Abstract
Neurobiology of female homicide perpetrators is not well understood. Data from private interviews and examinations of females were re-analyzed comparing those who committed homicide (n = 9); other violent crimes, no known homicide (n = 51); nonviolent crimes, no known violent convictions (n = 49); and noncriminals (n = 12). Homicide perpetrators suffered the most childhood sexual abuse (CSA); most recent abuse; had the most neurological histories, mainly traumatic brain injuries (TBIs); most health care access for abuse-related injuries; lowest AM and PM salivary cortisol; and greatest proportion who committed crime under the influence of alcohol. Only CSA, years since last abuse, TBI, neurological histories, and health care access for abuse-related injuries were significant. Those who committed homicide under the influence of alcohol suffered the most recent abuse and had the lowest AM cortisol and flattest diurnal cortisol slope (DCS) compared with others; though the n precludes determining significance. Amount of time since last abuse, AM cortisol and DCS progressively decreased as crime severity increased; other variables progressively increased as crime severity increased. These preliminary findings suggest that low AM cortisol, flat DCS, greater CSA frequency and severity, recent abuse, TBIs, and health care access for abuse-related injuries could be risk factors for females committing homicide. Further study is needed due to the small n of homicide perpetrators. Abuse victims may be at greater risk for alcohol use and cortisol dysregulation associated with perpetrating violence, especially homicide. Frontal lobe damage from TBIs may decrease ability to control behaviors associated with emotions from the limbic system. Health care providers released these women when their abuse-related injuries were not life-threatening; yet, they were life-threatening for victims of their subsequent homicides. Females accessing health care for abuse-related injuries present a critical opportunity for violent crime prevention interventions.
Keywords
Introduction
Of the 323,127,513 violent crimes in the United States in 2016, 17,250 were homicides, which is an 8.6% increase since 2015, compared with 7,942 homicides in 1950 (Federal Bureau of Investigation [FBI], 2017a, 2017b; Langberg, 1967). The 2016 U.S. homicide rate was 5.3 per 100,000, the first year it was above 5.0 since 2008. U.S. homicides declined in the 1990s (Weiss, Santos, Testa, & Kumar, 2016) before a dramatic increase in 2015 with the top 10 cities ranging from a 90.5% to a 12.9% increase over the previous year (Rosenfeld, 2016). This was much larger than annual changes in decades, and it increased again in 2016 (Rosenfeld, Gaston, Spivak, & Irazola, 2017). Of homicide perpetrators, women make up 11% in the United States (FBI, 2016), 16.6% in South Korea (Sea, Youngs, & Tkazky, 2018), 11% in Finland, the Netherlands, and Sweden (Liem et al., 2013), 6% in Russia (Eckhardt & Pridemore, 2009), and 5% globally (United Nations Office on Drugs and Crime [UNODC], 2014).
Studies differentiate male- and female-perpetrated homicide by location of the crime, relationship with the victim, situational dynamics, style or method of injury, and other psychosocial differences summarized by others (J. A. Fox & Fridel, 2017; Fridel & Fox, 2019; Sea et al., 2018; Yourstone, Lindholm, & Kristiansson, 2008) and described below. Yet, few studies address the neurobiological differences between genders of perpetrators, and little is understood about neurobiology of females who commit homicide.
