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This Article Full Text Full Text (PDF) All Versions of this Article: 573/3/857    most recent jphysiol.2006.108274v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Blouin, J.-S. Articles by Siegmund, G. P. Search for Related Content PubMed PubMed Citation Articles by Blouin, J.-S. Articles by Siegmund, G. P. Related Collections Integrative

¹ School of Human Kinetics
² International Collaboration on Repair Discoveries
³ Brain Research Centre, UBC, Vancouver, British Columbia, Canada
⁴ MEA Forensic Engineers & Scientists, Richmond, British Columbia, Canada

The human startle response produces muscle contractions throughout the body but the most brisk and synchronized contractions appear in the neck muscles. This response, which is greatest with the first exposure to a startling stimulus, could produce excessive and inappropriately directed muscle contractions that could explain the higher incidence of whiplash injuries in people who are unprepared for the collision. This study seeks neurophysiological evidence of startle responses in the neck muscles of 120 healthy subjects exposed to between 1 and 16 rear-end impacts or forward perturbations of different speeds. Startle responses were quantified by the synchronous electromyographic (EMG) activity between 10 and 20 Hz in bilaterally homologous sternocleidomastoid, scalene and cervical paraspinal neck muscles. Coherence analyses of EMGs from the left and right muscles were used to estimate synchrony for: (i) the first unexpected trial, (ii) subsequent habituated trials, and (iii) the superposition of habituated trials and a loud acoustic stimulus (40 ms, 124 dB sound). The peak in coherent EMG activity between contralateral muscle pairs in the 10–20 Hz bandwidth was related to startle. Synchrony in this bandwidth was observed between the left and right muscles during the first impact or whiplash-like perturbation. This synchrony decreased significantly in the habituated trials, but reappeared when the loud acoustic stimulus was introduced. Its presence in the first trial indicates that startle is part of the neuromuscular response to an unexpected rear-end impact. This startle component of the neuromuscular response could play a role in the aetiology of whiplash injuries.

(Received 22 February 2006; accepted after revision 23 March 2006; first published online 31 March 2006)
Corresponding author J. T. Inglis: 210-6081 University Boulevard, School of Human Kinetics, UBC, Vancouver, BC, Canada V6T 1Z1. Email: tinglis{at}interchange.ubc.ca

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