@ARTICLE\{IMM2007-05469,
    author       = "I. Griskova and M. M{\o}rup and J. Parnas and O. Ruksenas and S. Arnfred",
    title        = "The amplitude and phase precision of 40 Hz auditory steady-state response depend on the level of arousal",
    year         = "2007",
    month        = "sep",
    keywords     = "Steady-state response - Auditory - Multi-way matrix factorization - Arousal",
    pages        = "133-138",
    journal      = "Experimental Brain Research",
    volume       = "183",
    editor       = "",
    number       = "1",
    publisher    = "",
    url          = "http://www2.compute.dtu.dk/pubdb/pubs/5469-full.html",
    abstract     = "The aim of this study was to investigate, in healthy subjects, the modulation of amplitude and phase precision of the auditory steady-state response (ASSR) to 40 Hz stimulation in two resting conditions varying in the level of arousal. Previously, {ASSR} measures have shown to be affected by the level of arousal, but the findings are somewhat controversial. Generally, {ASSR} is diminished in sleep but it may be increased in drowsiness. Besides, {ASSR} reduction has been observed in schizophrenia. However, schizophrenic patients are known to have a disturbance of arousal level, what makes it pertinent to know the effects of fluctuations in arousal on passive response to gamma-range stimulation. In nine healthy volunteers trains of 40 Hz click stimuli were applied during two conditions: in the “high arousal” condition subjects were sitting upright silently reading a book of interest; in the “low arousal” condition subjects were sitting in a reclined position with eyes closed and the lights turned off. The 64-channel {EEG} data was wavelet transformed and the amplitude and phase precision of the wavelet transformed evoked potential were decomposed by the recently proposed multi-subject non-negative multi-way factorization (NMWF) (Morup et al. in J Neurosci Methods 161:361–368, 2007). The estimates of these measures were subjected to statistical analysis. The amplitude and phase precision of the {ASSR} were significantly larger during the low arousal state compared to the high arousal condition. The modulation of {ASSR} amplitude and phase precision by differences in the arousal level during recording warrants caution when investigating oscillatory brain activity and interpreting the findings of reduced {ASSR} in schizophrenia. It also emphasizes the necessity of standardized recording procedures and monitoring the level of arousal during {ASSR} testing."
}