The Effects of ECT and/or iTBS on Olfaction and Cognition in Patients With Depression

Overview

The sense of smell and cognition are known to be closely associated with mood and emotional processes. However, despite the clear links between olfaction and cognitive processes with emotional states, research into the role of olfaction, cognition, and mood disorders has so far yielded variable results. This study proposes to investigate the ability to detect and identify odours and assess cognition in a group of patients with unipolar and bipolar depression prior to and after receiving their scheduled electroconvulsive therapy (ECT) or intermittent theta burst stimulation (iTBS) treatments. Olfaction will be evaluated utilizing standard olfactory testing protocols using commercially available kits. Cognition will be evaluated utilizing standard cognitive test protocols in a functional magnetic resonance imaging protocol. The results will potentially shed light on the link between olfaction, cognition and mood disorders.

The research to date indicates that olfactory sensitivity and cognition are reduced in depressed patients. The data also suggest that higher order cognitive odour evaluation, measured via identification testing, is not altered in depression. Furthermore, research into the effect (if any) of treatment on olfactory performance (sensitivity and identification) has been sparse. Researchers have called for studies that examine olfactory sensitivity prior to psychiatric treatment and post-remission. To the best of our knowledge there has yet to be a study on the effect of electroconvulsive therapy (ECT) or intermittent theta burst stimulation (iTBS) treatments on the olfactory performance of patients with treatment refractory Major Depressive Disorder (MDD) and bipolar depression. ECT has been identified as today's most effective treatment for severe depression due to the remission rates, speed of response, and the completeness of remission. iTBS is a new remittent transcranial magnetic stimulation (rTMS) protocol that has gained more notoriety within the field for the speed of administration, effectiveness of the treatment, and speed of response. Unlike rTMS, TBS mimics the endogenous theta rhythms of the brain, which results in greater potency in inducing long-term potentiation of synaptic connections in the targeted brain regions. iTBS has been shown to be effective in treating mood disturbances, and increasing plasticity and inducing neurogenesis in patients. People with MDD often struggle with cognitive impairments such as decreased executive functioning, attention, concentration, speed of processing, and working memory. The brain areas associated with cognition, such as the prefrontal cortex and hippocampus are negatively affected by depression; studies have shown decreased volume, activity, and disturbed brain connectivity in those two areas. Currently, there is a lack of treatment options for improving cognition in depressed patients. The investigators are focussing on exploring the therapeutic potential of iTBS on cognition.The preliminary evidence from our study will add to scientists' understanding of the short and long term effects of iTBS treatment on the cognitive related areas in the brain through the use of fMRI. The investigators also hope our research will allow psychiatrists to deliver better care to patients with debilitating cognitive impairments associated with depression. Overall, a study examining the olfactory and cognitive performance of patients with treatment resistant MDD and bipolar depression, pre-ECT/iTBS, post-ECT/iTBS, and post-remission would yield valuable insight into the link between olfaction and mood disorders as well as cognition and mood disorders.