Dependency of human neck reflex responses on the bandwidth of pseudorandom anterior-posterior torso perturbations

Abstract

The vestibulocollic (VCR) and cervicocollic (CCR) reflexes are essential to stabilize the head-neck system and to deal with unexpected disturbances. This study investigates how neck reflexes contribute to stabilization and modulate with perturbation properties. We hypothesized that VCR and CCR modulate with the bandwidth of the perturbation and that this modulation is maintained across amplitudes and influenced by the eyes being open or closed. Seated subjects were perturbed in an anterior-posterior direction. The perturbations varied in bandwidth from 0.3 Hz to a maximum of 1.2, 2.0, 4.0, and 8.0 Hz, at three amplitudes, and with eyes open and closed. Frequency response functions of head kinematics and neck muscle EMG demonstrated substantial changes with bandwidth and vision and minor changes with amplitude, which through closed-loop identification were attributed to neural (reflexive) modulation. Results suggest that both reflexes were attenuated when perturbations exceeded the system's natural frequency, thereby shifting from a head-in-space to a head-on-trunk stabilization tendency. Additionally, results indicate that reflexive and mechanical stiffness marginally exceed the negative stiffness due to gravity; a stabilization strategy which minimizes effort. With eyes closed, reflexes were attenuated further, presumably due to a reduced ability to discriminate self-motion, driving the system to a head-on-trunk stabilization strategy at the highest bandwidth. We conclude that VCR and CCR modulate with perturbation bandwidth and visual feedback conditions to maintain head-upright posture, but are invariant across amplitude changes.

Neck motion, motor control, pain and disability: A longitudinal study of associations in neck pain patients in physiotherapy treatment

“…gain > 1, left axis, Figure 3) and studies agree on interpretations of this as an effect of mechanical resonance (Forbes et al, 2013;Goldberg and Peterson, 1986;Peng et al, 1996), meaning that the oscillatory response of a system is larger than the imposed perturbation. The Eigen-frequency of a system determines the threshold for mechanical resonance and depends on the systems mass and viscoelastic properties.…”

Dynamic head-neck stabilization in cervical dystonia

“…The experimental protocol and data analysis were similar to a previous study where healthy volunteers showed a profound modulation of stabilization strategies with perturbation bandwidth (Forbes et al,2013). In short, subjects were restrained by a four-point harness to a rigid chair with a 10° inclined backrest mounted on a motion platform and exposed to…”

“…1 (Forbes et al,2013;Kearney et al,1997;Mirbagheri et al,2000;Schouten et al,2008), likely to prevent oscillatory behaviour as a result of the time delay within afferent feedback loops. Subsequently, in this study we adopted the lowest bandwidth (0.2-1.2) and highest bandwidth (0.2-8 Hz) perturbations from Forbes et al (2013) with minor modifications described below. Exposing both patients and controls to these two perturbations while performing head-neck stabilization tasks allowed us to examine our hypothesis of impaired afferent feedback modulation in patients.…”

“…In preliminary tests, patients reported the high frequency content of the HIGH perturbations to be discomforting; therefore, the amplitude of the HIGH perturbation was reduced by 40% for both patient and control groups. Although perturbation amplitude can influence head-neck system dynamics, the effect is minor relative to bandwidth changes and the head-neck system can be considered close to linear across the amplitudes applied here (Forbes et al,2013;Keshner,2003;Keshner et al,1995).…”

“…Neck afferent feedback contributions are modulated with experimental conditions such as head inertia (Goldberg and Peterson,1986;Keshner et al,1999;Reynolds et al,2008), mental set (Keshner,2000) and the frequency content of torso movement (Forbes et al,2013).…”