This document discusses dysynchiria, a phenomenon where touching the unaffected limb of someone with Complex Regional Pain Syndrome (CRPS) causes pain in the affected limb. The document presents evidence that dysynchiria results from cross-activation of bimodal neurons in the secondary somatosensory cortex (S2) due to abnormal sensory processing and sensitization in CRPS. A diagram is provided showing how visual input could activate bimodal neurons in S2 and ignite a pain network in a sensitized state.

1. Lorimer Moseley
NHMRC Senior Research Fellow
Prince of Wales Medical Research Institute & School of Medical Sciences,
University of New South Wales, Sydney, Australia
Team leader
The GAMFI project
University of Oxford, UK

2. Dysynchiria
Watching the mirror image of the unaffected
limb elicits pain on the affected side
Acerra & Moseley 2005 Neurology 65: 751-3

3. This is Nicole.
She is touching
the good hand
of someone
with CRPS,
who has their
bad hand
behind
the mirror.
Acerra & Moseley 2005 Neurology 65: 751-3

4. So, one puts
their hands
either side of a
mirror….
Acerra & Moseley 2005 Neurology 65: 751-3

5. So, one puts their hands either
side of a mirror….then moves
their head a bit so that it looks
like they are seeing both hands
when they are actually seeing
the right hand and its mirror
image.
Acerra & Moseley 2005 Neurology 65: 751-3

6. So, one puts their hands either
side of a mirror….then moves
their head a bit so that it looks
like they are seeing both hands
when they are actually seeing
the right hand and its mirror
image.
Acerra & Moseley 2005 Neurology 65: 751-3

7. experience
When you touch the good
hand, nothing
normal extraordinary happens…..
Acerra & Moseley 2005 Neurology 65: 751-3

8. experience
When you touch the
intact hand, one feels
the touch on BOTH hands
Phantom/stroke
“Synchiria”
Acerra & Moseley 2005 Neurology 65: 751-3

9. pain
experience
When you touch the good
hand, one feels that
touch on that hand but it
CRPS1 also HURTS the other
hand.
“dysynchiria”
Acerra & Moseley 2005 Neurology 65: 751-3

10. A
Parasthaesia
Allodynia
x x x x
x x x x x x x
x x x x x x x x
x x x x
x x xx
p pp p p
p
x x
op x x
xx
x
Response to light
p x
p ppp
o p p
o o o
p p x
p p touch
o o o
B
ooo
Before Rx ooo
ADer Rx
opo ooo
p pp x po
o p p p o o o o
x o
o x p o oo
oo
o x x x o o o o
o x oo oo
o oo xx oo o
Acerra & Moseley 2005 Neurology 65: 751-3

11. S1 ‘representaJve’ neurons S2 ‘representaJve’ neurons
with bimodal input
Visual field input
Wide diameter sensory neuron
This is a possible explanaJon for the phenomenon of
dysynchiria.
Acerra & Moseley 2005 Neurology 65: 751-3

12. S1 ‘representaJve’ neurons S2 ‘representaJve’ neurons
with bimodal input
Visual field input
Wide diameter sensory neuron
Acerra & Moseley 2005 Neurology 65: 751-3

13. S1 ‘representaJve’ neurons S2 ‘representaJve’ neurons
with bimodal input
Visual field input
Normal state
Wide diameter sensory neuron
Acerra & Moseley 2005 Neurology 65: 751-3

14. S1 ‘representaJve’ neurons S2 ‘representaJve’ neurons
with bimodal input
Visual field input
SensiJsed state
Wide diameter sensory neuron
This is a possible explanaJon for the phenomenon of
dysynchiria.
In a sensiJsed state, the visually‐evoked acJvaJon of
bimodal neurons in S2 might be enough to ‘ignite’ the
network of neurons that evokes pain.
Acerra & Moseley 2005 Neurology 65: 751-3