Domestic violence, also known as Intimate Partner Violence (IPV), is typically attributed to a psychological cause; this is due to the fact that perpetrators are often diagnosed with personality disorders and psychopathy . However, neurobiology also plays an important role in mediating this offense. Emotional dysregulation and poor self control typical of these offenders have found roots in various neurological differences, in particular, hyperactivity in the parietal lobe and the limbic system , and frontal lobe deficit . Furthermore, cognitive impairments play a role in trapping victims in their abusive relationship as in the case of battered women with PTSD, whose cortical hyperactivity decreases their perception of pain. In contrast, certain neurological developmental differences could act as a coping mechanism for witnesses by lowering their level of distress during exposure to domestic violence  . For the benefit of developing effective preventions for potential offenders, treatment programs for perpetrators and victims, neuroscience is an ineligible discipline that should be further investigated into as it is evident that domestic violence is beyond the realm of psychology.
1 Psychological Influence
Compared to the general population, domestic violence perpetrators have a higher prevalence for many mental illnesses, in particular, Personality Disorder, Psychopathy, Social Phobia and Substance Abuse. The role of Personality Disorder and Psychopathy in mediating characteristics commonly found amongst domestic violence perpetrators will be discussed.
Research has found mixed results in the connection between psychopathy and domestic violence. Traditionally, psychopathy is correlated with repeated and more violent batterers . This is evident in a research that looked at IPV perpetrators in Spanish prisons, and found that 12% of these offenders are psychopaths . Furthermore, these individuals are more impulsive, less empathetic and have lower self-esteem than their fellow non-psychopathic counterparts . In contrast, Gondolf et al. show that repeated batterers have a similar percentage of psychopathic disorders diagnoses as non-repeated batterers, and that repeated batterers only show a higher tendency for mild psychopathic symptoms that are not severe enough to meet diagnostic criteria for psychopathic disorder . A potential explanation to these obscure findings is that a stronger psychopathic tendency is only detected in IPV perpetrators when results are interpreted on a smaller scale as shown in a study by Swogger et al. They have found that antisocial batterers could be distinguished from antisocial violent offenders if only specific aspects rather than the overall psychopathy disposition are compared. Antisocial batterers score higher on affective deficits, and lower on impulsivity and irresponsibility than antisocial violent offenders in PCL-R assessment. Unfortunately, as antisocial offenders are the main focus of this research, Swogger et al's findings may not generalize to all IPV perpetrators, thus further investigation is needed to validate their results.
1.2 Personality Disorder
|Attachment model by Mauricio et al., showing the correlations between attachment
styles, personality disorders, and domestic violence.
The most common types of personality disorder diagnosed in IPV perpetrators are antisocial personality disorder and borderline personality disorder. Interestingly, maritally distressed men are not more prone to developing the same personality disorders as do IPV perpetrators, suggesting that the manifestations of borderline and antisocial personality disorder in perpetrators are beyond the environmental influence of poor marital relationships. A possible mediator between personality disorder and IPV perpetrator is one’s attachment style. Attachment is the first interpersonal bond that infants form with their significant others, and the form of this attachment has significant impacts on one’s self-regard, future relationships, and expectations of others. Two kinds of attachment related to IPV perpetrators are avoidant attachment, which is characterized by high independence and a lack of trust in others, and anxious attachment, which is often found in dependent individuals with low self-worth and great fear of being rejected by others. Study by Mauricio et al. have found that avoidant attachment shows a greater correlation with physical and psychological IPV when it co-occurs with antisocial personality disorder, borderline personality disorder, or a combination of the two. On the other hand, anxious attachment is more correlated with physical and psychological IPV when it is comorbid with borderline or both borderline and antisocial personality disorders together, and show a greater correlation with only physical IPV when it is comorbid with antisocial personality disorder. This may explain why personality disorder is not found in all IPV perpetrators. Furthermore, neurological factor may also mediate the relationship between domestic violence and personality disorder.
2 Neurological Influence
Psychopathology alone cannot constitute domestic violence as it is not diagnosed in all IPV perpetrators. Moreover, psychological interventions have not yielded much success in rehabilitating these offenders. Batterers who have undergone psychological treatment only excel untreated batterers by 5% in violence elimination, suggesting the presence of another supplementary cause to domestic violence. Traumatic brain injury (TBI) and neurological differences are two candidate causes.
