@ARTICLE\{IMM2009-05807,
    author       = "I. Griskova and M. M{\o}rup and J. Parnas and O. Ruksenas and S. M. Arnfred",
    title        = "Two discrete components of the 20 Hz steady-state response are distinguished through the modulation of activation level",
    year         = "2009",
    pages        = "904-909",
    journal      = "",
    volume       = "120",
    editor       = "",
    number       = "",
    publisher    = "Clinical Neurophysioly",
    url          = "http://www2.compute.dtu.dk/pubdb/pubs/5807-full.html",
    abstract     = "OBJECTIVE: To investigate the modulation of amplitude and phase precision of the auditory steady-state response (SSR) to 20 Hz stimulation in two conditions varying in the level of activation. {METHODS}: Click stimuli (20 Hz) were applied while subjects were sitting upright silently reading a book of interest (high activation level) and while subjects were sitting in a reclined position with eyes closed and the lights turned off (low activation level). Sixty-one channel {EEG} data was wavelet transformed, the amplitude and phase precision measures extracted and decomposed by the multi-subject non-negative multi-way factorization (NMWF). {RESULTS}: The {NMWF} decomposition of amplitude and phase precision measures resulted in the observation of two distinct components: a component at the frequency of stimulation--20 Hz {SSR} and a component emerging at 40 Hz--20 Hz {SSR-}related 40 Hz activity. Modulation by the activation level was observed only for 20 Hz {SSR-}related 40 Hz activity as increased amplitude and phase precision during low activation level. No such effects were observed for 20 Hz {SSR}. {CONCLUSION}: The discrete components of the 20 Hz {SSR} are distinguished through modulation of activation level, 20 Hz {SSR-}related 40 Hz being higher in low activation state. {SIGNIFICANCE}: The biological modulation of 20 Hz {SSR-}related 40 Hz activity by the level of activation points to a physiological nature of this activity beyond a mere periodic effect in relation to the 20 Hz activity."
}