Attentional set effects on spinal and supraspinal responses to pain

The effects of attentional set on subjective magnitude ratings, spinal refl exes, and somatosensory evoked potentials (SEP) elicited by innocuous and p ainful sural nerve stimulation were investigated in 24 subjects. Cuing stim uli informed subjects as to whether a visual identification or a somatosens ory rating task would follow. Twenty percent of the trials were invalidly c ued, where the subjects were expecting a visual stimulus but were given a s ural nerve stimulus and vice versa. Subjective magnitude ratings were lower in the invalidly cued condition than the validly cued condition. Attention al set had no effect on innocuous-related spinal or early cortical response s; nor on the spinal nociceptive withdrawal reflex. The pain-related negati ve difference potential (NDP) and P2 component of the SEP were largest in t he 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-spe cific cognitive processes (e.g., orienting attention towards important stim uli 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 th is is the case, the pain-related P2 could serve as a useful index of neural processes involved in the cognitive-evaluative aspect of pain.