Full text of DOI:10.1007/s004210100494

Eur J Appl Physiol 52001) 85: 539±545
DOI 10.1007/s004210100494
ORIGINAL ARTICLE
Gilles Clement á Olivier Deguine á Marc Parant
Marie-Claude Costes-Salon á Pascale Vasseur-Clausen
Anne Pavy-LeTraon
Effects of cosmonaut vestibular training on vestibular function prior
to space¯ight
Accepted: 7 June 2001 / Published online: 9August 2001
Ó Springer-Verlag 2001
Abstract The purpose of this study was to quantify the
Introduction
e€ects of repetitive Coriolis and cross-coupled stimula-
tions, similar to the vestibular training the cosmonauts
When a rotating individual makes a head movement out
are exposed to prior to their space¯ight, on vestibular
of the axis of rotation, his or her semicircular canals
function in control subjects on Earth. Ten volunteers
undergo cross-coupled angular accelerations and his or
were passively rotated in yaw on a rotating chair while
her otolith organs are exposed to a linear Coriolis ac-
executing standardized pitch head-and-trunk move-
celeration. Such stimulation elicits disorientation 5often
ments. The chair stopped to change direction after 12
referred to in aviation as the ``Coriolis e€ect''), nystag-
head-and-trunk movements were made. The runs were
mus, and motion sickness symptoms 5Graybiel et al.
grouped in sessions of ten,which were repeated daily for
1977; Lackner and Graybiel 1986; Bles 1998).
10 days. The severity of motion sickness was assessed by
Since the ®rst manned space missions, Russian cos-
subjective judgment and measurements of skin pallor
monauts have been exposed to a ground-based adapta-
and salivary total protein concentration, and nystagmus
tion program, or cosmonaut vestibular training 5CVT),
was recorded. The severity of motion sickness and ny-
which includes Coriolis and cross-coupled angular ac-
stagmus decreased during cosmonaut vestibular training
celerations, in an attempt to minimize the occurrence of
5CVT). One month after the end of CVT, nystagmus
space motion sickness 5Gurovskiy 1966; Popov et al.
responses were still about 20±30% lower than control
1970). During CVT, cosmonauts in a rotating chair
values. These results indicate that CVT induces a ha-
execute pitch head movements until either vomiting is
bituation of vestibular responses. One important impli-
e€ected or a predetermined number of head movements
cation of this experiment concerns space studies on
is performed. This training is achieved through daily
cosmonauts who are exposed to such vestibular training
sessions of repeated exposure to body yaw rotation with
prior to their space¯ight.
chair acceleration and deceleration of 180°/s2. The
number of sessions ranges from 4 to more than 12,
depending on the initial susceptibility of cosmonauts to
Coriolis-induced sickness. CVT generally takes place
during the ®nal 2 weeks before launch 5Krioutchkov
et al. 1993).
Keywords Cosmonauts á Vestibular training á Motion
sickness á Nystagmus á Habituation
During initial exposure to weightlessness, head
movements, especially in pitch, tend to elicit space mo-
G. Clement 5&) á O. Deguine
Centre de Recherche Cerveau et Cognition,
tion sickness 5Graybiel 1980; Matsnev et al. 1983). This
may indicate that the lack of con®rming otolith cues
during head pitch is particularly provocative 5Oman
et al. 1986). The rationale behind CVT is that tolerance
to the con¯ict between the semicircular canals and
nonconforming otolith cues generated by Coriolis and
cross-coupled angular accelerations on Earth would
transfer to weightlessness conditions 5Popov et al. 1970).
Although there is no clear evidence of the e€ectiveness
of CVT on space motion sickness, the incidence of space
motion sickness in the Russian space program is
UMR 5549CNRS/UPS, Faculte de Medecine de Rangueil,
31062 Toulouse Cedex, France
E-mail: gclement@cerco.ups-tlse.fr
Fax: +33-562-172809
O. Deguine
Laboratoire d'Otologie et d'Otoneurologie, Hopital Purpan,
Place du Docteur Baylac, 31059Toulouse Cedex 3, France
M. Parant á M.-C. Costes-Salon á P. Vasseur-Clausen
A. Pavy-LeTraon
MEDES, Institut de Medecine et de Physiologie Spatiales,
Hopital Rangueil, 1 Avenue Jean Poulhes,
31043 Toulouse Cedex 4, France

540
trunk movement. At each metronome signal, the subjects tilted
their head and trunk in pitch through 45° from the upright position
and then return to the upright position. This movement was per-
formed in about 1±2 s. After 1 min of rotation, during which about
12 head-and-trunk movements were made, the chair was stopped
with the subjects in the upright position, and the post-rotatory
nystagmus was recorded. The magnitude of this angular decelera-
tion was 180°/s2. After 1 min of rest the chair rotated in the op-
posite direction for another minute of head-and-trunk movements.
The test was terminated at the request of the subjects when they
experienced severe nausea or vomiting. The subjects were then
placed supine on a bed for several minutes.
Based on the protocol used for the CVT of Russian cosmonauts
in Star City 5Krioutchkov et al. 1993; Cosmonaut C. Andre-
Deshays, personal communication), the objective was to achieve
10 runs per session, 5 sessions per week, for 2 consecutive weeks, thus
giving a total of 10 training sessions 5S1±S10) including 100 runs
5Fig. 1). All of the subjects were indeed exposed to ten training ses-
sions. However, due to time constraints, session 6 5S6) was reduced to
four runs instead of ten. The total number of runs per subject ranged
between 45 and 83 runs due to the occurrence of motion sickness.
generally claimed to be lower than that of the US space
program 5Davis et al. 1988).
There is some indication that on Earth the repeated
exposure to passive body rotation elicits a gradual de-
crease in vestibular responses, a phenomenon known as
vestibular habituation 5Collins 1973). During CVT, the
pattern of repetitive angular velocity steps during chair
starts and stops might also be responsible for the ha-
bituation of vestibular responses in cosmonauts before
they go to space. One important implication of CVT
concerns the use of ``habituated'' cosmonauts as subjects
for adaptive studies of vestibular functions 5i.e., per-
ceptual, vestibulo-ocular, or postural responses) to
weightlessness. Markedly lower vestibulo-ocular and
perceptual responses in cosmonauts compared to con-
trol subjects have been attributed to the potential e€ect
of CVT 5Clarke et al. 1993; Wetzig et al. 1993). There-
fore, it is of interest for the space vestibular research
community to know the actual e€ects of CVT. Previous
studies have described a reduction in illusory motion,
nystagmus, and nausea during continuous exposure to
Coriolis and cross-coupled vestibular stimulation 5Gue-
dry 1965). The aim of the present experiment was
to characterize the changes in the severity of Coriolis-
induced sickness and in the vestibulo-ocular responses
when subjects are exposed to the same vestibular train-
ing as cosmonauts prior to their space¯ight.
Motion sickness
At the end of each training session the severity of motion sickness
was evaluated by the medical ocer, based on a questionnaire
developed by Graybiel et al. 51968). The severity of motion sickness
ranged from 0 points for no symptoms to 51 points, calculated by
adding the scores obtained for symptoms such as nausea, temper-
ature, pallor, sweat, salivation, drowsiness, headache, and dizzi-
ness. In order to quantify objectively sickness levels during the
course of CVT, measurements of skin pallor and salivary protein
concentration were performed at the beginning, middle, and end of
the CVT. Forehead skin re¯ectance 5or skin pallor) was measured
in each subject before and after the ®rst, the ®fth, and the tenth
training sessions while at rest, with the aid of a spectrocolorimeter
5M-508i; Minolta, Japan; Bjerring 1995). Simultaneously, salivary
samples were obtained by placing sterile cotton in the subject's
mouth for 1 min, based on a method used in a previous study
5Igarashi et al. 1993). After centrifugation of the cotton at 3247 g,
analysis of salivary total protein concentration was obtained by
spectrophotometry 5Boehringer 911; Hitashi, Japan).
