In previous work, we primarily used neuropsychological investigations to determine the functional impairments associated with CD+CU. We identified that adolescents with this disorder showed marked difficulties with: (1) the processing of fearful expressions. Youth with CD+CU show impaired recognition of fearful expressions. In addition, related functional Magnetic Resonance Imaging (fMRI) demonstrates reduced responses within the amygdala to fearful expressions in youth with CD+CU;(2) a basic form of emotional learning, stimulus-reinforcement association, which is critical for socialization (and also is amygdala dependent);(3) decision making reliant on the appropriate representation of outcome reinforcement information, a neuropsychological marker of dysfunction within ventromedial prefrontal cortex. Indeed, in line with this, we demonstrated using fMRI that youth with CD+CU showed impaired ventromedial prefrontal cortex signaling of reinforcement information in the context of a reversal learning task. Notably, patients with Attention Deficit Hyperactivity Disorder (ADHD) but without CD show no difficulties in either their amygdala response to fearful expressions or the signaling of reinforcement information within orbital frontal cortex. This is important because CD and ADHD are often seen in the same youth. About 65% of our youth with CD+CU also meet criteria for ADHD. However, by showing that youth with ADHD, but without CD, show no problems in fearful expression or reinforcement processing, we can be sure that these difficulties are linked to CD+CU rather than the comorbid ADHD. In our most recent work, we have used event related functional Magnetic Resonance Imaging follow up our previous behavioral work on a basic form of emotional learning, stimulus-reinforcement association. In this study, we are examining the activity of the amygdala and orbital frontal cortex in youth with CD+CU and comparison youth during a stimulus-reinforcement learning task. We have seen that youth with CD+CU show notable difficulties in the recruitment of the amygdala during the performance of this task. In addition, they show problems in the role of orbital frontal cortex in representing reinforcement information, particularly experiences with unexpected reinforcement information. The appropriate response to unexpected reinforcement information is critical because it allows rapid learning to occur. The failure of youth with CD+CU to respond to this information probably underlies some of the emotional learning and socialization difficulties seen in this population. It should be noted that this study also revealed problems in youth with CD+CU in another region that is critical for the response to unexpected reinforcement information;the caudate. This latter region is becoming a focus for our future work.
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