Neurobiology of Female Homicide Perpetrators
There is growing literature on neurobiology of violence (Glenn & Raine, 2014; Haller, 2014b; Miczek & Meyer-Lindenberg, 2014; Rosell & Siever, 2015). Psychiatric conditions have been described in 34% to 90% of samples of homicide perpetrators (Fazel & Grann, 2004; Gajic et al., 2016; Shaw et al., 2018; Valenca, Nardi, Nascimento, Jozef, & Mendlowicz, 2014), though little is known about neurological conditions. For example, of male and female homicide perpetrators, 70.8% were diagnosed with mental disorder and diminished mental competency including acute alcohol intoxication, personality disorders (41%), alcohol addiction (8%), neurotic disorders (6%), schizophrenic psychosis (5%), affective disorders (3%), paranoid psychosis (3%), organic disorders (2%), psychoactive drug addiction (1%), and mental retardation (0.6%); but no information was provided about organic or neurological disorders (Gajic et al., 2016). Of intimate partner homicide perpetrators in Sweden, females were more likely to have been hospitalized for substance abuse in their lives and more likely diagnosed with a personality disorder than males, while no female perpetrators had a major mental illness (psychotic, bipolar and schizoaffective disorders, or severe depression with psychotic symptoms) (Caman, Howner, Kristiansson, & Sturup, 2016). South Korean female homicide offenders were twice as likely as males to have mental illness, such as postpartum depression or schizophrenia (Sea et al., 2018). Female homicide perpetrators in the United States, England, and Wales are more likely to have mental health problems than male perpetrators, but this may vary based on the perpetrator’s relationship to the victim (Ferranti, McDermott, & Scott, 2013; Flynn, Abel, While, Mehta, & Shaw, 2011; Poteyeva & Leigey, 2018; Richard-Devantoy et al., 2016). Although these aforementioned authors described psychiatric mental health conditions, none reported on neurological conditions.
Neurological conditions
Neurological conditions were found in 95% of a random sample of female prison inmates; traumatic brain injuries (TBI) were most prevalent (Brewer-Smyth, Burgess, & Shults, 2004; Brewer-Smyth, Pohlig, & Bucurescu, 2016). TBI prevalence in prisons is significantly higher than the general population (Farrer & Hedges, 2011). Although reports vary due to inconsistent measurement, greater than 88% of prisoners in some populations may have a TBI history (Allely, 2016; Durand et al., 2017; O’Rourke, Linden, Lohan, & Bates-Gaston, 2016). Women had more TBIs before their first crime than men (Colantonio et al., 2014). Females in the justice system have often been victims of multiple violence-related TBIs (Moore, Indig, & Haysom, 2014; Wall, Gorgens, Dettmer, Davis, & Gafford, 2018). TBI could be a risk factor for violence in females (Brewer-Smyth et al., 2004) and males (Fazel, Lichtenstein, Grann, & Langstrom, 2011; Fazel, Philipson, Gardiner, Merritt, & Grann, 2009; Williams et al., 2018). Others did not find this relationship, most likely due to methodological differences (O’Sullivan, Glorney, Sterr, Oddy, & da Silva Ramos, 2015). TBI could be the result of violent behavior rather than the etiology (Kaba, Diamond, Haque, MacDonald, & Venters, 2014). TBI is related to problematic substance use (Moore et al., 2014) that may precipitate violent crimes (Brewer-Smyth & Pohlig, 2017; Fishbein, Dariotis, Ferguson, & Pickelsimer, 2016).
Neuropsychiatry
Female homicide perpetrators were more likely than males to have a history of mood disorder, borderline personality disorder, abuse, and have cognitive impairment in verbal abilities that were related to sexual abuse (J. M. Fox, Brook, Heilbronner, Susmaras, & Hanlon, 2019). Males and females who solely killed children scored lower in language and verbal memory, compared with those who also killed adults, with few gender differences reported (Azores-Gococo, Brook, Teralandur, & Hanlon, 2017).
The Hypothalamic–Pituitary–Adrenal (HPA) Axis
The HPA axis is a major component of the “fight or flight” response to stress. The hypothalamus sends a signal to the pituitary, which then signals the adrenal gland to make cortisol, a primary product of the HPA axis stress response. This process is accelerated during stress. However, under usual conditions, the basal cortisol diurnal pattern peaks in the morning and then gradually decreases throughout the day, creating a steep diurnal cortisol slope (DCS) from morning (AM) to evening (PM). Although most research focuses on cortisol reactivity to acute stress, recent studies show the importance of DCS circadian variability related to health outcomes, which needs further study (Adam et al., 2017). HPA dysregulation with low AM cortisol and flatter DCS is reported in female victims (Bernard, Frost, Bennett, & Lindhiem, 2017; Cordero et al., 2017; Trickett, Noll, Susman, Shenk, & Putnam, 2010) and perpetrators (Brewer-Smyth & Burgess, 2008; Brewer-Smyth et al., 2004). HPA dysregulation could result from physical trauma to the hypothalamus or pituitary with TBI (Munoz & Urban, 2013), and/or emotional trauma, such as adverse childhood experiences (ACEs), which are all related to female violence (Brewer-Smyth & Burgess, 2008; Brewer-Smyth et al., 2004). This is complicated as female prisoners with TBI experienced more early life physical and sexual abuse than those without TBI (Colantonio et al., 2014).
