Spatial Tuning in Nociceptive Processing Is Driven by Attention

Abstract

When the source of nociception expands, one can observe an increase in pain. This effect is called spatial summation of pain (SSP) and has been a subject of several investigations. However, still, mechanisms shaping magnitude of this effect are largely unknown. The purpose of this study was to investigate how spatial attention modulates SSP, and thus reported pain. Forty pain-free volunteers (N=40, 20 females) participated in this within-subject experiment. Following training phase, volunteers took part in two sessions based on three different hand immersions in the cold water (Cold Pressor Task) with constant noxious temperature. Participants were asked to either immerse the ulnar side (A), radial side (B) or both sides (A+B, whole hand) and provide overall pain ratings they experienced. In case of immersions of merged sides (A+B) they were also asked to provide divided-attention rating(s), i.e., first pain in A then in B (or B then A) and directed- attention ratings (pain only in A or in B). Results confirmed clear SSP effect: Reported pain during immersions of A or B was less intense than pain during immersions of A+B (p < 0.001). Data also confirmed that spatial tuning was altered as SSP was fully abolished when participants provided two ratings in divided fashion (p < 0.001). Pain was significantly lowered when attention was directed only to one side (A or B) during immersion of A+B (p < 0.001). We conclude that SSP is attentionally driven phenomenon, and thus mechanisms of this effect must have a central component. SSP can be fully abolished when pain is rated in divided fashion or when attention is attracted to smaller painful area.