Mechanisms in the Association Between Abuse and Violence: CNS Injury
The possibility that brain damage is incurred by abused children through physical injury has been discussed by many writers. A recent estimate suggests that about 12% of skull fractures among children under the age of 3 are due to child abuse (Leventhal, Martin, & Asnes, 2008; there were 11,772 skull fractures in 2003 in the Kids’ Inpatient Database, which includes data for approximately 85% or more of the US population). Brain injury is frequently associated with cognitive, emotional, and intellectual deficits which are, in their turn, associated with violence.
Lee and Hoaken (2007) emphasize that maltreatment can have a “profound impact” in early childhood when the brain is particularly vulnerable to adverse environmental input due to rapid neuronal growth. In addition to physical injury to the brain due to blunt force trauma, difficulties with emotion regulation and cognitive processing may also be “hardwired into neural networks via the overactivation of certain brain regions and dysfunctional cognitive processes” (Lee & Hoaken, 2007, p. 281). They point to research suggesting that even mild uncontrollable stress can impair function in the pre-frontal cortex. Changes in brain function associated with maltreatment have included disrupted functioning of the HPA axis (e.g., van Voorhees & Scarpa, 2004), cortisol dysregulation (e.g., Murray-Close, Han, Cicchetti, Crick, & Rogosch, 2008; Sanchez, McCormack, Grand, Fulks, Graff, & Maestripieri, 2010 ) and low left hemisphere functioning in fMRI (Raine, Park, Lencz, Bihrle, LaCasse, Widom et al., 2001).
The possibility that real physical damage to the CNS is supported by research. Gross physical differences have been observed between abused children and normal comparisons. Kent (1976) followed children who had been in foster care in Los Angeles for more than 6 months. He found that abused children were small for their age (shorter and lighter). Some authors have hypothesized that neglect alone prevents the healthy development of the prefrontal cortex, thus causing executive deficits (Lee & Hoaken, 2007). Other studies have found that neglected children have had decreased metabolism in brain structures responsible for cognitive and social functioning, including the orbital frontal gyrus, the amygdala, and the pre-frontal cortex (Lee & Hoaken, 2007). Maltreated children may also have a smaller corpus callosum, which is interpreted as support for the hypothesis that lack of stimulation in neglected children can result in permanent differences in brain structure (Lee & Hoaken, 2007). Sexual abuse victims have also shown an unusually asymmetrical stress response (Shenk, Noll, Putnam, & Trickett, 2010).
Lee and Hoaken (2007) reason that since the developing brain is “extremely sensitive to stress,” (p. 291) exposure to stress at a young age results in functional deficits and problems dealing with future stress. For example, the interconnecting networks of the brain are developed based on usage. Stress and trauma may cause brain systems that are not normally active to be chronically activated. Findings by Lewis and colleagues indicate that physical abuse is most likely to be associated with delinquency and violence when the child suffers from a CNS dysfunction, in particular one that impairs emotion regulation, or the child suffers from a psychiatric disturbance (Lewis, Mallouh, & Webb, 1989). They argue that child abuse often results in brain injuries manifested by emotional lability, extreme anger, and behavioral dysregulation. In one of their studies, Lewis, Shanok, and Balla (1979) compared the medical histories of incarcerated and nonincarcerated delinquent adolescents and found that serious delinquents were more likely to have sustained a head injury. The “especially violent” subjects had more accidents and injuries compared to the others. The authors conclude that early CNS trauma is an important factor responsible for serious violent delinquency. In another study, Lewis et al. conducted extensive testing of 14 juveniles sentenced to death for violent crimes in the United States In addition to a shocking rate of brutal abuse (12 out of 14), 9 had major neurological impairment, 7 had significant organic dysfunction in neuropsychological testing, and 12 had IQ scores of 90 or below (Lewis, Pincus, Bard, Richardson, Prichep, Feldman, & Yeager, 1988).
Mechanisms in the Association Between Abuse and Violence:
Given the potential for brain damage in abuse cases, it is natural to hypothesize that abuse may reduce intelligence and attenuate specific intellectual functions, and studies have borne witness to important effects. For example, intelligence deficits have been seen in many studies of neglected children, and some studies of physically abused children. In Kent’s (1976) follow-up of foster children, he found that none of the 159 neglected children had an IQ score above the average range; 78% had IQ scores below 90 at intake (this improved at follow-up). Among the physically abused children, the IQ scores were also skewed to the low end with 24% scoring below 70. Kent (1976) also reported an unexpectedly high prevalence of motor and language developmental delays, especially among the neglected children; 72% of neglected children and 39% of the physically abused children had language delays. In data from the Minnesota Parent-Child Project, neglected boys and girls had significantly lower IQ scores than other children; this was not true for physically abused children (Yates, Dodds, Sroufe, & Egeland, 2003). In another study, abuse, especially chronic abuse, was associated with lower IQ scores, and the authors’ limited set of family risk factors did not account for the association between chronicity of abuse and IQ scores (Jaffee & Maikovich-Fong, 2011). The authors did not account for the possibility of child effects in this analysis. Lee and Hoaken (2007) review the evidence and cite research suggesting that neglect, but not physical abuse, is associated with deficits in executive functioning.