Emotional trauma from ACE, such childhood sexual abuse (CSA), can affect brain development during critical vulnerability periods and precipitate long-lasting HPA axis dysfunction (Bernard et al., 2017; Danese & McEwen, 2012; De Bellis, Spratt, & Hooper, 2011; De Bellis & Zisk, 2014). Prolonged childhood stress may chronically elevate HPA axis activity, which ultimately leads to reduced responsiveness of this system later in life (Trickett et al., 2010). Maternal deprivation is associated with elevated cortisol in the first year of life, but later low AM and flattened DCS, with hypocortisolism most extreme among those with the highest cortisol in infancy (Dettling, Feldon, & Pryce, 2002; M. M. Sanchez, 2006). Similarly, early neglect and abuse predicted later low AM cortisol and flatter DCS (van der Vegt, van der Ende, Kirschbaum, Verhulst, & Tiemeier, 2009) with even low to moderate abuse and neglect (Kuras et al., 2017). A meta-analysis suggests only a small, significant association between maltreatment and blunted AM cortisol, but not other cortisol indices, possibly because studies included children with a mean age of 1 year and adults (Bernard et al., 2017).
This cortisol attenuation is believed to be an adaptive strategy of down regulating the stress system to avoid continually evoking physiological responses to prolonged stress. This fight or flight response is effective for short-term, but problematic with long-term threats. Downregulation avoids chronic arousal and excessive energy expenditure, which would lead to morbidity and early mortality (Susman, 2006). Downregulated hypocortisolism in victims of chronic stress could be a physiological link to hyper-arousal (Daskalakis, Lehrner, & Yehuda, 2013; Dayan, Rauchs, & Guillery-Girard, 2016) that could prime one to violently overreact to circumstances.
Aggression-related psychopathologies are also associated with downregulated HPA axis and ACE. Mimicking this condition in rodents leads to abnormal aggression (Haller, 2014a, 2018). Far more female homicide offenders had a negative emotional family climate, were sexually abused, and had a custodian with mental problems in childhood compared with male homicide offenders (Yourstone et al., 2008). With HPA axis links to aggression, the lateral hypothalamus was implicated in deviant aggression resulting from chronic glucocorticoid deficiency (Haller, 2018). The ventromedial hypothalamus (Yang et al., 2013) and hypothalamic preoptic region (Moffitt et al., 2018) were also implicated. Greater aggression and rage were reported with hypothalamic hamartoma and epilepsy (Killeen, Bunch, & Kerrigan, 2017). Brain structures affected by childhood chronic stress hormone secretion include the hippocampus, prefrontal cortex, and amygdala, which affect cognitive function and emotion regulation, increasing vulnerability to later aggression and violence (Raymond, Marin, Majeur, & Lupien, 2018).
Alcohol
Women who kill are becoming more like men who kill (Batton, 2004; Putkonen, Weizmann, Lindberg, Rovamo, & Hakkanen, 2008), especially intoxicated females (Weizmann-Henelius, Putkonen, Naukkarinen, & Eronen, 2009). Researchers reported no difference between the proportion of male and female homicide perpetrators under the influence at the time of the crime (Häkkänen-Nyholm et al., 2009) which had been previously more common for men. Of male and female homicide offenders in Serbia, 57% were under the influence of alcohol at the time of the crime compared with just 2% on other psychoactive substances, whereas 21% of these homicide perpetrators drank alcohol daily and 8% had alcohol addiction (Gajic et al., 2016). Of intimate partner homicide perpetrators in Sweden, females were more likely to have been intoxicated by alcohol or other substance during the crime (Caman et al., 2016).
