Lecture 15: Motor Control in Complex Environments

Question 1

Microgravity

Answer 1

-conditions wherein the force of gravity is very small (in orbit/space)
-the sum of forces acting on the body is 0

Question 2

gravity in a parabolic flight

Answer 2

-at the peak trajectory, gravitational force is close to 0

Question 3

Einsteins equivalence principle

Answer 3

no measuring devices can distinguish between inertial and gravitational forces

Question 4

how are posture and locomotion possible

Answer 4

contact forces

Question 5

Experiments in Parabolic flights

Answer 5

-can achieve microgravity in seconds lasting 20-30s
-can have a variety of participants
-aircraft can rotate and conditions may not be as stable

Question 6

parabolic vs orbital flight

Answer 6

-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

Question 7

Experiments in orbit flight

Answer 7

-prolonged
-long time between launch and participation

Question 8

early work in microgravity focused on

Answer 8

vestibular-ocular reflexes (VOR)

Question 9

which systems does VOR involve?

Answer 9

eye and vestibular systems

Question 10

VOR

Question 11

when head rotation is sensed, eyes rotate…

Answer 11

in the opposite rotation. eyes move at the same velocity of the head but in the opposite direction

Question 12

once the limit of eye motion is reached…

Answer 12

the eye makes rapid adjustment to bring gauze to new location

Question 13

Nystagmus

Answer 13

eye movements that occur to adjust to prolonged fixation
-if head keeps moving nystagmus stops

Question 14

what happens of head stops abruptly

Answer 14

endolymph continues to move

Question 15

what do the otolith (utricle and saccule) organs of the vestibular system sense?

Answer 15

linear accelerations

Question 16

what do the semicircular canals sense?

Answer 16

head rotations (angular acceleration)

**these organs are unaffected by microgravity

Question 17

Coriolis Cross-Coupled Stimulation

Answer 17

-unusual combination of linear and angular accelerations (head tilt while spin)
-no disorientation or nausea

Question 18

Velocity Decay after quick head movements

Answer 18

-after quick head movements, vestibular ocular reflex works to move our eyes to stabilize vision

Question 19

velocity decay is?

Answer 19

measure of the reduction in eye-movement velocity in the slow phase after the initial response

Question 20

VOR during parabolic flights

Answer 20

-systematically studied by DiZio and Lackner
-steeper decay slope in microgravity than normal gravity

Question 21

VOR and microgravity

Answer 21

-velocity storage phenomenon is affected by microgravity

Question 22

Motor Control in Microgravity

Answer 22

-proprioception may be affected ex. perception of body position less acurate

Question 23

other hypothesis for proprioceptive deficits in microgravity

Answer 23

-lack of gravity leads to less muscle activation
-lack of vestibular inputs could impact integration strageties employed by the brain

Question 24

Propriception and loading

Answer 24

-absence of gravity affecting propriception supports original assertion of kinesthesia

Question 25

weber 1992

Answer 25

our muscle always percieves space as affected by gravity

Question 26

no loading in

Answer 26

microgravity (0G), therefore we expect an increase in error in proprioceptive tasks

Question 27

what could we do in 0G gravity experiement to reduce proprioceptive error?

Answer 27

replicate load using a form of resistance

Question 28

Bringoux et al

Answer 28

added external load (resistance bands) to make performance more similar to normal gravity environment (1G)

Question 29

findings of bringoux et al

Answer 29

-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

Question 30

how does microgravity affect online arm movement corrections?

Answer 30

-limb-position sense is altered in microgravity

Question 31

Double-Step paradigm

Answer 31

-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

Question 32

what can the double step paradigm be useful in examining

Answer 32

movement control processes

Question 33

CNS in gravity

Answer 33

CNS can flexibly adapt control processes to gravitational constraints - in microgravity we have totally different movements

Question 34

How does the NS adapt to microgravity

Answer 34

-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)

Question 35

Measuring sensory weighting

Answer 35

-EEG can be used to measure brain response to sensory stimulation (evoked potential)

Question 36

Evoked Potentials and Sensory Information

Question 37

Sensory Re-weighting in microgravity

Answer 37

-when preparing stepping movement, proprioceptive signals from the ankles are important for maintaining balance
-proprioceptive signals are less inportant for movement control in microgravity

Question 38

Saradjian 2013

Answer 38

-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

Question 39

why does microgravity present a challenge

Answer 39

-due to physiological changes and changes in sensory inputs

Question 40

what is altered in microgravity

Answer 40

vestibular and proprioceptive feedback

**the CNS can adapt sensory feedback use to overcome environmental constraints