Violence among married and unmarried couples carries a heavy public health burden (Krug, 2002
). Relationship violence is linked to psychological disorder, injury, and death, as well as to disrupted parenting and child mental and behavioral health problems (El-Sheikh et al., 2008
; Grych & Fincham, 2001
; Levendosky et al., 2006
; Tolan, Gorman-Smith, & Henry, 2006
). Recent data indicates this problem is much more prevalent than previously understood. Physical aggression between partners occurs in half of all families with young children each year, according to an anonymous, representative study (Slep & O'Leary, 2005
). Among these families, physical aggression does not only consist of relatively mild forms such as pushing and shoving—half of these families report high severity violence. And contrary to common stereotypes, the majority of violence does not consist of male-to-female aggression: Violence is reciprocal in most families reporting any aggression, with the remaining families demonstrating an approximately even split between male-to-female and female-to-male violence (Capaldi, Kim, & Shortt, 2007
; Straus, 1990
; Straus, Gelles, & Steinmetz, 1980
Given the prevalence and burden of couple violence, it is surprising that there has been almost no research seeking to understand the psychobiological correlates and concomitants of interpartner violence (IPV; but see (Hibel et al., 2009
)). Moreover, some of the best known work—that of Gottman and colleagues linking heart rate reactivity to a marital conflict discussion to observed verbal aggressiveness during that discussion among “batterers” (Gottman, Jacobson, Rushe, & Shortt, 1995
; Jacobson et al., 1994
)—was conducted on a small sample and independent replications failed to support the original findings (Babcock, Green, Webb, & Graham, 2004
; Meehan, Holtzworth-Munroe, & Herron, 2001
). Some other work has included IPV as a dimension of investigation, but did not report on links between physiology and IPV per se
: For example, one study found that physiological reactivity (heart rate, skin conductance) to couple conflict predicted antisocial behavior differently across couples stratified by level of violence (Babcock, Green, Webb, & Yetington, 2005
This gap in the literature on couple violence is notable given the mounting number of studies examining biological processes underlying antisocial and violent behavior outside of such relationships (Raine, 2002
). In this paper, we argue that--based on existing knowledge about the role of physiological systems in aggression--it is reasonable to expect that couple violence is linked to physiological arousal generally and to the activity of the hypothalamic-pituitary-adrenal (HPA) axis in particular.
The HPA axis is one of two main physiological components of the psychobiological of the stress response (Chrousos & Gold, 1992
). The HPA is activated in a systemic response to social evaluative threat or challenge (Dickerson & Kemeny, 2004
). Cortisol is the primary product released from the adrenals in response to HPA axis activation and its levels in the general circulation can be estimated accurately and non-invasively in saliva. In general, adaptive functioning is linked to moderate increases in cortisol in reaction to a stressor or challenge, followed by recovery to baseline (Dickerson & Kemeny, 2004
). Several studies have documented links between HPA activity, indexed by cortisol levels in blood or saliva, and aggressive or socially disruptive behavior (Granger et al., 1998a
; Oosterlaan, Geurts, Knol, & Sergeant, 2005
). For example, Granger and colleagues found that children’s pre-task cortisol levels were negatively associated with the open expression of aggression in the family (Granger et al., 1998a
We hypothesized that IPV is associated with increased HPA reactivity and delayed HPA recovery to interpersonal conflict. Perpetrators of IPV experience greater emotional arousal and anger (by both self-report and observation) during conflict tasks with a partner compared to non-violent individuals (Margolin, 1988
; O'Leary & Jouriles, 1994
). A meta-analysis found that male perpetrators of IPV experience higher levels of anger than non-perpetrators in conflictual relationships (Norlander, 2005
), and that among perpetrators of IPV, anger is associated with greater severity of violence. Anger and emotional arousal are often accompanied by increased cardiovascular activity and/or activation of the HPA axis (Abercrombie, Kalin, & Davidson, 2005
). HPA axis activation provides the individual with a physiological state of readiness to respond rapidly and energetically to an anger-provoking stimulus, thus facilitating aggressive responses. In addition, cortisol elevation affects cognitive processing in a manner that may increase the likelihood of selecting an aggressive response. For example, in the course of priming the body for action, HPA axis activation affects brain physiological functioning, executive functioning, and access to emotional memories (Abercrombie et al., 2003
; Cahill, Gorski, & Le, 2003
). Such effects may reduce the ability to engage in adaptive problem solving and increase the likelihood of primitive behavioral responses such as aggression.
