Lithium effects on impulsivity and emotional processing.

Lithium is an effective treatment for mood disorders. However, its mechanism of action concerning its effect on impulsivity and emotional processing is still unclear. The current study aimed to investigate the effect of a 5-day lithium treatment on decision-making, reward-seeking and emotional processing in healthy volunteers. We conducted a double-blind, placebo-controlled, cross-over design study involving sixteen participants aged 18-50 years. Participants received lithium 800 mg once daily followed by matching placebo or vice versa for five days in a random order. Impulsivity and emotional processing were assessed on day six using the Cambridge Gambling Task and the Emotional Testing Battery, respectively. There were significant interactions with large effect sizes between treatment and order for delay aversion (F1,14 = 13.79, p = 0.002, partial η2 = 0.496) and reward-seeking (F1,14 = 34.065, p = < 0.001, partial η2 = 0.709), but the post-hoc tests suggested only moderate, inconclusive effects at either visit. There was a significant interaction between treatment, emotion and order with a large effect size for the facial expression recognition task. The post-hoc analyses found that during the first visit, relative to placebo, lithium-treated participants showed a higher accuracy in recognising disgust and lower misclassification rates and response bias in recognising sad facial expressions, but higher accuracy and response bias in recognising fear during the second visit. We found a significant interaction between treatment and valence with a large effect size for emotional encoding of self-referent words. Post-hoc analysis showed that lithium was associated with a longer reaction time to encode negative self-referent words than placebo. Short-term lithium treatment in healthy participants produced a positive emotional bias in facial expression recognition and emotional encoding of self-referent words, but no significant effects on impulsivity and reward seeking. The early induction of positive bias in emotional processing may contribute to lithium's effectiveness in mood disorders.