Hypervigilance when falling asleep in insomnia
It is widely held that hyperarousal or difficulty in regulating arousal may be involved in the expression of insomnia symptoms. Hyperarousal is particularly prominent when initiating sleep, often described by patients as difficulty in “turning off one’s mind”.
In a new study, published in the journal of Biological Psychology, a team of researchers investigate brain activity, using combined functional magnetic resonance imaging (fMRI) and electroencephalography (EEG), while patients with insomnia attempt to initiate sleep. Seventeen female patients with insomnia (free from comorbidities) and seventeen matched healthy controls were recruited. All subjects completed two 20 minute scans at approximately midnight – one was a resting-state scan where the instruction was to “rest quietly with your eyes closed” and the other, a fall asleep scan, where the instruction was to “rest quietly with your eyes closed and let yourself fall asleep”.
For the analysis, the research team examined intrinsic brain networks, with particular focus on connected brain regions involved in arousal and emotion regulation, or so-called salience networks. Patients with insomnia were found to have increased coactivation of the anterior insula with both the ventral anterior insula salience network and dorsal anterior insula salience network, relative to healthy controls. Increased involvement of the anterior insula was also associated with negative mood and EEG gamma frequency power, in patients with insomnia.
This abnormal pattern of insula coactivation, the authors speculate, may reflect elevated self-awareness, negative mood, and processing of bodily sensations, which may contribute to difficulties initiating and maintaining sleep. Such continued activity, even during sleep, may contribute to the feeling of being awake, despite objective sleep recordings showing categorical sleep. The research team note that benzodiazepines, a short-term pharmacological treatment for insomnia, reduces blood flow to the anterior insula (as well as other regions involved in the generation and regulation of emotion); suggesting a potential mechanism for sleep improvement.
Chen, M.C., Chang, C., Glover, G.H., Gotlib, I.H. (2014). Increased insula coactivation with salience networks in insomnia. Biological Psychology, 97, 1-8, doi: 10.1016/j.biopsycho.2013.12.016