Methods
Subjects and equipment
The experiment was carried out in the Space Flight Medicine Clinic
of MEDES in Toulouse, France. The experiment was approved by
the Comite Consultatif de Protection des Personnes dans la Re-
cherche Biomedicale of the Midi-Pyrenees region of France. The
subjects signed a consent form that was approved by this com-
mittee. The subjects were four men and six women aged 23±
31 years [mean 5SD) 26.5 52.2) years]. During subject selection,
the results of screening of pathologic nystagmus 5spontaneous,
gaze-evoked), visual-oculomotor control 5optokinetic nystagmus,
smooth pursuit, saccades), and rotational vestibulo-ocular re¯ex
suggested that all subjects had putatively normal vestibular func-
tion.
The subjects were seated on a servo-controlled rotating chair
that was equipped with padding that served to delimit the upright
head position 5i.e., with the horizontal canals and utricular macula
inclined to approximately 20° relative to the plane of rotation) and
pitch forward 45° head-and-trunk tilt. The subjects were in com-
plete darkness. A goggle with an infrared light and video camera
was mounted in front of the subject's right eye to record eye
movements. The left eye was covered. No particular gaze instruc-
tions were given during the part of the test when they were per-
forming the head-and-trunk movements. However, during chair
acceleration and deceleration they were instructed to keep their
eyes open in the dark, to look straight ahead at an imaginary ho-
rizon, and not to try to follow imaginary points or noises in the
room.
Eye movements
As mentioned above, the horizontal post-rotatory nystagmus gen-
erated by deceleration of the chair after each run was analyzed, and
the slow-phase peak velocity was calculated during the course of
the CVT. Additional vestibulo-ocular tests were performed before,
at mid-training 5before S6), and on the day following the last ses-
sion, then 15 days, 30 days and 60 days after the ®nal training
session 5R+1, R+15, R+30 and R+60, respectively; Fig. 1).
These tests include ramp accelerations and decelerations in the dark
5180°/s2 and 1°/s2) in both the clockwise and counterclockwise di-
rections, and caloric insu‚ation of both ears with a warm 549°C) or
cold 525°C) ¯ux of air 5Vario-Air; Atmos, France). This permitted
determination of whether the nystagmus produced by passive yaw
angular acceleration of the entire body or by caloric stimulation
was in¯uenced by CVT in which the inner ear was repetitively
stimulated by head movements involving Coriolis and cross-cou-
pled angular accelerations. The very low acceleration of 1°/s2 was
utilized to assess the e€ects of CVT on the nystagmus threshold.
These tests were performed for a long period after the end of the
CVT to assess its long-term retention e€ects.
The signal from the video camera mounted on the subject's
right eye was fed into a computer where an algorithm detected the
center of the pupil for each video frame 5VNG Ulmer version 2.0;
Synapsis, France). This successive on-line analysis of video frames
Protocol
The chair was rotating in yaw at an angular velocity of 180°/s. A 550 Hz) allowed the recording of horizontal and vertical eye
metronome gave a signal every 5 s for the standardized head-and- movements with an accuracy of about 0.1°. For calibration, the left

541
Fig. 1 A During each run: 51) the chair was accelerated up to 180°/
s, 52) the subjects performed 12 head-and-trunk movements in
about 1 min 5only one head-trunk tilt is shown on this diagram),
53) the chair was decelerated at 180°/s2 with the subjects upright,
and 54) subjects were at rest for 1 min. B One training session
included ten runs with rotation alternatively in the clockwise 5CW)
and counterclockwise 5CCW) direction. C The objective was to
expose the subjects to ten sessions 5S1±S10) of ten runs each.
