The Impact of Targeted Cathodal Transcranial Direct Current Stimulation on Reward Circuitry and Affect in Bipolar Disorder

Bipolar Disorder is costly and debilitating, and many treatments have side effects. Transcranial Direct Current Stimulation (tDCS) is a well-tolerated neuromodulation technique that may be a useful treatment for Bipolar Disorder if targeted to neural regions implicated in the disorder. One potential region is the left ventrolateral prefrontal cortex (vlPFC), which shows abnormally elevated activity during reward expectancy in individuals with Bipolar Disorder. We used a counterbalanced repeated measures design to assess the impact of cathodal (inhibitory) tDCS over the left vlPFC on reward circuitry activity, functional connectivity, and affect in adults with Bipolar Disorder, as a step toward developing novel interventions for individuals with the disorder. -1mA cathodal tDCS was administered over the left vlPFC versus a control region, left somatosensory cortex, concurrently with neuroimaging. Affect was assessed pre and post scan in remitted Bipolar Disorder (n = 27) and age/gender-matched healthy (n = 31) adults. Relative to cathodal tDCS over the left somatosensory cortex, cathodal tDCS over the left vlPFC lowered reward expectancy-related left ventral striatal activity (F(1,51) = 9.61, p = 0.003), and was associated with lower negative affect post scan, controlling for pre-scan negative affect, (F(1,49) = 5.57, p = 0.02) in all participants. Acute cathodal tDCS over the left vlPFC relative to the left somatosensory cortex reduces reward expectancy-related activity and negative affect post tDCS. Build on these findings, future studies can determine whether chronic cathodal tDCS over the left vlPFC has sustained effects on mood in individuals with Bipolar Disorder, to guide new treatment developments for the disorder.