Effects of cerebellar transcranial direct current stimulation on reversal learning performance during threat of shock

According to the cerebellar lateralization hypothesis of motivational direction, relative left-to-right dominant posterior cerebellar activity is associated with avoidance motivation and anxiety, whereas relative right-to-left dominant posterior cerebellar activity is associated with approach motivation and anger. The present study tested this hypothesis in avoidance-related behavior during rule learning combined with threat of shock. In a randomized double-blind sham-controlled between-subjects design, ninety healthy right-handed adult volunteers received either active (n = 45) or sham (n = 45) cerebellar left anodal-right cathodal transcranial direct current stimulation (tDCS) to the posterior cerebellum. During tDCS participants performed a gambling task with two changing reward-punishment schedules (reversals) and were believed to think that based on performance they could receive mild electric shocks to the forearm. Self-reported measures of anxiety, anger and impulsivity were assessed to examine affective state- and trait-dependent effects of cerebellar tDCS on reversal learning performance. Results showed no main effect of cerebellar tDCS on reversal learning performance. However, higher levels of shock anxiety were associated with increased reversal learning rate after the first reversal in the active compared to sham tDCS condition. Additionally, higher scores on trait impulsivity were associated with reduced reversal learning rate after the second reversal in the active compared to sham tDCS condition. These findings provide support for the cerebellar lateralization hypothesis of motivational direction and yield further evidence for context-relevant affective state- and trait-dependency in tDCS-related effects.