The amplitude and phase precision of 40 Hz auditory steady-state response depend on the level of arousal

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.

Converging evidence for gamma synchrony deficits in schizophrenia

“…This might suggest that auditory gamma band measures could serve as proxies for measures of gamma activity across cortical regions, regardless of the sensory system or cognitive process engaged. Arguing against this possibility are the roles attention (Ross et al, 2004, Skosnik et al, 2007) and arousal (Griskova et al, 2007) play in modulating the phase consistency of the 40 Hz ASSR across trials and its event-related change in power. Skosnik et al (Skosnik, Krishnan, 2007) used 20Hz and 40Hz steady-state stimuli as frequent and infrequent stimuli in an oddball paradigm, revealing 40Hz ASSR PLF and evoked power enhancement on 40Hz targets relative to 40Hz standards even after matching the trial numbers for each stimulus type.…”

A crossmodal crossover: Opposite effects of visual and auditory perceptual load on steady-state evoked potentials to irrelevant visual stimuli

“…First, there is evidence that increasing arousal decreases rather than increases steady-state evoked responses to auditory stimuli (Griskova et al, 2007). Second, one would expect a generalised increase in arousal to influence responses to both attended…”

Dexamphetamine selectively increases 40 Hz auditory steady state response power to target and nontarget stimuli in healthy humans

“…54 The amplitude and phase of the ASSR was demonstrated to be larger during a low arousal state than a high arousal state. 54 The authors assumed that the attention modulation in their study was sparse owing to the study design and the instruction to participants not to pay attention to the stimulation. Despite this, the study failed to appropriately control for attention.…”