1 Putting Pain in a New Perspective, Or… Mary Christenson, PT, PhD DPT 781 O

2 What Makes Pain Matter?  Traditional Model Papercut stimulates free nerve endings of mechanical nociceptors Travels via A delta and C fibers to the dorsal horn of the spinal cord Synapse on second neuron in substantia gelatinosa / T cell, crosses midline and joins the anterolateral spinothalamic system Travels to ventral posterior lateral nucleus of thalamus where synapses on third neuron Information carried to area of the primary somatosensory cortex which interprets “papercut - pain”

3 Personal Stories: Need for a New Model?  Phantom Limb Pain  CRPS  Traumatic injuries where a greater threat is perceived  Life more important than pain  Step on a Tack: Basic Up a notch

4 Pain versus Tissue Injury  “Pain does not provide a measure of the state of the tissues.” 1  % people with bad OA and no pain?  % people with bad disc protrusion and no pain?  Etc.

Questions  Have you ever had no pain with damage to your body?  Have you ever experienced pain when no damage has occurred to your body? 5

The Threat  Get pain when brain perceives there is a potential for danger to tissues and action is needed  The brain is managing countless messages in very short time intervals – determines priorities” 6 Brain = “Orchestra” per Butler and Moseley 2

7 Rethinking Sensors  Sensors = receptors = “reporters” 2 keeping track of the body’s business  Located in walls and at the free nerve endings of neurons  Stimulation can open receptors, ions exchanged, action potential  Rapid turnover of sensors? Importance?  Can increase/decrease in number – Result?

Spinal Cord Involvement  Messages can come from the brain to shut down neurotransmission of signals from 2 nd order neurons (“danger messengers” 1 ) stop  Powerful chemicals (stories) reverse flow of ions and therefore can stop signals

Rethinking the Brain’s Involvement  Many centers in the brain involved in pain to interpret and respond Pre-motor/motor cortex Cingulate cortex Pre-frontal Amygdala Sensory cortex Hypothalamus/ thalamus Cerebellum Hippocampus 2

10 Peripheral Sensitization  Increased responsiveness to stimuli after initial injury  Potential mechanisms: Lower threshold to stimulus Increase in neuron activity Increase in area of receptor fields Increase in response to the same stimulus

Central Sensitization  Neurons in dorsal horn High-threshold – respond to noxious stim Low-threshold – respond to innocuous stim Wide-dynamic-range (WDR) – respond to both  Tissue injury: increased sensitivity of high- threshold and WDR neurons Expansion of receptive fields in central neurons common  As pain persists, neurons in brain that induce pain become sensitized

Sensitization  Continued input from sensitized nociceptors can maintain sensitization of dorsal horn neurons Need to reduce peripheral input?  Sensitization of dorsal horn neurons can also be maintained in absence of peripheral input Need to reduce central sensitization?

Multiple Sites within the Brain – Decision-Making Power  Brain has billions of neurons – each neuron can connect with up to 5000 other neurons 13

At first glance: Is the yellow panel in front or back? 14 BIR&qs=n&sk=#focal=aa51b477d526faca84a9a39bfdf0456a&furl=http%3A%2F %2Fwww.at- bristol.org.uk%2Fassets%2Fimages%2Fillusions%2F11.%2520The%2520Necker %2520Cube.jpg

15 The Neuromatrix Model  Pain is Complex  The Neuromatrix Theory 2 Neuromatrix distributed throughout brain Wide network of neurons that generate patterns Processes information flowing through it Produces a pattern felt as whole body Pain is an event that takes up part of this space Event space = neurosignature

16 The Threat: “Danger”  Body Perceives a Threat Many systems engage  Endocrine/hormones – down and up regulate  Motor – Mobilizes  ANS SNS – increase HR, metabolism, “awareness” PNS – will act in healing processes  Immune – fight “invasion,” heal, sensitize  Pain – motivator: get help, prompt to move Pain may be the conscious response to threat

It is the perception of the threat that determines the output, not the tissue damage itself or threat to the tissues… 1 Neuromatrix Theory The Brain Interprets the Messages Received to Determine an Output

18 The Pain Experience  Somatic  Psychological Attention Anxiety Expectation Meaning of pain  Social Provides context to the pain

Patient and Clinician Education  What effect will each of these (listed on previous slide) influences have on the perceived threat?  CRPS

20 Change in the Brain: Remember the Homunculus?  Proprioceptive representation of pained part changes in primary somatosensory cortex 1

21 Homunculus  Skin and soft tissue representation  Change in representation of parts of the brain; Example: phantom limb pain 4  “Use-dependent brain” 2  Demand more of a part, representation in the brain will be bigger – ex. musicians

22 How persistent pain develops  Tissue injury may not be present – pain continues  Continued input sensitizes central neurons  Pain can occur without tissue damage

Brain Imaging

24 SOOOO…How can we help our patients with persistent pain?  It’s time for lab…..

25 References  1 Moseley GL. Reconceptualizing pain according to modern pain science. Phys Ther Reviews. 2007;12:  2 Butler D, Moseley GL. Explain Pain. Adelaide: NOI Group Publishing,  3 Melzack R. Evolution of the neuromatrix theory of pain. The Prithvi Raj Lecture: Presented at the Third World Congress of World Institutes of Pain, Barcelona Pain Practice. 2005;5(2):85-94  4 Colapinto J. Brain games: The Marco Polo of neuroscience. The New Yorker. May 3, 2009.