Experimental Brain Research

, Volume 236, Issue 2, pp 365–379 | Cite as

Mechanical perturbations can elicit triggered reactions in the absence of a startle response

  • Christopher J. Forgaard
  • Ian M. Franks
  • Kimberly Bennett
  • Dana Maslovat
  • Romeo Chua
Research Article


Perturbations delivered to the upper limbs elicit reflexive responses in stretched muscle at short- (M1: 25–50 ms) and long- (M2: 50–100 ms) latencies. When presented in a simple reaction time (RT) task, the perturbation can also elicit a preprogrammed voluntary response at a latency (< 100 ms) that overlaps the M2 response. This early appearance of the voluntary response following a proprioceptive stimulus causing muscle stretch is called a triggered reaction. Recent work has demonstrated that a perturbation also elicits activity in sternocleidomastoid (SCM) over a time-course consistent with the startle response and it was, therefore, proposed that the StartReact effect underlies triggered reactions (Ravichandran et al., Exp Brain Res 230:59–69, 2013). The present work investigated whether perturbation-evoked SCM activity results from startle or postural control and whether triggered reactions can also occur in the absence of startle. In Experiment 1, participants “compensated” against a wrist extension perturbation. A prepulse inhibition (PPI) stimulus (known to attenuate startle) was randomly presented before the perturbation. Rather than attenuating SCM activity, the responses in SCM were advanced by the PPI stimulus. In Experiment 2, participants “assisted” a wrist extension perturbation. The perturbation did not reliably elicit startle but despite this, two-thirds of trials had RTs of less than 100 ms and the earliest responses began at ~ 70 ms. These findings suggest that SCM activity following a perturbation is the result of postural control and is not related to startle. Moreover, an overt startle response is not a prerequisite for the elicitation of a triggered reaction.


Startle reflex Triggered reaction StartReact effect Reaction time Stretch reflex Prepulse inhibition 



This work was supported by the National Sciences and Engineering Research Council of Canada.

Compliance with ethical standards

Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2017

Authors and Affiliations

  • Christopher J. Forgaard
    • 1
  • Ian M. Franks
    • 1
  • Kimberly Bennett
    • 1
  • Dana Maslovat
    • 1
  • Romeo Chua
    • 1
  1. 1.School of KinesiologyUniversity of British ColumbiaVancouverCanada

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