title: Frequency response of vestibular reflexes in neck, back, and lower limb muscles.
abstract: Vestibular pathways form short-latency disynaptic connections with neck motoneurons, whereas they form longer-latency disynaptic and polysynaptic connections with lower limb motoneurons. We quantified frequency responses of vestibular reflexes in neck, back, and lower limb muscles to explain between-muscle differences. Two hypotheses were evaluated: 1) that muscle-specific motor-unit properties influence the bandwidth of vestibular reflexes; and 2) that frequency responses of vestibular reflexes differ between neck, back, and lower limb muscles because of neural filtering. Subjects were exposed to electrical vestibular stimuli over bandwidths of 0-25 and 0-75 Hz while recording activity in sternocleidomastoid, splenius capitis, erector spinae, soleus, and medial gastrocnemius muscles. Coherence between stimulus and muscle activity revealed markedly larger vestibular reflex bandwidths in neck muscles (0-70 Hz) than back (0-15 Hz) or lower limb muscles (0-20 Hz). In addition, vestibular reflexes in back and lower limb muscles undergo low-pass filtering compared with neck-muscle responses, which span a broader dynamic range. These results suggest that the wider bandwidth of head-neck biomechanics requires a vestibular influence on neck-muscle activation across a larger dynamic range than lower limb muscles. A computational model of vestibular afferents and a motoneuron pool indicates that motor-unit properties are not primary contributors to the bandwidth filtering of vestibular reflexes in different muscles. Instead, our experimental findings suggest that pathway-dependent neural filtering, not captured in our model, contributes to these muscle-specific responses. Furthermore, gain-phase discontinuities in the neck-muscle vestibular reflexes provide evidence of destructive interaction between different reflex components, likely via indirect vestibular-motor pathways.
authors.affiliation: Department of Biomechanical Engineering, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Delft, The Netherlands;
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Forbes
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Dakin
authors.forename: Alistair N
authors.initials: AN
authors.lastname: Vardy
authors.forename: Riender
authors.initials: R
authors.lastname: Happee
authors.forename: Gunter P
authors.initials: GP
authors.lastname: Siegmund
authors.forename: Alfred C
authors.initials: AC
authors.lastname: Schouten
authors.forename: Jean-Sébastien
authors.initials: JS
authors.lastname: Blouin
mesh_terms: D000328:Adult; D000344:Afferent Pathways / Q000502:physiology; D064131:Back Muscles / Q000294:innervation / Q000502:physiology*; D005260:Female; D006801:Humans; D035002:Lower Extremity / Q000294:innervation / Q000502:physiology; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D009046:Motor Neurons / Q000502:physiology; D009334:Neck Muscles / Q000294:innervation / Q000502:physiology*; D012018:Reflex; D014722:Vestibule, Labyrinth / Q000294:innervation / Q000502:physiology*
keywords: bandwidth; electrical vestibular stimulation; neck muscles; neural filtering; vestibular reflexes