title: Automatic sleep classification using a data-driven topic model reveals latent sleep states.
abstract: BACKGROUND
  The golden standard for sleep classification uses manual scoring of polysomnography despite points of criticism such as oversimplification, low inter-rater reliability and the standard being designed on young and healthy subjects.
  
  
  METHODS
  To meet the criticism and reveal the latent sleep states, this study developed a general and automatic sleep classifier using a data-driven approach. Spectral EEG and EOG measures and eye correlation in 1s windows were calculated and each sleep epoch was expressed as a mixture of probabilities of latent sleep states by using the topic model Latent Dirichlet Allocation. Model application was tested on control subjects and patients with periodic leg movements (PLM) representing a non-neurodegenerative group, and patients with idiopathic REM sleep behavior disorder (iRBD) and Parkinson's Disease (PD) representing a neurodegenerative group. The model was optimized using 50 subjects and validated on 76 subjects.
  
  
  RESULTS
  The optimized sleep model used six topics, and the topic probabilities changed smoothly during transitions. According to the manual scorings, the model scored an overall subject-specific accuracy of 68.3 ± 7.44 (% μ ± σ) and group specific accuracies of 69.0 ± 4.62 (control), 70.1 ± 5.10 (PLM), 67.2 ± 8.30 (iRBD) and 67.7 ± 9.07 (PD).
  
  
  CONCLUSIONS
  Statistics of the latent sleep state content showed accordances to the sleep stages defined in the golden standard. However, this study indicates that sleep contains six diverse latent sleep states and that state transitions are continuous processes.
  
  
  CONCLUSIONS
  The model is generally applicable and may contribute to the research in neurodegenerative diseases and sleep disorders.
authors.affiliation: Technical University of Denmark, Department of Electrical Engineering, Ørsteds Plads, Building 349, 2800 Kgs. Lyngby, Denmark. Electronic address: henriette_koch@hotmail.com.
authors.forename: Henriette
authors.initials: H
authors.lastname: Koch
authors.affiliation: Technical University of Denmark, Department of Electrical Engineering, Ørsteds Plads, Building 349, 2800 Kgs. Lyngby, Denmark; Danish Center for Sleep Medicine, Department of Clinical Neurophysiology, Glostrup Hospital, Nordre Ringvej 57, 2600 Glostrup, Denmark; H. Lundbeck A/S, Ottiliavej 9, 2500 Valby, Denmark.
authors.forename: Julie A E
authors.initials: JA
authors.lastname: Christensen
authors.affiliation: Danish Center for Sleep Medicine, Department of Clinical Neurophysiology, Glostrup Hospital, Nordre Ringvej 57, 2600 Glostrup, Denmark; Center for Healthy Ageing, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen N, Denmark.
authors.forename: Rune
authors.initials: R
authors.lastname: Frandsen
authors.affiliation: Bispebjerg Hospital, Department of Neurology, Bispebjerg Bakke 23, 2400 Copenhagen NV, Denmark.
authors.forename: Marielle
authors.initials: M
authors.lastname: Zoetmulder
authors.affiliation: H. Lundbeck A/S, Ottiliavej 9, 2500 Valby, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Arvastson
authors.affiliation: H. Lundbeck A/S, Ottiliavej 9, 2500 Valby, Denmark.
authors.forename: Soren R
authors.initials: SR
authors.lastname: Christensen
authors.affiliation: Danish Center for Sleep Medicine, Department of Clinical Neurophysiology, Glostrup Hospital, Nordre Ringvej 57, 2600 Glostrup, Denmark; Center for Healthy Ageing, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen N, Denmark.
authors.forename: Poul
authors.initials: P
authors.lastname: Jennum
authors.affiliation: Technical University of Denmark, Department of Electrical Engineering, Ørsteds Plads, Building 349, 2800 Kgs. Lyngby, Denmark.
authors.forename: Helge B D
authors.initials: HB
authors.lastname: Sorensen
mesh_terms: D000368:Aged; D001921:Brain / Q000502:physiology / Q000503:physiopathology; D004569:Electroencephalography / Q000379:methods*; D004585:Electrooculography / Q000379:methods*; D005123:Eye / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020189:Nocturnal Myoclonus Syndrome / Q000503:physiopathology; D009799:Ocular Physiological Phenomena; D010300:Parkinson Disease / Q000503:physiopathology; D010363:Pattern Recognition, Automated / Q000379:methods*; D017286:Polysomnography / Q000379:methods*; D011336:Probability; D020187:REM Sleep Behavior Disorder / Q000503:physiopathology; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D012890:Sleep / Q000502:physiology*
keywords: Automatic sleep classification; Electroencephalography (EEG); Electrooculography (EOG); Neurodegenerative diseases; Sleep state switching; Topic modeling