The key findings from this longitudinal study are that poor electrodermal fear conditioning from ages 3 to 8 years is associated with aggression at age 8 years. Two different designs examining the fear conditioning - aggression relationships indicate a robust and bidirectional effect: individuals with good conditioning from ages 3 to 8 years are less aggressive at age 8, and also less-aggressive children are better conditioners. To our knowledge, only one prior study has demonstrated such bidirectionality in the relationship between a biological risk factor (low resting heart rate) and aggression in children (Raine et al., 1997
). Moreover, the observed conditioning – aggression relationship applies to both males and females and could not be accounted for by the personality traits of anxiety and fearfulness. Findings constitute the first longitudinal study linking early fear conditioning deficits with aggressive behavior in children.
Neurological and brain-imaging research has shown that the amygdala and the prefrontal cortex are crucial for both the acquisition and expression of electrodermal conditioned fear in humans (Büchel, Morris, Dolan, & Friston, 1998
; Knight, Nguyen, & Bandettini, 2005
). Furthermore, neuroimaging studies have reported amygdala and prefrontal cortical deficits in aggressive and violent adults (Critchley et al., 2000
; Raine, Lencz, Bihrle, LaCasse, & Colletti, 2000
). Future child developmental studies which assess both amygdala and prefrontal functioning in conjunction with electrodermal fear conditioning could help substantiate the hypothesis that poor fear conditioning in aggressive children is predicated on dysfunction of these brain structures.
Until functional imaging studies are more easily able to scan young children in the 3–8 year age range, a relative strength of the electrodermal fear conditioning paradigm for child clinical researchers is that it allows for an indirect assessment of the brain circuit implicated in fear conditioning, including the amygdala and the orbitofrontal cortex. Given the technical ease with which it can be measured, the short test time duration (c. 10 minutes), its low cost (c. $5,000), and moderate aversive quality required for the UCS (90 dB), it is recommended that electrodermal fear conditioning should be increasingly assessed in both laboratory and field studies of disruptive behavior problems in children where it can be integrated with other variables to better understand the etiology of disruptive behavior disorders. It is noteworthy that intercorrelations between conditioning and antisocial/aggressive behavior at each ages were non-significant, whereas the average of conditioning across ages was significantly related to aggressive antisocial behavior at age 8 (see ). These finding are in accordance with the findings of LCGA, and suggest that conditioning measurement at multiple time points provides a more reliable assessment of conditioning.
While poor conditioners had significantly higher non-aggressive antisocial scores than good conditioners, children with high non-aggressive antisocial scores did not significantly differ on conditioning compared to those with low scores. This failure to find significant bidirectionality could be due to the moderate internal reliability of the non-aggressive antisocial scale (alpha = .67) and reduced statistic power. Nevertheless, children with poor conditioning showed significantly increased antisocial behavior using the biological design. On balance, the reduced conditioning - non-aggressive antisociality relationship should be interpreted with caution.
Using different sub-samples of the same larger cohort, prior studies have reported early psychophysiology in relation to later aggression and psychopathic personality (Gao, Raine, Venables, Dawson, & Mednick, in press b
; Glenn, Raine, Venables, & Mednick, 2007
; Raine, Reynolds, Venables, & Mednick, 1997
; Raine, Venables et al., 1997
). Specifically, among the original cohort of 1,795 subjects, low resting heart rate at age 3 was related to high aggression at age 11 (Raine, Venables et al., 1997
), while deficient electrodermal conditioning at age 3 predisposed to criminal offending at age 23 years (Gao et al., in press b
). In addition, reduced electrodermal orienting responses at age 3 have been found to be associated with high aggression at age 11 only among children from high socioeconomic homes (Raine, Reynolds et al., 1997
). Glenn et al. (2007)
found that long electrodermal half-recovery times to aversive stimuli and increased arousal and orienting at age 3 years were associated with high psychopathy scores in adulthood. However, only 29 out of the 200 subjects in the current sample were assessed on psychopathy at ages 25–28, and consequently we could not test for conditioning – psychopathy relations. The age 8 behavioral data were the focus of the current study because only the “200” (out of 1,795) were followed up on conditioning every year from ages 3 to 8, and at age 8, behavioral data were available for most of the subjects (143 out of 200) at the same time-point as the end of conditioning data collection, thus providing adequate statistical power. Importantly, to our knowledge this is the only study to date examining the longitudinal changes of autonomic conditioning at any age and its association with any child or adult behavior problem.
This study has complementary strengths and limitations. A potential limitation is that this sample is composed of community- recruited children from the African sub-continent. Nevertheless, findings on these non-Western children broadly confirm findings from adult studies in Western cultures. This is the only study to the authors’ knowledge investigating the early development of autonomic fear conditioning in relation to aggressive/antisocial behavior. This longitudinal assessment of conditioning fills a critical gap in the literature and provides an initial step towards clarifying the early links between fear conditioning and aggression in children. Furthermore, findings provide further support for the view that at least for early childhood behavior problems, there are common biological correlates to male and female aggressive behavior (Moffitt et al., 2001
). Behavioral measures were limited to teacher ratings and future multi-informant studies would be desirable. Importantly, it can neither be claimed nor concluded that conditioning deficits are specific to antisocial/aggressive behavior because the internal reliability of the hyperactive-inattentive scale was relatively low, and Type II error is possible; nevertheless, findings are consistent with prior studies showing normal conditioning in ADHD children (Pliszka et al., 1993
). Finally, preliminary evidence has shown that reactively aggressive children show heightened physiological responses to anger provocation (Hubbard et al., 2002
; Pitts, 1997
), suggesting that poor fear conditioning may not be found in all aggressive children. We were not able to measure reactive vs. proactive aggression to assess whether the poor fear conditioning – aggression relationship may be specific to proactive aggression, a form of aggression linked to psychopathy (Raine et al., 2006
). Although the current findings are suggestive, the question of whether or not poor fear conditioning in early childhood could be considered a developmental precursor to adult
antisocial and aggressive behavior requires further substantiation from longitudinal research.
The future promise of these findings for child psychopathology research is that the utilization of the electrodermal fear conditioning paradigm in a longitudinal context offers a relatively unique window into the interface between developmental science, neuroscience, and clinical science. This interdisciplinary convergence may potentially allow clearer elucidation of the etiology of child, adolescent, and adult behavior problems in future research.
- Previous studies have associated poor fear conditioning with adult psychopathy and criminality, but little is known on whether poor fear conditioning early in life is related to childhood aggressive/antisocial behavior.
- Findings from this longitudinal study indicated that poorer electrodermal fear conditioning from ages 3 to 8 years is associated with the development of aggressive behavior at age 8 years.
- Results suggest that abnormal amygdala functioning, as indirectly assessed by fear conditioning, may influence the development of childhood aggression.
- The utilization of the electrodermal fear conditioning paradigm in future studies of young children may help elucidate the etiology of both child and adult clinical disorders.