[home] [Personal Program] [Help]

---

Session: Motor Control I
Session starts: Friday 25 January, 10:30
Presentation starts: 11:45
Room: Lecture room 558

---

Patrick Forbes ()
Gunter Seigmund ()
Alfred Schouten ()
Riender Happee ()
Jean-Sébastien Blouin ()

Abstract:
Vestibular sensory input is critical to facilitate system wide effective balance control in the face of unpredictable perturbations as observed in responses of the lower limb, lumbar and neck muscles. Neck muscles in particular possess strong connections to the vestibular organ composed of primarily disynaptic pathways innervated by cranial or high level spinal nerves, which elicit short latency response (~10 msec) during natural or electrical stimulation. Defined as vestibulocollic reflexes (VCR), these responses can be studied in humans by perturbing the system through acoustic, vibratory or electrical stimulation of the vestibular organ. Here we use electrical stimulation to elicit vestibulomuscular responses in neck muscles and aim to show that their responses are independent of the balance task. We compare standing and sitting conditions with the head-free, as well as head-free and head-fixed conditions during sitting, where different directions of force were applied in the head-fixed sitting conditions. In head-free conditions (standing and sitting) subjects (n = 8) were asked to rotate their head 60º to the left while bipolar stochastic vestibular signals (0-75 Hz) were delivered. In head fixed conditions (sitting) subjects performed isometric neck contraction in twist at orientations of 0º and 60º, as well as flexion, extension and right lateral flexion at an orientation of 0º. EMG levels were controlled in all conditions to mimic the contraction measured in the head free conditions. Intramuscular EMG was collected bilaterally in the sternocleidomastoid (SCM) and splenius capitis (SPL) muscles. Significant muscles responses (P < 0.05) correlated to the input stimuli were observed for all conditions provided the muscle was actively used in the contraction task. For both muscles no significant differences were observed between standing and seated conditions, or between the head free and head fixed conditions at 60º. The force direction had a significant effect (P < 0.05) on the magnitude of the muscle responses where the highest responses were observed in conditions where muscle contraction was most imbalanced relative to the perceived vestibular roll stimulation, i.e. in the SCM the magnitudes from highest to lowest were lateral flexion, twist and forward flexion. This study demonstrates neck muscle responses to vestibular input are irrespective of the balance state (i.e. seated vs standing and head-free vs head fixed). Unlike lower limb muscles which limit vestibular input when balance control is not required [1], the central nervous system continues delivers vestibular input to activate neck motoneurons in head fixed conditions. REFERENCES 1. Luu, B.L., et al., Human standing is modified by an unconscious integration of congruent sensory and motor signals. Journal of Physiology-London, 2012. Accepted Article.