The Effects of Intermittent Theta Burst Stimulation on Working Memory in Depressed Patients
Depression , iTBS , Working Memory
Background: People with depression struggle with cognitive impairments such as decreased working memory. The brain areas associated with working memory, such as the prefrontal cortex and hippocampus are negatively affected by depression; studies have shown decreased volume, activity, and disturbed brain connectivity. Currently, there is a lack of treatment options for improving working memory in depressed patients. Therefore, the therapeutic potential of intermittent theta-burst stimulation (iTBS) on working memory was explored. iTBS has been shown to be effective in treating mood, increasing plasticity and inducing neurogenesis. These findings suggest a potential for iTBS as a treatment tool for working memory. Objective: The objective of the present study was to determine whether iTBS treatment is associated with improvement in working memory, and connectivity changes between areas in the prefrontal cortex, hippocampus and the rest of the brain. Methods: We recruited 10 patients with major depressive disorder (MDD). Patients received the standard 25 days of iTBS treatment. We used the n-back (2-back) task to test working memory during functional magnetic resonance imaging (fMRI) scan. Participants received a fMRI scan before and after the final iTBS treatment. Participants also completed clinical measures (i.e., depression scales) before and after their treatments. Results: The participants did not show significant improvements in mood and the n-back task (accuracy and reaction time) after the iTBS treatments. There were significant changes in functional connectivity during the resting state scans and for the 0 and 2 back conditions of the n-back task between various areas including the left hippocampus and the frontal poles with structures such as the caudate, occipital cortex, lingual gyrus and the temporal lobe. Conclusion: Our pilot study showed that iTBS treatment may not be an effective tool for improving behavioural performance on the n-back task. However, the significant functional connectivity changes suggest that iTBS may be responsible for beneficial brain changes in depressed patients. These changes could be explained by increased efficiency and/or cognitive control in the context of the n-back task. Future research with sham controlled design and different working memory tasks are needed to determine the effects of iTBS treatment on WM.