Session S6 included a maximum of only four runs. The severity of
induced sickness and post-rotatory nystagmus was evaluated
during the course of the cosmonaut vestibular training 5CVT; C,
®lled rectangles). Saliva samples were taken before and after S1, S5
and S10. In addition, per- and post-rotatory and caloric nystagmus
were tested before 5Pre), at mid-training just before S6 5Mid), and
1 day 5R+1), 15 days 5R+15), 30 days 5R+30), and 60 days
5R+60) after the ®nal training session
sponding to approximately 12 runs on average. The se-
verity of symptoms decreased thereafter. The correlation
coecient between the motion sickness score on the
Graybiel scale and the number of runs was r=±0.61
5P<0.01). After 30 runs, motion sickness points scored
about 50% lower than noted during the ®rst runs. Three
of the 10 subjects were even symptom free after 30 runs
5Fig. 2).
Univariate repeated-measures ANOVA analysis
indicated that forehead skin re¯ectance 5skin pallor)
increased signi®cantly for all subjects after the ®rst
training session 5S1) compared to the control measure-
ments 5Fig. 3). Subsequent changes were not signi®cant.
When averaged across subjects, the control level of total
protein concentration in saliva before sessions S1, S5
and S10 was 0.46 50.24) g/l. There were large inter-
eye was uncovered and the subjects were asked to look with the left
eye at four wall-mounted targets subtending 20°. To quantify the
characteristics of the nystagmus dynamics, the delay between
the chair acceleration/deceleration and the ®rst beat of nystagmus,
the duration of the primary phase of nystagmus 5i.e., the delay
between the stimulus onset and the reversal of nystagmus), and the
peak slow-phase velocity of both rotatory and caloric nystagmus
were calculated.
Statistical analysis
Analysis of variance 5ANOVA) with post-hoc t-tests and calcula-
tion of correlation coecients were performed using Super-Anova
and StatView 5Abacus Concepts, Berkeley, Calif., USA) statistical
analysis software packages, respectively. A criterion value of
P £ 0.05 was used for hypothesis testing, unless indicated other-
wise. The results are presented as the mean 5SEM).
Results
Motion sickness
Fig. 2 Severity of induced sickness for each subject during the
course of CVT, as assessed by points according to the symptoms
scale de®ned by Graybiel et al. 51968), with the ®tted regression
Most of the subjects experienced severe motion sickness
symptoms during the ®rst 3 training sessions, corre- line. The maximum possible score is 51

542
individual di€erences 50.15±1.26 g/l). Calculation of Tangential Coriolis accelerations were also generated
Pearson's coecient indicated no signi®cant correlation during such a head-and-trunk movement, which acted
between individual pre-session control levels of salivary on the otolith organs. A radial, centripetal acceleration
total protein and post-session motion sickness scores was also generated when the head tilted forward, mov-
5r=±0.23). This result is in contrast with a previous ing away from the axis of rotation, which created otolith
study 5Igarashi et al. 1993) in which an inverse correla- stimulation associated with a pitch head movement. As a
tion was noted 5r=±0.74) between control total protein consequence of this complex pattern of stimulation and
concentration and time to reach nausea for the same sensation, the eye movements that occurred during the
stimulus. In agreement with this previous study, how- head movement had vertical, horizontal, and torsional
ever, salivary total protein concentration was systemat- components 5Benson 1982). A decrease in the intensity
ically higher after the training sessions compared with of eye movements was clearly visible during the head-
the pre-stimulus control level before the sessions, but trunk tilts throughout the CVT. However, since our eye
this increase was only signi®cant after S1 5Fig. 3).
movement analysis technique was limited to the hori-
zontal and vertical eye motion components, we focused
our study on the horizontal post-rotatory nystagmus
generated by the chair deceleration at the end of each
run. The nystagmus peak slow-phase velocity and du-
Vestibulo-ocular responses
The head movement involved a natural acceleration and ration decreased throughout the CVT 5Fig. 4). Nystag-
deceleration in the pitch plane. However, since the body mus peak slow-phase velocity and duration during the
was rotating in yaw, the horizontal semicircular canal last training session were 31.7% and 28.9% lower
lost angular velocity so that the subject experienced 5P<0.01) than those measured at the beginning of CVT,
rotation in yaw, and simultaneously, the anterior and respectively.
posterior canals came into and then out of the plane of
Nystagmus results from the vestibulo-ocular re-
rotation, so that the subject also experienced roll sponses to rotational tests performed before, at mid-
motion, in addition to the pitch and yaw motions. training, and after the training, are shown in Fig. 5.
