title: Non-zero mean and asymmetry of neuronal oscillations have different implications for evoked responses.
abstract: OBJECTIVE
  The aim of the present study was to show analytically and with simulations that it is the non-zero mean of neuronal oscillations, and not an amplitude asymmetry of peaks and troughs, that is a prerequisite for the generation of evoked responses through a mechanism of amplitude modulation of oscillations. Secondly, we detail the rationale and implementation of the "baseline-shift index" (BSI) for deducing whether empirical oscillations have non-zero mean. Finally, we illustrate with empirical data why the "amplitude fluctuation asymmetry" (AFA) index should be used with caution in research aimed at explaining variability in evoked responses through a mechanism of amplitude modulation of ongoing oscillations.
  
  
  METHODS
  An analytical approach, simulations and empirical MEG data were used to compare the specificity of BSI and AFA index to differentiate between a non-zero mean and a non-sinusoidal shape of neuronal oscillations.
  
  
  RESULTS
  Both the BSI and the AFA index were sensitive to the presence of non-zero mean in neuronal oscillations. The AFA index, however, was also sensitive to the shape of oscillations even when they had a zero mean.
  
  
  CONCLUSIONS
  Our findings indicate that it is the non-zero mean of neuronal oscillations, and not an amplitude asymmetry of peaks and troughs, that is a prerequisite for the generation of evoked responses through a mechanism of amplitude modulation of oscillations.
  
  
  CONCLUSIONS
  A clear distinction should be made between the shape and non-zero mean properties of neuronal oscillations. This is because only the latter contributes to evoked responses, whereas the former does not.
authors.affiliation: Neurophysics Group, Department of Neurology, Campus Benjamin Franklin, Charité - University Medicine Berlin, D-12200 Berlin, Germany. vadim.nikulin@charite.de
authors.forename: Vadim V
authors.initials: VV
authors.lastname: Nikulin
authors.forename: Klaus
authors.initials: K
authors.lastname: Linkenkaer-Hansen
authors.forename: Guido
authors.initials: G
authors.lastname: Nolte
authors.forename: Gabriel
authors.initials: G
authors.lastname: Curio
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D001683:Biological Clocks / Q000502:physiology*; D002540:Cerebral Cortex / Q000502:physiology*; D005071:Evoked Potentials / Q000502:physiology*; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods; D009415:Nerve Net / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted