The Orofacial Pain Assessment Device (OPAD) was developed by Neubert and colleagues (2005) as an operant system of pain assessment that relies on voluntary behavior. Popular pain batteries offer a unidimensional assessment of pain. Pain responses involve executive functioning and other experiences, thus, relying simply on reflex and innate responses do not provide the complete picture. Further, pain management drugs can have sedative effects and may also affect psychomotor abilities in addition to providing pain relief. Therefore, a conflict-based paradigm proves to be a more sensitive method that enables in-depth analysis of pain.
The OPAD system is composed of Peltier-based thermode, and metal wires that allow assessment of thermal and mechanical pain sensitivity. The starved animal is placed in the operant chamber where it can access the food reward only when it contacts the thermal and mechanical stimuli. Essentially, the subject is tasked with choosing to tolerate the pain to gain the reward. Unlike traditional pain assays that are typically based on reflex behaviors, the OPAD allows the subject to choose its own pain threshold in order to attain the reward. This reward-conflict paradigm offers better face, content, and predictive validity. Additionally, the OPAD also encompasses psychological and affective dimensions of pain as observed in humans.