Dual roles of the amygdala–hippocampus circuit in the regulation of rapid eye movement sleep and depression symptoms by repetitive transcranial magnetic stimulation in patients with insomnia

To the editor: It is commonly reported that people with insomnia often experience comorbid emotional disorders, such as mood and anxiety disorders.1 2 A study found that fragmented rapid eye movement (REM) sleep in individuals with insomnia is associated with higher Beck Depression Inventory (BDI) scores.3 REM sleep architecture disruption is a typical symptom of insomnia.4 Sleep homeostasis and plasticity interact with each other and jointly regulate sleep patterns and sleep quality. Sleep homeostasis is a complex neurobiological phenomenon involving molecular pathways, neurotransmitter release, synaptic activity and neural networks.5 Repetitive transcranial magnetic stimulation (rTMS) is a commonly used non-invasive neuroregulation technique that regulates sleep by modulating synaptic plasticity and the strength of connections between brain regions.6 While evidence suggests the potential of 1 Hz trams at the left dorsal lateral prefrontal cortex (DLPFC_L) to improve sleep quality for patients with insomnia,7 the extent to which it influences REM sleep and the mechanisms involved remain unclear. REM sleep is initiated by basolateral amygdala dopamine signalling.8 Restless REM sleep interferes with the adaptation of the amygdala circuits, consequently affecting emotion processing.4 Individuals with insomnia are more likely to experience symptoms of depression or anxiety and they are closely connected by a bidirectional relationship.9 However, the effect of rTMS on depression in patients with insomnia and the underlying correlation with REM remain unknown. A recent study revealed that diverse patterns of synchronic interaction between the amygdala, hippocampus and neocortex play crucial roles in emotional processes.10 Thus, we hypothesised that 1 Hz rTMS at DLPFC_L may improve REM sleep and mood by modulating the amygdala–hippocampus circuits in patients with insomnia. The inclusion criteria of this study for patients with insomnia are as follows: aged 18–65 years; right-handed; meeting the diagnostic criteria for insomnia disorders in the …