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Journal of Vestibular Research, Vol. 8, No. I, pp. 57-59, 1998
Copyright CO 1998 Elsevier Science Inc.
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Review
THE RELATIVE ROLES OF THE OTOLITH ORGANS AND SEMICIRCULAR
CANALS IN PRODUCING SPACE MOTION SICKNESS
Donald E. Parker
Department of Otolaryngology-HNS, University of Washington, Seattle, Washington
Reprint address: Donald E. Parker, Box 357923, Department of Otolaryngology-HNS, University of
Washington, Seattle , WA 98195-7923 . Tel : (206) 285-7528; Fax: (206) 616-1828;
E-mail: [email protected]
o Abstract
Intljgbt and post.lauding ''immu
nity" to the "coriolis sickness susceptibility test",
observed during the Skylab M131 experiment, suggests that the otolith organs play a major role in
space motion sickness (SMS). This view is supported
by the report that ocular counter-torsion asymmetries correlate with SMS incidence and severity.
Further data indicate that sensory-motor adaptation to microgravity includes a process whereby
central interpretation of otolith signals is biased
from ''tilt'' toward translation. However, unexpected responses to linear acceleration suggest the
importance of graviceptors distributed throughout
the body in addition to the vestibular otolith organs.
Research is needed to assess distributed graviceptor
effects. © 1998 Elsevier Science Inc.
o Keywords -
'.
ine effeet5 of pwionged micrograviLy ollIIlotion
sickness produced by this procedure.
The surprising finding from this experiment
was that astronauts who reported motion sickness during CSSI testing preflight on earth were
nearly "immune" in orbit. Further, this immunity persisted for up to 18 days postflight before
preflight susceptibility returned.
The main importance of these findings was
to focus attention on the otolith receptors. There
was no reason to expect that, in contrast to the
otolith organs, canal stimuli or function would be
radically altered by microgravity. This suggests
that a canal-otolith conflict, absent or much reduced in microgravity, is the main contributor to
the motion sickness elicited by CSSI testing on
earth. The M131 results also suggested revision
of the view that orbital flight produced "physiologicaJ deafferentation of the otoliths."
1L should be noted that CSSI testing was not
begun until 5 da~'s in orbit hac elapsed : conse-
graviceptors.
Orbital Flight Reduced Motion Sickness
Elicited by Coriolis Sickness
Susceptibilit~,· Index Testin~
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opment was nOl observed. Further. po~tt1ighi
CSSI leSi immunity 'v\'a~ not (lb~e"ved during informal observations following the 6-day STS-S
Space Shuttle mission.
The Coriolis Sickne~~ Susceptibility Index
(CSS1) motion sicknes~ lest developed at the
Pensacola Naval Aeromedical Laboratory during
the 1960s requires subjects to move their heads
in pitch and roll while seated upright on a chair
rotating around an earth-vertical axis. This procedure produces "cross-coupled" stimulation to the
canals, which was thought to cause the motion
sickness produced by the CSSI test. The Skylab
Ml31 experiment (1) was undertaken to exam-
Ocular Counter-Torsion Predicts Space
Motion Sickness
Diamond and Markham (2) developed procedures to assess precisely ocular counter-torsion
'.
57
D. E. Parker
58
elicited by both static and dynamic roll-axi s
stimulation. To examine differences in otolith
responses to altered gravity, they recorded torsional eye movements during parabolic flight on
NASA's KC-135 aircraft. Subjects were placed
in a rotatable chair upright, left-ear down or
right-ear down (with respect to the gravito-inertial force vector). Torsional eye movements were
determined during the hypogravity (approximately 0 G) and hypergravity (aboLlt 1.8 G) segments of the parabolas. Oi fferences in the mag.iilL.!tie j: L,r:<l-, t: L.l ~ ~ L'L' 1~; :.i; :..:: 1~~ 0- ,.\';~ ,: ~h e
hy pogra\ It:' ,1I1ci l y pergr ~l\ ny :tJl1Jil!On:-, ;prrelaleLi with SiVlS ·,e':erir~..11lt.! !l.Irauoll rc,:nned
by [he S astronaLlts during orbitai rliglH. :-./1) correlation between SMS .tnd torsional Jisconjugacy evoked by roll on earth was noted.
