Figure 4. Pain intensity ratings for two-point vs. line stimuli (means±SEM. upper panel) and individual responses (lower panel).

Despite involving markedly larger stimulation areas than the two-point stimuli, the line stimuli were perceived as significantly less painful than two-point stimuli. This effect remained consistent over the two different stimulation distances. Inspection of individual ratings (lower panel) reveals some individual variation in this response, however, female subjects (grey circles) did not appear to exhibit responses that varied systematically from those of male subjects (black squares). Nevertheless, this discordance between stimulus area and perceived pain intensity indicates that the pattern of stimulus application represents a critical variable that shapes the balance of facilitory vs. inhibitory interactions between nociceptive inputs arising from multiple body regions. Thus, the greater pain experienced during the two-point vs. the line stimuli provides evidence for lateral inhibition during nociceptive processing.