Scalp topography and intracerebral sources for ERPs recorded during auditory target detection

The goal of this study was to measure the scalp topography of the event-related potentials (ERPs) during the detection of improbable auditory targets and to determine the intracerebral sources of these potentials. ERPs were recorded when subjects listened to a sequence of spoken words and detected occasional (p = 0.2) targets defined either by the gender of the speaker (male/female) or the meaning of the word (animate/inanimate). Waveforms were evaluated in relation to category (target versus standard) and task (voice versus semantic). Dipole source analysis was performed using locations obtained from fMRI. Fronto-central negative waves (N450 and N600 ms) generated by sources in both the auditory cortex and frontal regions were larger for semantic tasks and larger over the left hemisphere. A large parieto-occipital positive wave (P700) occurring with a peak latency about 150 ms before the reaction time was mainly generated in the left temporo-parietal regions for the semantic task and bilaterally for the voice task. About 300 ms after the P700, a highly lateralized right temporo-parietal positive wave P1000r occurred with a source in the right temporo-parietal area. These results indicate three distinct physiological processes underlie the detection of auditory targets. Perceptual discrimination is related to interactions between the frontal and temporal regions, stimulus-response association occurs in the temporo-parietal regions and post-perceptual processing in the right temporo-parietal region.