Behavioral assessments of the aversive quality of pain in animals

Abstract

Animals and humans share similar mechanisms of pain detection and similar brain areas involved in pain processing. Also, they show similar pain behaviors, such as reflexed sensation to nociceptive stimuli. Pain is often described in sensory discrimination (algosity) and affective motivation (unpleasantness) dimensions. Both basic and clinical findings indicate that individuals with chronic pain usually suffer more from pain-associated affective disturbances than from the actual pain sensations per se. Although the neural systems responsible for the sensory component of pain have been studied extensively, the neural mechanisms underlying negative affective component are not well understood. This is partly due to the relative paucity of animal paradigms for reliable examination of each component of pain. In humans, the experience of pain and suffering can be reported by language, while in animals, pain can only be inferred through physical and behavioral reactions. Animal behaviors, cognitive psychology and functional brain imaging have made it possible to assess pain affection and pain memory in animals. Animals subjected to either neuropathic injury or inflammatory insult display significant conditioned place aversion to a pain-paired environment in behaviors. The present review aims to summarize the common methods of affective unpleasantness assessment in rats.

Neurobiology of aversive states

“…Therefore, the frequency of the vocalization response is the important parameter that separates a reflex from a response indicative of an aversive state. Other researchers measure avoidance motivation in an aversive state [14], or use classic fear conditioning to determine how quickly an animal learns to respond with fear to a neutral stimulus which has been contingently paired with an aversive stimulus [15–17]. …”

“…tactile, visual, and/or olfactory). When later tested in the normal state, withdrawals and the amount of time spent in compartments previously associated with negative stimuli serve as an indicator of preference and a measure of reward learning versus aversion [14]. …”

Central sensitization of the spino‐parabrachial‐amygdala pathway that outlasts a brief nociceptive stimulus

“…In animals, this association can be measured as pain‐induced conditioned place aversion (Zhang et al . ) and relies on the central nucleus of the amygdala (CeA), including the laterocapsular CeA, for its expression (Tanimoto et al . ; Gao et al .…”

Concurrent validity of different functional and neuroproteomic pain assessment methods in the rat osteoarthritis monosodium iodoacetate (MIA) model

“…Operant testing is opposite to reflexive response testing as it allows the quantification of behavioral responses at higher levels of the brain, reproducing multiple dimensions of pain, including affective and cognitive changes and not only sensory-discriminative perception [ 42 , 43 , 45 , 46 ]. This type of measure allows the observer to evaluate the aversive component of pain as operant tests give the animal an opportunity to avoid the painful condition [ 33 , 40 – 43 , 47 – 49 ].…”