An intense electrical stimulus can elicit a startle reflex and trigger a prepared movement


Volitional movements rely on efficient motor planning and preparation. It has been shown that planned actions can be triggered involuntarily by a startling acoustic stimulus (SAS), resulting in very short reaction times (RT). This phenomenon, known as the StartReact effect, is thought to result from the startle-related activation of reticular structures. However, other sensory modalities also can elicit a reflexive startle response. Here, we assessed the effectiveness of an intense startling electrical stimulus (SES) in eliciting the StartReact effect compared to SAS. We tested electric stimulus intensities at 15 and 25 times the perceptual threshold of each participant to match average intensities used in the literature, as well as auditory stimuli of 114 dB and 120 dB for SAS trials. The startling stimuli were presented on 20% of the trials in a simple RT paradigm involving a wrist extension movement of 20 degrees. Results showed that the proportion of trials with an observed startle reflex was significantly lower on SES trials compared to SAS, as evidenced by sternocleidomastoid (SCM) activation. Nevertheless, the proportion of SAS trials exhibiting a startle reflex was similar to what is reported in the literature. Interestingly, the data also showed similarly short RTs for both SES and SAS conditions, suggesting that the StartReact effect is independent of stimulus type. Finally, further testing is needed to establish an optimal electric stimulus intensity that can possibly generate comparative proportion of StartReact responses between SES and SAS.

Acknowledgments: Supported by NSERC