A Fielding Graduate University paper reviewing the neurobiological correlates of impulsive (ImO) and instrumental (InO) offending, mapped to non-psychopathic and psychopathic antisociality (NPA, PA). The literature converges on a cortical-versus-subcortical distinction: NPA impulsive offending is largely a frontal-lobe and executive-dysfunction story; PA instrumental offending is largely a subcortical, affective-deficit, and learning-impairment story. The paper argues for a dimensional rather than categorical reading of psychopathy and antisociality, and for type-specific intervention design.
This paper reviews the neurobiological correlates of impulsive and instrumental offending in light of antisocial and psychopathic offender types. The literature reveals that while these two types of offenders are not mutually exclusive, they do each represent certain differentiating neuroanatomical, neurochemical, neuropsychological, and neurological characteristics. The paper expresses the importance of understanding the difference between psychopathy and antisociality and calls for a dimensional approach to these two constructs. The apparently cortical nature of antisocial-impulsive offending and the subcortical nature of psychopathic-instrumental offending suggests the possibility of developing type-specific, neurobiologically informed interventions and treatments for these two groups.
Despite only one to three percent of the male population and less than one percent of the female population being psychopathic (Pitchford, 2001), the repetitious antisocial behavior associated with psychopathy is disproportionately harmful to communities, and the fiscal societal costs of psychopathy annually exceed those of substance abuse, obesity, smoking, and other severe persistent mental disorders such as schizophrenia (Kiehl & Hoffman, 2011). Psychopathic antisociality (PA) is associated with greater recidivism, increased crime severity and variety (Porter & Woodworth, 2006), and elevated rates of violent (Blais, Solodukhin, & Forth, 2014) and sexual offenses (Hawes, Boccaccini, & Murrie, 2013).
The relationship between antisocial behavior and psychopathy has too often resulted in an inappropriate conflation of the two terms and the incorrect belief that antisocial personality disorder (ASPD) is the clinical diagnosis for psychopathy. ASPD is a highly operationalized, behaviorally oriented diagnosis that does not meaningfully include or exclude psychopathy. Antisociality is a behavioral profile. Psychopathy is a psychological profile. Both are capable of existing without the other.
The Hare Psychopathy Checklist-Revised (PCL-R; Hare, 1991, 2003) is the most widely used research measure of psychopathy. Despite Hare's use of firm cut-off scores, factor analysis reveals a two-factor structure with Factor 1 capturing affective and interpersonal traits and Factor 2 capturing impulsive and antisocial behaviors. Considered independently, Factor 1 scores are a better assessment of psychopathy, while Factor 2 more closely measures antisociality (Crego & Widiger, 2015). Woodworth and Porter (2002) found Factor 1 scores positively correlated with instrumental offending (InO) and Factor 2 scores positively correlated with impulsive offending (ImO). The same study found that 93.3% of homicides committed by PA offenders are instrumental, motivated by external, dispassionate, and often material goals.
Offenses regularly defy simple either-or categorization, with violent actions sometimes functioning as both means and ends (Bushman & Anderson, 2001). For this reason the paper treats psychopathy, antisociality, and offense type as dimensional rather than categorical constructs. Following Müller (2010), the neurobiological markers below are considered correlational reflections of severity rather than diagnostic thresholds.
Baseline readings and emotional processing in the peripheral nervous system are a core physiological component of psychopathy. Child and adult violent offenders consistently show low baseline heart rates (Ortiz & Raine, 2004; Scarpa & Raine, 1997) regardless of PA or NPA status. Where the two groups diverge is in reactivity.
PA is positively correlated with low baseline electrodermal activity and negatively correlated with electrodermal reactivity (Herpertz, 2007). InO perpetrators maintain a hypoarousal state. ImO perpetrators, including juveniles (Lorber, 2004), display increased electrodermal reactivity to stressful or aversive stimuli (Patrick, 2008). Vagal-parasympathetic heart-rate regulation and general cardiac reactivity are positively correlated with ImO across age groups (Mezzacappa et al., 1997; Peters et al., 2003; Smith & Gallo, 1999). Beauchaine, Katkin, Strassberg, and Snarr (2001) hypothesize that weak vagal control combined with autonomic hypoarousal produces a lowered threshold for emotionally reactive aggressive behavior. Davidson, Putnam, and Larson (2000) describe enhanced autonomic reactivity as a downstream consequence of the dysfunctional affective regulation underlying ImO.
