| Richard Ramirez-a serial killer, also known as the Night Stalker. Known for keeping "trophies" e.g. body parts of the victim after mutilated them. Image source: archaicradio.com |
People with ASPD are believed to be cold blooded and remorseless for committing terrible crimes that often involves inhuman elements, therefore the thought of being able to identify individuals with biological vulnerability to ASPD by early brain imaging becomes intriguing. The earliest sign of ASPD individuals is the problem of conduct disorder (which will be discussed briefly after this introduction section) during adolescence where one's psychopathic traits begin to surface and causes conduct problems in places like schools. Psychopathic traits are often originated from core impairments in empathy (e.g. hard to understand other's expressions of distress), and in decision making (significantly impaired prediction error signalling resulting a heightened need for instrumental reward outcomes like power or sexual gratification)[1]. Known regions of the brain related to these impairments are the amygdala, vmPFC and striatum. Current research using advance neuroimaging tools like MRI scans, stereological volumetric assessment and computer software like SPSS shows some of the notorious characteristics of ASPD individuals such as reduced empathy and stimulation seeking are caused by early brain abnormalities including the thalamus, amygdala and the striatum (caudate head and body).
Current framework for conduct behavior
For background information, conduct disorder is a good indication for psychopathic traits developed later in life. There are two core impairments for psychopathic individuals as mentioned earlier, a callous–unemotional component (reduced empathy from amygdala resulting insensitivity to other's distress) and an impulsive–antisocial component (dysfunctional ventromedial prefrontal cortex and striatum resulting impairment in decision making and reward pathway). In addition, genetic and social-environmental factors also influence one's motivation and probability to engage in antisocial behaviours despite having abnormal brain developments.
| Framework of conduct behavior |
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| Framework of conduct behavior. Image source: James & Blair, 2013 |
The model of framework for conduct behavior summed up the current ideas on the earliest hallmarks and cause of ASPD (see above[1]) , by identifying the etiological (both genetic and environmental), neural, cognitive and behavioral factors of conduct disorder. Take note that genetic factors can play a role in decreasing amygdala activity leading to reduced responsiveness to distress cues followed by lack of empathetic expression; it can also influences influence striatal and vmPFC responsiveness to prediction error and reward pathway resulting impaired decision. Perinatal factors refer to any substance abuse in pregnant mother. All these factors can cause similar severity of cognitive deficiency and potentially forming the disposition of callous–unemotional traits, and elevated antisocial behaviors and instrumental aggression. These individuals tend to have frustration-based reactive aggression due to poorer decision making (also influenced by impulsivity). Past or current experience of trauma, violence and neglect can lead to hypersensitivity to threatening cues (also associated with anxiety disorder), and subsequently triggers reactive aggression. This model thus suggests that there may be two types of conduct disorder- the first type (also the focused type in this essay) is conduct disorder with psychopathic traits and the associated behaviors are in the red brackets which include callous-unemotional traits, antisocial behavior and instrumental aggression; whereas the second type is conduct disorder related with anxiety and emotional expression with associated behaviors in the blue brackets which include threat based reactive aggression and anxiety)
Thalamus
Reduced thalamic volume impairs normal sensory information processing and leads to specific crime patterns [2]. psychosocially-deprived individuals (PSD) may have learnt to be violent due to prolonged stress from past or current experiences in a maladaptive environment (e.g. with a history of childhood abuses) and therefore PSD is associated with many brain abnormalities (stress-linked brain areas). This is the first study to identify the specific structural brain volume changes in ASPD that are influenced by PSD which include childhood maltreatment involving physical and sexual abuses. This study also reconfirms the link [3)] between the type of childhood abuse and the type of crime committed in later life (i.e. physically-abused children commit serious physical violence whereas sexually-abused children engage in sexual violence crime later in life) by providing a neural-basis evidence.
| Correlation maps |
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| Correlation maps showing PSD ratings forms a negative correlation with grey matter in non-violent and violent participants. Image source: Kumari, et al., 2013 |
This study has demonstrated a global examination on brain areas involved in inducing violence in ASPD individuals. A novel finding from this study is the reduced thalamic volume in psychosocially-deprived violent individuals compared to non-deprived violent individuals and normal control groups. This finding is well supported by the subsequent correlation analyses that they performed, showing a negative correlation between thalamus volume and PSD ratings (the total score and separately on those with a history of sexual abuses or physical abuses).
