Sensitivity of EEG and MEG to the N1 and P2 Auditory Evoked Responses Modulated by Spectral Complexity of Sounds

Abstract

Acoustic complexity of a stimulus has been shown to modulate the electromagnetic N1 (latency ~110 ms) and P2 (latency ~190 ms) auditory evoked responses. We compared the relative sensitivity of electroencephalography (EEG) and magnetoencephalography (MEG) to these neural correlates of sensation. Simultaneous EEG and MEG were recorded while participants listened to three variants of a piano tone. The piano stimuli differed in their number of harmonics: the fundamental frequency (f 0 ), only,or f 0 and the first two or eight harmonics. The root mean square (RMS) of the amplitude of P2 but not N1 increased with spectral complexity of the piano tones in EEG and MEG. The RMS increase for P2 was more prominent in EEG than MEG, suggesting important radial sources contributing to the P2 only in EEG. Source analysis revealing contributions from radial and tangential sources was conducted to test this hypothesis. Source waveforms revealed a significant increase in the P2 radial source amplitude in EEG with increased spectral complexity of piano tones. The P2 of the tangential source waveforms also increased in amplitude with increased spectral complexity in EEG and MEG. The P2 auditory evoked response is thus represented by both tangential (gyri) and radial (sulci) activities. The radial contribution is expressed preferentially in EEG, highlighting the importance of combining EEG with MEG where complex source configurations are suspected.

Spatial Correspondence Between Functional MRI (fMRI) Activations and Cortical Current Density Maps of Event-Related Potentials (ERP): A Study with Four Tasks

“…The cortical current density distributions of the N100 and P200 were very diffuse and resembled their known distributions on the overlying scalp (Huotilainen et al 1998;Shahin et al 2007). This is in contrast with established MEG results localising their sources in superior temporal regions (Huotilainen et al 1998;Shahin et al 2007).…”

“…The cortical current density distributions of the N100 and P200 were very diffuse and resembled their known distributions on the overlying scalp (Huotilainen et al 1998;Shahin et al 2007). This is in contrast with established MEG results localising their sources in superior temporal regions (Huotilainen et al 1998;Shahin et al 2007). It is also in contrast with other ERP studies conducted with a larger number of electrodes, reporting high current density in superior temporal regions for these components (Mulert et al 2005;Zaehle et al 2007).…”

“…Results from previous studies indicate that this was not due to a true spatial mismatch in the activated regions (Huotilainen et al 1998;Shahin et al 2007). Rather, it was a consequence of the ill-posed nature of the inverse problem, exacerbated by the small number of recording electrodes and, particularly for this task, by the perpendicular orientation of the activated cortex with respect to the overlying scalp.…”

“…In light of established findings on the origin of the auditory N100 and P200, this is not interpreted as indicating a true spatial mismatch between the heamodynamic response and the sources of event-related electrical activity (Huotilainen et al 1998;Shahin et al 2007). Rather, it is a consequence of the severely ill-posed nature of the inverse problem of reconstructing the cortical current density distribution from a small number of electrodes.…”

Pre-attentive Spectro-temporal Feature Processing in the Human Auditory System

“…This inconsistency might be related to differences in the used stimulus material and task requirements. Also different sources underlying MEG and EEG signal might contribute to this inconsistency (Shahin et al 2007). With respect to the varying stimulation materials it is reasonable to assume that differences in the functional lateralization in some studies are caused by the differential use of a ''between-channel'' gap detection paradigm in contrast to a ''within-channel'' paradigm (Phillips et al 1997(Phillips et al , 1998Phillips and Smith 2004).…”