1. Introduction
Psychopathy is characterized by a cluster of personality traits including a lack of affect, egocentricity, manipulativeness, and a tendency toward risky and antisocial behavior (Cleckley, 1941; De Brito et al., 2021; Hare & Neumann, 2008). The deleterious consequences of these traits including risk for antisocial and criminal behavior has motivated considerable research into the potential physiological underpinnings of psychopathy. Among these studies a growing body of research has shown that autonomic nervous system (ANS) activity at rest and in response to stress is associated with psychopathic traits (de Looff et al., 2021; Lorber, 2004; Portnoy & Farrington, 2015).
Associations between ANS activity and psychopathic traits may be understood in the context of ANS function. The ANS includes the sympathetic and parasympathetic nervous systems (SNS, PNS; Gabella, 2001). The SNS is responsible for a variety of physiological and psychological changes in support of the body’s response to stress and can be roughly characterized as potentiating the ‘fight or flight response’. In contrast, the PNS enacts physiological and psychological changes to return the body to homeostasis after stress (Akselrod et al., 1981; Warner & Cox, 1962). Studies exploring the association between ANS activity and psychopathic traits often index ANS activity with heart rate (HR) and skin conductance (SC).
Heart rate is influenced by both the SNS and PNS with the SNS exerting an excitatory influence and the ANS an inhibitory influence. SC is influenced solely by the SNS. ANS hypo-activity in response to stress may be associated with the development of personality traits characterized by blunted affect through impaired fear conditioning (Lykken, 1957). The suggestion that ANS activity is associated with psychopathic traits through fear conditioning is supported by work showing reduced SC reactivity (SCR) in anticipation of aversive stimuli (e.g. Arnett, 1997, Lyken, 1995). Raine (2002) suggested that low resting heart rate may be associated with increased risk for antisocial behavior through either fearlessness or sensation seeking. Subsequent work has found support for the mediating role of sensation seeking in the HR-antisocial behavior relationship (Portnoy et al., 2014; Sijtsema et al, 2010),
Three meta-analyses have explored the association between ANS activity and psychopathic traits. Lorber (2004) reported resting HR (RHR) was not associated with psychopathy (d = .06, p > .05), while Portnoy and Farrington (2015) later reported a negative association (d = -.19, p < .05). In a recent meta-analysis by de Looff et al. (2021), RHR had a negative and statistically significant association with Factor 2 psychopathy (ES = - 0.16, p = .017), while the association between RHR and Factor 1 psychopathy was negative but lacked statistical significance (ES = - 0.21, p = .059). Factor 1 psychopathy is characterized by a manipulative and callous egocentricity while Factor 2 centers on tendency to engage in impulsive and antisocial behaviors (Karpman, 1948). Variability in the results for associations between SC and psychopathic traits are even more pronounced. For example, Lorber (2004) found SC and SCR were negatively associated with psychopathy (SCd = -.30, p < .05, SCR d = -.31, p< .05). Later, de Looff et al. (2021) disaggregated studies of SC level and SC response and found neither was associated with psychopathy (SC level ES = 0.01, p = .887; SC responseES = -0.12, p = .148).11Skin conductance response is commonly measured as an increase in conductivity exceeding .05 microsiemens in amplitude (e.g., Fung et al., 2005; Wang et al., 2012). Skin conductance level is the average value of skin conductance for a given time period. de Looff et al. (2021) also SCR for measures of SC level and SC response were not related to psychopathy (SCR level,ES = -0,14, p = .137; SCR response ES = 0.12, p = .162).
While meta-analyses offer some evidence for associations between ANS activity and psychopathic traits, it is possible that results obscure important variation across studies that can help to specify the role of ANS activity in the development of psychopathy. Specifically, aggregate associations between ANS reactivity and psychopathy factors may mask important variation across the type of stimulus used to illicit change in ANS activity. In what is to our knowledge the only direct investigation of the role of stimulus type in associations between SCR and psychopathy factors, Dindo and Fowles (2011) found SCR during social stressor speech task (SSST; preparation and delivery of a speech about one’s faults) was positively associated with Psychopathic Personality Inventory Factor 2 - Impulsive Antisociality (PPI-2; Lilienfeld & Andrews, 1996), while SCR in response to signaled noise blasts during the countdown task was negatively associated with PPI-1 - Fearless Dominance.
Negative associations between SCR to signaled noise blasts and aspects of psychopathy consistent with Factor 1 have been found by other work (Fung et al., 2005; McDougal et al., 2019; Wang et al., 2012). For example, studies in children and adolescents have found SCR resulting from noise blasts during the countdown task is negatively associated with total psychopathy scores, (Fung et al., 2005), manipulative/deceitfulness (Wang et al., 2012), and callous-unemotional traits (McDougal et al., 2019). In contrast, research testing associations between psychopathy factors and SCR to the SSST finds SCR is not related to callous unemotional traits but provides some equivocal evidence for an association between the SSST and the sensation seeking facet of Factor 2 psychopathy (Kavish et al., 2019; Portnoy et al. 2020). Both Kavish et al. (2019) in a large university sample and Portnoy et al. (2020) in a sample of physically maltreated youth reported that the SSST was not associated with aspects of callousness captured by the Inventory of Callous Unemotional Traits (ICU; Frick, 2004). Kavish et al. (2019) also found SCR in response to the SSST was not associated with total psychopathy scores or scores on psychopathy factors present in the Levenson Self-Report Psychopathy Scale. However, SCR in response to the SSST was positively associated with thrill seeking as measured by the Sensation Seeking Scale - Form V (SSS-V; Zuckerman, Eysenck, & Eysenck, 1978). Studies have also shown that associations between HRR and psychopathy factors vary considerably across experimental stimuli. HRR from the SSST was not associated with callous unemotional traits in the work of Portnoy et al. (2020) or Kavish et al. (2019). In contrast, Wang et al. (2012) reported increased HRR during the countdown was positively associated with callous/disinhibited scores in a sample of children.
Collectively the studies reviewed above suggest that associations between ANS reactivity and psychopathy factors are influenced by the stimuli used to elicit reactivity and by the ANS measure (HR/SC). Research in this area also suggests that relatively minor differences in the conceptualization of psychopathic traits may influence results. For example, SCR for signaled noise blasts were negatively associated with callous-unemotional traits in the work of MacDougall et al. (2019) but not related to callousness-disinhibition in the work of Wang et al. (2012).
While the potential influence of heterogenous experimental stimuli on patterns of association between ANS activity and psychopathic traits has long been recognized (Lorber, 2004), relatively little direct attention has been given to the influence of different stimuli on the strength of association between ANS activity and psychopathic traits. To our knowledge Dindo and Fowles (2011) present the only study to directly contrast results from a social stressor with those from an anticipation of noise task. In their study all subjects were exposed to four experimental paradigms. The countdown task and the social stressor were the third and fourth.22Results for the first two experimental paradigms (concealed information and picture viewing) were not presented and were described by the authors as “somewhat complex and, for that reason, were not as clearly of theoretical relevance” (Dindo & Fowles, 2011, p. 560). It is possible that the strength of association between SCR and psychopathy factors during these later experimental paradigms was attenuated. Therefore, to further inform our understanding of the association between ANS activity and psychopathic traits we extend the work of Dindo and Fowles (2011) by randomly assigning subjects to either the countdown task or the SSST. We also explore the influence of the quantification of psychopathy on results through the use of multiple measures of psychopathic traits.