In DSM-IV and the Hare Psychopathy Checklist, a core feature of the diagnosis of antisocial personality disorder is the lack of empathy and the absence of committed, intimate relationships. Relationships are shallow, opportunistic, and exploitative. Central to this is the notion of altered emotional processing and there is consistent evidence of abnormalities in this area in antisocial groups. A number of studies have demonstrated reduced ability to recognize and discriminate emotional facial expressions (Blair et al, 2001), and vocal tone (Blair et al, 2002). Moreover, there are robust findings of lowered somatic markers of CNS arousal in response to emotional stimuli. For example, subjects with ASPD show reduced electro dermal skin response, event related potentials, and other physiological response in response to aversive conditioning (Flor et al, 2002). Although psychopaths show reduced reactivity to many emotions, they are particularly insensitive to distress and, most specifically, fear (Blair et al, 2002).
In an fMRI study of ASPD subjects' response to fear-inducing visual stimuli, there was lowered activation of the limbic prefrontal circuit, including the orbito-frontal cortex, insula, amygdale and anterior cingulate cortex relative to a control group, consistent with a blunted fear response to emotionally salient perceptual stimuli (Veit et al, 2002). Similar findings in criminal psychopaths showed decreased affect-related activity in the amygdala, hippocampus, parahippocampal gyrus, ventral striatum, and the anterior and posterior cingulate (Kiehl et al, 2001). The amygdala is centrally involved in the activation of emotional responses to perceptual stimuli and is particularly sensitive to fearful stimuli. The hippocampus is involved in memory and rich interconnections with the amygdala make it particularly salient to the processing of emotional memory. This reduced processing of and reactivity to emotions in general, and fear in particular, may underlie the lack of empathy characteristic of antisocial individuals. The reduced fear response, however, is also consistent with the lowered harm avoidance associated with impulsivity. Thus impaired emotional processing may link impulsivity and lack of empathy in psychopathic individuals.
There is also growing interest in the neurobiology of attachment, which is clearly deficient in antisocial individuals, although to our knowledge, this line of research has not yet extended to antisociality. Animal studies have demonstrated the central role of two neuropeptides, vasopressin and oxytocin, in the attachment system (Panksepp, 1998; Insel, 1997). Based on these findings, a number of studies have investigated the role of oxytocin in autism, another psychiatric disorder characterized by attachment deficits (Green et al, 2001). Oxytocin and vasopressin, nine-amino acid peptides (nonapeptides) synthesized in the hypothalamus, differ only by 2 amino acids. Receptors for both peptides are distributed throughout the limbic system and the brain stem. Both are part of a family of nonapeptides that date back to invertebrates. Earlier versions of nonapeptides have been associated with non-mammalian reproductive behaviors such as nest-building. Unique to this family of nonapeptides, oxytocin and vasopressin are found only in mammals and each differ from their putative evolutionary precursor, arginine vasotocin, by only one amino acid. Both peptides are also implicated in characteristic mammalian functions, such as uterine contractions during labor, and milk ejection during nursing.
Of interest to the study of human attachment, these nonapeptides are involved in sexual activity and associated adult pair bonding, parental behavior and infant attachment. More specifically, in the highly monogamous prairie vole, but not in the non-monogamous and less generally affiliative montane vole, oxytocin receptors are found in the nucleus accumbens and prelimbic areas associated with the dopaminergic reward circuitry. Two measures of pair bonding found in the monogamous prairie vole but not the montane vole include time spent preferentially in proximity to the mate (partner preference) and, in males, aggressiveness towards third parties after mating (mate guarding). In females oxytocin, but not vasopressin, administered into the lateral ventricle facilitates development of partner preference, even in the absence of mating. Furthermore, an oxytocin antagonist given prior to mating blocks partner preference but does not interfere with mating. In males, partner preference and mate guarding was facilitated selectively by vasopressin and blocked with a vasopressin antagonist. Neither mating behaviors nor non-mating aggression were affected. Of note, both oxytocin and vasopressin are released during human sexual behavior (Insel, 1997; Panksepp, 1998). Further, in rats, onset of maternal behavior is facilitated by administration of oxytocin and blocked following administration of oxytocin antagonists. Vasopressin in male prairie voles is also associated with parenting behavior (See Insel, 1997 for a review).
Oxytocin may have an effect on dopamine function from the ventral tegmental area and on opioid release. As noted above, there may be two distinct components of the reward system, appetitive and consummatory pleasure, which are mediated, respectively, by dopaminergic and beta endorphin systems (Panskepp, 1998). Activating "appetitive" pleasure is subserved by the meso-limbic dopaminergic reward circuitry, and is characterized by a kind of eager excitement associated with the anticipation of reward. "Consummatory" pleasure, associated with beta endorphin release at the mu opiate receptors, particularly in the septal area, is characterized by a pleasurable release of tension after obtaining a reward. Thus oxytocin (and possibly vasopressin) may serve to link attachment related behaviors to both the appetitive and consummatory reward circuitry. If vasopressin and oxytocin are deficient in antisocial individuals, it could explain their excessive need to obtain gratification via non-attachment related pleasures, such as illicit substances and impersonal sex. In fact, drugs of abuse such as cocaine directly stimulate the dopaminergic reward circuitry, while heroin and other opiates act upon the endogenous opioid system. Future research could investigate the relationship between oxytocin, vasopressin and the reward circuitry in antisocial individuals.
Was this article helpful?