2023-06-28 12:21:28
Anhedonia is central to the symptoms of depression. More specifically, olfactory anhedonia, defined as the inability to feel olfactory pleasure, might be partly responsible for a disturbance in behavior (food intake, social interaction, mood) leading to an aggravation of depressive symptoms1. At the neurobiological level, anhedonia has been associated with an imbalanced activity between a hypoactive ventral striatum and an overactive prefrontal cortex (PFC), suggesting a key role for dopamine. A study (COBRA) conducted in this area at the Le Vinatier hospital center is drawing promising clinical avenues.
Non-invasive transcranial stimulation (NIBS) techniques, such as repeated transcranial magnetic stimulation (rTMS) which can modulate (facilitate or reduce) the activity of a targeted brain region, have been proposed as innovative treatments to reduce symptoms in depressed patients. It has been shown that CPF stimulation can, on the one hand, improve anhedonia and, on the other hand, lead to a release of dopamine in patients. Moreover, studies suggest that the effects of NIBS are greater if the stimulation is performed on a cerebral network activated during the performance of a behavioral task, for example, rather than at rest2.
The COBRA study (Combining Olfactory and BRAin stimulation in treatment resistant depression) started in January 2023 proposes to combine rTMS targeting the CPF with hedonic olfactory stimulation. The latter consist of diffusing pleasant odors in the room, to activate the dopaminergic system in depressed patients in order to reduce the symptoms of depression. In a randomized controlled clinical trial, 80 patients with a depressive episode were divided into 2 groups and received 50 sessions of: 1-rTMS and hedonic olfactory stimulation, or 2-rTMS only.
We perform pre- and post-treatment assessments that measure depression severity, physical, social, and olfactory anhedonia, and the connectivity and activity of regions involved in the pathophysiology of depression and the reward circuitry. We hypothesize that the combination of treatment with rTMS applied to the left PFC and hedonic olfactory sensory stimulation will have greater clinical effects than those observed following treatment with rTMS alone.
To date, 11 patients out of the 80 expected have been recruited, suggesting an end of recruitment at the end of 2026, and the publication of the results in 2027.
Laetitia Imbert, doctoral student in neurosciences, member of PsyR², team of the Center for Research in Neurosciences of Lyon (CRNL), CH du Vinatier.
1- Brand, G., & Schaal, B. (2017). Olfaction in depressive disorders: Interests and perspectives. The Brain, 43(2), 176-182.
2- Silvanto, J., Muggleton, N., & Walsh, V. (2008). State-dependency in brain stimulation studies of perception and cognition. Trends in cognitive sciences, 12(12), 447-454.
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