Correlation between amygdala volume and impulsivity in adults with attention-deficit hyperactivity disorder

Background: Attention-deficit hyperactivity disorder (ADHD) is a chronic neurobiological disorder with childhood onset and persistence through adolescence and adulthood. ADHD patients frequently show exaggerated emotional responses. The amygdala plays an important role in emotion processing and in the activation of the frontal lobe. We hypothesised that smaller amygdala volumes in ADHD patients would be associated with less control of impulsivity and emotional instability. Methods: We studied nine adult patients with ADHD and nine group-matched healthy volunteers using a 1.5 T magnetic resonance imaging scanner. We manually obtained morphometric measurements, which were later processed and compared. Results: Significant negative correlation between the right amygdala volume and Barratt's impulsivity scores was observed (r = -0.756, p = 0.018). No correlation was found between impulsivity scores and the volume of the left amygdala. Age was not found to be a contributor of the results. Conclusions: Smaller amygdala volumes have been observed in patients with ADHD. Our results suggest that greater emotional processing and less control of impulsivity are associated with smaller amygdala volumes in ADHD patients. Furthermore, the right amygdala would play a bigger role in impulsivity and behaviour control than the left amygdala. Further studies involving larger samples of adult patients with ADHD and using multimodal designs are needed.