2.1 Traumatic Brain Injury
Traumatic brain injury is relatively typical in batterers, and manifests many of the characteristic traits of IPV perpetrators. According to a meta-analysis by Farrer et al., there is a 53% TBI prevalence in batterers as opposed to 10-38.5% in the general population. The higher concurrence of IPV and TBI could be explained by Hibbard et al's finding that 66% of participants in their study develop at least one personality disorder after a TBI, in particular, borderline and avoidant personality disorders which are commonly diagnosed in batterers. In addition, personality changes such as increase in annoyance, irritability, verbal aggression, impulsivity, and a decrease in sensation seeking are reported by both patients and their family after a TBI incident. In addition, TBI batterers show poorer executive functioning than non-TBI batterers, implicating TBI’s involvement in mediating cognitive deficits in IPV.
2.2 Neurological Changes
Neurological differences, whether caused by an innate disposition or extrinsic factors such as TBI, can cause cognitive impairments in batterers that facilitate and sustain their violent perpetration towards their partner.
Batterers are more sensitive to visually threatening stimuli than non-batterers, resulting in their overreactivity and aggression towards women as shown in the fMRI study by Lee et al. Greater activations in the hippocampus, occipital and parietal lobes are found in batterers compared to non-batterers when both groups are shown threatening pictures without women, and pictures of aggressive threat towards women. The study also found that the precuneus of batterers are hyperactive when aggressive-female pictures are presented. As the precuneus may induce a greater recall of memories associated with visual triggers, a high precuneus activation level may further increase batterers’ hyperresponsivity to female-related visual threat and aggravate their response to threatening situations. Besides attention bias, research has also found that batterers show a poorer overall performance than non-batterers in various neuropsychological tests, especially in the executive functioning, and impulsivity domains, lending supports to earlier findings that frontal lobe deficits are prevalent in batterers. Interestingly, IPV perpetrators are also less verbally skilled than the general population. This verbal incompetence may hinder perpetrators from expressing themselves and resolving conflicts verbally, thus indirectly facilitating domestic violence by making aggression a seemingly easier solution for these individuals.
|fMRI scan of batterers and non-batterers|
|Areas of the brain that are more active in batterers than
non-batterers are indicated by red dots and white arrows.
A study by Chan clearly demonstrates the neuroanatomical differences in IPV offenders by coupling fMRI scan with emotional stroop task, where batterers and non-batterers have to determine whether the neutral or aggressive word on a computer screen and the word previously presented are in the same color. Overall, batterers give slower responses than do non-batterers, and have an even longer reaction time for aggressive words, suggesting that they spend more time processing aggressive words, and are more sensitive to aggressive stimuli than the controls. Comparing the fMRI scans, perpetrators show hypoactivity in the left anterior cingulate cortex and the left middle frontal gyrus. Deficit in the former weakens the ability of prefrontal cortex in regulating cortical regions associated with emotions, while the latter decreases the inhibition of negative affect such as anger and aggression. Hyperactivity is found in the right amygdala, which produces excessive fear, and the right hippocampus, which reacts to this excessive fear by retrieving more negative memories that feeds back to the amygdala, intensifying the negative emotion. In addition, batterers have a right lateralization tendency, which is hyperactivity in the right hemisphere, leading to oversensitivity to emotional stimuli as the right hemisphere is greatly involved in emotion processing. The insula, which is responsible for self-elicited thoughts and the production of hypothetical fear, is also more active in batterers, further distorting their interpretations of situations.
Leslie Morgan Steiner talks about what it is like to be an IPV victim, and why it is so hard for IPV victims to leave their abuser from experience.
3.1 Brain Injury and PTSD
Brain injury is also a common phenomenon amongst battered women. A study that examined 53 battered women found that 92% of them have had head injuries from IPV. This finding is also supported by Valera & Berebaum's study in which 75% of the 99 IPV victims in their sample have had at least 1 head injury from their abusive partner, and 50% have suffered from more than one injury. This study has also found a positive correlation between the degree of brain injury and abuse severity, meaning the more severe the brain injury, the more severe the abuse.
Traumatic Brain Injury is also associated with the psychological health of IPV victims as it frequently co-occurs with [ http://www.nimh.nih.gov/health/topics/post-traumatic-stress-disorder-ptsd/index.shtml Post Traumatic Stress Disorder (PTSD)], a psychopathology commonly diagnosed in battered women. Moreover, many brain regions associated with TBI are found to be related with PTSD. Overlapping neural correlates between TBI and PTSD include the dorsolateral prefrontal cortex, the orbital frontal cortex, and the hippocampus, which causes similar symptoms such as deficits in memory, cognition, and emotion between the two. As both PTSD and TBI are highly prevalent amongst IPV victims, it is important to take into consideration the relationship between PTSD and TBI when treating these individuals.
