Effects of Transcranial Direct Current Stimulation on Reward Learning in Subclinical Depression.

The development of non-invasive brain stimulation techniques offers new approaches for the treatment of depression. TMS is an approved treatment for treatment-resistant depression in the UK and USA. tDCS is currently under investigation as a potentially cheaper, safer and more accessible alternative. A recent meta-analysis suggests that it has a moderate antidepressant effect (Razza et al., 2020).

One potential way of improving the antidepressant efficacy of tDCS might be to combine it with a reward learning task. There is evidence from rodent and human studies that tDCS enhances activity-dependent synaptic plasticity and behavioural learning and retention (Fritsch et al., 2010; O'Shea et al., 2017; Reis et al., 2009).

In depression, people prioritize the processing of negative information at the cost of positive information and this negative bias is theorized to play a major role in the maintenance of depressive symptoms (Kube, Schwarting, Rozenkrantz, Glombiewski, & Rief, 2020). Therefore, by having depressed participants learn from reward, and increase their learning/retention via tDCS, this could potentially counteract negative bias and thus increase the antidepressant potential of tDCS.

In an earlier proof-of-concept study in young healthy volunteers (without low mood), we showed that tDCS applied during, but not before, an information-bias learning task increased reward learning rates. Here, we will test for the same effect in young healthy volunteers with subclinical depression. The study will involve online screening, a face-to-face screening session and two tDCS + learning sessions. Task performance will be fitted with a computational reinforcement learning model. Analyses will include both computational and non-computational measures of task behaviour.

Primary hypotheses: