Pain grey region of the brain. This pathway

Pain perception is not entirely dependent on physical injury.

When we damage a part of our bodies, for example, when we burn ourselves, break a bone etc the pain we feel is very subjective.  Pain perception is the awareness of pain and we all perceive pain differently for many reasons.  There are pain pathways that allows us to feel pain and a pain pathway that may inhibit how much pain we feel.  We may expect that a person with a severe physical injury to feel a high intensity of pain but there are cases where this does not happen.  Conversely, some people may feel a higher level of pain than we would expect.  You may also perceive pain, despite not having a physical injury.

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When we injure ourselves before we perceive pain the information about the painful stimulus has to reach the brain. There is a pathway to the brain called the spinothalamic pathway.  A nociceptor (which is responsible for detecting a panful stimulus), synapses with a transmission cell which is situated in the spinal cord and extends to the part of the brain called the thalamus. Signals about the painful stimulus are sent to the somatosensory cortex and then onto other areas of the brain for processing. 

Dr Melzack and Walls believed that it was possible to close off pain signals so no pain could be felt, this is known as the ‘gate control theory’.  They believed that there were cells situated in the spinal cord that could stop the brain receiving information about painful stimuli (The Open University, 2018a).  Further studies on gating pain have since been carried out which helps supports their theory.  To feel pain an action potential has to fire, without an action potential no pain can be perceived.  There is a suppressive pathway from the brain to the spinal cord in the periaqueductal grey region of the brain.  This pathway excites interneurons in the spinal cord and the neurotransmitters GABA and enkephalin inhibit transmission cells in the spinothalamic pathway so no action potential occurs. 

There are different factors that are thought to gate pain.  Scientist Susanna Bantick wanted to find out if pain perception could be reduced if attention was directed away from the painful stimulus (The Open University, 2018b).  Brain activity was measured by fMRI whilst the participants took part in an activity when receiving heat to the hand. Bantick suggested that they would feel less pain and the brain would process the pain differently if they were distracted by the activity.  The results of this study showed that the participants did feel less pain when they were distracted.  fMRI scans showed that there was decreased activity in the spinothalamic pathway and increased activity in the ACC region of the brain.  It was concluded that the distraction from pain resulted in an increase of activity in the ACC resulting in a greater signal being sent to the interneurons which allows us to gate pain (The Open University, 2018c). 

Dr Beecher noticed that some people did not feel as much pain as you would expect them to in relation to the physical injuries they had.  Beecher observed this phemonom with WW2 soldiers.  He noticed that some soldiers who had severe war injuries did not experience as much pain as you might expect.  Beecher studied and compared the intensity of pain in soldiers to civilians and their need for pain relief.  The results showed that soldiers with severe physical wounds surprisingly did not always ask for pain relief or felt the need for any.  Beecher concluded that there was no relationship between the severity of a physical injury and the pain perceived and he believed that the pain we perceive is not down to the severity of an injury, but how we feel about it (The Open University, 2018d).  

Additionally, some people might experience more pain than we would expect. Pain perception may be affected by how we learn about pain.  We might expect that a small cut for example will only lead to a small amount of pain, but that isn’t always the case.  We are able to learn about pain from watching others around us.  Without experiencing the pain ourselves we all know what injuries may cause us pain and how painful something might be.  This is know as intentional learning about pain.  Goubert et al, believed that we could feel the emotional aspects of pain without feeling the pain ourselves and children may experience high intensity of pain themselves if they have witnessed a care giver showing a high intensity of pain from a certain injury (The Open University, 2018e).  This helps supports Dr Beecher’s conclusions that how we feel about pain may affect the amount of pain we feel, helping to prove that the physical injury may not have much baring on how much pain we perceive. 

It is also possible to feel pain when no injury has occurred.  Emotional distress may lead a person to perceive pain; this is known as psychogenic pain.  Gundel et al carried out a study on pain and grief.  fMRI scans were used to measure brain activity in a group of women who were grieving the loss of a loved one.  The participants were shown pictures and given descriptions of the person they lost. The fMRI scan showed that certain areas of the brain that are activated in physical pain were also activated during this study (The Open University, 2018f).  Another similar study about psychogenic pain was carried out by Singer et al.  They wanted to investigate what happened in certain areas of the brain when people witnessed their loved ones feeling physical pain.  Imaging technology was used whilst their partners were receiving a painful stimulus, and once again the areas of the brain that are activated during physical pain were activated when they were watching their partners in pain (The Open University, 2018g).  These participants had no physical injuries themselves but it was entirely possible they felt physical pain because of the emotional distress they were under.  People often report emotional pain hurting them physically. 

It is clear that pain perception is quite a complicated matter and the amount of pain one feels is dependant on many factors and not just the severity of the physical damage alone.  How we feel and how we learn about pain all has an affect on how we perceive pain.  Two people with the same injuries could feel very different intensities of pain, perhaps due to the way they have learnt about pain, the attention they pay to it or from the biological mechanisms that allows us to gate pain.  Thanks to brain imaging technology scientists have been able to make great discoveries in the world of pain to show that pain perception isn’t entirely dependant on physical injury. 


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