PSD total scores
PSD total score from this study forms a negative correlation with the volumes of the temporal lobe and thalamus, but a positive correlation with putamen size. In particular for violent individuals, larger volume of the occipito-parietal region are found, whereas the occipito-parital region is smaller in non-violent individuals. The more physical abuses received , the smaller the whole brain volume is and larger putamen volume are found in violent individuals only.
with a history of physical or sexual abuses
However high physical abuse rating results in smaller cerebellum for both violent and non-violent individuals. Higher ratings of sexual abuse is linked to smaller thalamic volume for violent individual, whereas non-violent individuals have smaller volume of the occipito-parietal region
Why is this study so crucial to understanding ASPD individuals?
Since the thalamus is responsible for sensory processing and gating for all incoming information before reaching the cerebral cortex[4]. This study thus suggests that this dysfunctional thalamus in ASPD individuals causes them to have poor gating of incoming information or memory, thus making these individuals unable (or hard to) to suppress intrusive memories and thoughts related to their past abuse/maltreatment (often from childhood). Therefore this study reconfirms the link (see above for [3]) between the type of childhood abuse and the type of crime committed in later life (i.e. physically-abused children commit serious physical violence whereas sexually-abused children engage in sexual violence crime later in life) by providing a neural-basis evidence.
Amygdala
Localized Deformation and decreased responsiveness of amygdala lead to reduced empathy and aberrant social learning pathways. Many past studies have shown the involvement of amygdala in generating ASPD behaviors, but this recent study [5] is important as it has identified the specific corresponding regions of psychopathy facets implied in amygdala by examining surface deformations with the use of structural MRI and SPSS for analyses of the amygdala volumes. In figure 2, it is a statistical map highlighting the specific regions of amygdala surface deformations (encoded by color bar) in psychopathic individuals. These specific regions are located in the basolateral, lateral, cortical, and central nuclei of the amygdala. In addition, significant correlations are found between deformation (reduced amygdala volumes) and increased total and facet psychopathy scores, with the most significant correlation for the affective and interpersonal facets of psychopathy.
| Statistical maps |
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| Statistical map highlighting the specific regions of amygdala surface deformations in psychopathic individuals. Image source: Yang, et al., 2009 |
Other supporting evidence on this amygdala study
Psychopathic adolescent shows selective emotional empathy, such that they have normal recognition of anger and disgust expressions [6] shown in their blood oxygen level-dependent (BOLD) responses to angry expressions almost identical to control. However they only show impaired processing to distress social cues (e.g. fearfulness, sadness or pain) and positive expressions like happiness therefore indicating there is aberrant social learning pathway in them; these studies show consistent results with those in adults (with psychopathic traits) [7][8]. Another important case study is in a video interviewing Richard Ramirez [9], a serial killer (and psychopath with ASPD) that is comparable to Ted Bundy, he appears to relish the idea of evilness (by stating it out and have no sense of remorse to the victims he slaughtered inhumanly) and interestingly he claims that he has given up happiness and related positive emotions back when he was a kid, which is consistent with the study above on impairment in processing positive expressions like happiness.
Striatum (Caudate head and body)
The caudate head volume is linked with interpersonal and affective features of ASPD individuals while the caudate body volume is responsible for their stimulation seeking and impulsivity nature.
| Statistical maps |
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| Scatter plots comparing the left and right striatum volumes in the control and psychopathic groups. Image source: Glenn, et al., 2010 |
In this study [10], the scatter plot shows that the psychopathic group has increased left and right striatum volume and the followed up analysis indicates a trend for a much larger right caudate body. Furthermore, the correlation analysis found the strongest association between the caudate body and interpersonal and the affective subfacets; whereas the head of the caudate is with the lifestyle subfacet of psychopathy (refers to the impulsivity and stimulation-seeking aspects). Stimulation seeking aspect is linked to self gratification due to witnessing others/target suffering. This is also the first study showing structural difference (a 9.6% increase in striatum volume of psychopathic individuals compared with control subjects). This study is important because the increase in striatum cannot be blamed on environmental factors like head injury (as this tend to result in reduction of brain volumes) or due to substance and alcohol abuses which are normally held constant.
Other supporting evidence on this striatum study
This study's findings on how increased striatum volumes may predispose to psychopathy is well supported by other striatum studies, such that adolescents with aggressive conduct disorder show heightened striatum activity when looking at images of distress faces (it means they enjoy the idea of seeing painful faces) [11]. Those who score high on psychopathy also more willing to violate their own moral principles (e.g. performing acts that are often associated with outlaws, which is linked to stimulation seeking again) in return for a lesser amount of money than those who scored lower (suggests they enjoy doing things for the thrill of it instead of the actual quantity of the reward) [12]. Furthermore, striatum activity is correlated with individual differences in impulsivity, when shown by a preference for immediate over delayed gratification [13]