The Brain
in Space
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The Brain in Space
Effects of Space Flight on
the Central Nervous System
Gilles Clément
International Space University
Strasbourg, France
The Brain
in Space
Lecture Outline
• How the central nervous system
evaluates our position and motion.
The sense of motion
• How we use gravity to control
our posture and balance
(sensori-motor function)
• The effects of space flight
on posture, balance, eye
movements, and cognition
• The possible causes, symptoms,
and treatment for space motion
sickness
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The Brain
in Space
The Sense of Motion
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Vestibular
organs
Peripheral
vision
Proprioceptive
receptors
Muscles
Tendons
and Joints
Skin
Gillingham & Wolfe (1986)
The Brain
in Space
The Neuro-Vestibular System
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The Brain
in Space
For the Engineers…
Central Nervous System
Static or
Moving
Visual
Stimuli
Cerebral
Cortex
Spatial
Orientation
Retina
Ocular Muscles
Oculomotor
Nuclei
Autonomic
Centers
Cerebellum
Angular
Acceleration
Semicircular
Canals
Linear
Acceleration
Otoliths
Movement
of Support
Surface
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Eye
Movements
Motion
Sickness
Vestibular
Nuclei
Peripheral Nervous System
Somatic
Musculature
Body
Posture
The Brain
in Space
Inner Ear — Semi-Circular Canals
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The Brain
in Space
Inner Ear — Otoliths
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The Brain
in Space
Gravity = Linear Acceleration
Einsteinʼs equivalence
principle states that all
linear accelerometers
must measure linear
acceleration and
gravity
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The Brain
in Space
Tilt and Translation — Pre-Flight (1g)
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The Brain
in Space
Tilt and Translation — In-Flight (0g)
• In 0g, the otolith organs
of the vestibular system
are stimulated by head
translation movements
only, not by head tilt
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The Brain
in Space
Tilt and Translation — Post-Flight
• Post-flight, after adaptation to 0g, the otolith signals
generated by a forward head tilt could be interpreted
as the result of a backward head translation
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Fukuda (1983)
The Brain
in Space
Gravity and Posture
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Hoff & Schilder (1927)
The Brain
in Space
Gravity and Posture (Humans)
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The Brain
in Space
Rest
(Semi-Flexed)
Posture in 0g
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The Brain
in Space
Locomotion in 0g
• Humans must adapt their mode of locomotion to 0g
• Astronauts use their arms and fingers for locomotion,
•
rather than their legs and feet
They mostly translate forward and look up
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The Brain
in Space
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“Upright”
Posture
in 0g
The Brain
in Space
Seeing is Believing
As an astronaut begins to
adapt to space, the nervous
system respond more to
non-vestibular signals,
particularly visual inputs
When a large part of
the visual field is
moving, a subject feels
the sensation of
moving, even though
she remains stationary
When the dot-patterned
dome rotates in one
direction, the astronaut
senses a full movement in
the opposite direction
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The Brain
in Space
Visual Performance in Space
• Level of illumination is
about 25% higher than
on Earth
• No scattering of light.
Areas not under direct
solar illumination appear
much darker
• Astronauts report ability
to see 10-20% more stars
and minute details
• Tests of visual acuity in
Gemini and Shuttle
astronauts showed no
changes in visual acuity
• Near focus accommodative
shift (submariner's eye)
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The Brain
in Space
Depth Perception and Space Flight
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• Atmospheric perspective
is absent. Lighting
conditions change color,
shading, contrast
• Lack of familiar
landmarks, e.g, trees,
vehicles, people
• Less scenes with linear
perspective, e.g., streets,
buildings, horizon
• Objects only present in
near or far space; none in
intermediate space
Linear perspective
Is depth perception altered during space flight ?
The Brain
in Space
Distance Perception
• When we look down from the top of a 100-m tall building, the
people below look noticeably small. But when we look 100 m
"down" the street, the people don't look small
• The reason is we have learned the "rules" for scaling people
at a horizontal distance, but not from a height
Is distance perception altered during space flight?
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The Brain
in Space
Visual Perception and Gravity
• On Earth, the perceived shape of an object depends more
on the orientation of this object in spatial (world) coordinates
than in retinal coordinates
– A diamond is perceived as a diamond in an upright
subject, but as a square in a tilted subject (Mach 1897)
"square"
"diamond"
"square"
Is the perception of an object's shape altered
in microgravity?
