title: Topographic analysis of engagement and disengagement of neural oscillators in photic driving:  a combined electroencephalogram/magnetoencephalogram study.
abstract: OBJECTIVE
  A coupled system of nonlinear neural oscillators with an individual resonance frequency is assumed to form the neuronal substrate for the photic driving phenomenon. The aim was to investigate the spatiotemporal stability of these oscillators and quantify the spatiotemporal process of engagement and disengagement of the neuronal oscillators in both multitrial and single-trial data.
  
  
  METHODS
  White light-emitting diode flicker stimulation was used at 15 frequencies, which were set relative to the individual α frequency of each of the 10 healthy participants. Simultaneously, the electroencephalogram (EEG) and the magnetoencephalogram (MEG) were recorded. Subsequently, spatiotemporal matching pursuit (MP) algorithms were used to analyze the EEG and MEG topographies.
  
  
  RESULTS
  Intraindividually similar topographies were found at stimulation frequencies close to (1) the individual α frequency and (2) half the individual α frequency in the multitrial and the single-trial cases. In both stimulation frequency ranges, the authors observed stable topographies 5 to 10 stimuli after the beginning of the stimulation and lasting three nonexisting periods after the end of the stimulation. This was interpreted as the engaging/disengaging effect of the observed oscillations, because especially the frequency parameter adopted before and after stable topographies were observed. Topographic entrainment was slightly more pronounced in MEG as compared with that in EEG.
  
  
  CONCLUSIONS
  The results support the hypothesis of nonlinear information processing in human visual system, which can be described by nonlinear neural oscillators.
authors.affiliation: Institute of Biomedical Engineering and Informatics, Ilmenau University of Technology, Ilmenau, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Halbleib
authors.forename: Maciej
authors.initials: M
authors.lastname: Gratkowski
authors.forename: Karin
authors.initials: K
authors.lastname: Schwab
authors.forename: Carolin
authors.initials: C
authors.lastname: Ligges
authors.forename: Herbert
authors.initials: H
authors.lastname: Witte
authors.forename: Jens
authors.initials: J
authors.lastname: Haueisen
mesh_terms: D000328:Adult; D000465:Algorithms; D001683:Biological Clocks / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D004569:Electroencephalography; D005260:Female; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D009474:Neurons / Q000502:physiology*; D010775:Photic Stimulation