Alcohol use, associated with TBIs & CSA (Brewer-Smyth & Pohlig, 2017) could increase risk for female-perpetrated violence (Denson, O’Dean, Blake, & Beames, 2018; Hedlund, Forsman, Sturup, & Masterman, 2018). It was believed that past trauma, such as ACE, resulted in alcohol self-medication. Self-medication theories are now challenged as physiological links have been reported. Cortisol alterations could predict posttraumatic increases in alcohol use (Trautmann et al., 2018). With lower baseline hair cortisol, the number of new-onset traumatic events was related to subsequent daily alcohol use (Trautmann et al., 2018). Chronic HPA axis changes are linked to heavy alcohol use (Badrick et al., 2008). Flatter DCS at age 11 predicted greater alcohol use from ages 15 to 18, and heavier alcohol use predicted further DCS flattening at age 18.5 years (Ruttle, Maslowsky, Armstrong, Burk, & Essex, 2015).
Regardless of family alcoholism history, changes were reported in healthy young adult ACE victims including reduced cortisol reactivity, flatter DCS, diminished cognitive capacity, and unstable affect regulation, leading to impulsivity and antisocial tendencies (Lovallo, 2013). A proposed model describes physiological, cognitive, and affective tendencies consistent with altered frontal-limbic and dopaminergic brain function that may explain a pathway from ACE to stress system changes that could lead to impulsive and high-risk behaviors such as greater alcohol use (Lovallo, 2013) and violence.
Yet, the role of alcohol in the neurobiology of female homicide perpetrators needs further inquiry. The purpose of this study was to re-analyze data from our previous studies described below, to identify potential neurobiological risk factors for female-perpetrated homicide. We hypothesized a positive relationship between CSA, neurological histories, including TBI, abuse-related injuries, being under the influence of alcohol at the time of the crime, and female-perpetrated homicide, and a negative relationship between basal AM cortisol, DCS, amount of time since last abuse, and female-perpetrated homicide.
Method
This is a nonexperimental cross-sectional secondary analysis of data from our data set used in previous studies. The purpose of the current study is to elucidate neurobiological risk factors for female-perpetrated homicide. Original studies compared females who committed violent versus nonviolent crimes (Brewer-Smyth et al., 2004), females sexually abused by a family member versus those not abused by a family member (Brewer-Smyth & Burgess, 2008), and those under the influence of alcohol versus other substances at the time of the crime (Brewer-Smyth & Pohlig, 2017). Although differences between violent and nonviolent criminals have been reported, data on homicide perpetrators and noncriminals have not.
Methods for this data set were described in the articles above. Briefly, females were recruited from minimum and maximum security sections of a Mid-Atlantic U.S. prison. Homicide perpetrators could be placed in minimum or maximum security sections of the prison depending upon their behavior in the prison and suspected current level of threat. Homicide perpetrators who killed their abuser, but posed no threat in the prison may be housed in a minimum security section of the prison. Subjects volunteered, signed informed consents, and all procedures were in compliance with institutional review boards and Federal regulations for studies of prison inmates (Brewer-Smyth, 2008). Subjects were included if they were convicted, sentenced, and incarcerated in this prison for at least 2 months to avoid acute stress of sentencing or substance withdrawal (Buydens-Branchey & Branchey, 1992) that could affect cortisol. Exclusion criteria included corticosteroid use, pregnancy, oral lesions, bleeding gums, dehydration, and other illness that could affect saliva flow or cortisol. In addition, noncriminal comparisons were randomly recruited from female day shift prison staff because they were on the same sleep–wake cycle, in the same environment that could affect cortisol, and had background checks confirming they were never convicted of a crime.
Measures
All subjects were interviewed and examined privately by the first author of this and all publications on this data set. She is a neuro-rehabilitation clinical nurse specialist who was blinded to the crimes. Neurological histories were validated by neurological examinations for all subjects in this data set and data collection was consistent for all subjects. Neurological history and examination methods were validated by neurologists and have been described in our previous publications (Brewer-Smyth et al., 2004; Brewer-Smyth et al., 2016). The purpose was to obtain examination evidence of conditions that may be more prevalent in violent versus nonviolent females and evidence to support histories provided by each inmate, such as neurological deficits and cranial–facial scars or palpable areas of skull damage consistent with self-reports of traumatic injuries and other neurological histories. The full health history and examination was conducted before saliva samples were taken to also identify anything that might affect cortisol results such as bleeding gums, certain medications, or illness.
