Two discrete components of the 20 Hz steady-state response are distinguished through the modulation of activation level.
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.


CONCLUSIONS
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.


CONCLUSIONS
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.
Department of Psychiatry, Hvidovre Hospital, University Hospital of Copenhagen, Copenhagen, Denmark. inga.griskova@gf.vu.lt
Inga
I
Griskova
Morten
M
Morup
Josef
J
Parnas
Osvaldas
O
Ruksenas
Sidse M
SM
Arnfred
D000161:Acoustic Stimulation; D000328:Adult; D001307:Auditory Perception / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods; D002540:Cerebral Cortex / Q000502:physiology*; D004566:Electrodes; D004569:Electroencephalography / Q000379:methods*; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009415:Nerve Net / Q000502:physiology; D009483:Neuropsychological Tests; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult