Increased impulsivity, or a lack of impulse control, is a key characteristic of many psychiatric disorders, including alcohol dependence. Recent studies suggest that increased impulsivity is involved in a predisposition to developing these disorders. A new study of brain processes provides support for this theory.
Results are published in the January issue of Alcoholism: Clinical & Experimental Research.
"Altered impulsivity is a prominent manifestation in many disinhibitory psychiatric disorders, such as alcohol- or substance-related disorders, conduct disorder, attention-deficit hyperactive disorder (ADHD), antisocial personality disorder (ASP), bipolar disorder, impulse control disorders, and so on," said Bernice Porjesz, professor and director of the Henri Begleiter Neurodynamics Laboratory at SUNY Downstate Medical Center. "Individuals suffering with these disorders may frequently and unpredictably act without planning in advance or without regard to the negative consequences of their behaviors, which in turn can result in serious aftermath. In severe cases, it may lead to danger to the patient or to others."
Porjesz added that the majority of psychiatric diseases are "complex diseases," meaning that their development is influenced by an underlying biological susceptibility of genetic factors, environmental factors, and interactions among multiple genes and the environment.
"Disinhibitory disorders share many similar clinical presentations as well as similar neurobiological abnormalities such as brain waves," said Porjesz. "This suggests that this group of disorders may have some underlying genetic vulnerabilities in common that contribute to the disorders. One recent study of genetic and environmental contributions to internalizing and externalizing disorders determined that the single most important factor underlying externalizing disorders is a genetic liability involving impulse control."
For this study, researchers recruited 57 alcohol-dependent individuals and 58 healthy adult "controls" from the New York City area. All participants were assessed with a standard visual oddball task, where the subject presses a button only to rarely occurring target stimuli (the letter "X") embedded in a series of frequent non-target stimuli. Meanwhile, brain waves or event-related potentials (ERPs) were recorded with a non-invasive technique using 61 scalp electrodes to measure P3 amplitudes. (P3 amplitudes reflect level of neural inhibition in the central nervous system - the larger the P3, the more the inhibition.) Levels of impulsivity were also measured through a standardized self-report scale, the Barratt Impulsiveness Scale. Self-reported measures of impulsivity were also gathered through questionnaires. Furthermore, source localization of brain sources contributing to P3s was computed through a recently developed method of low-resolution electromagnetic tomography called LORETA.
Results showed that the alcohol-dependent subjects, as well as those individuals with high impulsivity, had significantly lower P3 amplitudes and reduced frontal-lobe activity while processing the visual target signals.
"This is the first study to demonstrate that reduced brain activity in the frontal lobe during processing of target visual stimuli is highly related to impulsivity, regardless of a clinical diagnosis such as alcoholism," said Porjesz. "Genetically influenced underlying factors, such as neural disinhibition and impulsivity, involve frontal-lobe function and influence a wide range of clinical outcomes. Thus, the low P3 amplitude and reduced frontal activation that we found reflect risk for the development of many externalizing disorders, not just specifically alcohol dependence."
Porjesz noted that impulsivity as a behavioral process is essential for normal and socially relevant functioning. "However," she added, "an increased level of impulsiveness may indicate that an individual is more vulnerable than others to behaviors such as excessive drinking, abuse of illicit drugs, and perhaps the development of other disinhibitory disorders. Awareness of this increased vulnerability can aid in better prevention strategies, and early identification of individuals manifesting high impulsivity may prevent more serious clinical outcomes."
Porjesz and her colleagues plan to continue with their research, and will next examine the relationship between impulsivity and ERPs in the offspring of alcoholics. As part of a large nine-center collaborative study known as COGA (Collaborative Study on the Genetics of Alcoholism), they are also trying to identify genes associated with impulsivity, and the underlying predisposition involved in disinhibitory disorders, by following young offspring of alcoholics with "risk genes" as they go though the age of risk and respond to their environmental factors.
Alcoholism: Clinical & Experimental Research (ACER) is the official journal of the Research Society on Alcoholism and the International Society for Biomedical Research on Alcoholism. Co-authors of the ACER paper, "Reduced Frontal Lobe Activity in Subjects with High Impulsivity and Alcoholism," were: Madhavi Rangaswamy, Chella Kamarajan, Yongqiang Tang, Kevin A. Jones, David B. Chorlian, Arthur T. Stimus, and Henri Begleiter of the Neurodynamics Laboratory in the Department of Psychiatry at SUNY Downstate Medical Center in Brooklyn. The study was funded by the National Institute on Alcohol Abuse and Alcoholism.
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