Attentional interference, but no attentional bias, by tonic itch and pain stimulation

Introduction: Attentional processes are involved in the experience of itch and pain. They interrupt task performance (ie, attentional interference) or bias allocation of attention toward the somatosensory stimulation, that is, attentional bias (AB). Research on AB toward pain is mostly focused on stimuli with short durations; hampering generalization to tonic pain sensations. Evidence for AB toward itch is lacking so far. This study investigated attentional interference by—and AB toward—experimentally induced tonic itch and pain. Methods: Fifty healthy volunteers performed a somatosensory attention task (SAT), that measured attentional interference and AB during tonic (35 s duration) pain, itch and vibrotactile stimuli. In addition, a dot-probe task measured AB toward visual representations of itch and pain, a Flanker task was used to assess attentional inhibition, and self-reported characteristics were measured. Results: Attentional interference during itch and pain stimuli compared with vibrotactile stimuli was found during the SAT. Exploration of shorter time segments within one tonic stimulus showed slowed responses for all three stimulus types during the first 5 seconds of stimulation. However, no prolonged interference in the following time segments was found. There was no AB toward somatosensory and visual stimuli. Furthermore, there was no association between any of the attentional measures and self-reported characteristics. Discussion: These findings suggest that the beginning of any somatosensory stimulus is interfering with cognitive performance, but the results for prolonged interference by itch and pain are equivocal. There was no indication for biased attention allocation. Whether this pattern is different in patients remains to be investigated in the future. Itch and pain signal potential threats to the body. In most situations, this is an adaptive mechanism that leads to behavioral adjustment. It has been suggested that itch and pain interrupt ongoing behavior, and that attention is drawn toward the location of these stimuli, that is, an attentional bias (AB) toward itch and pain occurs1–4. This is in accordance with the functional attentional system as described by Allport5, which states that the attentional system makes a difference between stimuli that are irrelevant to the ongoing behavior (eg, distracting noises in the office) while relevant stimuli that adaptively interrupt behavior (eg, a fire alarm) are drawing attention. Studies using somatosensory stimuli have shown that pain interferes with the performance of a concurrent task. These studies mostly used short (phasic) stimuli6–9, but support also comes from studies with longer (tonic) stimuli10–12, and from studies that used naturalistic pain13–16. Evidence for itch is lacking; the only 2 studies on interference by tonic itch on a cognitive task yielded conflicting results11,17. However, similarities in the physiology of itch and pain, and their shared protective function18,19, suggest that itch also causes attentional interference. Besides overall interference of itch and pain on task performance, people might show an AB toward itchy or painful somatosensory stimuli. Findings regarding AB toward painful stimuli are mixed for experimental pain in healthy participants, and AB toward itchy stimuli has not yet been demonstrated11,17,20,21. With regard to differences between phasic and tonic stimuli, an AB toward phasic pain has been shown20,22, whereas an AB toward tonic pain is not yet supported11. Studies suggest that during tonic stimuli attention may fluctuate, which calls for a more fine-grained analysis of the time course of attention effects11. There is some evidence of an AB toward visual representations of itch and pain4,17,23–26, but visual stimuli are inherently different from the somatosensory sensation of itch and pain, which promotes more research on actual somatosensory stimuli. In addition, inconclusive evidence has emerged from explaining the mixed findings by individual differences (eg, neuroticism or catastrophizing)11,17,22,23,27. Lastly, investigations of attentional inhibition, that is, inhibiting irrelevant information and attending to the relevant information28, may predict how well people can adjust their task performance when experiencing pain or itch29–31. Therefore, the current study aimed to examine attentional interference by tonic itch and pain stimuli (ie, representing acute itch and pain) and an AB toward these stimuli in a healthy sample. It was hypothesized that responses on a concurrent task would be slowed down by somatosensory itch and pain compared with vibrotactile control stimulation. Secondly, it was hypothesized that people show an AB toward the itch and pain stimulation. In addition, it was explored whether fluctuations in attention occur during the stimulus and whether there is an AB toward visual representations of itch and pain