Q: How is Pain Subjective and Different from Nociception?
A: Pain is not nociception because their definitions are different. The usual definitions are like this:
Nociception refers to the peripheral and central nervous system (CNS) processing of information about the internal or external environment, as generated by the activation of nociceptors. Typically, noxious stimuli, including tissue injury, activate nociceptors that are present in peripheral structures and that transmit information to the spinal cord dorsal horn or its trigeminal homologue, the nucleus caudalis. From there, the information continues to the brainstem and ultimately the cerebral cortex, where the perception of pain is generated. Pain is a product of higher brain center processing … (1)
“Nociception (also nocioception, from Latin nocere 'to harm or hurt') is the sensory nervous system's process of encoding noxious stimuli. In nociception, intense chemical (e.g., cayenne powder), mechanical (e.g., cutting, crushing), or thermal (heat and cold) stimulation of sensory nerve cells called nociceptors produces a signal that travels along a chain of nerve fibers via the spinal cord to the brain.1 Nociception triggers a variety of physiological and behavioral responses and usually results in a subjective experience (or perception) of pain in sentient beings.”(2)
That is, nociception is defined to be the processing of noxious stimuli, which involves several levels of processing, but pain is defined to be the perception of the result of nociception processing. As there are many factors that can affect nociception at each level of processing, such as the pain control mechanism (e.g. the pain gate control) in the spinal cord and brainstem, analgesics, and even the mood of the subject, the pain perception can be altered/modified, and the final pain perception can be different even if it occurs in the same individual and from the same noxious stimuli. Also, because these factors are different among different subjects, the final pain perception in each individual is subjective – depending on various factors in each subject and different among different subjects even if it occurs from the same noxious stimuli.
When your shin hits something hard and you feel pain there, if you stroke or massage the injured shin lightly, you’ll feel better with less pain – this is because the pain is modified by the pain gate control or other pain control mechanisms by the touch sensation. (3,4)
In a person who has a spinal cord transection with a loss of all sensations and voluntary movements of the legs, if you prick his foot, his foot will involuntarily jerk away from the prick, which means nociception is still being processed, but you won’t feel any pain because the pain perception in the brain does not occur (due to the spinal cord transection).
Alice has been given a flu shot in her arm, but she is a strong person and is in a good mood, so she feels little pain in her arm. On the contrary, Bob has been given a flu shot with the same needle size and ease of injection, but Bob is an irritable person and already in a bad mood, so he feels that the pain from the shot is very severe. So, the pain perceived from the same noxious stimuli is different among different subjects, depending on various factors in each subject.
Therefore, the pain is different from nociception and is subjective.
National Research Council. 2009. Mechanisms of Pain In: Recognition and Alleviation of Pain in Laboratory Animals. Washington, DC: The National Academies Press. https://doi.org/10.17226/12526.
Nachum Dafny.Chapter 8: Pain Modulation and Mechanisms. Neuroscience Online. The University of Texas Health Science Center at Houston (UTHealth).
Wikipedia. Gate Control Theory