These findings support the hypothesis that
SMS is p:.u1ly due to otolith asymmetry. von
Baumgarten (3) suggested that the left and right
otolith receptors would ordinarily differ in mass
and other response properties, and that these
asymmetries would normally be compensated by
central processes. Alteration of ambient gravitoinertial force may disturb this compensation and
result in SMS.
respect to gravity. In microgravily, central interpretation of graviceptor signals as indicating tilt
would lead to inappropriate compensatory responses. Consequently, sensory-motor adaptation to microgravity appears to include a reinterpretation of graviceptor signals such that all
are taken to indicate translational motion (4,5).
This has become known as the "tilt-translation
reinterpretation . hypothesis" of s~nsory-motor
adaptation [0 l11icrogravity .
Responses to Linear A~c~jeration
hl-mghi:~md
Post-night Do
Confirm Predictions
~O{
As part of the Microgravity Vestibular Investigations (MVI), astronauts reported perceived selforientation and self-motion during and after exposure to sustained constant angular velocity stimulation produced by a rotator. Due to space constraints, the subjects were placed on the rotator
eccentrically with their heads about 0.5 m from
the axis of rotation; this resulted in a maximum
linear acceleration at the otoliths of 2.2 rnIs 2
aligned with the longitudinal (Z) head/body axis.
Based on the stimuli at the otoliths, self-inversion
was predicted. A major finding from MVI was
Sensory-Motor Adaptation to
the lack of reported self-inversion inflight durWeightlessness Includes Reinterpretation ing "pitch" and "roll" ramp stimulus profiles (6).
of Graviceptor Signals
Failure to report self-inversion may have resulted from the non-uniform force gradient pro-----------~s possible changes in Ijnear:mQti~du_c.e_cLby the eccentric placement of the astrodetection thresholds following orbital flight, nauts on the rotator. In microgravity, the vector
subjects were exposed to translational oscilla- directions at the head and feet were in opposi-
pected finding from this experiment was that
pure roll stimulation elicited a complex perceived self-motion path that included a strong
translation component immediately post-landing
but not preflight (4). The basic finding of translational scene or self-motion evoked by roll head
motion has repeatedly been confirmed by observations performed in the Space Shuttle middeck
during entry and immediately after landing.
Signals from graviceptors, including the
otoliths, are fundamentally ambiguous: a signal
may indicate accelerated translation or tilt with
ceptors. The MVI findings are
reports by Mittelsteadt (7) that graviceptors located in the trunk, and perhaps associated with
displacement of the viscera, may have an even
stronger influence on perceived self-orientation
than do the otolith graviceptors.
Conclusion
As reported elsewhere in this issue, vestibular
receptors affect autonomic function as well as
eye movements, posture, and locomotion, and
Otolith Organs and Semicircular Canals in SMS
perceived self-orientation and self-motion. Development of "countermeasures" for the many
disturbances experienced during transitions between different gravito-inertial force environments requires more complete understanding
than is currently available of linear acceleration
effects in microgravity as well as on earth. This
understanding should also inform research and
intervention strategies for falling and other agerelated disturbances. Future research should focus on graviceptors distributed throughout the
body as well as those in the vestibule.
REFERENCES
I . Graybiel A. Miller EF. Hornick JL. Experiment M 131.
Human vestibular function. In: Johnson RS , Dietlein LF,
59
editors. Biomedical results from Skylab (NASA SP377). Washington: National Aeronautics and Space
Administration; 1977. p74-103.
2. Diamond SG, Markham CH. Validating the hypothesis
of otolith asymmetry as a cause of space motion sickness. In : Cohen B. Tomko DL, Guedry F. editors. Sensing and controlling motion. Ann N 'Y Acad Sci 1992:
656. p725-31.
3. von Baumganen RJ. Thumler RA. A model for vestibular function in altered gravitational states. Life Sci Space
Res 1978; 15:161-70.
4. Parker DE, Reschke MF, Arrot! AP, Hornick JL. Lichtenberg BK. Otolith tilt-translation reinterpretation following prolonged weightlessness: implications for
preflight-training. Aviat Space Environ Med 1985:56:
601-6.
aptation to earth's
6. Benson AJ . Guedry FE. Parker DE. Reschke ME Microgravi ty vestibular investigations: perception of self-orientation and self-motion. J Vestib Res (in press).
7. Mittelstaedt H. Somatic versus vestibular gravity reception in man. In: Cohen B. Tomko DL. Guedry F. editors.
Sensing and controlling motion. Ann N Y Acad Sci
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