When Commander Chris Hadfield is on the International Space Station what happens to his brain during his mission? What are the physiological changes that scientists are concerned about for attempting long voyages into the final frontier? What have we learned from all the brave men and women during the decades of human space exploits ? We have learned the perspective of two very important views on our world. The first is the social aspect of seeing our own planet Earth from space, from men standing on the moon. We have seen the orb of life in the blackness of infinity. We have not seen the absent gravity but the entire signalling systems have been seen by the cells of all the astronauts in the absence of gravity. These cells don’t actually see but they sense. Our cells sense shape only when we are in a gravity force field. What is gravity ?
Einstein revealed to us the observers experience within a closed elevator with an atmosphere inside this small room, gravity is felt on Earth as our position standing on the floor of the elevator. Everything seems normal for the observer. Position the same elevator into travelling in space the elevator would have to be continuously accelerated at 32ft/sec2 in order for the observer to stand upright inside the elevator. The observer would not be able to distinguish either experience from inside the closed elevator. We can experience brief episodes of approximately 20 seconds of micro-gravity during the flight profile of parabolic flight, the swooping diving surge into a soaring upwards into a flinging arc that permits participants to be accelerated just like being in the accelerating elevator against the acceleration of the pull of Earth’s gravity. All the accelerations of the participants match in the opposite direction to the Earth’s acceleration cancelling out to zero releasing the participants to float free. What is the usual thing that happens next to participants? They usually vomit.
During parabolic flight for those brief 20 seconds of simulated micro-gravity various experiments have been performed as an alternative to sending these experiments into outer space. One such experiment was for mice with one side of their labyrinths surgically disabled. How did these animals behave in micro-gravity, how did they make vestibular compensation to their behaviour?
Vestibular decompensation in labyrinthectomized rats placed in weightlessness during parabolic flight in Neuroscience Letters 344 (2003) 122-126 by Annie Reber, Jean-Hubert Courjon, Pierre Denise and Gilles Clement provides the answers to this particular question. The authors casually remark that, “It is well-known that after a lesion of the vestibular apparatus on one side (only), there is asymmetry in posture and eye movements.” Remember from previous essays I have drawn the hypothetical neurological observation that micro-gravity stimulation provokes the cascade of concussion like effects starting first within the brain’s gravity sensing apparatus, our own accelerometers within the saccules and utricules. As a blow hits the head, the head is decelerated as if behaving within a changing gravity field of acceleration. Gravity is a continuum complete within microgravity linked to magnified gravity. If you want to learn what happens to a human head at the instant a concussion is happening you have to slow every thing down as if it were happening in a slow motion video of the event. Parabolic flight affords the observer of the opportunity to watch the vestibular changes in a less compressed format of cascading events. If you want to watch dominoes hitting one after another watch them in a fluid that slows down the contact motions, as long as the fluid is not too buoyant. Think of gravity as a fluid retarding the acceleration uniformly. Notice also the authors stress changes in posture and eye movements. What do concussed people complain about? They complain about loosing their balance easily and they have trouble reading or watching television, they have trouble with the coordination of their eyes.
The interesting thing about lesioned ears (one sided labyrinthectomy) is that the head tilts toward the side of the lesion when compensated animals are placed in darkness. In other words in the absence of visual cues vestibular compensation occurs. The specific elegant observation from this is that vestibular signalling has a higher priority than visual signalling in terms of proprioception. Vestibular decompenstaion is also present within lesions of relay structures of the central nervous system that relay how the body positions itself on surfaces, the sense of space in 3-dimensional space that has the ever present gravity vector pointing as a reference direction.
“We therefore compared the posture of compensated animals during free-floating in weightlessness with that of lesioned animals at an acute stage (2–7 h after surgery) during water immersion. Both weightlessness and water immersion alter tactile cues (no cues during free-floating; cues distributed all over the body during water immersion) and challenge processes such as navigation and spatial orientation. We also compared the surface righting response of compensated animals at the end of the weightlessness phase during parabolic flight when the animals hit the ground with that of acute animals after a short free-fall on land (drop test).”
“The bulla tympanica was exposed through a ventral approach, the vestibulum was opened and the organs of the inner ear were mechanically destroyed. The wound edge was sutured and repetitively infiltrated with 1% xylocaine for 2 h after the surgery.”
“For the water immersion test, the animals were placed in the prone position at the surface of an aquarium (0.85×0.6×0.7 m) filled with water heated to body temperature for a period of about 20 s repeated three times.”
“For the drop test, the animals were held in the prone position about 60 cm above a cushion and then dropped. Each animal was tested three times.”
