Lecture 15: Motor Control in Complex Environments Flashcards
Microgravity
-conditions wherein the force of gravity is very small (in orbit/space)
-the sum of forces acting on the body is 0
gravity in a parabolic flight
-at the peak trajectory, gravitational force is close to 0
Einsteins equivalence principle
no measuring devices can distinguish between inertial and gravitational forces
how are posture and locomotion possible
contact forces
Experiments in Parabolic flights
-can achieve microgravity in seconds lasting 20-30s
-can have a variety of participants
-aircraft can rotate and conditions may not be as stable
parabolic vs orbital flight
-parabolic is seconds, orbital is days
-parabolic has alternated between gravity, orbital is continuous microgravity
-parabolic can test immediately after orbital must wait to test
-more motion sickness in orbital flight
Experiments in orbit flight
-prolonged
-long time between launch and participation
early work in microgravity focused on
vestibular-ocular reflexes (VOR)
which systems does VOR involve?
eye and vestibular systems
VOR
when head rotation is sensed, eyes rotate…
in the opposite rotation. eyes move at the same velocity of the head but in the opposite direction
once the limit of eye motion is reached…
the eye makes rapid adjustment to bring gauze to new location
Nystagmus
eye movements that occur to adjust to prolonged fixation
-if head keeps moving nystagmus stops
what happens of head stops abruptly
endolymph continues to move
what do the otolith (utricle and saccule) organs of the vestibular system sense?
linear accelerations
what do the semicircular canals sense?
head rotations (angular acceleration)
**these organs are unaffected by microgravity
Coriolis Cross-Coupled Stimulation
-unusual combination of linear and angular accelerations (head tilt while spin)
-no disorientation or nausea
Velocity Decay after quick head movements
-after quick head movements, vestibular ocular reflex works to move our eyes to stabilize vision
velocity decay is?
measure of the reduction in eye-movement velocity in the slow phase after the initial response
VOR during parabolic flights
-systematically studied by DiZio and Lackner
-steeper decay slope in microgravity than normal gravity
VOR and microgravity
-velocity storage phenomenon is affected by microgravity
Motor Control in Microgravity
-proprioception may be affected ex. perception of body position less acurate
other hypothesis for proprioceptive deficits in microgravity
-lack of gravity leads to less muscle activation
-lack of vestibular inputs could impact integration strageties employed by the brain
Propriception and loading
-absence of gravity affecting propriception supports original assertion of kinesthesia
weber 1992
our muscle always percieves space as affected by gravity
no loading in
microgravity (0G), therefore we expect an increase in error in proprioceptive tasks
what could we do in 0G gravity experiement to reduce proprioceptive error?
replicate load using a form of resistance
Bringoux et al
added external load (resistance bands) to make performance more similar to normal gravity environment (1G)
findings of bringoux et al
-the addition of gravity like torque made joint position sense more similar to 1G environment in midsaggital reaching task
-supports idea that proprioception during movement planing and control is tuned to gravitational environment
how does microgravity affect online arm movement corrections?
-limb-position sense is altered in microgravity
Double-Step paradigm
-the double-step or target jump paradigm is commonly used in motor control
-participants performs reaches to target location and on some percentage the target jumps so individual must adjust
what can the double step paradigm be useful in examining
movement control processes
CNS in gravity
CNS can flexibly adapt control processes to gravitational constraints - in microgravity we have totally different movements
How does the NS adapt to microgravity
-to derive sense of body position and make goal-directed actions, we must rely on sensory information
-in environments where sensory information is comprise, we may weight other sources of sensory information more (visual & auditory)
Measuring sensory weighting
-EEG can be used to measure brain response to sensory stimulation (evoked potential)
Evoked Potentials and Sensory Information
Sensory Re-weighting in microgravity
-when preparing stepping movement, proprioceptive signals from the ankles are important for maintaining balance
-proprioceptive signals are less inportant for movement control in microgravity
Saradjian 2013
-participants exhibited increased late somatosenosry evoked potential when preparing a step in normogravity
-in absence of postural constraints in microgravity, no facilitation of somatosenosry information was found
-NS can dynamically adjust weighting of sensory information to gravitational constraints
why does microgravity present a challenge
-due to physiological changes and changes in sensory inputs
what is altered in microgravity
vestibular and proprioceptive feedback
**the CNS can adapt sensory feedback use to overcome environmental constraints
