Localizing P300 generators in visual target and distractor processing: a combined event-related potential and functional magnetic resonance imaging study

Abstract

Constraints from functional magnetic resonance imaging (fMRI) were used to identify the sources of the visual P300 event-related potential (ERP). Healthy subjects performed a visual three-stimulus oddball paradigm with a difficult discrimination task while fMRI and high-density ERP data were acquired in separate sessions. This paradigm allowed us to differentiate the P3b component of the P300, which has been implicated in the detection of rare events in general (target and distractor), from the P3a component, which is mainly evoked by distractor events. The fMRI-constrained source model explained >99% of the variance of the scalp ERP for both components. The P3b was mainly produced by parietal and inferior temporal areas, whereas frontal areas and the insula contributed mainly to the P3a. This source model reveals that both higher visual and supramodal association areas contribute to the visual P3b and that the P3a has a strong frontal contribution, which is compatible with its more anterior distribution on the scalp. The results point to the involvement of distinct attentional subsystems in target and distractor processing.

Figure 3.

Source activity in target and distractor condition A, A surface of a standard head (MNI template) with standard 81 electrode configuration. B, Position of the RSs on a surface reconstruction of the MNI template brain. C, Source activity waves and topographical maps of scalp voltage of the main current flow direction of each RS for the target and distractor conditions. ^* indicates significant differences between RS peak amplitude in the target and distractor conditions.

Figure 2.

Positions of the regional sources and fMRI activation maps. Positions of the RSs resulting from the seeding procedure and group statistical maps of blood oxygenation level-dependent signal increase for the target and distractor conditions compared with baseline (standard condition) at F_(1,18510) = 31; p < 0.001 (corrected), superimposed on a surface reconstruction of the MNI template brain.

Figure 1.

ERP responses in target and distractor condition. A, Grand average difference ERP waveforms to distractor (red line) and target (black line) stimuli at 81 standard electrodes sites exported from 63 recorded electrodes. B, Spline-interpolated topographical maps of scalp voltage and CSD calculated at the respective peak latencies in the target and distractor condition. C, Enlarged view of key midline electrodes from A.