Interaction of attention and localization of pain maxima shift the balance between lateral inhibition and spatial facilitation in nociceptive processing

Spatial interactions among noxious inputs can enhance or suppress pain, but the conditions determining whether spatially organized nociceptive processing is dominated by facilitation or inhibition remain unclear. The present study examined whether attentional tuning and localization of pain maxima regulate the balance between lateral inhibition (LI) and spatial summation of pain (SSP). Thirty healthy participants completed a within-participant psychophysical experiment with electrocutaneous stimulation across LI, sham-control, diffuse noxious inhibitory control, and SSP trials. The spatial configuration of noxious input was manipulated by varying the number and arrangement of activated electrodes. Depending on the attentional instruction, participants continuously rated either pain intensity attributed to a target electrode or overall pain from all activated electrodes using an electronic visual analogue scale. Secondary measures assessed target-pain extraction, attentional focus, and localization of the pain maximum. Rather than observing the predicted inhibitory profile, pain ratings increased suggesting a predominance of facilitatory spatial interactions that were strongly modulated by attention and the perceived location of the pain maximum. When the pain maximum was localized outside the target electrode, facilitation was absent and overall pain intensity was lower. Bilateral stimulation of homologous sites elicited SSP, indicating integration of noxious input across body sides. These findings suggest that LI and spatial facilitation are not fixed consequences of stimulus geometry. Instead, their expression depends on the interaction between top-down attentional selection and spatial attribution of the most intense component of pain.