Violence
After individual forensic evaluations, crimes were grouped as violent or nonviolent. Violent crimes were against people including homicide, manslaughter, robbery, assault, sexual assault, and kidnapping. Nonviolent crimes included theft, burglary, forgery, conspiracy, driving, and drug-related non-violent offenses. Subjects convicted of a violent crime due to negligence or as an accomplice but did not commit violence were categorized as nonviolent. Criminal records verified crimes.
Adverse Experiences in Childhood (ACE) and Adulthood were measured with Muenzenmaier’s scale (Meyer, Muenzenmaier, Cancienne, & Struening, 1996; Muenzenmaier, Meyer, Struening, & Ferber, 1993) that was slightly modified to assess frequency and severity of sexual and physical abuse before and after age 18. It is valid and reliable in studies of women of similar age, ethnic background, mental illness, and prisoners (Brewer-Smyth & Burgess, 2008; Brewer-Smyth et al., 2004; Meyer et al., 1996; Muenzenmaier et al., 1993).
Cortisol
Salivary cortisol measures plasma-free cortisol at lower costs than invasive, more stressful blood studies. To evaluate basal AM, PM, and DCS, saliva was taken in the first 30 min after awakening before eating, drinking, or smoking, and again before dinner. Subjects were asked not to smoke, eat, or drink anything other than water between the noon meal and PM sample. Samples were frozen until all were analyzed at the same time under the same conditions by researchers who were blinded to all data at Salimetrics, State College, Pennsylvania.
Results
In terms of diversity variables, all in the sample population identified as females, lived in the same state in the United States, and ranged from 18 to 58 years of age. Demographics, racial ethnic representation, and type of crimes of those in this sample were similar to the total prison population, though noncriminals were slightly higher educated than inmates. The prison sample was more economically impoverished than noncriminals. Of homicide perpetrators, six were African American and three Caucasian. Those of other racial ethnic groups who made up a smaller percent of the study sample were not known to have committed homicide.
Neurological histories of homicide perpetrators included TBIs, lead or other toxin exposure, headaches, memory problems, serious learning disability, seizures, and one had a neurosurgical procedure. Homicide perpetrators experienced the greatest CSA frequency and severity, most recent abuse, most neurological histories, primarily TBIs; most health care access for abuse-related injuries; lowest AM and PM cortisol; and greatest proportion under the influence of alcohol at the time of the crime (though significance cannot be determined for cortisol or alcohol). Homicide perpetrators under the influence of alcohol at the time of the crime had the most recent abuse, lowest AM cortisol, and flattest DCS (though the small alcohol homicide n precludes determining significance; Figures 1 and 2). Time since last abuse, AM cortisol and DCS progressively decreased as crime severity increased, whereas other variables progressively increased as crime severity increased (Figures 1 to 5).
AM cortisol and DCS between AM and PM decreased as crime severity increased.
Females who committed homicide while under the influence of alcohol had been victims of more recent abuse than those not under the influence of alcohol, though the number of alcohol-related homicides precludes accurate statistical significance.
A greater percent of those who committed homicide were under the influence of alcohol and a lower percent were under the influence of other substances at the time of the crime.
Homicide perpetrators had significantly more neurological histories especially TBIs and greater health care access for abuse-related injuries compared with noncriminals.
Homicide perpetrators suffered significantly greater frequency and severity of childhood sexual abuse (CSA) compared with noncriminals.
Generalized regressions using negative binomial link functions yielded significant differences for noncriminals versus homicide perpetrators who had more neurological histories (−1.620; 95% confidence interval [CI] = [−2.531, −0.710]; Gen R2 = .11; p = .0005*) mainly TBIs (beta = −3.201; 95% CI = [−5.530, −0.872]; Gen R2 = .08; p = .0071*) were victims of greater CSA frequency and severity (beta = −1.520; 95% CI = [−2.932, −0.110]; Gen R2 = .05; p = .0348*) and accessed health care more frequently for abuse-related injuries (beta = −2.0164; 95% CI = [−3.697, −0.336]; Gen R2 = .05; p = .0187). Logistic regression revealed that homicide perpetrators had less years since last abuse controlling for age (odds ratio [OR] = 0.85, 95% CI = [0.74, 0.99]; Gen R2 = .48; p = .0326) compared with noncriminals.
