Major depressive disorder (MDD) is the most widespread psychiatric disorder, affecting 5% of adults according to the World Health Organization. Anhedonia, defined as the loss of the ability to experience pleasure, is one of the key symptoms of depression, possibly due to a dysfunction of the reward system. Intermittent theta-burst stimulation (iTBS) targeting the dorsolateral prefrontal cortex (DLPFC) has been demonstrated as an emerging treatment option for treatment-resistant depression. One explanation is that iTBS could work through modulating the reward system (increasing dopamine release). One way to improve the therapeutic benefits of non-invasive brain stimulation is to combine it with other therapeutic strategies. Interestingly, olfactory training -daily short-term exposure to pleasant odors- improves significantly depressive symptoms in MDD patients. Indeed, the olfactory system and the reward system are closely related through the olfactory tubercle, which is in the ventral striatum and directly connected to the ventral tegmental area.~The general aim of this research project is to test whether a combination of iTBS targeting the left DLPFC with an olfactory training can improve treatment outcome in MDD, compared to iTBS targeting the left DLPFC alone.~The investigators hypothesize that combining iTBS treatment on DLPFC with hedonic olfactory stimulation potentiates the effect of iTBS treatment administered alone on depressive symptoms, especially anhedonia (physical, social or olfactory). Moreover, the investigators also hypothesize that the superiority of the combined approach is underpinned by greater modulation of connectivity activity and strength between brain regions involved in dopaminergic transmission, compared with iTBS alone.
This is a prospective, randomized, double-blind, parallel-group controlled trial. The aim of this research project is to compare the clinical benefits achieved in patients with major depressive disorder (MDD) following two types of intervention: iTBS active alone or iTBS active combined with olfactory stimulations.