The effects of attentional set on subjective magnitude ratings, spinal reflexes, and somatosensory evoked potentials (SEP) elicited by innocuous and painful sural nerve stimulation were investigated in 24 subjects. Cuing stimuli informed subjects as to whether a visual identification or a somatosensory rating task would follow. Twenty percent of the trials were invalidly cued, where the subjects were expecting a visual stimulus but were given a sural nerve stimulus and vice versa. Subjective magnitude ratings were lower in the invalidly cued condition than the validly cued condition. Attentional set had no effect on innocuous-related spinal or early cortical responses, nor on the spinal nociceptive withdrawal reflex. The pain-related negative difference potential (NDP) and P2 component of the SEP were largest in the invalidly cued condition. These results provide further support for our hypothesis that the NDP is generated in part by the anterior cingulate, and suggest that the anterior cingulate response to pain reflects non-pain-specific cognitive processes (e.g., orienting attention towards important stimuli in the environment and/or response competition) and not some aspect of the pain experience. The effects of attentional set on the pain-related P2 suggests that it might correspond to the P3a event-related potential. If this is the case, the pain-related P2 could serve as a useful index of neural processes involved in the cognitive-evaluative aspect of pain.

We used a novel application of principal components analysis (spatiotemporal PCA) to decompose the event-related brain potentials (ERPs) obtained with a dense electrode array, with the purpose of elucidating the late ERP components elicited by deviant stimuli under “attend” and “ignore” conditions. First, a “spatial” PCA was performed to identify a set of scalp distributions (spatial factors or “virtual electrodes”) that accounted for the spatial variance in the data set. The data were expressed as spatial factor scores or “virtual ERPs” measured at each of the virtual electrodes. These virtual ERPs were submitted to a “temporal” PCA, yielding a set of temporal factors or “virtual epochs.” Statistical analyses of the temporal factor scores found that (1) attended deviant stimuli elicited the P300 and Novelty P3 components, the latter being largest for highly salient nontargets; (2) “ignored” deviants elicited a small Novelty P3, and depending on the primary task, a small P300; and (3) the classical Slow Wave consisted of separate frontal-negative and posterior-positive components.

Whole-head magnetoencephalographic (MEG) responses to repeating standard tones and to infrequent slightly higher deviant tones and complex novel sounds were recorded together with event-related brain potentials (ERPs). Deviant tones and novel sounds elicited the mismatch negativity (MMN) component of the ERP and its MEG counterpart (MMNm) both when the auditory stimuli were attended to and when they were ignored. MMNm generators were located bilateral to the superior planes of the temporal lobes where preattentive auditory discrimination appears to occur. A subsequent positive P3a component was elicited by deviant tones and with a larger amplitude by novel sounds even when the sounds were to be ignored. Source localization for the MEG counterpart of P3a (P3am) suggested that the auditory cortex in the superior temporal plane is involved in the neural network of involuntary attention switching to changes in the acoustic environment.

P300 differences for target (.10), nontarget (.10), and standard tones (.80) were assessed using a three-stimulus oddball paradigm in which participants responded only to the target (n = 12). Target/standard (easy or difficult) and nontarget/standard (large or small) pitch differences were manipulated orthogonally. In all conditions, target tones elicited a parietal P300, which was affected only by the target/standard discrimination ease. Nontarget in the easy/large and difficult/small conditions elicited a parietal but smaller P300 than the target but in the easy/small condition elicited similar ERPs to the standard. However, nontarget stimuli in the difficult/large condition elicited an anterior maximum and earlier P300 (P3a) component. The findings suggest that target P300s are not influenced by the nontarget stimulus configuration, whereas the nontarget P300 outcomes are determined directly by the stimulus context. The theoretical implications are discussed.