Search

Background: Hypomania is associated with impulsive decision making and risk taking, characteristics that may arise from hypersensitivity to reward. To date, the neural dynamics underlying intertemporal reward processing have neither been characterized clinically nor in the general population. Taking vulnerability to hypomania as a surrogate model of impulsivity, we utilized event-related potentials to study the neural mechanisms of delay discounting. Methods: In the first experiment, 32 participants completed an established Two Choice Impulsivity Paradigm in which free choice between immediate and delayed rewards was used to quantify impulsivity behaviorally. In the second experiment, electroencephalography was recorded while 32 separately recruited participants completed a speeded response task involving gains and losses of monetary incentives to be paid at three different delays after the experiment. Results: In the first experiment, the hypomania-prone group made significantly more immediate choices than the control group. In the second experiment, the hypomania-prone group evidenced greater differentiation between delayed and immediate outcomes in early attention-sensitive (N1) and later reward-sensitive (feedback-related negativity) components. Proneness to hypomania was also associated with greater N1 amplitude to rewards per se. Conclusions: These results indicate steeper delay discounting in hypomania at multiple stages of information processing. The N1 modulation by valence and delay suggests an attentional bias to immediate rewards, which may drive subsequent cognitive appraisal of outcomes (feedback-related negativity). These results highlight the early influence of attention on reward processing and provide support for reward dysregulation accounts of bipolar disorder. Potential implications for mindfulness training and other therapeutic interventions are highlighted. [Copyright &y& Elsevier]

Abstract: Background: Mania is argued to stem from the dysfunctional processing of reward. Investigation of hypomania in healthy samples has the potential to offer refined insight into the particular aspects of reward processing in mania that are dysfunctional. Method: In this study, fMRI was employed in contrasting a sample of 12 unmedicated subclinical hypomanic individuals with a sample of 12 unmedicated controls in order to investigate reward-related processing in a reinforcement-learning task. Results: Four findings in the hypomania-prone group relative to the control group supported atypical reward processing. Firstly, striatal activation that correlated with reward value and prediction error was stronger in response to cues and outcomes respectively, consistent with hypomania being related to an enhanced perception of the value of goals that may lead to reward. Secondly, value-related medial temporal activation was stronger in response to cues, suggesting that in hypomania-prone individuals, stimuli in memory were represented in accordance with their perceived value. Thirdly, these effects failed to be modulated by the actual value of outcomes, suggesting that hypomania is related to a decreased ability to discriminate between cues differing in value. Fourthly, increased insula activation in response to expected, but absent, reward was consistent with a bias towards expecting positive outcomes in decision-making. Conclusion: Together, the findings suggest that enhanced perception and representation of goal-value that nonetheless fails to discriminate on the basis of actual goal-value, coupled with a positive outcome-expectancy bias, could be causally related to insatiable and indiscriminate reward seeking in mania. [Copyright &y& Elsevier]