“For the parabolic flight test, parabolic flight was conducted on-board the CNES airplane during a series of three flights, including 22 parabolas each. In each parabola, a period of level flight (1 g) was followed by a pull-up phase of 1.8 g for about 20 s, a 0-g phase lasting 20 s, a pull-out phase at 1.8 g also lasting 20 s, and a return to 1 g for 1–2 min. The animals were placed inside a transparent box (0.5×0.5×0.5 m) with a cushioned surface on its bottom for seven consecutive parabolas. Before being introduced in the observation box, the animals were restrained in a smaller enclosure, which prevented them from free-floating.”
“For gaze deviation, the animals were gently restrained in a tissue bag that limited body movements. The head was fixed, pitched 30° nose-down so that the utricle was approximately horizontal. Movements of both eyes were recorded in darkness with a search coil technique. Each animal was tested during seven parabolas.”
As you can verify the researchers were rigorous in their methodology of measuring the variables that were important for their study, except one that they missed. Despite video taping all the procedures they missed one subtle measurement. Here is more from their detailed report.
” In all other conditions (water immersion, drop, parabolic flight) the experiment was performed in ambient light. For posture analysis, the animal’s swimming or free-floating behavior and surface righting reflexes were videotaped at 50 frames/s. Lesioned animals generally responded by a rotation of their bodies around the longitudinal axis (roll motion). Both the percentage of time spent rotating for each condition and the rotation frequency were measured using frame-by-frame analysis. After the drop test and at the end of the weightless period, the latency required for the animals to ‘right’ themselves and resume an upright posture was measured using slow motion playback of the videotapes.”
“Just after surgery, the UL animals showed the typical symptoms of postural and ocular imbalance after unilateral labyrinthectomy. The postural symptoms were characterized by a tilt of the head and a twist of the body toward the lesioned side, a flexion of both hind- and forelimbs on the side ipsilateral to the lesion, and an extension of both limbs on the contralateral side. BL rats had a more symmetrical posture, with a reduced muscular tone compared to control animals.” ( UL is a unilateral labyrnthectomy lesion or one side only and BL is bilateral labyrnthectomy lesions, or both sides)
“After 40–43 days following the surgery, when the animals’ posture was tested during the 1-g phase of parabolic flight, there was no difference between the normal and lesioned animals. During the 0-g phase, normal and BL animals extended their four limbs and occasionally rolled on themselves at a frequency of about 1 Hz. By contrast, when free-floating the UL animals twisted and turned at a velocity that exceeded 2000°/s in one animal. Their head was tilted toward the lesioned side (left) and they rolled around their long body axis in the counter-clockwise direction. When the UL animals tenaciously grasped at the cushion on the bottom of the cage in weightlessness, they adopted the typical asymmetrical static posture observed just after labyrinthectomy, with a deflection of the head on the lesioned side, and a full extension of the contralateral fore- and hind limbs. The same posture was also observed when the airplane began its pull-out maneuver. However, a return to the normal (i.e. compensated) posture was observed after 4.5 s on average.”
“By comparison, between 2 and 7 h after surgery, during the water immersion test, the lesioned animals spent most of the time rolling, at a frequency ranging from 1.2 to 3.2 Hz (velocity from 430 to 1150°/s). UL animals always rotated toward the lesioned side, whereas BL animals rotated either to the right or to the left. After a drop, which simulated a transient weightlessness on Earth, the BL animals resumed a prone posture almost immediately, whereas the latency for the surface righting response was about 3.5 s on average for the UL animals.”
“During the parabolas, the UL animals rotated for about half of the duration of a parabola on average because they were able to grasp at the cage bottom surface for the other half (whereas there was no surface to grasp during water immersion). It is important to note though that they immediately started to roll over when they released their support. By contrast, both the BL and normal animals could spend a considerable time free-floating without rolling. The latency of the surface righting reflex of the UL animals at the end of the 0-g phase was not significantly different from that measured after the early drop tests. The frequency of rotation of the UL animals was also comparable in weightlessness and during the early water immersion test. “
“When the UL animals were restrained and the head fixed, during parabolic flight at 0 g and in the dark the left eye was deviated by 26.1°±6.6° downward and the right eye was deviated by 26.4°±4.5° upward compared to their position in normal gravity (mean and SD of three rats during 21 parabolas). The direction and amplitude of these eye deviations are comparable to those observed in UL rats at an acute stage. By contrast, the changes in eye deviation in 0 g compared to 1 g never exceeded 3° in BL and normal animals.”