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The Brain
in Space
Mental Representation of Spatial
Cues during Space Flight
Co-PIs: G Clément (ESA), C Lathan (NASA)
• FO1–Depth perception
• FO2–Distance perception
• FO3–Handwriting/Drawing
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The Brain
in Space
Visual Orientation in Space
The Earth is
generally
perceived as
being “below”
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Courtesy of NASA
The Brain
in Space
Mental Rotation
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The Brain
in Space
Examples of Cognitive Tests
Mental Rotation of 3-D Objects
These two figures are the same
These two figures are different:
they are mirror image isomorphs
6 seconds
3 seconds
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Symmetry Detection
The Brain
in Space
Spatial Memory – Navigation
• Spatial memory
(the sense of location)
is thought to reside in
the hippocampus,
which receives tactile,
visual, auditory, and
vestibular sensory inputs
• Hippocampus encodes
cognitive maps of the
individual's environment
• Navigation inside the ISS
through path integration
might be affected in the
absence of the gravitational
reference
Red arrows represent egress paths to
Crew Return Vehicle in case of emergency
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The Brain
in Space
Impaired Cognitive Performance
• In-orbit – "space stupids",
"space fog", "mental viscosity"
– Drowsiness and/or fatigue
– Mental dullness, e.g. the pace of
astronauts' cognitive tasks is
slowed by microgravity
– Spatial disorientation
– Time compression
• Following landing – G state
flashbacks
– Illusion of free-floating when lying
in bed, or during unusual vestibular
stimulation such as on a rotating
chair or driving a car in a bank turn
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Courtesy of NASA
The Brain
in Space
Return to Earthʼs Gravity
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The Brain
in Space
Post-Flight Postural Illusions
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"Giant Hand"
phenomenon
Pitch movement
results in
forward
tumble
homogenous
visual
environment
b
a
a : Actual movement
b : Perceived movement
Perceived
path
Actual path
The Brain
in Space
Balance Test
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The Brain
in Space
Balance After Space Flight
Preflight
From Paloski et al. (1993)
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The Brain
in Space
Vestibulo-Ocular Reflex
The vestibulo-ocular reflex causes the eyes to rotate in
a direction opposite from the headʼs rotation
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Voluntary Head Rotation
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Photos NASA
The Brain
in Space
Courtesy of NASA
The Brain
in Space
Space Motion Sickness (SMS)
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The Brain
in Space
•
•
•
•
•
•
•
•
•
•
•
•
•
Space Motion Sickness Symptoms
Malaise
Drowsiness
Dizziness, disorientation
Apathy
Impaired concentration
Headache
Sweating
Dry mouth, loss of appetite
Salivation
Pallor
Stomach awareness
Nausea
Vomiting
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The Brain
in Space
Space Motion Sickness Categorization
• Mild SMS:
•
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• Severe SMS:
– One to several transient symptoms
– No operational impact
– All symptoms resolved in 36-48 hrs
Moderate SMS:
– Several symptoms of a persistent nature
– Minimal operational impact
– All symptoms resolved in 72 hrs
USA
– Several symptoms of a persistent
nature
– Significant performance
decrement
– Symptoms persist beyond 72 hrs
USSR/Russia
post STS-26
ASTP: Apollo-Soyuz Test Project
The Brain
in Space
Space Motion Sickness Experience
• Shuttle SMS experience (1961-2000):
– Total crewmembers
– Total cases of SMS
• Mild
• Moderate
• Severe
471
325 or 69%
35%
23%
11%
• Shuttle SMS experience on second flight compared to first flight:
– No changes
56%
– Slight improvement
35%
– Worst
9%
• Post-flight motion sickness: 8%
• Shuttle anti-SMS drug use:
– 30% of Shuttle crewmembers have received
medication for SMS symptoms relief
– Scopolamine (0.35 mg) + Dexedrine (5 mg)
– IM Promethazine (50 mg) (Phenergan, anti-histaminic)
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The Brain
in Space
SMS—What do we know?
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• We know :
– About 2/3 of space travelers experience symptoms of SMS
(mostly 'Moderate' or 'Mild'; 11% 'Severe')
– First symptoms occur in minutes
– SMS rarely exceeds 2 days
– The problem is generally brought on
by head movements in pitch and roll
roll
pitch
– Occupation (pilot, non-pilot), age, gender – no difference
– Symptoms are not significantly reduced on a re-flight
– Incidence of post-flight motion sickness is larger after
long-duration space missions
– The current favorite drug treatment is IM (intra-muscular)
injection of promethazine, rather than the use of scopolamine
or other prophylactic (preventive) medications
The Brain
in Space
SMS—What do we know?
• We don't know :
– A reliable and validated predictor of SMS :
• Susceptibility to SMS is not correlated with
susceptibility to motion sickness on Earth
• Inflight prevention devices have not proven
to be successful
• Preflight Adaptation Training (PAT)
looks promising, but for research only
(requires voluntary consent)
– The cause of SMS:
• Possible relationship between spatial
disorientation and SMS
• Possible influence of otoliths asymmetry
• Sensori-motor conflict. How to validate?
– The side effects of promethazine
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The Brain
in Space
Preflight Adaptation Training (PAT)
Head tilts whereas visual
scene translates
Head Roll
Head Pitch
normal
PAT
Symptom
No PAT
PAT
Improvement (n=40) (n=18)
Impaired
Concentration 23
11.1
Headache
55
27.7
Malaise
38
22.2
Stomach
Awareness
65
44.4
Vomiting
48
38.9
Nausea
60
55.6
(%)
51.7
49.6
41.6
31.7
19.0
7.3
% of crewmembers
reporting symptom(s)
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The Brain
in Space
Summary
ON A MARCHE SUR LA LUNE by Hergé
Art © 1954 by Editions Casterman, Paris & Tournai
Library of Congress Catalogue n° R 17608
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The Brain
in Space
Additional Reading
• Clément G, Reschke MF (2008) Neuroscience
in Space. New York: Springer
• Clément G (2005) Fundamentals of Space
Medicine. Dordrecht: Springer and El Segundo:
Microcosm Press
• Clément G (1998) Alteration of eye movements
and motion perception in microgravity.
Brain Research Reviews 28: 161-172
• Buckey JC, Homick JL (eds) (2003) The Neurolab
Spacelab Mission: Neuroscience Research
in Space. NASA SP-2003-535
• Crampton GE (1990) Motion and Space Sickness.
Boca Raton, FL: CRC Press Inc
• Lathan CE, Clément G (1997) Response of the
neurovestibular system to spaceflight. In:
Fundamentals of Space Life Sciences. Volume 1.
S Churchill (ed) Malabar, FL: Krieger, pp 65-82
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