Volume 18, Number 1
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The role of vestibular and somatosensory systems in
intersegmental control of upright stance
Featured Article (182 KB)
pp. 39 - 49
Rob Creath, Tim Kiemel, Fay Horak, John J. Jeka
Upright stance was perturbed using sinusoidal platform rotations
to see how vestibular and somatosensory information are used to
control segment and intersegmental dynamics in subjects with
bilateral vestibular loss (BVL) and healthy controls (C).
Subjects stood with eyes closed on a rotating platform (±1.2°
for frequencies ranging from 0.01–0.4 Hz in the presence and
absence of light fingertip touch.
Trunk movement relative to the platform of BVLs was higher than
Cs at higher platform frequencies whereas leg movement relative
to the platform was similar for both groups. With the addition
of light touch, both groups showed similar trunk and leg segment
movement relative to the platform. Trunk-leg coordination was
in-phase for frequencies below 1 Hz and anti-phase above 1 Hz.
Interestingly, BVLs showed evidence of a "legs-leading-trunk"
relationship in the shift from in-phase to anti-phase around 1
Hz. Controls showed no preference for either segment to lead the
coordinative shift from in- to anti-phase.
The results suggest that the balance instability of BVL subjects
stems from high variability of the trunk, rather than the legs.
The high trunk variability may emerge from the "legs-leading"
intersegmental relationship upon which BVLs rely. Because BVLs
derive information about self-orientation primarily from the
support surface when their eyes are closed, the legs initiate
the shift to anti-phase trunk-leg coordination that is necessary
for stable upright stance control. Higher trunk variability
suggests that this strategy results in lower overall postural
stability. Light touch substitutes for vestibular information,
leading to lower trunk variability along with a trunk-leg phase
shift similar to controls, without a preference for either
segment to lead the shift. The results suggest that
vestibulospinal control acts primarily to stabilize the trunk in
space and to facilitate intersegmental dynamics.