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The experience of pain

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A brief slideshow on pain, including a fascinating example of extreme perceived pain in the absence of tissue damage.
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  • THE EXPERIENCE OF PAIN A Question of Perception
  • A FAMILIAR EXPERIENCE Pain is often experienced in connection with some form of physical trauma. As we grow up, this association is frequently reinforced. For centuries, it was assumed that only tissue damage triggered pain.
  • NOTABLE EXCEPTIONS Medical doctors and nurses frequently noticed that soldiers injured in battle often felt little or no pain until later. And sometimes, pain and other sensations could still be felt in limbs that had been lost. These and other phenomena cast doubt on the old explanations for pain.
  • DEFINITIONS In the 20th century, scientists and clinicians studying pain from different perspectives developed a taxonomy for discussing pain and various manifestations/experiences of it. The International Association for the Study of Pain (IASP) defines pain as
  • PAIN (FULL DEFINITION) An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Note: The inability to communicate verbally does not negate the possibility that an individual is experiencing pain and is in need of appropriate pain-relieving treatment. Pain is always subjective. Each individual learns the application of the word through experiences related to injury in early life. Biologists recognize that those stimuli which cause pain are liable to damage tissue. Accordingly, pain is that experience we associate with actual or potential tissue damage. It is unquestionably a sensation in a part or parts of the body, but it is also always unpleasant and therefore also an emotional experience. Experiences which resemble pain but are not unpleasant, e.g., pricking, should not be called pain. Unpleasant abnormal experiences (dysesthesias) may also be pain but are not necessarily so because, subjectively, they may not have the usual sensory qualities of pain. Many people report pain in the absence of tissue damage or any likely pathophysiological cause; usually this happens for psychological reasons. There is usually no way to distinguish their experience from that due to tissue damage if we take the subjective report. If they regard their experience as pain, and if they report it in the same ways as pain caused by tissue damage, it should be accepted as pain. This definition avoids tying pain to the stimulus. Activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state, even though we may well appreciate that pain most often has a proximate physical cause. ~ International Association for the Study of Pain (IASP) Taxonomy
  • PAIN (SUMMARIZED DEFINITION) An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Key Points Pain is always subjective. Pain is always an emotional experience. Pain is often reported in the absence of tissue damage or any likely pathophysiological cause, usually for psychological reasons. If reported in the same ways as pain caused by tissue damage, it should be accepted as pain. Activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state, even though we may well appreciate that pain most often has a proximate physical cause. ~ derived from IASP Taxonomy
  • A PERCEIVED PAIN EXPERIENCE Despite no tissue damage, the patient experienced extreme pain and had to be sedated. Case report from the British Medical Journal (BMJ), 1995. A builder aged 29 came to the accident and emergency department having jumped down on to a 15 cm nail. As the smallest movement of the nail was painful he was sedated with fentanyl and midazolam. The nail was then pulled out from below. When his boot was removed a miraculous cure appeared to have taken place. Despite entering proximal to the steel toecap the nail had penetrated between the toes: the foot was entirely uninjured. - J P FISHER, senior house officer, D T HASSAN, senior registrar, N O'CONNOR, registrar, accident and emergency department, Leicester Royal Infirmary.
  • HOW DID THIS PATIENT FEEL PAIN? Despite no tissue damage, the patient experienced extreme pain and had to be sedated. Case report from the British Medical Journal (BMJ), 1995. We need to look at how the brain perceives and interprets sensory input.
  • THE NEUROMATRIX THEORY OF PAIN Inputs include biological, psychological, and social factors. Outputs include all aspects of how we experience and respond to the world. Many different forms of inputs affect how the brain interprets incoming sensory data to create our experience(s) of reality.
  • BIOLOGICAL FACTORS IN PAIN Nociceptive input is transmitted to brain via peripheral nerves and the spinothalamic tract. Other forms of sensorimotor input are received and processed by various parts of the brain to create a mental image of where pain occurs.
