences, rapid unplanned reactions to stimuli (without adequate processing of information), and lack of regard for long-term consequences. “Disorders of impulse control” have been characterized as repeated failures to resist an impulse or perform an act that is harmful, with a preceding subjective sense of increasing tension (or arousal) and an experience of pleasure or gratification, ie, catharsis, while committing the act.1,2 In both cases, the consequences of the acting out are usually deleterious, with subsequent feelings of regret or guilt.

No studies have directly compared individuals whose impulsivity only takes the form of acting precipitously to stimuli with those who act solely because of impelling urges. In practice, there are many who possess an admixture of both aspects, such as those with borderline personality disorder who repeatedly act out their urges and can also respond explosively to stimuli. In DSM-5, an important criterion for borderline personality disorder is impulsivity, which also encompasses risk-taking activities that are exemplars of poor impulse control, such as excessive spending, promiscuity, and reckless driving. Individuals with intermittent explosive disorder, a “pure” impulse control disorder, exhibit “impulsive (or anger-based) aggressive outbursts” in response to minor provocations or stressors. Whatever the distinctions, individuals with these disorders all have in common a deficit in inhibiting damaging behavior.

In clinical practice, it may actually be difficult to differentiate between compulsions, addictions, and irresistible impulses. Almost all self-damaging behaviors, especially if they occur in the context of a psychiatric disorder, can be reframed as impulse disorders, such is the looseness of the definitions. Commonly, individuals who habitually cannot control their aggressive impulses also have other impulse control disorders, such as gambling and alcohol and substance abuse.

Forensic psychiatrists and the courts have long grappled with the difficult distinction between “impulses that cannot be resisted” and “impulses that are not resisted”—namely the “irresistible impulse” defense. In the former, there is the possibility that the person has an inherent biological propensity to act violently and therefore ought to be excused; the latter implies that the loss of control was voluntary and consequently not excusable. This applies mostly when someone responds violently following provocation. But impulses can also build up over an extended period until they demand urgent expression. Even serial killers who plan their homicides, sometimes meticulously, often report that they had to surrender to overwhelming urges.

Neurobiology and experience

Over 30 years ago, Linnoila and colleagues3 found that impulsive violent offenders had significantly lower cerebrospinal fluid (CSF) concentrations of the major metabolite of serotonin, 5-hydroxyindoleacetic acid (5-HIAA). Their findings have been convincingly validated.4,5

Serotonin is an important inhibitory neurotransmitter, especially in the amygdala, anterior cingulated cortex, and dorsal-lateral prefrontal and orbitofrontal cortices. Reduced or dysregulated serotonin activity is associated with impulsivity and aggression. The possible mechanism may be the disruption of circuits between the amygdala and the medial prefrontal cortex, which results in amygdala hyperactivity and reduced prefrontal inhibition.6 Impulsive aggression presumably occurs consequent to ongoing arousal (from the amygdala) that primes negative urgency—the tendency to respond impulsively and aggressively to provocations or perceptions of threat.

Individuals who have the X-linked allele that codes for low-functioning monoamine oxidase A (MAOA-L), the most important enzyme for the metabolism of central serotonin, tend to display enhanced activation in subcortical limbic areas (especially the amygdala) and reduced prefrontal inhibition. This allele has now acquired the moniker “warrior gene” because of its consistent association with impulsive aggressive behavior.

Individuals who have the s/s allele for the serotonin transporter promoter gene also tend to exhibit patterns of impulsive violence, probably because of the reduced presynaptic re-uptake of serotonin. It may seem paradoxical that low-functioning versions of MAOA and serotonin promoter genes are associated with impulsive aggression because these genes lead to increased levels of serotonin. The most likely mechanism is that increased levels of serotonin occupy serotonin 1A and serotonin 1B autoreceptors that “switch” the presynaptic neuron off and functionally cause a serotonin deficiency.5

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