The experience of pain is a subjective sensation, controlled by multiple factors (Trout, 2004).
Pain affects the majority of the population, daily. Therefore, research into pain is important
in order to understand the pain process and how to treat pain effectively.
Pain is a complex, social problem that has evolved and adapted significantly over time.
Prior to 1965, a simple neurophysiologic model of pain predominated. All physical pain was
thought to emanate from activation of specific pain receptors in the periphery, initiating
pain impulses through a spinal pathway to the brain (Rosenzweig, Leiman, Breedlove, 1999).
This model was a simple sensory stimulus-response model.
Psychological contributions to pain were not recognised. Significant theories such as The
Gate Control Theory (GCT) (1965) and Neuromatrix Pain Theory (NPT) (1999) are used to
understand and explain pain.
This essay will discuss the biological process of pain and how psychology and biology can be
incorporated to describe how pain.
Pain is a psychological response produced by the body to indicate injury or illness.
Research is able to explain the process of pain in terms of biology.
From a biological perspective, it is known that beneath the skin in the periphery, where
muscles and tissue are located, are nociceptors (pain sensory cells).
When noxious stimulus occurs (injury), chemicals are released to stimulate nociceptors.
Depending on the type of injury of pain, a different type of nociceptor will be released – the
alpha delta which are small cells that produce fast well localised pain and the C fibre which
produce slow poorly localised pain such as burning or throbbing.
These nociceptors propagate the information about the pain to the spinal cord through the
dorsal sensory fibre (located at the back of the spinal cord) to pass information into the
spinal cord and to the brain.
Chemicals reach the brain via the spinothalamic pathway towards the thalamus; this is
known as the relay station.
Following this, the second order neuron releases chemicals that pass pain information to
the third order neuron which locates the pain to the part of the somatosensory cortex that
correlates with the position of the injury. This process is known as the ascending pathway
(Kalat, 2009).
The gate control theory recognized the perception of pain is inherently more complex than
simple receiving and recording.
The gate control theory forced medical and biological sciences to accept the brain as an
active system that filters, selects and modulates inputs (Melzack, 1999).
This was a major advance in recognising the contribution of the brain not only to the
ultimate perception of pain, but also to the nature of pain itself (trout, 2004).
Implicit in GCT was the idea that a gate was either opened or closed at the level of the spinal
cord (i.e., impulse transmission was either facilitated or inhibited at that level).
If impulse transmission is sufficiently inhibited at the level of the spinal cord, then
perception of pain (which occurs in the brain) is blocked.
The number of fibres entering the spinal cord can affect the intensity of pain that we feel.
An example of this is rubbing an area that has been bumped, triggering more nociceptor and
essentially blocking the gate allowing only some nociceptors to get through, potentially
dampening the intensity of the bump or fall.
This theory fails to account for the perception of pain in the absence of sensory stimuli
(such as occurs with phantom limb pain), and it fails to account for the perception of the
body as a unity (Melzack, 2001).
However, other processes can allow the gate to open and close such as emotion and
attention (Melzack and Wall, 1965).
These processes may have an influence because they travel through the same location of
the gate system (Hagbarth and Kerr, 1954).
Cognitive, sensory and emotional factors that could open the gate and increase pain
intensity include physical inactivity, worrying about pain, having no distractions, depression,
anxiety, anger and stress.
Factors that can close the gate include meditation, distractions, high physical fitness, stress
management and positive attitude (Deardorff, 2003).
However, GCT still leaves unanswered questions regarding chronic pain, sex difference and
the effects of previous pain experience.
NPT retains some key aspects of the gate theory of pain, but it offers a more comprehensive
framework for under-standing the subjectivity of pain.
It recognizes the importance of both ascending and descending inputs to the conscious
experience of pain and includes additional inputs that were not part of the gate theory, such
as the important contributions of memory and past experiences (Melzack, 2001).
NPT suggests we are all born with a genetically determined neural network in our brain
known as the body-self neuromatrix (BSN). The BSN creates the perceptions we have of our
bodies and our sense of self and can generate chronic pain through processing inputs.
Cognitive, sensory and affective inputs such as memories, past experiences, emotions and
sensory inputs travel into the neuromatrix and cause an output such as a stress response, a
voluntary or involuntary physical movement and a cognitive evaluation.
Over time and through life experiences, the body-self neuromatrix can change and
therefore the way in which an individual processes different types of pain can alter.
Prior experience with intense pain can be a positive influence if managed in a way that
elicited a feeling of accomplishment, or this past experience can cause increased anxiety
when anticipated a second time. Eg., women who experience little pain in a prior pregnancy
may be more confident because the previous experience with pain was manageable
(Hodnett,2002).
The BSN is also influenced by cultural values and therefore explains as to why individuals
from different cultural backgrounds view pain differently. NPT explains that even without
nociceptive stimuli, pain can occur.
The main advantage of this model is its ability to explain how sensory, behavioural, visual
and nociceptive components can come together and influence one another. However, the
model fails to explain sex difference in pain in that females report more pain than men
(Unruh, 1996).
To conclude, researchers have found increasing evidence that psychology plays a part in the
pain process.
GCT changed the idea of pain and found evidence psychological thoughts, emotions and
ideas can impact the biological process of pain by influencing the ‘gate’ mechanism that
either opens or closes depending on the nature of these factors.
Furthermore, NPT analysed processes in the brain that can create pain without the input of
a painful stimuli and showed that memories, previous experiences and emotions can cause
the feeling of pain.
Highlighting, clear evidence that shows both biology and psychology play a major part in
the pain process.