  • Figure 1 Schematic drawing of the pathways between the substantia nigra and pain- processing areas Wasner, G. & Deuschl, G. (2012) Pains in Parkinson diseasemany syndromes under one umbrella Nat. Rev. Neurol. doi:10.1038/nrneurol.2012.54 Efferent pathways from the substantia nigra project to pain-processing areas (red boxes), as indicated by black arrows. Together with further pain-processing areas (yellow boxes), these brain structures form a network that is essential for transmission of nociceptive input and central pain processing, as indicated by red dotted lines. Sensory cortices (S1 and S2) are suggested to be involved in the descriptive component of pain, whereas the anterior cingulate and prefrontal cortices seem to be essential for the affective dimension of pain. Abbreviations: S1, primary sensory cortex; S2, secondary sensory cortex. NEUROBIOLOGY OF PAIN
  • PSYCHOSOCIAL FACTORS OF PAIN Conscious cognition, including thoughts and feelings Unconscious (conditioned) responses to various stimuli Unconscious stimuli without a conditioned response Context provided by psychological and social factors play an important role in determining how biological factors are interpreted.
  • PSYCHOSOCIAL FACTORS OF PAIN The frontal cortex and temporal lobes are of primary importance in determining the psychosocial context. Context provided by psychological and social factors play an important role in determining how biological factors are interpreted.
  • HOW DID THIS PATIENT FEEL PAIN? Despite no tissue damage, the patient experienced extreme pain and had to be sedated. Case report from the British Medical Journal (BMJ), 1995. The patient would have Felt the sensations of landing and possibly of having an object penetrate his boot Heard the sound of his landing Seen a huge nail through his boot Seen and heard the reactions of his coworkers
  • HOW DID THIS PATIENT FEEL PAIN? Despite no tissue damage, the patient experienced extreme pain and had to be sedated. Case report from the British Medical Journal (BMJ), 1995. The patient would have Expected that a nail penetrating his boot would probably penetrate his foot Perceived that his foot had been punctured by the nail Had both conditioned and unconditioned negative responses to being punctured by a sharp object
  • HOW DID THIS PATIENT FEEL PAIN? Despite no tissue damage, the patient experienced extreme pain and had to be sedated. Case report from the British Medical Journal (BMJ), 1995. This patient perceived an experience of what seemed to have happened, and responded to that His pain was created by his brain, despite the lack of any nociceptive input from his peripheral nerves
  • HOW DID THIS PATIENT FEEL PAIN? This patient perceived an experience of what seemed to have happened, and responded to that, even though it was not real His discomfort was generated solely from psychosocial factors, yet was as intense as if his foot had actually been punctured
  • A FASCINATING ORGAN Understanding the Brain: The Neurobiology of Everyday Life with Peggy Mason, Ph.D. is a great Coursera class The course provides a foundation for understanding the roles and relationships of the various parts of the nervous system in relation to itself, to other organs/systems, and the world around us. Though pain was not addressed in detail, the course material covered sensorimotor inputs, perception, memory, and cognition, which are essential for analyzing the biological and psychosocial elements of pain.
  • FOR MORE INFORMATION ON PAIN Video Why Things Hurt Lorimer Mosely, http://youtu.be/gwd- wLdIHjs Book Explain Pain by David Butler and Lorimer Mosely, from http://NOIgroup.com Paper Pain by Ronald Melzack and Joel Katz, http://onlinelibrary.wiley.com/doi/10.1002/wcs.1201/full Commentary on Pain paper by Diane Jacobs, PT, http://humanantigravitysuit.blogspot.com/2013/05/melzacks-and- katz-new-paper-pain-part-1.html Paper Getting the pain you expect: mechanisms of placebo, nocebo and reappraisal effects in humans by Irene Tracey, http://www.nature.com/nm/journal/v16/n11/full/nm.2229.html
  • CONTACT For more information about this slideshow, contact Jason Erickson via [email protected]
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