Grey matter abnormalities in ADHD and Bipolar disorder: two structural MRI meta-analyses on the shared mechanisms and differences in brain functioning.

In the last decade several studies recognized that bipolar disorder (BD) and attention deficit-hyperactivity disorder (ADHD) frequently co-occur. Despite the fact that the two disorders are phenomenologically different, numerous studies have found some symptomatologic similarities between ADHD and BD (e.g., impulsivity and emotional dysregulation). The purpose of our research was to study similarities and differences in gray matter abnormalities of ADHD and BD patients during adulthood, and to investigate a potential link between these two different mental disorders. Through a precise and careful selection of voxel-based morphometry studies, two separate meta-analyses were conducted: the first meta-analysis was focused on a sample of adult ADHD patients, whereas the second meta-analysis included a sample of adult BD patients (drug-naïve or at first manic/hypomanic onset). The research showed that the two patients’ samples have different gray matter atrophies: nonetheless, these atrophies are mostly located in a common region, the cingulate cortex. As this region is directly connected to the limbic lobe and the prefrontal cortex, structural and functional abnormalities of the cingulate cortex can be translated into deficits in executive and emotional functions. Consequently, we hypothesize that impulsivity, emotional dysregulation, and inability to manage unpleasant emotions, that are directly related to both ADHD and BD, could be the consequence of atrophy found in the cingulate cortex in these disorders.