1 Department of Exercise Science, Concordia University, Montréal, QC, Canada; Department of Psychology, Concordia University, Montréal, QC, Canada; Center for Studies in Behavioral Neurobiology, Concordia University, Montréal, QC, Canada; PERFORM Center, Concordia University, Montréal, QC, Canada; Center for Clinical Research in Health, Concordia University, Montréal, QC, Canada; Centre de Recherches de l'Institut Universitaire de Gériatrie de Montréal, Montréal, QC, Canada; Department of Neurosciences, Université de Montréal, Montréal, QC, Canada. Electronic address: tt.dangvu@concordia.ca.
2 Department of Psychology, Concordia University, Montréal, QC, Canada; Center for Studies in Behavioral Neurobiology, Concordia University, Montréal, QC, Canada; PERFORM Center, Concordia University, Montréal, QC, Canada.
3 Department of Exercise Science, Concordia University, Montréal, QC, Canada; Center for Studies in Behavioral Neurobiology, Concordia University, Montréal, QC, Canada; PERFORM Center, Concordia University, Montréal, QC, Canada; Centre de Recherches de l'Institut Universitaire de Gériatrie de Montréal, Montréal, QC, Canada.
4 Department of Exercise Science, Concordia University, Montréal, QC, Canada; Department of Psychology, Concordia University, Montréal, QC, Canada; PERFORM Center, Concordia University, Montréal, QC, Canada; Centre de Recherches de l'Institut Universitaire de Gériatrie de Montréal, Montréal, QC, Canada.
5 Physip SA, Paris, France.
6 Department of Psychology, Concordia University, Montréal, QC, Canada; PERFORM Center, Concordia University, Montréal, QC, Canada; Center for Clinical Research in Health, Concordia University, Montréal, QC, Canada.

Background: While cognitive-behavioral therapy for insomnia constitutes the first-line treatment for chronic insomnia, only few reports have investigated how sleep architecture relates to response to this treatment. In this pilot study, we aimed to determine whether pre-treatment sleep spindle density predicts treatment response to cognitive-behavioral therapy for insomnia.

Methods: Twenty-four participants with chronic primary insomnia participated in a 6-week cognitive-behavioral therapy for insomnia performed in groups of 4-6 participants. Treatment response was assessed using the Pittsburgh Sleep Quality Index and the Insomnia Severity Index measured at pre- and post-treatment, and at 3- and 12-months' follow-up assessments. Secondary outcome measures were extracted from sleep diaries over 7 days and overnight polysomnography, obtained at pre- and post-treatment. Spindle density during stage N2-N3 sleep was extracted from polysomnography at pre-treatment. Hierarchical linear modeling analysis assessed whether sleep spindle density predicted response to cognitive-behavioral therapy.

Results: After adjusting for age, sex, and education level, lower spindle density at pre-treatment predicted poorer response over the 12-month follow-up, as reflected by a smaller reduction in Pittsburgh Sleep Quality Index over time. Reduced spindle density also predicted lower improvements in sleep diary sleep efficiency and wake after sleep onset immediately after treatment. There were no significant associations between spindle density and changes in the Insomnia Severity Index or polysomnography variables over time.

Conclusion: These preliminary results suggest that inter-individual differences in sleep spindle density in insomnia may represent an endogenous biomarker predicting responsiveness to cognitive-behavioral therapy. Insomnia with altered spindle activity might constitute an insomnia subtype characterized by a neurophysiological vulnerability to sleep disruption associated with impaired responsiveness to cognitive-behavioral therapy.