A recent study in the American Journal of Psychiatry suggests that frontal lobe abnormalities of those with APD may contribute to violent behavior. Using magnetic resonance imaging (MRI), Dr. V.M. Naryan has completed the first investigation of the relationship between violence and brain structure in those diagnosed with antisocial personality disorder. Findings suggest that violent individuals with APD do have significant anomalies in brain anatomy.
Violence and Frontal Lobe Abnormalities
Violent behavior has been linked to abnormalities in the frontal lobe, the area of the brain responsible for regulating inhibition, emotions, movement and overall social and cognitive behavior. Studies dating back to the late 1800s have consistently found that damage to the frontal lobes results in an altered personality, particularly in increased impulsivity and impaired judgment (Damasio 1994).
Antisocial Personality Disorder (APD)
Common traits of APD include impulsivity, failure to conform to social norms, aggressiveness, disregard for safety, glibness, and deceitfulness. Not all violent criminals have Antisocial PD, but there those who do, show a higher rate of severe violence than does the general population.
There have been few brain imaging studies of people with Antisocial PD. However, Raine et al (2000) found that individuals with APD have 11% less prefrontal gray matter than do healthy comparison subjects, suggesting that there may be significant anatomical anomalies with respect to the brains of antisocial individuals.
APD Study’s Method
Subjects: The subjects of this study included 14 men with a history of violence who had been diagnosed with Antisocial Personality Disorder according to DSM-IV-TR criteria, and 15 healthy nonviolent comparison subjects. Both violent and nonviolent individuals who had been diagnosed with schizophrenia were also studied. For study results related to schizophrenia, see the original research paper, as these results will not be covered in this summary.
Neuroimaging: Each subject’s brain was examined with a series of high-resolution three-dimensional magnetic resonance images.
The Body’s Response to Risk
The organs of our body are regulated by a part of the nervous system called the autonomic nervous system (ANS). In most situations, we are unaware of the workings of the ANS, because it functions in an involuntary, reflexive manner.
The ANS is most important in two situations:
1. Fear-inducing emergencies that cause us to “fight” or take “flight”
2. Non-emergencies when we “rest” and “digest.”
Our body’s fear response sometimes prevents us from doing dangerous things, or triggers us to engage in behaviors that will help us avoid perceived danger. It is a powerful motivator of behavior. The ANS response is normally associated with unpleasant physiological sensations such as sweaty hands, increased heart rate, tensing of muscles and dry mouth.
Psychopath’s Don’t Experience Fear
Violent APD individuals in this study exhibited substantial cortical thinning of the ventromesial frontal and sensorimotor cortex.
Somatic Cortical Loop: The involvement of the ventromesial frontal cortex has been associated with the body’s reaction to risky decision making via the somatic cortical loop. Involvement of mesial frontal and sensorimotor cortical thinning in APD may reflect disturbances in the somatic cortical loop. When parts of this circuit are dysfunctional, the appropriate behavioral responses may not be triggered and dangerous decisions or actions may be made (Fukui 2005, Damasio 1996, 1990).
Psychopaths’ Reduced Autonomic Arousal: In his book on psychopathy, Robert Hare (1999) cites studies which have demonstrated psychopaths’ lack the physiological responses normally associated with fear. Psychopaths do not experience the physical clues that signal how to behave in dangerous or threatening situations. A study by Raine et al. (1990) found that a low level of autonomic arousal in adolescents was predictive of criminal behavior in adulthood. APD Study Conclusions
Taken together, these data suggest that because of a deficit in mesial prefrontal and somatosensory cortices, violent subjects have a compromised autonomic emotional response when making decisions, and this insufficient autonomic response may be associated with violent decisions.
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Narayan, V.M., Narr, K.L., Kamuri, V., Woods, R.P. et al. (2007) Regional Cortical Thinning in Subjects With Violent Antisocial Personality Disorder or Schizophrenia. The American Journal of Psychiatry, 164, 9.
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