The Role of mGluR5 in CBT-I

Cognitive behavioral therapy for insomnia (CBT-I), a treatment solely aimed at improving sleep, reduces depression with rates similar to conventional antidepressants. Although this efficacy reflects the interrelationship between sleep and depression, CBT-I's antidepressant mechanism of action is currently unknown. One potential mechanistic pathway is through the metabotropic glutamate receptor subtype 5 (mGluR5), due to its strong association with both depression and sleep. The investigators hypothesize that CBT-I's antidepressant efficacy may occur through the downregulation of mGluR5 associated with improved sleep. This study is a mechanistic clinical trial in a cohort of adults with MDD and a range of sleep latencies (time it takes to fall asleep). Prior to and following CBT-I, the investigators will quantify hippocampal mGluR5 density (with using positron emission tomography \[PET\] imaging) and sleep latency (with polysomnography performed in the Sleep Lab). CBT-I will be delivered through an online program, Sleep Healthy Using The Internet (SHUTi).