Modulating reward learning with transcranial direct current stimulation: Applications for the treatment of depression

Background Negative attention biases are thought to be a causal factor in the development and maintenance of depression. It has been proposed that this bias may be caused by a belief that negative events are more informative than positive events. In the present study, it was investigated whether transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, could modulate information content estimates for rewarding and aversive outcomes in healthy adults [1], [2]. Methodology Forty healthy volunteers aged 18–45 participated in one sham and one active tDCS session in randomised order. During each session, participants completed an information bias learning task (IBLT) while receiving tDCS targeting bilateral dorsolateral prefrontal cortex (DLPFC) for 20minutes at 2mA. Information content estimates for positive and negative outcomes were reflected in participants’ learning rates on the IBLT, which were derived from the data with the use of computational models. Results Active bifrontal tDCS was associated with an increase in learning rates for positive but not negative outcomes on the IBLT (F=5.47, P<0.05). These behavioural changes were maintained following cessation of the stimulation. No significant alterations in other computational learning parameters (e.g., choice stochasticity) were observed with neurostimulation, suggesting that the effects of tDCS were specific to learning rates. Conclusion These findings provide the first experimental evidence that modulating activity in the DLPFC can enhance learning from positive stimuli in healthy adults. This change in learning rates suggests an alteration in participants’ beliefs of how informative positive outcomes are compared to negative outcomes. Additional research is needed to assess whether this effect of tDCS can be harnessed to ameliorate negative attention biases associated with psychiatric disorders. The present results provide an exciting early step in the development of novel interventions for depression.