Emotional bias and inhibitory control processes in mania and depression

Despite markedly different clinical presentations, few studies have reported differences in neuropsychological functioning between mania and depression. The disinhibited behaviour characteristic of mania and evidence that subgenual prefrontal cortex is differentially activated in mania and depression both suggest that dissociable deficits will emerge on tasks that require inhibitory control and are subserved by ventromedial prefrontal cortex.

Manic patients and controls undertook computerized neuropsychological tests of memory and planning ability. In addition, manic and depressed patients were directly compared with controls on a novel affective shifting task that requires inhibitory control over different components of cognitive and emotional processing.

Manic patients were impaired on tests of memory and planning. Importantly, affective shifting performance of manic patients differed from that of depressed patients. Manic patients were impaired in their ability to inhibit behavioural responses and focus attention, but depressed patients were impaired in their ability to shift the focus of attention. Depressed patients exhibited an affective bias for negative stimuli, and we believe this to be the first demonstration of an affective bias for positive stimuli in manic patients.

Observed impairments on tests of memory and planning suggest a global pathology for mania consistent with previous profiles for this disorder and similar to established profiles for depression. The results on the affective shifting task demonstrate the presence of mood-congruent bias and dissociable components of inhibitory control in mania and depression. Against a background of memory and planning impairments in the two groups, these findings are consistent with a role for the ventromedial prefrontal cortex in mediating mood-cognition relationships.