3.2 Neural Correlates of Victims with PTSD
|IPV victims with PTSD show a decrease in subjective pain when stimulated
with heat in the second experimental trial. This is evident in their decreased RAI activation
and increased ACC activation.
Cognitive and affective impairments arisen from neurological changes in IPV victims with PTSD could be a major attribution to revictimization. A study by Strigo et al. demonstrates how neurological differences can alter pain response in IPV victims with PTSD by administering heat stimuli repeatedly to these individuals and a control group of non-abused women without PTSD. Battered women show more activity in their right anterior insula (RAI), prefrontal and parietal cortices than the controls in the first experimental trial. As the RAI is the integrating center that passes emotions made vigilant by the sensory system onto the cortex, hyperactivity in this region suggests that victims are more sensitive to pain than non-victims in their first experience of the stimuli. Interestingly, even though IPV victims are more sensitive to the heat stimuli, their subjective estimation of the temperature of heat administered is similar to that of the controls. Furthermore, in subsequent heat stimulations, victims report a lower pain level than the controls. This decrease in subjective pain in the presence of threatening stimuli is evident in the decrease in activity of the victims' RAI, parietal and occipital cortices, making the victims more tolerable of the abuse and have more difficulty leaving their abusive relationship.
It has also been proven using various methods including fMRI, H-MRS, and the stroop task, that hyperactivity in the dorsal cingulate cortex and the amygdala found in battered women with PTSD make it more difficult for them to leave their abusers. Fonzo et al. compared the BOLD fMRI results between battered women with PTSD and non-battered controls without PTSD as they work on a face-matching task for 3 emotions (happy, fearful, angry). They found that there is a higher activation level in the anterior insula and amygdala in these victims when they are viewing angry and fearful faces. This result indicates that more anxiety is induced in IPV victims with PTSD as the amygdala is responsible for fear processing, and the insula is involved in the detection of others and one’s own emotions. In addition, this research has also found a decrease in the connectivity between the dorsal anterior cingulate cortex, the insula, and the amygdala. This neurological abnormality signals poorer emotional regulation in victims because there are fewer interactions between the prefrontal cortex, which is responsible for affect control, and the limbic system, whose role is to regulate sensory and emotional processing. Moreover, as the dorsal anterior cingulate cortex is involved in arousal and attention control, victim’s hyperactivity in this region when viewing a male faces as opposed to a female’s, suggests that IPV victims are more alarmed and more sensitive to males than non-victims. Expanding the findings of this research, Simmons et al found that victims with PTSD show the same neurological pattern when anticipating negative stimuli.
IPV victims with PTSD are more fearful of their perpetrators, are more prone to making inaccurate evaluations, and have greater difficulty recovering from the abuse owing to their neurological differences. Although Seedat et al has demonstrated that these specific changes are unique to victims with PTSD, other studies have found contrasting results which implicates that PTSD may not be the sole reason to the brain changes. A MRI study by Fennema-Notestine et al. did not find any statistically significant differences in the frontal and occipital cortices between IPV victims with and without PTSD. These two groups also have similar results in neuropsychological tests that assessed their working memory, executive functioning, and verbal ability.
Domestic violence influences children witnesses by altering their neurological and psychological development. A research studying the mental health of children demonstrates in its sample of 7865 participants that 4% of these children have witnessed IPV, and that these witnesses are three times more likely to develop conduct disorder than non-witnesses. Exposure to domestic violence is also demonstrated in a 20-year cohort study as the second greatest environmental risk that predisposes children to becoming a batterer, and confers witnesses the greatest susceptibility to becoming an IPV victim. Moreover, children witnesses of IPV
show a lower value of fractional anisotropy than non-witnesses in their inferior longitudinal fasiculus (ILF). It has been hypothesized that exposure to IPV may have caused this region to overactivate, eventually stunting its growth in adolescence. This underdevelopment in ILF, in turn, helps lower distress and fear for the witness when they encounter subsequent episodes of IPV. In support of this hypothesis, Anderson & Bang found that female children witnesses have better resilience, which is measured by one’s self-acceptance and control. Although they exhibit mild traumatic symptoms, female witnesses are less susceptible to PTSD than non-witnesses. Further research should be conducted to determine whether this low PTSD prevalence in female witnesses is related to ILF underdevelopment, and whether this finding also applies to male IPV witnesses.