Cognitive neurostimulation as an antidepressant strategy?

With a lifetime prevalence of around 10%, depression is one of the most common health conditions worldwide1. With conventional treatments (eg: drugs) many patients do not respond or experience a relapse2. There is therefore a clinical need for new and more effective interventions.
Non-invasive brain stimulation (NIBS) offers potential new strategies for treating depression. NIBS applies magnetic or electric fields painlessly through to skull, aiming to excite or inhibit localized brain activity, and consequently change mental function3. The physiological effects of stimulation can persist minutes to hours after a single stimulation session. Since depression is associated with dysfunction in brain networks controlling emotion and its regulation (including dorsolateral prefrontal cortex, DLPFC), NIBS has been used to target DLPFC to try and restore normal network interplay and emotional regulation4. Excitatory transcranial magnetic stimulation (TMS) to left DLPFC, which is hypoactive in depression, is an approved treatment for drug-resistant depression in the USA and UK5. The efficacy of a related technique, transcranial direct current stimulation (tDCS), is under investigation. TDCS induces weak, diffuse electric currents in the brain. It offers a potentially cheaper, safer, easier to use alternative. Some studies have found antidepressant effects of tDCS over DLPFC that are comparable to the effects of TMS and drug treatment6. Others have reported very small effects7. In all these clinical trials, tDCS was applied at rest. However, tDCS is likely to be more effective if applied during learning. Work in animals has shown that tDCS can enhance long-term potentiation, a cellular substrate of learning and memory formation8-10. Proof of concept has been demonstrated for motor learning8,10.

The aim of my DPhil project is to extend this work and investigate the effect of tDCS during reinforcement learning on negative biases in depression. My project consists of three studies that will be conducted on community volunteers with subclinical depression (BDI-score of 10 or above).