Is Pain Physical or Mental?
Teresa Hardy
UMass Boston
Abstract
The nature of pain is complex; the basic neural mechanisms responsible for transmitting pain signals have largely been elucidated, but other factors influence the perception of pain that cannot be satisfactorily described by neurobiology (Fields, 2007). Fields (2007) states that “all pain is mental” – yet there are clearly physical causes for many types of pain. This paper will explore the causes, mechanisms and and modulators of pain and attempt to answer the question of whether pain is physical, mental, or both.
Is Pain Physical or Mental?
Is pain physical, mental or both? To examine this question, we need to understand what pain is, what causes it, and how the brain processes it. Here, I will examine the mechanisms underlying pain and some of the factors that influence the perception of pain. I will also discuss how the meaning that we ascribe to pain and our past experiences effect pain before answering the fundamental question of whether pain is physical or mental.
What is Pain?
According to Woolf (2010), pain is an unpleasant sensation that may result from tissue damage or which can be idiopathic. Woolf identifies three types of pain: nociceptive pain, inflammatory pain, and pathological pain. Nociceptive pain is an early-warning system designed to protect from tissue damage. When we touch something cold, hot, or sharp, this type of pain causes an unpleasant sensation and a reflex to pull away from the source of the damage (called a “noxious stimulus”). Inflammatory pain is also protective. After an injury (tissue damage), the immune system causes inflammation in the injured body part which results in tenderness or hypersensitivity. Contact with the injured body part which ordinarily would be harmless becomes painful due to this inflammation. This helps us to protect ourselves after injury to avoid further damage.
The third type of pain that Woolf (2010) discusses, pathological pain, results from malfunctioning of the nervous system. In some cases, there is a known cause for this type of pain, such as damage to the nervous system – this is known as neuropathic pain. In other cases, the pain is known as “dysfunctional pain,” because there is no known cause or previous damage. According to Woolf (2010), pathological pain has the greatest clinical need; for the other types of pain, the treatment is to address the tissue damage and protect the injured body part. Pathological pain often becomes ongoing (chronic); some of these chronic conditions pose a substantial economic burden on society (Ambrose & Golightly, 2015).
Mechanisms of Pain
In nociceptive pain, neurons known as nociceptors detect physical stresses (heat, cold, mechanical or chemical stress) by expressing proteins that respond to these stresses (Woolf, 2010). The nociceptors then send a signal to the central nervous system. Neural circuits in the brain project a sensation of pain to the site of injury (Fields, 2007). Circuits in the central nervous system can increase or reduce pain depending on mood, cognitive function, and memories (Woolf, 2010). Many of these effects increase pain, but some of them reduce it, which is why a placebo effect can be seen when a patient is falsely informed that they are being given a painkiller. This may also explain the effectiveness of “alternative treatments,” such as acupuncture, against pain.
In the presence of inflammation, nociceptors undergo significant changes which cause them to respond with heightened sensitivity (Woolf, 2010). Light touch and pressure can cause these hypersensitive nociceptors to signal pain. A similar change can occur in the central nervous system, which is called “central sensitization” (Woolf, 2010). When this happens, pain signals can be sent in the absence of any noxious stimulus. This can also be done in a laboratory experiment; if the neural pathway for pain is triggered by electrical stimulation, the individual will feel pain at the site that corresponds to that pathway (Fields, 2007). Nothing is actually happening at that site; the pain is entirely projected.
Research over the past half century has greatly advanced our understanding of how pain is sensed in the body and processed in the brain. However, Fields (2007) emphasizes that discussions of the neurobiology of pain are insufficient to understanding pain. He says:
“Just as it would be pointless to analyze a book by investigating the chemical composition of paper and ink, a reductionist analysis of brain activity, that is, taking it apart and analyzing its nucleic acids, enzymes, receptors, and ion channels, fails to explain what brain activity accomplishes.”
The level of pain that an individual perceives can be strongly influenced by the context they’re in, their past experiences, and the meaning they ascribe to the pain (Fields, 2007).
Other Factors Influencing Pain
Pain can be exacerbated or alleviated by external factors as well as psychological ones. Medications are available to reduce pain, but the effectiveness can be limited. Non-pharmacological interventions have been studied to help remedy pain conditions. One such intervention is physical exercise, which has been researched as a way to mediate chronic pain (Ambrose & Golightly, 2015). Chronic pain effects many people (approximately 100 million Americans) and often limits the activity of those afflicted with it (Ambrose & Golightly, 2015). Chronic pain conditions can arise from a definite biological cause (such as arthritis) or be idiopathic (such as fibromyalgia); treating these conditions can be challenging (Ambrose & Golightly, 2015). According to Ambrose & Golightly (2015), studies have shown that exercise programs which combine different types of exercise (aerobic, resistance and flexibility exercises) reduce pain significantly in patients suffering from arthritis, fibromyalgia and chronic low back pain. Ambrose and Golightly do not speculate on the mechanism underlying this improvement, but mention that exercise can improve patient’s lives in a variety of ways: improving overall well-being, reducing weight gain, and improving mood and sleep.
