Simultaneous EEG and fMRI of the human auditory system

Abstract

While attempting to examine the physiological correlates of human cognitive functions, neuroscientists are restricted to noninvasive measures when dealing with healthy subjects. Correlates of cognitive brain processes are present in electromagnetic fields and haemodynamic responses that can be recorded with electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), respectively. While EEG offers a temporal resolution on the millisecond timescale, intracranial sources of activity must be inferred from extracranial recordings - a phenomenon referred to as the inverse problem. fMRI offers spatial resolution on the millimetre scale but suffers from a suboptimal temporal resolution, since the blood oxygen level dependent (BOLD) signal is an indirect haemodynamic consequence of electrical brain activity. Combining EEG and fMRI is an approach that promises to integrate the good temporal resolution of EEG with the good spatial resolution of fMRI (for recent reviews, see Debener et al. 2006; Herrmann and Debener (2007); Menon and Crottaz-Herbette 2005). However, it should be noted that some authors have questioned the implicit assumption that both measures pick up more or less the same neural activity. A number of studies have demonstrated that EEG and BOLD responses do not reflect identical neural activity, resulting in the notion of EEG signals without fMRI correlates, and vice versa (Ritter and Villringer 2006). © Springer-Verlag Berlin Heidelberg 2010.