Figure 1. Hypothesized sensitization process. The normal response curve (double line) portrays the relationship between pain perception and stimulus intensity. In the presence of sensitization, this curve shifts to the left (double dashed line). (A) represents pain onset in the normal response condition; (B) represents hyperalgesia, in which a stimulus intensity that causes pain onset in the normal condition is perceived as more painful after sensitization; (C) represents allodynia, in which a stimulus intensity below that of normal onset is now perceived as painful.