Auditory Startle Alters the Response of Human Subjects Exposed to a Single Whiplash-like Perturbation

Abstract

Human volunteers were exposed to a single whiplash-like perturbation. To determine how muscle and kinematic responses are affected by the superposition of a rear-end collision and loud startling noise. Many whiplash studies use forward perturbations without reproducing the sound of a car crash. Loud sounds are known to evoke startle responses in the neck muscles and therefore could affect whiplash injuries. Sixty-five subjects (30 female, 35 male) were exposed to a single forward horizontal perturbation. Head and torso kinematics, and electromyographic activity in the sternohyoid, sternocleidomastoid, scalenus, and cervical paraspinal muscles were measured. Two awareness conditions (deceived and unaware subjects) nested in two startle conditions (with or without a 40 milliseconds, 124 dB sound) were tested. Startle and gender affected the amplitude and timing of numerous kinematic and muscle variables. Awareness affected only one muscle variable. Startled individuals exhibited greater peak head and trunk accelerations, increased activity of the cervical paraspinal muscles, and a reduced head retraction and trunk angle. An acoustic startle alters the neck muscle and kinematic responses and may be as important as gender in the genesis of whiplash injury.