Massage therapy has also been explored to reduce pain symptoms. In a study performed at Memorial Sloan-Kettering Cancer Center, cancer patients received massage therapy to help manage their symptoms (Cassileth & Vickers, 2004). Pain was the second most common symptom that patients were seeking relief from, after anxiety. Outpatients received longer massage sessions than inpatients. Patients reported major improvements in their presenting symptom after massage sessions. Outpatients reported that the benefits persisted up to 48 hours after their massage therapy session, although the effect on inpatients was shorter in duration (less than a day). These authors also did not comment on the possible reasons that massage therapy benefited their patients.
Interestingly, sound can also influence the perception of pain. Gardner and Licklider (1960) reported that sound has been used to suppress the pain associated with dental procedures such as tooth extraction. They used a combination of music and a random noise which sounds like a waterfall that is controlled by the patient. They reported that 65% of their patients found sound to prevent pain well enough that they didn’t need nitrous oxide or local anesthesia. According to the authors, the music serves to relax the patient and distract them from the procedure to prevent pain and reduce anxiety. This study predates much of the research into the mechanisms of pain (Fields, 2007), but the authors proposed a mechanism: pain circuits in the brain may be inhibited by auditory processing systems. They also noted that the power of suggestion may also be at play.
These examples show ways that external factors can reduce pain, but pain can also be amplified by psychological factors such as fear and anticipation (Fields, 2007). In one study, subjects were attached to electrodes and told that they would receive an electric shock (Fields, 2007). They were told that a visible gauge and a sound would show how intense the electric stimulus would be, but they actually received no shock. Half of the subjects reported feeling pain from the electrodes, and a quarter requested pain medicine. This study shows how strong the power of suggestion can be on the perception of pain.
Is Pain Physical or Mental?
Fields (2007) explains that pain-transmitting neurons can be electrically stimulated to produce a sensation of pain in a distant part of the body. This process is called “projection.” Fields states: “Once one understands and accepts the concept of projection, it becomes obvious that all pain is mental” (2007). In my interpretation, this means that all pain is processed in the brain, whether or not it has a physical cause. This is not the same as pain being “in your head” or imagined, which Fields’ statement could be interpreted to mean when quoted out of context. We have seen that pain is often caused by physical means, although in some cases, the response is exaggerated (as in inflammatory pain after an injury) or persistent long after the physical cause (as in pathological pain after nerve damage). However, pain can be caused or exacerbated by factors that are entirely psychological.
The context and meaning surrounding pain have powerful effects on the perception of pain (Fields, 2007). The human brain is innately curious and constantly seeking understanding of the environment and its effects on the individual (Fields, 2007). Pain is part of an adaptation to avoid potentially life-threatening damage, and our brains seek to understand the causes of pain and avoid them in the future (Fields, 2007). Thus, the perception of pain is influenced by memories of painful experiences and the associations that we draw between external factors and pain. Pain serves as a punishment for doing something risky; our brains then seek to avoid the cause of that pain (Fields, 2007). This can result in a conditioned response, even to stimuli that do not inherently cause harm. This can be seen when rodent are placed in a box and then given an electrical shock; after a few exposures, the rodent comes to associate the environment of the box with pain (Fields, 2007). The rodent will freeze up when placed in the box, a response that protects it from predators in the wild.
The meaning that we ascribe to objects and actions can intensify pain or even cause us to perceive pain in the absence of any physical damage. This was seen in the experiment where subjects were told they would receive an electric shock; they anticipated pain and received visual and auditory cues that they believed would correspond to a painful stimulus, so their brains processed these signals as pain. This is why a neurobiological explanation of pain is insufficient to fully understand pain; an individual’s beliefs and prior experiences, which cannot accounted for by neurological experiments, can impact the perception of pain greatly.
Conclusion
The study of pain is complex. Pain can be studied at the molecular and cellular level, but this does not paint the entire picture of how pain is perceived and what factors can influence it. Much is yet to be understood about the mechanisms underlying the modulation of pain, and researchers working to ameliorate pain with treatments such as massage or exercise tend to report the results rather than the mechanisms responsible (Cassileth & Vickers, 2004; Ambrose & Golightly, 2015). A holistic approach which considers how context, meaning and psychology influence pain can help improve our understanding of how pain works (Fields, 2007). All pain is mental in the sense that the sensation of pain is generated in the brain; this process can be uncoupled from any physical stimulus. However, pain usually has a physical cause, even when that physical cause is damage to nerves that may have occurred years earlier. Even biological causes, such as hypersensitization of neurons, can be considered physical. Thus, pain is both physical and mental.