Objective:  Bipolar disorder is increasingly recognized as a significant source of psychiatric morbidity in children and adolescents. Younger bipolar patients symptomatically differ from adults, and frequently present with comorbid disorders, particularly attention‐deficit hyperactivity disorder (ADHD). The neurophysiological relationship between these two disorders, however, remains unclear. In this study we utilized functional magnetic resonance imaging (fMRI) to compare activation patterns during performance of a simple attention task between bipolar adolescents with and without ADHD.

Methods:  Eleven bipolar adolescents with comorbid ADHD and 15 bipolar adolescents without comorbidity were recruited to participate in fMRI scans. A single‐digit continuous performance task alternated with a control task in a block‐design paradigm. between‐group comparisons were made using voxel‐by‐voxel analysis. Follow‐up correlations were made between performance and activation.

Results:  Group performance did not significantly differ in percentage correct (p = 0.36) or discriminability (p = 0.11). ADHD comorbidity was associated with less activation in the ventrolateral prefrontal cortex (Brodmann 10) and anterior cingulate, and greater activation in posterior parietal cortex and middle temporal gyrus. Comorbid ADHD was associated with substantial differences in patterns of correlation between performance and voxel‐by‐voxel activation.

Conclusions:  Our findings suggest that comorbid ADHD in bipolar adolescents is associated with activation of alternative pathways during performance of a simple attention task. The pattern of differences suggests that bipolar adolescents with comorbid ADHD demonstrate decreased activation of prefrontal regions, compared with bipolar adolescents without ADHD, and preferentially recruit portions of posterior parietal and temporal cortex.