Effect of bipolar disorder on left frontal cortical responses to goals differing in valence and task difficulty.

BACKGROUND: The behavioral activation system (BAS) dysregulation theory of bipolar disorder predicts that bipolar individuals will show an excessive increase in approach motivation during reward striving. Building on past research showing that the left frontal cortical region is involved in approach motivation, we predicted that individuals with bipolar disorder would evidence increased relative left frontal cortical activity in response to goal striving, particularly in response to positive challenges.
METHODS: Right-handed individuals (age 18-24) with a bipolar spectrum diagnosis (n = 41) and individuals with no major affective psychopathology (n = 53) were presented with cues indicating that, on a given trial, an easy, medium, or hard anagram (scrambled word) would be presented in 7 seconds and that they would receive money or avoid losing money for the correct solution (10 anagrams of each of the 6 types). During this preparation period, electroencephalogram (EEG) alpha power was measured and hemispheric asymmetry indexes were computed.
RESULTS: Compared with the nonbipolar individuals, individuals with bipolar disorder showed greater relative left frontal cortical activation in preparation for the hard/win trials. Whereas nonbipolar individuals showed a decrease in left frontal cortical activation from medium to hard win trials, bipolar individuals did not. In addition, among bipolar individuals, current self-reported activation related to greater left frontal activation to the hard/win trials.
CONCLUSIONS: These results provide support for an integrative biopsychosocial model of bipolar disorder, BAS dysregulation theory, and suggest that relative left frontal activity, which may be involved in mania, is triggered by challenging and potentially rewarding events.