Vol. 7, No. 2, 2001 Page 2

Brainwave patterns point to underpinnings of
impulsive, aggressive violence

Many crimes are unplanned, impulsive acts committed by people with hair-trigger tempers who over- react to minor insults or irritations. New research by Rebecca Houston et al. indicates that abnormalities in sensory processing contribute to these individuals' loss of control, and that medication may help correct both the neurological deficits and the behavior problems of these human "time bombs."

Houston and colleagues evaluated 15 individuals with strong histories of impulsive aggression, and 15 non-aggressive, non-impulsive control subjects. The researchers measured the subjects' brainwave responses to light flashes presented in groups of increasing intensity. They report that:

• Compared to controls, the impulsive aggressive subjects exhibited significantly reduced P1 amplitudes, suggesting that they are unable to process stimuli efficiently. This defect in initial sensory processing, the researchers say, may impair ensuing cognitive processes. Houston et al. say their finding is consistent with earlier studies revealing abnormal brainwave responses in impulsive aggressive individuals during decision-making tasks.
• Impulsive aggressive subjects also exhibited larger N1 amplitudes than those of control subjects, indicating enhanced attention to the stimuli. The finding is interesting, the researchers say, in light of the large body of evidence showing that impulsive aggressive people have lower-than-normal arousal levels. "This enhancement of attentional orienting," they say, "may serve as a compensatory response in order to boost arousal to more optimal levels." They add, "It has been suggested that... sudden change in arousal induces an agitated and irritable state. Often impulsive individuals report having these feelings directly preceding an outburst."
• Aggressive impulsive subjects also exhibited shorter P1, N1, and P2 peak latencies, which the researchers say is additional evidence that these individuals "jump on" any stimulus as quickly as possible in order to increase their abnormally low arousal levels. They note, too, that the subjects displayed increasing arousal in response to increasing intensity of stimuli, which is consistent with evidence that impulsive aggressive individuals are more physiologically reactive than other people.

In a separate study, Houston, Matthew Stanford, and colleagues investigated the effects of the anticonvulsant drug phenytoin on subjects with impulsive aggression. Previous studies had shown the drug to be effective in controlling aggressive behavior.

The researchers administered the drug to 23 impulsive aggressive subjects, and report that subjects experienced fewer outbursts and improved mood. In addition, they say, phenytoin exerted a normalizing effect on the brainwaves of the subjects.

The results of their study strongly suggest, the researchers say, that "the expanded use of such inexpensive techniques and medications as phenytoin could make a significant impact in the management, treatment and prevention of impulsive aggressive behavior in both the mental health and criminal justice systems."

"Mid-latency evoked potentials in self-reported impulsive aggression," Rebecca J. Houston and Matthew S. Stanford, International Journal of Psychophysiology, Vol. 40, 2001, pp. 1-15; and, "A double-blind placebo-controlled crossover study of phenytoin in individuals with impulsive aggression," Matthew S. Stanford, Rebecca J. Houston, Charles W. Mathias, Kevin W. Greve, Nicole R. Villemarette-Pittman, and Donald Adams, in press. Address for both papers: Matthew S. Stanford, Department of Psychology, University of New Orleans, New Orleans, LA 70148.

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