SANTA FE, N.M. – A study of children's autonomic responses to reward and negative mood induction suggests that when conduct disorder and depression are comorbid, depression is the primary disorder.
In a poster presentation at the annual meeting of the Society for Psychophysiological Research, Hilary K. Mead, a graduate student working in the Child and Adolescent Adjustment Project at the University of Washington (Seattle), noted that previous studies have suggested that comorbidity rates for the two conditions may be as high as 82%, but that it's unclear whether conduct disorder (CD) arises from depression or whether depression arises from CD.
A third possibility is that neither condition is primary and that both are driven by a common etiological substrate, with each representing an alternative manifestation of a single biological disposition. This hypothesis found no support in the experimental results, Ms. Mead noted.
The experiment involved 116 children, aged 8–12 years. Eighteen of those children had conduct disorder and/or oppositional defiant disorder, 15 had depression and/or dysthymia, 37 had comorbid depression and conduct disorder, and 46 had no psychiatric condition.
All children had their electrodermal responses (EDR), their respiratory sinus arrhythmia (RSA), and their cardiac pre-ejection period (PEP) measured during three successive experimental conditions: a 5-minute baseline, a monetary incentive task, and negative mood induction via an emotionally evocative film clip.
If CD were the primary disorder, groups with CD alone and with comorbid CD and depression would be expected to have a similar pattern of autonomic responses.
On the other hand, if depression were primary, groups with depression alone and comorbid CD and depression would show similar autonomic responses. If neither condition were primary, all three groups of children with psychiatric disorders would be expected to be similar, Ms. Mead said in her poster.
As it turned out, children with CD had a pattern of autonomic responses that differed significantly from the other groups. The EDR of children with CD did not change across trials of the reward incentive task, while all other groups showed decreases in EDR. During negative mood induction, children with CD had decreasing PEP and increasing RSA, while the other groups showed no change from baseline.
The investigators concluded that depression is the primary disorder in children with comorbid internalizing and externalizing psychopathologic symptoms.
The National Institutes of Health funded the study.