As the researchers remarked any vertebrate when exposed to weightlessness reveals a temporary spatial disorientation. As I mentioned earlier in this essay humans suffer motion sickness and the illusion of being upside down. Across species including fish, our primate ancestors and humans, ‘ changes in reflexive eye movements occur.’ Animals when they are – either in space or parabolic flight microgravity no longer have the tactile contact cues from being on a surface to give automatically the down position. “One commonly observed response of animals in weightlessness is to react as though they are upside-down and to initiate a repetitive righting response. Typically the animal rolls over and over, since in weightlessness there is no vestibular confirmation that the action was successful. This roll movement was casually seen in our normal and BL animals, and was directed toward either the right or the left. However, when the animals grasped at surfaces and tactile cues were present, they eventually came to perceive themselves as upright in an upright aircraft and the roll motion stopped.” When the authors use the roll term, it is the spinning around the body axis head to toe, like rolling yourself holding a blanket, you get completely wrapped up like a big FedEx package.
“By contrast, the UL animals showed a continuous roll motion in weightlessness, in the direction corresponding to the lesioned vestibular apparatus. Although the parabolic flight took place late after surgery, when normal posture was observed in a 1-g environment, the acute symptoms of unilateral labyrinthectomy were again apparent in weightlessness and continued for 4–5 s after the end of the weightless period. The similarity between the response pattern of UL animals during parabolic flight at a compensated stage and on Earth at an acute stage is suggestive of a vestibular decompensation in weightlessness.”
“Recent electrophysiological studies in frogs have shown that after unilateral section of the VIII nerve, the asymmetry that resulted was compensated by a functional reorganization of the somatosensory map in the vestibular recipient structures. This reorganization was manifested by an expansion of contralateral afferent vestibular signals onto the deprived ipsilateral neurons. It led to an increase of excitatory commissural inputs from the intact side and a decrease of inhibitory commissural responses. In very much the same way, following unilateral labyrinthectomy in rats and guinea pigs, an increase in spontaneous discharge and excitability has been observed in the vestibular neurons on the operated side. This increase in the resting discharge could be responsible for the consequent recovery of static vestibular function. During the 20 s of weightlessness, the static gravitational force no longer stimulates the otolith organs of the intact ear, thereby weakening temporarily their excitatory inputs on the vestibular neurons on the operated side. In 0 g, their resting discharges would presumably not be strong enough to allow the activation of the vestibular neurons on the lesioned side, hence a temporary return to the acute vestibular deficits.”
“In the absence of a surface support, a return to an imbalanced posture in decompensated animals would generate rotation in the direction of the lesioned, i.e. flexed, side. Indeed, in normal gravity, the postural tone maintains an attitude or posture in relation to the acceleration of gravity. Postural control is determined by the overall balance of muscle forces acting on the head, limbs, and torso. According to Newton’s first and second laws of biomechanics, an asymmetrical posture with an extension of the right limbs and a flexion of the left limbs creates a momentum as soon as the body is released from the surface support. In weightlessness, this momentum generates a rotation to the left (i.e. toward the lesioned side in our animals) which continues unless new forces (such as grasping reaction) impress on it and rebalance the posture.”
” Postural decompensation has been reported for various species and experimental conditions. For example, UL animals placed in the dark at a compensated stage exhibit asymmetrical posture, but normal posture is immediately restored when animals are again placed in the light. Postural decompensation also takes place during handling of operated animals. In our study, the fact that the UL animals also present the typical postural asymmetry even when they are in contact with the floor in 0 g (during grasping at the cage surface) suggests that tactile cues are not primarily responsible for the vestibular decompensation. Nevertheless, tactile inputs sensitive to body weight are not stimulated when the animals grasp at a support surface in the weightless condition, and the muscle groups involved during grasping and standing are different (flexor vs. extensor, respectively). It is therefore possible that the vestibular decompensation observed in weightlessness could also be due to the changes in tactile and proprioceptive cues in the free-floating animals.”
” It is interesting to note that the upright posture was restored well before the end of the hypergravity phase (4.5 s compared to 20 s). In addition, no decompensation was observed during the hypergravity phase prior to the 0-g phase. Therefore, it seems that it is not hypergravity per se that caused a decompensation. The decompensation seen during the first few seconds of hypergravity following zer0 G presumably is an after-effect of the decompensation triggered by the removal of gravitational information in weightlessness. It is also possible, however, that in our experiment the recovery of a normal posture after the transient vestibular decompensation provoked by weightlessness is even faster because the animals are exposed to hypergravity after the 0-g phase of parabolic flight. Indeed, recent studies have shown that guinea pigs stimulated with 2 g on a centrifuge following unilateral labyrinthectomy showed faster compensation in head deviation than when maintained in normal gravity.”
