- Statistics regarding pain: 3% have cancer, 6.5% have heart disease, 7.5% have diabetes, 30% of the
pop’n report having chronic pain, 10% report chronic pain due to disability >15, 1% of budget devoted
to research on pain, 4% to diabetes, 8% to heart disease.
- WHAT IS PAIN? Pain is a mechanism of self-preservation. Its considerable ability to capture attention
makes it difficult to ignore, and its averseness strongly motivates reactions aimed at its reduction.
According to the IASP, pain is an unpleasant sensory or emotional experience associated with actual or
potential tissue damage, or described in terms of such damage.
- Pain is the most common symptom in medical practice and the most common reason people seek
medical care. th
- Considered the 5 vita sign after: blood pressure, respiration, temperature, pulse.
- >20% of pop’n of chronic pain patients has contemplated suicide (3.5% of US pop). 5-14% has
committed suicide (.5% of US pop).
- Pain is often described as the invisible condition as it cannot be measured objectively. Even fMRIs
cannot tell us since certain parts of the brain light up to pain and non-pain events. So we must heavily
rely on self-reports. With no way to objectively quantify pain, many people go without the powerful
drugs they need because docs prescribe them sparingly for fear that they may be addicts or licensure
issues. People, who do their best to cope, are told that since they’re coping they must be ok. So they
don’t get the medical care, or understanding from those around them. Chronic pain wrecks lives,
causes untold suﬀering and loss.
- An important part of the limbic system, the cingulate gyrus helps regulate emotions and pain. The
cingulate gyrus is thought to directly drive the body's conscious response to unpleasant experiences. In
addition, it is involved in fear and the prediction (and avoidance) of negative consequences and can
help orient the body away from negative stimuli. Learning to avoid negative consequences is an
important feature of memory.
- Sensory vs. Emotional experiment (Rainville): Ps asked to immerse hand in warm water or painfully
water. Used hypnotic suggestion without changing perceived pain. Scanned brain using PET during
conditions of hypnotic control, hypnotic suggestion, and alert control to increase/decrease pain
unpleasantness. A comparison of rCBF changes in hypnotic suggestion and hypnotic control, the
following areas showed activations: SI, ACC, IC during both ↑UNP and ↓UNP conditions. Hypnotic
suggestion conditions revealed that only the ACC was responsive to suggestions to
increase/decrease pain unpleasantness.
- WHY PAIN?
- Pain is powerful motivator compelling action aimed at: preventing injury and preventing further
injury; promoting healing.
- Congenital Insensitivity to Pain with Anhidrosis (CIPA): rare inherited disorder which is the inability to
feel pain and temperature, and decreased or absent sweating (anhidrosis). They bite their own tongue,
lips and ﬁngers to the point of mutilation. Most people do not make it past age 25. Diabetics who have
numb feet get injured, don’t know it, and get gangrene.
- Pain is a homeostatic emotion. Homeostasis: the maintenance of the internal conditions necessary
for life through active physiological and behavioral means.
- Dehydration ➞ thirst ➞ drinking
- Elevated CO2 levels ➞ air hunger ➞ breathing
- Injury ➞ pain ➞ protective behaviors
- Pain becomes a problem when it becomes persistent and chronic. It becomes a serious disease of its
- Pain experience exists entirely in the brain even though we feel pain in the body. Pain is therefore
subject to the inﬂuence of anything going on in the brain. Pain experience impacted by numerous
factors: mood, genetics, context, fear, depression etc. Pain is the only physical health malady that
exists almost entirely in the brain.
- Pain used to be viewed as a simple linear relationship between magnitude of tissue damage and
pain. Pain can occur in the absence of tissue injury. Pain can be absent in the presence of tissue injury.
- Classifying Pain: Time, Part of the body, Type of tissue, Nature of cause.
- Measuring Pain: Intensity and affect: NRS, VAS, Category intensity scale, faces or oucher scale.
- McGill Pain Questionnaire: Sensory, Evaluative, Aﬀective, Temporal, Intensity.
- CRIES Pain Assessment for Infants. - Pain thermometer: 7 intensity
- Nonverbal checklist for pain: 6
- Pain behaviours: 5
- Ronal Melzack and Gate control theory (GCT): Proposed the existence of neural structures in the
spinal cord and the brain that function like a gate, swinging open to increases the flow of transmission
from nerve fibers and swinging shut to decrease the flow. With the gate open, signals coming in the
spinal cord stimulate sensory neurons called transmission cells which in turn relay signals upward to
reach the brain and trigger pain. With the gate closed, signals are blocked to reach the brain and no
pain is felt. What causes the spinal gate to close? Depending on which pain fibres are activated, the
substantia gelatinosa – the gatekeeper – will open/close the gates. Activity in the fast pain fibre system
tends to close the gate whereas activity in the slow pain fiber system tend to force the gate open.
Central control mechanism – signals from brain can also shut the gate – accounts for feelings/thoughts
on the perception of pain. Anxiety amplifies experience of pain and distraction dampens experience of
- According to the GCT, why do you feel relief after rubbing a sore area? Temporary relief was the
result of stimulating one area to reduce pain in another. You feel relief because deep massage
activated the fast pain fibre system which in turn triggered activity in the substantia gelatinosa which in
turned closed the gate in the spinal cord and at least temporarily prevented the painful messages
carried by the slow pain fibre system from reaching the brain.
- Hormonal reason: In the absence of input from C-fibers, tonically active inhibitory interneuron
suppresses pain pathway. With strong pain, C-fiber stops inhibition from the pathway allowing a strong
signal to be sent to the brain. Pain can also be modulated by somatosensory input. Touch or non-
painful stimulus such as rubbing activates the A_beta fibers which suppresses the pain pathway
temporarily. This is why rubbing or shaking an injured part can reduce pain. Also a reason why a band-
aid can reduce hurt -- the pressure from the bandaid activates the A-beta ﬁbers.
Chemicals that suppresses pain pathway: A-beta fibes: inhibitory amino acids, GABA,
For c-fiber: excitatory amino acids, neuropeptides, glutamate, aspartate, substance P.
- HOW PAIN WORKS: Different types of sensory neurons: pacinian corpuscle (senses vibration), ruffini
corpuscle (Responds to hair stretch), meissner’s corpuscle (responds to flutter/stroking movements),
merkel receptors (Sense steady pressure/texture).
- Nociceptors – Charles Sherington. High threshold sensitivity.
- Two types of nocicetors:
- Spinal regions: A-delta and C-fiber in dorsal horn (II). A-alpha (6,7,9), A-beta (3,4,5,6).
- Cortical regions: As pain pathways pass through cortex, pain experience is imbued with different
features (sensations, emotions, memories).
- Limbic areas
- Amygdala --> emotion, fear
- Hippocampus --> memories
- Hypothalamus --> modulation
- Cortical areas c