Intact interference and inhibitory functions in participants with bipolar disorder and their first-degree relatives.

Introduction: Bipolar disorder (BD) is considered a highly heritable disorder. Several cognitive endophenotypes, such as executive functions and verbal memory, have been suggested. A key component of executive functioning is inhibition, a complex construct consisting of various subtypes. Only some of these subtypes have been investigated in BD participants and their relatives. Recent findings suggest that difficulties with more basic functions such as processing speed may account for some of the deficits observed in BD. This possibility has not been explored for inhibitory functions.

Method: The current study investigated interference, behavioral and cognitive inhibition, and set-shifting in 36 BD participants, 24 of their unaffected first-degree relatives, and 40 healthy controls. We first used analysis of variance to assess group differences. This was followed by a second analysis in which we controlled for age and processing speed.

Results: Group performances after adjustment for age and processing speed were similar in tasks assessing interference and inhibition. However, shifting to a different task set required more time in BD participants than in controls even after adjustment for age and processing speed. BD relatives appeared to show a similar slowing but findings did not reach significance.

Conclusions: The findings suggest that responses to interference and inhibitory functions may be preserved in BD participants; however, set-shifting abilities appear to be impaired in BD participants and may be affected in their relatives. Our findings further underline the importance of adjusting for more basic functions such as processing speed when evaluating neuropsychological functions.