FOOD & PAIN: New Brain Clues Depicting Their Association
By ¹Obiri Darko Stella, ²Sackey Lyanne, and ³Kwakye Sylvester.
Physical pain has typically been approached from a biological perspective, with relatively little experimental work available on the behavioural and cognitive consequences of physical pain. In contrast, the consequences of social pain have been extensively explored in the last several decades.
Social pain represents an unpleasant emotional response that occurs in reaction to separation from people or groups and has been associated with multiple changes in behavioural and cognitive outcomes.
Although physical and social pain are not synonymous, they both engage similar neural circuitry and both types of pain can result in aggression and temporary numbness to subsequent physical pain. Such findings have resulted in theoretical conceptualizations that social pain and physical pain overlap in the sense that they share similar antecedents and consequences.
Social pain has been demonstrated to increase a variety of poor choices related to impulsive processing, including consumption of unhealthy foods, preferences for immediate gratification, and procrastination. One explanation for the impact of social pain on choice is that the experience of pain depletes resources that are required for self-control, resulting in people giving in to their impulses.
Because of the overlap between social and physical pain, there is reason to expect that physical pain will similarly impair choices related to impulsive processing. As with social pain, there is some evidence that chronic and acute physical pain can increase preferences for immediate gratification. An impaired choice on tasks related to impulsive processing could result from physical pain as a result of overburdened regulatory resources, particularly for chronic pain, although this possibility has not been directly tested. However, there are reasons to expect that the effects of acute physical pain on choice could be driven by a process other than reduced regulatory resources.
A research probe into physical pain gave an alternative explanation that chronic pain and obesity interact at the level of the central nervous system. The brain plays a key role in the regulation of energy intake and expenditure, with recent findings emphasizing the role of reward limbic circuits in the current obesity epidemic. According to this explanation, interindividual differences in brain response to food cues interact with a modern diet environment rich in fats and carbohydrates, resulting in excessive caloric intake in segments of the population.
On the other hand, recent pre-clinical and neuroimaging studies by these researchers demonstrated that chronic pain is associated with neuroadaptations in the brain limbic system and that the risk of transition to chronic pain can be predicted from the structural and functional properties of the limbic system. Consistently, both chronic pain and obesity are characterized by anhedonia (inability to feel pleasure in normally pleasurable activities), hypo-dopaminergic state in the mesocorticolimbic system, and altered opioid transmission within the limbic system.
Building on this overlap, the research probe revealed that chronic low back pain (CLBP) patients exhibit decreased liking of high-fat puddings but not of high sucrose drinks, suggesting an overlap between circuits underlying CLBP and fat valuation. More importantly, the research showed that liking predicted caloric intake from a high-fat pudding offered ad-libitum in healthy controls but not in CLBP patients, indicating the presence of disrupted satiety signals in the latter group.
Researchers also found the structure of nucleus accumbens (the neural interface between motivation and action, playing a key role on feeding, sexual, reward, stress-related, drug self-administration behaviours) was normal in patients who initially experienced changes in their eating behaviour but whose pain did not become chronic. However, patients whose eating behavior was normal, but whose pain became chronic had smaller nucleus accumbens. Interestingly, the nucleus accumbens predicted pleasure ratings only in chronic back pain patients and in patients who became chronic after an acute bout of back pain suggesting that this region becomes critical in the motivated behavior of chronic pain patients.
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