Abnormal autonomic activity supports the commission of violent acts, but it has to be paired with some form of affective dysfunction to result in violent offending. PA individuals show insensitivity to punishment and reduced capacity for fear (Lykken, 1995). NPA individuals who engage in ImO do not show this same pattern (Porter & Woodworth, 2006). PA individuals are unusually immune to cognitive errors arising from negative emotional stimuli, and they show under-activation in brain regions that integrate factual and emotional information (Müller et al., 2008).
Inhibition depends on both emotional and cognitive processes, including guilt, fear, empathy, and consideration of consequences. Effective inhibition requires balance: emotional impulses cannot overrun cognitive abilities, as appears to be the case in NPA, and executive functioning cannot be deprived of inhibitory emotional information, as appears to be the case in PA. ImO is associated with frontal-lobe dysfunction that hampers the regulation of threat responses. InO results from the absence of moderating emotional influences such as guilt, shame, and fear (Blair, 2010; Pemment, 2013).
The startle reflex is informative because eye-blink responses route through a neuroanatomical pathway connecting the orbicularis oculi muscle to the nucleus of the amygdala (Davis, 1989). Eye-blink startle studies show that psychopathy, but not antisociality alone, uniquely predicts an atypical lack of increased eye-blink response at longer startle latencies to aversive stimuli (Loomans, Tulen, & van Marle, 2014; Vaidyanathan, Patrick, & Bernat, 2009). PA individuals appear deprived of the inhibitory contribution of fear because the underlying aversive learning is disrupted by subcortical dysfunction.
Computerized tomography of violent psychiatric patients and homicidal offenders reveals both temporal and frontal lobe abnormalities (Blake, Pincus, & Buckner, 1995; Hirono et al., 2000; Patrick & Verona, 2007; Soderstrom et al., 2000; Wong et al., 1994), but only ImO perpetrators reliably show dysfunction in the prefrontal cortex (PFC; Raine et al., 1998). Subcortical dysfunction, which is largely hypoactive for PA individuals, is inversely reflected in NPA individuals, who show subcortical hyperactivity, specifically in basal ganglia and limbic regions (Amen, Stubblefield, Carmichael, & Thisted, 1996).
Hypoactive dysfunction in the hippocampus, anterior cingulate cortex (ACC), and anterior insula in response to aversive stimuli appears responsible for the insensitivity to danger cues and impairments in contextual fear conditioning found in PA (Blair, 2006; Decety, Skelly, & Kiehl, 2013; Kiehl et al., 2001; Raine et al., 2004; Seara-Cardoso & Viding, 2015). The hypoactivity extends to the amygdala and contributes to PA-typical resistance to aversive conditioning, passive avoidance learning, and recognition of fearful faces (Blair, 2010).
Magnetic resonance imaging shows that both ImO and InO offenders demonstrate reduced functional connectivity between the left insula and the left dorsal ACC (Ly et al., 2012), between frontal cortex and temporo-limbic structures (Debowska, Boduszek, Hyland, & Goodson, 2014), and between the amygdala and ventromedial PFC (Anderson & Kiehl, 2012; Koenigs, Baskin-Sommers, Zeier, & Newman, 2011). These connections are particularly limited in PA, especially the regions Baron-Cohen (2012) describes as the empathy circuit: amygdala, caudal ACC, dorsal and ventral medial PFC, OFC, and middle cingulate cortex.
Both groups display increased resting slow-wave electroencephalogram activity (Patrick, 2008). The discriminating brain-wave marker is P300, an event-related potential involved in stimulus evaluation and decision making. Reduced P300 amplitude is found primarily in NPA offenders (Stanford, Houston, Villemarette-Pittman, & Greve, 2003) and is a dimensional indicator of executive dysfunction (Gerstle, Mathias, & Stanford, 1998), consistent with ImO being the more executive-dysfunction-driven of the two groups.
