• ADHD and Bipolar Disorder and the difference of executive control and emotional processing
In research published in Behavioral Neuroscience, Soncin and colleagues (2016) compared executive functioning in ADHD and BD relative to controls using an oculomotor task, in which participants were cued (by color of the fixation point) to either look toward (prosaccade trials) or away from (antisaccade trials) a visual target.
Critically, on antisaccade trials participants must inhibit the automatic response of looking toward the visual target. Thus, slower reaction times and direction errors on antisaccade trials are indicative of response inhibition difficulties.
To examine whether response inhibition is differentially influenced by emotion processing in these groups, task-irrelevant emotional faces (fear, happy, sad, neutral) were presented before or with the target on a subset of trials. Participants were told to ignore the face images, and to make the quickest and most accurate eye movement in response to the task cue and target location.
On antisaccade trials, both ADHD and BD groups were slower to initiate the correct saccade, had more variable reaction times, and made more direction errors (look toward when cued to look away or vice versa) than controls, but only the differences in variability and direction errors between control and ADHD groups reached significance.
Thus, although there were subtle differences between how ADHD and BD groups compared to controls on trials that taxed executive function, they were largely indistinguishable from each other qualitatively. Indeed, the BD-control group comparisons likely did not reach significance due to more variance in the BD versus ADHD group.
Importantly, deficits in reaction times on antisaccade trials were exacerbated in the BD group when a negative (fear, sad) or neutral task-irrelevant face was presented. The authors interpret these results to suggest that there are commonalities in pathophysiology related to response inhibition and inattentiveness, likely mediated by the dorsolateral prefrontal cortex, in both ADHD and BD.
However, BD patients have additional dysfunction in the orbitofrontal cortex, which is involved in emotional control and mediating responses during emotional regulation. Thus, the interaction between executive control and emotion processing differentiated between ADHD and BD patients, which suggests a fruitful avenue for better characterizing deficits in these groups in a clinically useful manner.
Soncin, S., Brien, D. C., Coe, B. C., Marin, A., & Munoz, D. P. (2016). Contrasting emotion processing and executive functioning in attention-deficit/hyperactivity disorder and bipolar disorder. Behavioral Neuroscience, 130(5), 531–543. http://dx.doi.org/10.1037/bne0000158