With SPSS, adjusting for number of years since last abuse (OR = 1.039; 95% CI = [0.998, 1.081]) and number of neurological histories (OR = 0.873; 95% CI = [0.761, 1.002]), higher CSA (OR = 1.137; 95% CI = [1.003, 1.288]) and having committed a crime under the influence of alcohol (OR = 2.428; 95% CI = [1.051, 5.607]) predicted flatter DCS. Although Hosmer–Lemeshow was .5, further analyses with JMP suggest that this is a weak model and only CSA (R2 = .05; p= .0161*) weakly predicted flatter DCS. For each CSA score increase, DCS drops by −0.017259.
A greater percent of those who committed homicide were under the influence of alcohol and a lower percent were under the influence of other substances at the time of the crime, though significance cannot be determined (Figure 3). Those who committed violent a crime under the influence of alcohol had significantly less years since last abuse than those not under the influence of alcohol at the time of their crime (OR = 0.942; 95% CI = [0.890, 0.998]; Figure 2).
Discussion
These preliminary findings suggest that having been a victim of recent abuse; greater CSA frequency and severity; multiple neurological histories, especially TBIs; health care access for abuse-related injuries; low AM and PM cortisol; and being under the influence of alcohol could be risk factors for females perpetrating homicide, though further study is needed. Those who committed homicide under the influence of alcohol suffered the most recent abuse and had the lowest AM cortisol and flattest DCS, though significance cannot be determined. Recent abuse, CSA, TBIs, neurological histories, and health care access for abuse-related injuries were weakly significantly different between homicide perpetrators and noncriminals. These findings suggest neurobiological links between TBI, having been a victim of abuse, cortisol downregulation, and females being under the influence of alcohol when committing homicide. Others also reported that negative consequences increase as abuse severity increases (Fergusson, McLeod, & Horwood, 2013). ACE victims with long-lasting HPA axis alterations more likely also experience stressful events in adulthood (Morris, Abelson, Mielock, & Rao, 2017).
Of female perpetrators of homicide and other violence, 81.7% were intoxicated at the time the crime (Weizmann-Henelius et al., 2009). The majority (79.4%) were under the influence of alcohol compared with illicit drugs (5.3%) while committing homicide (Tiihonen et al., 2015). Alcohol may increase violence because of its direct effect on cognitive function that reduces inhibition, impairs conflict resolution, exacerbates stressors, and may lead to behaviors perceived as offensive or disrespectful contributing to relational tension.
Homicide perpetrators had more TBIs with examination evidence of frontal cortex injury, also implicated by others (Choy, Raine, & Hamilton, 2018; Leutgeb et al., 2015) which is critical in controlling neuronal aggression from the limbic system and hypothalamus (Bogerts, Schone, & Breitschuh, 2018) with HPA dysregulation. Some homicide perpetrators seemed to have overreacted to their circumstances when there was no evidence that it was in self-defense.
Familial sexual abuse, cortisol, TBI, and abuse-related injuries suggest neurobiological and socializing risk factors for female-perpetrated violence (Brewer-Smyth & Burgess, 2008). Yet, the majority of CSA victims do not commit homicide or other violence. Research shows individual differences in genomic information regulation by dynamically changing gene patterns of transcription and translation that elucidates wide variability in neurobiological ACE sequelae that can lead to later consequences such as bio-behavioral problems for some but not others (Alexander et al., 2018; Bouvette-Turcot, Meaney, & O’Donnell, 2018; Buchmann et al., 2014; Harker, 2018). Although victims are often not identified immediately after CSA, it is critical to intervene as early as possible to prevent female victims from perpetrating homicide and to study ways to prevent chronic stress such as from CSA from affecting behavior of the victim and epigenetics of future generations (Jawaid, Roszkowski, & Mansuy, 2018; Yehuda & Lehrner, 2018).
