Compared to normal controls, youths with early and adolescent onset of conduct disorder displayed reduced responses in brain regions associated with social behavior (i.e., amygdala, ventromedial prefrontal cortex, insula, and orbitofrontal cortex).[20] In addition, youths with conduct disorder also demonstrated less responsiveness in the orbitofrontal regions of the brain during a stimulus-reinforcement and reward task.[30] This provides a neural explanation for why youths with conduct disorder may be more likely to repeat poor decision making patterns. Lastly, youths with conduct disorder display a reduction in grey matter volume in the amygdala, which may account for the fear conditioning deficits.[31] This reduction has been linked to difficulty processing social emotional stimuli, regardless of the age of onset.[32] Aside from the differences in neuroanatomy and activation patterns between youth with conduct disorder and controls, neurochemical profiles also vary between groups.[33] Individuals with conduct disorder are characterized as having reduced serotonin and cortisol levels (e.g., reduced hypothalamic-pituitary-adrenal (HPA) axis), as well as reduced autonomic nervous system (ANS) functioning. These reductions are associated with the inability to regulate mood and impulsive behaviors, weakened signals of anxiety and fear, and decreased self-esteem.[33] Taken together, these findings may account for some of the variance in the psychological and behavioral patterns of youth with conduct disorder.