Preliminary evidence for increased frontosubcortical activation on a motor impulsivity task in mixed episode bipolar disorder

Abstract

Of all mood states, patients in mixed episodes of bipolar disorder are at the greatest risk for impulsive behaviors including attempted suicide. The aim of this study was to examine whether the neural correlates of motor impulsivity are distinct in patients with mixed mania. Ten patients with bipolar disorder in a mixed episode (BP-M), 10 bipolar comparison participants in a depressed episode (BP-D), and 10 healthy comparison (HC) participants underwent functional MRI while performing a Go/No-Go task of motor impulsivity. Both patient groups had elevated, self-rated motor impulsiveness scores. The BP-M group also had a trend-level increase in commission errors relative to the HC group on the Go/No-Go task. While the full sample strongly activated a ventrolateral prefrontal-subcortical brain network, the BP-M group activated the amygdala and frontal cortex more strongly than the HC group, and the thalamus, cerebellum, and frontal cortex more strongly than the BP-D group. This study is primarily limited by a relatively small sample size. Higher commission error rates on the Go/No-Go task suggest increased vulnerability to impulsive responding during mixed episodes of bipolar disorder. Moreover, the distinct pattern of increased brain activation during mixed mania may indicate a connection between behavioral impulsivity and a failure of neurophysiological "inhibition", especially in the amygdala.