Here are the conclusions from these authors. ” Our results support the hypothesis that an imbalance in the otolith system underlies the ocular and postural asymmetry observed after unilateral labyrinthectomy. In the compensated UL rats, weightlessness uncovered an asymmetry in the otolith system, which was previously cancelled on Earth. These results are in agreement with those obtained in perinatal rats gestated during space flight which suggest a direct effect of gravity on the development of the vestibular system due to a reduction of the otolith input. They also suggest that vestibular compensation after unilateral lesion can be disrupted momentarily and is a fragile state during which the otolith system in the remaining vestibular apparatus plays a continuous role. This finding is consistent with the fragility of the vestibular compensation also observed in humans during the early phase of recovery following unilateral vestibular loss. The decompensation is less evident after bilateral lesion, because since there are no longer otolith inputs, vestibular compensation would predominantly be achieved based on proprioceptive, somatosensory and visual cues.”
The amazing advantage that parabolic flight affords the observer is that despite the induced nauseous state toward the inclination to vomit the observer reflects on the scene of people performing experiments flying through the cabin space untethered to the acceleration force of gravity then the abrupt transfer to doubling the force of gravity. This pattern repeating itself close to two dozens times in the duration of the series of parabolic porpoising motions through air space. The constant changing effects within the otolith structures, the one-sided labyrinthectomized rats roll spinning in free flying with their eyes twisting into different eye saccade positioning into aberrant directions as the animal rearranges it’s sense of where is up. But here are some fresh observations from a curious observer.
As the aircraft settles into the bottom of the descent phase the scientists catalogued the animals lay turned toward the side of the otholith lesion, lying immobile for 4.5 seconds average. From the previous essay citing Ilan Golani in the Behavioural Brain research 231 (2012) 309-316 from the review: The developmental dynamics of behavioral growth processes in rodent egocentric and allocentric space, this rat is not just revealing a resting reaction this rat behaviour is the start of a recovery display of movement re-capture of the cartesian coordinates. Despite the lack of otoliths on one side of the cranium the rat is trying to establish the start of a recovery sequence at the origin of a 3 dimensional starting point, the rat’s X-Y-Z. But the researchers didn’t wait long enough past the resting position they were more concerned about the next phase of the parabolic flight. They also didn’t pay attention to the individual rat who was yawing at this point. In the back of their minds if questioned by a curious observer, “Why didn’t you measure how many times the rat may have yawned during the entire parabolic sequence? Their collective reply would be along the lines of, ….”Why should we be concerned if the rat yawns, perhaps he’s tired or stressed, I don’t know….” Their report clearly misses the most critical aspect of their experiment, the observation that yawning is associated with nausea. As the gravity vector experienced by both the humans and little mammals aboard the aircraft swooped and dove their otoliths reacted as a vestibular challenge. We are taught to not pay attention when someone yawns, we literally don’t see it as important, it’s such a regular occurrence for both the rats onboard and the humans, except when the gravity vector disappears which affects the central pattern generator for yawning. There is only one startling observation now in a closed environment with changing gravity levels, yawning is triggered by gravity change, yawning is the Einstein Reflex.
What this experiment using parabolic flight reveals is the omnipresence of a one gravity vector that has affected all central brain shape signalling by singularly dominating cellular communication orienting as a vestibular reference to which the entire cellular net signalling of every single life form has evolved to pivot around since the beginning of coherent signalling first appeared on planet Earth. Our brain is first and foremost based on the vestibular sense of the direction of Earth’s gravity. Our heart our lungs our muscles our sense of life the total of totals spirals around the sensing of gravity. We yawn to continuously perfect where gravity has its vector to orient to this source of direction that shapes the entire signalling diversity on life as we know it on our planet Earth. When we are concussed we lose the acute sense of our position in 3 dimensional space. We are unbalanced, we stagger, we sway we can even vomit at times. Our eyes are no longer coordinated to our body we see the horizon as no longer being flat it is now banked. We are tilted we lean trying to find the gravity that has guided us so effortlessly up until this moment. We are adrift, we have lost our sense of position on Earth, we are lost. Our brain will attempt to find the gravity, we will yawn. That is why yawning is the Einstein Reflex. We sense within the continuum of space time warping around gravity, we sense gravity all species sense gravity except the autistic children. Autistic children do not yawn.
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