Although most of those at risk, such as female TBI and CSA victims, do not commit violence under the influence of alcohol, these victims may want to limit alcohol intake to prevent violent behavior, as CSA and TBI were risk factors for females committing a violent crime when under the influence of alcohol (Brewer-Smyth & Pohlig, 2017). These victims often regretted their violent acts and said they would not have done it if they were not under the influence of alcohol. Although they may not be received favorably, policies restricting alcohol availability affected alcohol-related homicides and other violence (UNODC, 2014). Increased homicides were reported with moderately restrictive policies compared with the most restrictive policies, and even greater homicides with lax policies (A. I. Sánchez et al., 2011). Restricted alcohol sales and drinking hours led to a decrease of almost nine homicides a month in Diadema, Brazil (Duailibi et al., 2007). A 1% increase in alcohol cost, 1 hr earlier establishment closing time, and establishments limited to less than 25 per postal code substantively reduced violent crime (Fitterer, Nelson, & Stockwell, 2015).
Limitations and Direction for Future Research and Clinical Practice
Causation cannot be determined with this study design. Yet, weak significance suggests that frontal cortex damage from TBIs and cortisol downregulation related to past abuse may increase risk of female-perpetrated homicide, especially when under the influence of alcohol. Intervention effects on the HPA axis reported for children before 24 months of age suggest a sensitive period during which stress response systems are most strongly influenced by a change in environment for those randomized into a foster care intervention versus remaining institutionalized in Romania (McLaughlin et al., 2015). In addition, the transition between middle childhood and adolescence may be a sensitive period for diurnal cortisol patterning when ACE victims might benefit from improved environments, potentially contributing to a steeper DCS in adolescence (Flannery et al., 2017). Furthermore, early trauma can induce long-lasting epigenetic changes such as in an FK506-binding protein 5 (FKBP5) gene, an important regulator of stress hormone systems, in those who carry a variant, which leads to dysregulated stress hormone responses throughout life (Klengel et al., 2012). This DNA methylation seems restricted to childhood trauma exposure, but not adulthood, suggesting a sensitive period in early development for these epigenetic effects. Future studies need to evaluate HPA axis plasticity in adulthood and determine whether violence decreases if cortisol regulation can be improved.
In addition to the HPA axis, the psychobiology of stress involves the autonomic nervous system (ANS) (Savia & Granger, 2016) which was not evaluated in this study and could further explain violent behavior. Low levels of HPA axis activity were associated with higher levels of both externalizing and internalizing problems, but only in children with low ANS arousal evaluated with alpha-amylase measurements (Chen, Raine, Soyfer, & Granger, 2015). Salivary alpha-amylase may be a reliable marker of hypervigilance and trauma-related reactivity to negative affective information in women (Yoon & Weierich, 2016). Also, beyond the HPA axis, ACE may affect the limbic–hypothalamic–pituitary–adrenocortical (LHPA) system, a critical system fostering both stress resilience and vulnerability (Gunnar & Vazquez, 2015). Future studies could evaluate these factors plus expand the variables of diversity to better understand this high-risk population.
Similar to this study, female homicide perpetrators made up a small percent of the sample for others: 4% (Myers, Chan, & Mariano, 2016), 6% (Eckhardt & Pridemore, 2009), 7% (Gerard, Browne, & Whitfield, 2017), 8% (Gajic et al., 2016; Hedlund et al., 2018), 9% (Sea et al., 2018), 9.6% (Trägårdh, Nilsson, Granath, & Sturup, 2016), and 20% (Caman et al., 2016) because there are so few female homicide perpetrators. Yet, these findings provide valuable information to inform future studies of the neurobiology of female homicide perpetrators.
Greater health care access for abuse-related injuries was significantly related to committing homicide, consistent with reports that more females than males sought help prior to committing homicide, as one in two female perpetrators was in contact with the medical system, police, or social welfare authorities prior to the homicide (Yourstone et al., 2008). Females accessing health care for seemingly minor abuse-related injuries, TBIs, and other neurological conditions provide opportunities to evaluate and prevent further abuse and potential subsequent homicides and other violence perpetrated by victims. These females were often too fearful to report abuse to avoid retaliation by the abuser, or they believed they had nowhere else to go. Health care providers need to probe into suspicious cases and provide referrals for their psychological, physical, housing, and safety needs. Health care providers released these women when their abuse-related injuries were not believed to be life-threatening. Yet, they were life-threatening to their subsequent homicide victims.
Footnotes
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: The authors received funding from Sigma Theta Tau International Honor Society and the Rehabilitation Nursing Foundation.
