Physiological modulation of auditory steady-state response: arousal, activation and attention

The auditory steady-state response (ASSR) is used to monitor the ability of the brain to generate synchronous response to the external stimulation. However it is not know how registration conditions influence ASSR. The aim of the study was to investigate the effects of varying arousal, activation and attention levels on the 20Hz and 40Hz auditory steady-state responses. Additionally, transient auditory responses were analyzed to monitor the effect of experimental modulation on P1-N1-P2 auditory complex that is similar to the initial part of auditory steady-state responses. Higher phase precision and larger evoked amplitudes were obtained for gamma range activity of 20Hz and 40Hz ASSRs in low arousal/activation closed eyes condition. The effect of arousal was obtained only for the total intensity of 40Hz ASSR-it was larger in low arousal condition, and for P1 potential amplitude that was diminished in low arousal condition. The effect of arousal/activation and attention was prominent for phase precision and evoked amplitude of 40Hz ASSR: measures were diminished in high arousal/activation low attentional demands –“distraction” conditions and were largest during low arousal/activation and unfocused attention conditions. Largest N1 amplitudes were also obtained in low arousal/activation unfocused attention condition. The current results suggest important improvements of the practical use of ASSRs: 1) a careful monitoring for arousal fluctuations should be performed and 2) in cases where ASSRs are applied to investigate the ability to generate high frequency cortical activity a "distraction" task is not favorable