According to a repeated-measures ANOVA, the peak
velocity and duration of horizontal nystagmus generated
by passive yaw acceleration/deceleration 5180°/s2) were
signi®cantly reduced by 28% and 22%, respectively, at
mid-training compared to the values measured before
training 5Fig. 5A, B). This reduction was still signi®cant
when tests were performed at R+60 520% for peak
velocity, 15% for duration).
The e€ects of CVT on nystagmus threshold were
determined by measuring the delay in the appearance of
the ®rst beat of nystagmus after very low yaw angular
acceleration and deceleration 51°/s2). When averaged
across directions of stimulation and subjects, a signi®-
cant increase in nystagmus delay relative to baseline
Fig. 3 E€ect of CVT on skin re¯ectance 5A) and salivary total
protein concentration 5B). The values re¯ect averages for all ten
subjects of the di€erences in the measurements made after sessions
S1, S5, and S10, and those made just before. Error bars indicate
standard error of the mean. *P<0.05 relative to control values
before rotation
values 5P<0.03) was observed just at the end of CVT
5Fig. 5C). Nystagmus delay had returned to normal by
R+30 days.
These results indicate no decrement in the nystagmus
reaction to caloric stimulation. Caloric nystagmus
Fig. 4 Average of nystagmus
peak slow-phase velocity 5A)
and duration 5B) measured
during chair deceleration dur-
ing the ®rst and the last run of
each training session 5S1±S10)
for ten subjects. Error bars
indicate standard error of the
mean for both the nystagmus
parameters 5y-axis) and the
corresponding cumulative
number of runs 5x-axis)

543
Fig. 5A±D Results of the ves-
tibulo-ocular tests performed
before 5Pre), during 5Mid), and
after 5R+1±R+60) the CVT.
A, B Nystagmus peak slow-
phase velocity and duration,
respectively, measured during
chair acceleration and deceler-
ation of 180°/s2. C Delay
between chair motion and the
appearance of nystagmus
during chair acceleration and
deceleration of 1°/s2. D
Nystagmus peak slow-phase
velocity during caloric insu‚a-
tion of both ears with a warm
549°C) and cold 525°C) ¯ux of
air. The values re¯ect averages
across directions of stimulation
and subjects. Error bars are the
standard error of the mean.
5Nyst Nystagmus). *P<0.05
relative to pre-training values
velocity did not change throughout the training 5Fig. 5D). study was to assess the actual e€ects of CVT on ves-
Although some subjects showed a slight decline, some also tibular function prior to space¯ight.
exhibited an increase. Most subjects showed equivalent
A decrease in induced sickness and nystagmus elicited
reactions before and after the CVT 5Fig. 6). Habituation by such a complex pattern of stimulation has already
to repetitive head and body movements that initially been described after continuous exposure of subjects to a
produced horizontal 5as well as vertical and torsional) slowly rotating room 5Guedry 1965; Graybiel and
nystagmus did not transfer to stimulation of the hori- Knepton 1978). Although the total number of head-and-
zontal semicircular canals by caloric stimulation.
trunk movements was about the same 5about 1000) in
our study as in these earlier studies, we used repetitive
exposure. In addition, these previous studies did not
take into account the inter-individual di€erences in
susceptibility to motion sickness. The present study used
Discussion
The use of ground-based training procedures for the both subjective and objective methods to quantify sick-
control of space motion sickness is based on the prin- ness levels and compared the e€ects of training across
ciple that the lowering of an individual's susceptibility to subjects having di€erent susceptibility to motion sick-
motion sickness in one motion environment will transfer ness.
to the space situation. The objective of the present study
The salivary protein content was measured according
was not to evaluate the eciency of CVT with regard to to the method used by Igarashi et al. 51993), who found,
space motion sickness. Such a validation would be dif- based on data from six subjects, an inverse correlation
®cult and would require at least the following: 51) to between control baseline salivary total protein and the
obtain data on control groups 5i.e., individuals not duration of Coriolis stimulation required to reach the
participating in the training), 52) to use subjects with the nausea endpoint. Our results, which were obtained with
same original level of motion sickness susceptibility and/ a larger cohort of subjects, do not con®rm their ®ndings,
or the same space¯ight experience, and 53) to assess the and suggest that baseline salivary total protein levels
severity of space motion sickness in the absence of in- cannot be of use in predicting an individual's suscepti-
¯ight medication. Instead, the objective of the present bility to Coriolis-induced sickness.

