Temporal association between changes in primary sensory cortex and corticomotor output during muscle pain.
BACKGROUND
Integration of information between multiple cortical regions is thought to underpin the experience of pain. Yet studies tend to focus on pain related changes in discrete cortical regions. Although altered processing in the primary motor (M1) and sensory cortex (S1) is implicated in pain, the temporal relationship between these regions is unknown and may provide insight into the interaction between them.


METHODS
We used recordings of somatosensory-evoked potentials (SEPs) and transcranial magnetic stimulation to investigate the temporal relationship between altered excitability of the primary sensory cortex and corticomotor output during and after muscle pain induced by hypertonic saline infusion into the right first dorsal interosseous. SEPs and motor-evoked potentials (MEPs) were recorded in 12 healthy individuals.


RESULTS
Participants reported an average pain intensity of 5.4 (0.5) on a 10-cm visual analogue scale. The area of the N20-P25-N33 complex of the SEP was reduced during and after pain, but MEP amplitudes were suppressed only after pain had resolved.


CONCLUSIONS
Our data show that pain reduces sensory processing before motor output is altered. This temporal dispersion, coupled with the lack of correlation between pain-induced changes in S1 and M1 excitability, imply either that independent processes are involved, or that reduced excitability of S1 during acute experimental muscle pain mediates latent reductions in motor output via processes that are non-linear and potentially involve activation of a wider brain network.
The University of Queensland, NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Science, St. Lucia, Brisbane, Queensland 4072, Australia. s.schabrun@uq.edu.au
S M
SM
Schabrun
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E
Jones
J
J
Kloster
P W
PW
Hodges
D000328:Adult; D000704:Analysis of Variance; D004558:Electric Stimulation; D004569:Electroencephalography; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005260:Female; D006225:Hand / Q000294:innervation / Q000502:physiology; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000503:physiopathology*; D059352:Musculoskeletal Pain / Q000139:chemically induced / Q000503:physiopathology* / Q000523:psychology; D010147:Pain Measurement; D012462:Saline Solution, Hypertonic; D013003:Somatosensory Cortex / Q000503:physiopathology*; D050781:Transcranial Magnetic Stimulation; D014459:Ulnar Nerve / Q000502:physiology
D012462:Saline Solution, Hypertonic