Non-zero mean and asymmetry of neuronal oscillations have different implications for evoked responses

Abstract

Event Abstract Back to Event Non-zero mean and asymmetry of neuronal oscillations have different implications for evoked responses Vadim Nikulin1*, Klaus Linkenkaer-Hansen2, Guido Nolte3 and Gabriel Curio4 1 Charité - University Medicine Berlin, Athena project team, Germany 2 Center for Neurogenomics and Cognitive Research, Athena project team, Netherlands 3 Fraunhofer FIRST, Athena project team, Germany 4 Charité, Athena project team, Germany Evoked responses in MEG/EEG are the most frequently used measures of neuronal processing in humans. Thus, it is profoundly important to understand the neurophysiological mechanisms underlying the generation of evoked responses. The aim of the present study was to show analytically and with simulations that it is specifically the non-zero mean of neuronal oscillations [1] that is a prerequisite for the generation of evoked responses through a mechanism of amplitude modulation of oscillations. Secondly, we detail the rationale and implementation of the "baseline-shift index" (BSI) for deducing whether empirical oscillations have non-zero mean. Finally, we illustrate with empirical data why the alternative approach based on amplitude asymmetry of peaks and troughs ([2], "amplitude fluctuation asymmetry", AFA) should be used with caution in research aimed at explaining variability in evoked responses through a mechanism of amplitude modulation of ongoing oscillations. We used an analytical approach, simulations and empirical MEG data in order to compare the specificity of BSI and AFA index to differentiate between a non-zero mean and a non-sinusoidal shape of neuronal oscillations. Both, the BSI and the AFA index were sensitive to the presence of non-zero mean in neuronal oscillations. The AFA index, however, was also sensitive to the shape of oscillations even when they had a zero mean. Importantly, we also showed that the asymmetry of oscillations alone did not lead to the generation of evoked responses. Our results indicate that it is the non-zero mean of neuronal oscillations, and not an amplitude asymmetry of peaks and troughs, that is a prerequisite for the generation of evoked responses through a mechanism of amplitude modulation of oscillations.