Combining electrophysiological and hemodynamic measures of the auditory oddball

The neural mechanisms of deviancy and target detection were investigated by combining high density event-related potential (ERP) recordings with funct ional magnetic resonance imaging (fMRI). ERP and fMRI responses were record ed using the same paradigm and the same subjects. Unattended deviants elici ted a mismatch negativity (MMN) in the ERP. In the fMRI datal activations o f transverse/superior temporal gyri bilateral were found. Attended deviants generated an MMN followed by an N2/P3b complex. For this condition, fMRI a ctivations in both superior temporal gyri and the neostriatum were found. T hese activations were taken as neuroanatomical constraints for the localiza tion of equivalent current dipoles. Inverse solutions for dipole orientatio n provide evidence fur significant activation close to Heschl's gyri during deviancy processing in the 110-160-ms time interval (MMN), whereas target detection could be modeled by two dipoles in the superior temporal gyrus be tween 320 and 380 ms.