544
visual cues were present during the slowly rotating room
experiment. However, since the continuous rotation of
the slowly rotating room involved no starts and stops, it
is most likely that the habituation of nystagmus to an-
gular acceleration in the CVT is related to the angular
velocity steps delivered at the beginning and end of each
run.
Since the protocol of the CVT used in this experiment
was the same as the vestibular training of the cosmo-
nauts at Star City, a habituation of the nystagmus and
symptoms is to be expected on cosmonauts exposed to
this type of training. However, as observed in various
types of training 5Parker and Parker 1990), other ves-
tibular-driven functions, such as self-motion perception
and perception of vertical subjective and postural con-
trol, might also be a€ected by CVT. In the light of recent
studies in which a role for the vestibular system in au-
tonomic and respiratory control is postulated 5Ray and
Hume 1998; Yates and Miller 1998), some changes in
vestibulo-autonomic re¯exes might also be expected to
occur as a result of CVT. Retention of the vestibular
habituation induced by CVT may interfere with the
normal adaptation of these functions to weightlessness.
It is therefore recommended that space experiments on
cosmonauts exposed to CVT include pre¯ight control
values before and after the CVT in order to assess its
impact on the response studied.
Fig. 6 Tracing of nystagmus elicited by caloric stimulation of each
ear by warm 549°C) and cold 525°C) air before 5A) and after 10
sessions 5B) of vestibular training 5total 79runs) in 1 subject. Note
the apparent lack of transfer of habituation to this stimulus
Acknowledgements The saliva protein concentration analysis was
performed at the Laboratoire de Biochimie, Hopital Rangueil,
Toulouse 5Dr. Durand). We are grateful to E. Quetel 5Institut de
Recherche P. Fabre, Castanet-Tolosan) for his help with the skin
re¯ectance measurements. This research was supported by the
Centre National de la Recherche Scienti®que 5CNRS) and the
Centre National d'Etudes Spatiales 5CNES). This experiment was
approved by the Comite Consultatif pour la Protection des Per-
sonnes dans la Recherche Biomedicale 5CCPPRB) Toulouse,
France.
Our results show a reduction in induced motion
sickness and nystagmus after CVT. The reduction in
responses during CVT is presumably the result of a
central vestibular habituation, as indicated by an ac-
quisition throughout the repetition of the tests, and a
retention from the end of a session to the beginning of
the next session. The lowering of responses for up to
60 days after the CVT suggests that this habituation is
retained for long periods. The transfer of habituation
from one vestibular stimulus to another has generally
been observed for repetitive stimuli that elicit the same
direction of response 5Collins 1973). For example, the
habituation induced by repetitive clockwise velocity
steps does not transfer to counterclockwise velocity steps
5Clement et al. 1981). It was also noted that habituation
may fail to transfer when the directions of responses are
the same but they are elicited by di€erent forms of
stimulation. For example, in the cat, caloric habituation
does not transfer to rotational stimuli and rotational
habituation does not transfer to caloric stimuli 5Collins
1964). In our study, there was no indication of transfer
from the CVT to the caloric nystagmus, but the
nystagmus produced by passive whole-body angular
acceleration was habituated. This last result seems in
contrast with a previous study using Coriolis and cross-
coupled accelerations in a slowly rotating room, in
which it was shown that no transfer of habituation to
the nystagmus was produced by passive angular accel-
eration 5Guedry et al. 1964). The di€erences in transfer
of habituation between both protocols might arise from
the fact that the rotation was eccentric and a variety of
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