The primary neurochemicals implicated in violent behavior are cortisol, testosterone, serotonin, and oxytocin. Cortisol potentiates fear, creates sensitivity to punishment, and initiates withdrawal behavior. Testosterone initiates approach behavior, reward sensitivity, and fear reduction. Serotonin is central to mood regulation.
Gao, Glenn, Schug, Yang, and Raine (2009) hypothesize that the combination of increased testosterone with reduced cortisol explains the hyporesponsivity to stressors, threat cues, and punishment observed in PA. Single-photon emission computed tomography has provided evidence for abnormal dopaminergic neurotransmission in the striatum and diminished serotonin transporter density in the midbrain of NPA individuals (Tiihonen et al., 1997). Positron emission tomography work shows blunted serotonin agonist reactivity in clinical NPA populations (New et al., 2002) and a significant negative relationship between acts of violence and serotonin-binding potential in the amygdala (Parsey et al., 2002).
Oxytocin is a powerful modulator of amygdala activity, especially in moral decision making (Blair, 2007), interpersonal empathy (Dadds et al., 2014), and fear and anxiety (Gorka et al., 2015). PA individuals reliably show hypoactive amygdala oxytocin reception. Reduced amygdala functioning during moral-decision tasks correlates strongly with InO (Blair, 2007), and methylation of the oxytocin receptor gene is positively related to the callousness and reduced emotionality typical of psychopathy (Dadds et al., 2014).
When compared to controls, both PA and NPA individuals show significantly thinner cortex bilaterally in the precentral gyri, anterior temporal cortices, left insula, dorsal ACC, and right inferior frontal gyrus, independent of age, intelligence, or substance use (Ly et al., 2012). Where structural findings start to differentiate the two groups:
| Marker | NPA / ImO (cortical) | PA / InO (subcortical) |
|---|---|---|
| Primary locus | Frontal lobe, PFC | Amygdala, hippocampus, ACC, insula |
| Baseline autonomic | Low | Low |
| Autonomic reactivity | Hyperreactive to aversive stimuli | Hyporeactive, sustained hypoarousal |
| Vagal control | Weak | Closer to normal |
| Fear conditioning | Affected by inhibitory failure | Disrupted aversive learning |
| Startle reflex | Normal | Lacks increase at long latencies |
| P300 amplitude | Reduced | Closer to normal |
| Cortisol | Variable | Reduced |
| Testosterone | Elevated | Elevated |
| Serotonin | Reduced transporter density (midbrain) | Reduced amygdala 5-HT binding |
| Oxytocin | Less affected | Hypoactive amygdala reception; OXT-R methylation |
| Temporal lobe volume | ~20% reduction (Dolan et al., 2002) | Less affected |
| Uncinate fasciculus | Reduced white-matter integrity | Less affected |
| Corpus callosum | Less affected | ~22.6% larger (Raine et al., 2003) |
| Empathy circuit connectivity | Less affected | Markedly limited |
| Acquired by frontal lesion | Yes (reactive, impulsive) | No |
NPA and PA can be neurobiologically differentiated from each other and from the general population across neurological, neuroanatomical, neuropsychological, and neurochemical categories. NPA reads as a largely cortical disorder where executive dysfunction is paired with heightened reactivity to negative stimuli. PA reads as a subcortical disorder that produces broadly impactful affective deficiencies and learning impairments.
Treating both NPA and PA as dimensional rather than categorical conditions has a clinical consequence: neither group represents persons who are wholly, fundamentally, and unchangeably different from the rest of the population, and group-specific protocols become a coherent design goal. The implication for future research is the development of NPA interventions aimed at improving executive functioning and neural connectivity while down-regulating affective reactivity, and PA interventions aimed at addressing affective deficits, impaired aversive learning, and limited receptivity to conditioning. The cost basis of psychopathy alone justifies the work.
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