What Factors Impact Our Perception of Pain?

Post by Lani Cupo 

Do individuals perceive pain differently?

Describing how bad our headache is, how much our broken arm hurts, or what childbirth feels like are complex and nuanced exercises in communication. If you and your sibling both have your wisdom teeth removed, what factors determine whether one of you will be in enough pain to fill a prescription for medication and the other won’t?

Among humans, the perception of pain can vary dramatically among individuals. According to a biopsychosocial model of pain, the perception of painful stimuli are influenced by three main types of factors: biological, psychological, and social factors. This means that there is not necessarily a consistent correspondence between pain and pathology. In other words, the same stimulus — consider a broken bone for example — may correspond with high degrees of distress in some individuals while others barely register the break as painful.

How do sex and gender impact the perception of pain?

Two widely investigated, nuanced factors impacting pain perception and expression are gender identity and biological sex. Scientific studies repeatedly report that in comparison with men, women exhibit more robust perceptual responses to experimentally-induced pain. For example, women report lower thresholds and tolerances to stimuli such as heat and pressure. Nevertheless, recent research suggests that differences in pain perception are fairly subtle, and driven by context. Sex differences are in part explained by the way in which experiments are conducted, as women may be more sensitive to rapid or dynamic changes in noxious stimuli, such as when the stimulus begins or increases in intensity. In contrast, women have been shown to habituate or adapt faster than men when a painful stimulus is consistently applied. Further, it is important to note that women tend to be more perceptive in general than men across many sensory modalities, including temperature, smell, taste, and vision. It can be easy to misconstrue reported sex differences and view them with an archaic lens that portrays women as oversensitive or weak in the face of adversity.

In humans, it can be tricky to separate the impact of biological sex from the impact of sociological factors. Rodent studies can lend insight, where biological sex is considered at the exclusion of gender. Such studies also reveal sex differences in pain perception, but recent research suggests that there is an interaction between sex and background genetic strain in mice and rats, with some strains demonstrating increased sensitivity in females, others demonstrating the opposite, and still others showing no difference.

The causes underlying sex or gender differences in pain perception have yet to be fully investigated, however, there are several proposed mechanisms. One hypothesis states that gender roles may alter the perception of pain; women may feel it is more permissible to express and feel pain. From a biological viewpoint, sex hormones have been shown to alter nociceptive processing. Castration of male rats and androgenization of female rats in the first week of life has also been shown to reverse sex-dependent effects of pain perception, pointing to a role of gonadal hormones on altered perception.

How does age impact the perception of pain?

Another common factor that can alter pain perception is age. As humans age, the threshold for pain increases, meaning it takes a more intense noxious signal to alert an older individual that something is wrong. This increases the risk of injury in older adults. Contrarily, tolerance for pain usually decreases, with older participants withdrawing from painful stimuli sooner than younger participants in experimental settings. This could be in part due to increased perception of pain as unpleasant in older ages. Unpleasantness differs from intensity, with the former representing how bothersome the pain is and the latter representing how severe it is. Most studies in humans, however, neglect to report data on the changing perception of pain unpleasantness.

Aging is associated with degradations to both neurons themselves and connections between brain cells. Changes in brain regions involved in the processing of painful stimuli, such as the prefrontal cortex, primary and secondary somatosensory cortex, hippocampus, anterior cingulate, insula, and thalamus, may in part be responsible for the changes in pain perception over the lifetime.

How do psychosocial factors impact pain perception?

Mood is one of the major psychosocial factors investigated in relation to pain perception. In patients with chronic pain, negative mood, such as transient anxiety and depression, are associated with greater intensity of pain. Of course, more intense pain could also result in lowered mood, however, in studies examining acute pain stimulus in healthy individuals, negative mood has also been linked with greater pain sensitivity. In contrast, positive moods can relieve pain, with pleasant stimuli such as music, pictures, and funny movies reducing pain perception. While not all pain can be mitigated by distraction or a positive mood, the idea that positive affect can help reduce the valence of painful stimuli is very powerful, providing alternative routes of analgesia to individuals experiencing acute or chronic pain in some cases instead of pharmaceutical drugs. Finally, some studies have investigated the impact of brief mindfulness or meditative practices on the perception of acute pain in the lab, finding reductions in pain responses and inspiring further research on the topic.

What does it all mean for me?

While there is a robust body of literature suggesting the role sex, gender, and age have on perceptions of pain, individual differences can, of course, outweigh the impact of demographic variables, meaning some women may have a higher pain threshold than men, or some older individuals may have a higher tolerance than some teenagers. Because pain sensation is so subjective and can be extremely difficult to communicate, it is important to recognize that individual differences can affect how people cope with pain and even what they consider to be painful. The fact that psychological variables, such as mood, can ameliorate pain provides an exciting future avenue that has the potential to help some individuals mitigate the negative impact of both acute and chronic pain.

References

Bushnell et al. Cognitive and emotional control of pain and its disruption in chronic pain. Nature Reviews Neuroscience. (2015). Access the original scientific publication here. 

Diatchenko et al. Genetic basis for individual variations in pain perception and the development of a chronic pain condition. Human Molecular Genetics. (2004). Access the original scientific publication here.

Fillingim. Sex, gender, and pain: Women and men really are different. Current Review of Pain. (2000). Access the original scientific publication here.

Gibson & Farrell. A review of age differences in the neurophysiology of nociception and the perceptual experience of pain. Clinical Journal of Pain. (2004). Access the original scientific publication here.

Hashmi & Davis. Deconstructing Sex Differences in Pain Sensitivity. Journal of Pain. (2013). Access the original scientific publication here.

Mogil et al. Sex differences in thermal nociception and morphine antinociception in rodents depend on genotype. Neuroscience & Biobehavioral Reviews. (2000). Access the original scientific publication here.

Sandhu & Leckie. Orthodontic pain trajectories in adolescents: Between-subject and within-subject variability in pain perception. American Journal of Orthodontics and Dentofacial Orthopedics. (2016). Access the original scientific publication here.

Taenzer et al. Influence of psychological factors on postoperative pain, mood and analgesic requirements. The Journal of Pain. (1986). Access the original scientific publication here. 

Zeidan et al. The effects of brief mindfulness meditation training on experimentally induced pain. The Journal of Pain. (2009). Access the original scientific publication here.