Multisensory processing, integration and adaptation for the control of human standing balance

Human standing balance relies upon the integration of cues from multiple
sensory systems. Vestibular, visual, somatosensory and auditory inputs all
contribute to the control of standing balance both during quite stance and when
responding to external perturbations. A central issue with standing balance is
that sensory signals that are encoded in one coordinate system (e.g., the head)
must be transformed into a whole-body coordinate system to be relevant for
standing balance control. These transformations need to be suitable for the
current balancing conditions, where the different sources of sensory
information may vary in their relevance to the task of standing. What are the
mechanisms involved in transforming these sensory signals to be relevant to the
ongoing balance control? Under what circumstance(s) are certain sensory inputs
more relied upon than other sensory inputs? What are the capabilities and
mechanisms for the balance controller to adapt to novel conditions? With the
research being proposed here, we seek to understand the way in which humans
integrate the multiple sources of sensory information relevant to the postural
control of standing, as well as adapt standing control to novel balance tasks.
Using a robotic balance simulator and advanced sensory stimulation techniques,
we will investigate how the human balance system responds and adapts to
standing balance tasks with altered mechanical and/or sensory conditions. We
will compare human standing behaviour (whole-body movement), sensory-evoked
balance responses and conscious perception of motion across baseline (i.e.
normal standing) and experimental trials. This work will help in revealing the
adaptive capabilities of the human balance controller, as well as disentangling
the mechanical and sensory factors that contribute to upright stance.

Primary objective: To investigate the neuromechanical and sensorimotor
principles underlying the multiaxial control of standing balance.

Specific sub-objectives of this proposal are:
1) To determine how multiple axes of balance control are coordinated to
maintain upright stance.
2) To identify the neural mechanisms underlying balance adaptation to novel
sensory-motor relationships of standing balance and to characterize the errors
driving these changes in balance control.
3) To determine how sensory and motor cues are combined for the conscious
perception and control of standing balance.

Repeated-measures intervention study

Performing novel standing balance tasks on a robotic balance simulator with
(and without) sensory stimulation.

Healthy participants will visit the Erasmus MC at least once (up to 5 days) and
an experiment will last for a maximum of 3 hours. The total time spent testing
a subject will be limited to 9 hours regardless of experimental protocol. In
this study, the safety measures are applied as described in recent human
balance and sensory stimulation reviews. There are no serious risks associated
with this study. The discomfort and risks associated with the experiments
described in this proposal are minor but vary according to the methods used for
each experiment. The risks/discomfort for the various techniques used are
provided below.

Electrical vestibular stimulation
There are no known physical or psychological risks associated with the
non-invasive electrical vestibular stimulation technique that may be used in
this study. Some participants who are highly susceptible to car motion sickness
may possibly experience mild nausea, light-headedness or mild headaches for a
brief period (up to 1 hour) following the experiment (in about 5% of
participants tested by the co-investigator in the past). The stimulation may
cause slight flashing in the visual field due to stimulation of the nearby
optic nerve.

Robotic balance simulator
Standing in the robotic balance simulator may cause vertigo and nausea for
participants who are particularly subject to those complaints. When a subject
indicates vertigo and/or nausea during any experiment and indicates that they
wish to end the experiment, this request will be granted immediately.

Scleral lens
There are no known risks with the use of scleral lenses. Possible side effects
include stinging or itchy eyes, increased sensitivity to light and excessive
tears, and primarily occur when there is not sufficient fluid between the
cornea and the lens. When this occurs the lens will be removed and reapplied
with more liquid.

Virtual reality head-set
There are no known physical or psychological risks associated with using
virtual reality environments. Some subjects who are highly susceptible to car
motion sickness may possibly experience mild nausea, light-headedness or mild
headaches.

Gas exchange measurement
The gas exchange measurement is a method commonly employed in the sports field
to monitor energetic consumption during exercise. There are no known physical
or psychological risks associated with its use. To ensure more accurate
results, participants will be asked to fast for at least 3 hours before the
experiment. This precaution is taken to minimize digestive activity during the
testing process.