Auditory evoked responses are additive to brain oscillations.
The generation mechanism of stimulus-evoked electro- and magnetoencephalographic (EEG & MEG) responses has remained controversial. One view holds that evoked responses are independent components, additive to ongoing brain activity. The other view holds that evoked responses are generated via stimulus-induced phase reorganization of ongoing brain activity. This issue has been commonly addressed with signal processing techniques that assume a high level of stationarity (i.e., unchanging properties over time) of the measured signal. Here we used signal analysis methods suitable for analyzing non-stationary signals. We found that auditory stimulation leads to a large power increase of the poststimulus signal compared to prestimulus level. Linear superposition of the (time-domain) averaged response and the unaveraged prestimulus signal accounted for 90% of the power increase. Further, we found that auditory stimulation does not lead to a phase-coherent state of ongoing oscillations. Taken together our results show that auditory evoked responses are directly additive to ongoing oscillations and only 10% of the observed power increases are explained by non-phase-locked brain activity. When examining evoked brain activity with methods providing simultaneous frequency and time information, emphasizing temporal accuracy is likely to provide more accurate descriptions of non-stationary processes of the human brain.
Mäkinen
V T
VT
Apperception and Cortical Dynamics, Department of Psychology, University of Helsinki, Finland. ville.makinen@biomag.hus.fi
Tiitinen
H
H
May
P J C
PJ
D000161:Acoustic Stimulation / Q000379:methods*; D001683:Biological Clocks / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D004569:Electroencephalography / Q000379:methods; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*