Further circumstantial support for the hypothesis that IPV is associated with HPA activity is provided by the documented associations of both to hostile, conflictual couple interaction. Several studies report dyadic conflict to be associated with increases in cortisol (Granger et al., 1998b
; Kiecolt-Glaser, Bane, Glaser, & Malarkey, 2003
; Robles, Shaffer, Malarkey, & Kiecolt-Glaser, 2006
), an association that is moderated by individual coping and romantic attachment styles (Gunlicks-Stoessel & Powers, 2009
; Powers, Pietromonaco, Gunlicks, & Sayer, 2006
). Negative couple interaction, marked by low warmth, high hostility, and verbal and psychological aggression, is also linked to perpetration of IPV (Cano & Vivian, 2003
; Riggs & O'Leary, 1996
; Riggs, O'Leary, & Breslin, 1990
). However, IPV and HPA activity have not yet been linked directly.
Based on the findings for HPA reactivity and couple conflict, we would expect high levels of HPA activity to be positively associated with IPV. However, there is also reason to expect that low HPA activity levels would predict greater IPV. Research on general aggression and violence frequently finds that aggressive and/or violent children, adolescents, and adults demonstrate relatively low levels of physiological activity or reactivity (Loney et al., 2006
; Oosterlaan et al., 2005
; Raine et al., 2000
). A leading theory is that hypo-responsive individuals do not react strongly to negative consequences of behavior—such as being hit back by a peer or punished by a parent. Thus, the normal mechanisms through which impulses to physical aggression are socialized into more adaptive behavior do not occur, resulting in “under-socialized aggression”. One goal of this study was to assess whether HPA reactivity would relate to IPV in the same direction as it does to couple conflict (a positive association) or as it does to general violence (i.e, a negative association).
Most prior physiological research on couple conflict has been framed in terms of reactivity—that is, comparing a change in cortisol following conflict to a pre-conflict baseline. However, adaptive functioning is characterized by both reaction to a stimulus and then recovery toward baseline. Indeed, the recovery process from a stressful episode may be as important for individual well-being as the reaction (Burke, Davis, Otte, & Mohr, 2005
). Physiological recovery may also play an important role for couple relationship dynamics (Frankenhaeuser, 1986
; Powers et al., 2006
). Individual capacity for recovery may contribute to the successful repair of dyadic conflict episodes, which facilitates positive relationship quality over time (Dindia & Baxter, 1987
). Repair of negative interaction episodes includes acknowledging and/or apologizing for an insult, re-establishing a mutual sense of respect or affection, and/or returning to a positive affective state. Individual recovery may set a lower limit on capacity for repair.
The temporal pattern of the psychobiology of the stress response allows for a simple assessment of reactivity and recovery. HPA axis response to an acute stressor, as assessed in salivary cortisol, generally peaks after approximately 20 minutes, and recovery toward baseline develops over the subsequent 20–40 minutes (Dickerson & Kemeny, 2004
). Although a spike in hostile conflict during an argument may pass without violence, individuals who have difficulty down-regulating physiological arousal may be primed to react aggressively when a second (or third, etc) conflict stimulus occurs before levels of cortisol have returned to baseline.
Finally, in addition to reactivity and recovery, we examine the possibility that baseline level of cortisol is related to IPV. If, as we note above, HPA axis activation facilitates rapid reaction to adverse or threatening stimuli, then the existing level of HPA activity marked by cortisol level may influence the way an individual responds to an ambiguous or hostile social situation.
In this report, our aim is to test the link between HPA activity and IPV as a prelude to future work that should attempt to more precisely understand context, process, and temporal influence (e.g., moderators, mediators, and causality). We focused this investigation on the transition to parenthood because this developmental period is often marked by heightened stress and brings new challenges to couple relationships (Cowan, 1995
; Feinberg, 2002
). Cumulative stressors during this time may increase the likelihood of violence, which poses physical risk to the mother and developing fetus (Jasinski, 2004
). Additionally, both prenatal and postnatal violence and hostility can have negative implications for parenting and child development (Katz & Low, 2004
To assess HPA activity, we collected data from the couples in their home. We collected baseline saliva samples from each member of a couple before two 12-minute videotaped interactions, the second of which was a conflict discussion. We then collected a second saliva sample 15 minutes after the end of the interaction period to measure reactivity, and a third 20 minutes later to measure recovery. We then utilized this data to predict several dimensions of couple violence obtained through self-report measures.
We examined the prediction of low and high severity violence separately based on the notion that different processes may be involved. For example, high-severity violence might be the result of relatively more intense anger or a greater loss of conscious inhibitory control. Research supports the notion that perpetrators of low- and high-severity violence may be comprised of two or more somewhat distinct groups (Holtzworth-Munroe & Meehan, 2004
). Although sample limitations did not allow us to examine subtypes of violence perpetrators, assessing separately the prediction of low and high severity may provide some information relevant to subgroup issues. We also examined violence resulting in injury as a separate outcome, as causing injury to a partner could result from “low severity” violence behaviors (e.g., slapping or pushing) enacted during extreme experiences of anger or physiological arousal. Finally, we examined prediction of psychological aggression, which consists of behaviors such as insulting or shouting. Psychological aggression has negative effects on victims, and commonly occurs alongside physical aggression among couples (Capaldi, Shortt, & Crosby, 2003