Biomedical subjects

A Graybiel

Publications and source records attributed to A Graybiel.

At least 19 recordsLinked to original sources

PubMed1991

Altered sensorimotor control of the body as an etiological factor in space motion sickness.

Exposure to nonterrestrial force levels affects the activity of gravitoinertial force sensitive receptors of the body, both of labyrinthine and nonlabyrinthine origin. It also disrupts the normal patterning of motor control of body orientation and movement. The patterns and levels of muscle innervation necessary to achieve particular body configurations and to bring about particular body movements are greatly affected by background force level and body orientation relative to the force vector. The present studies demonstrate that such altered sensorimotor control of head and body posture along with altered vestibulomotor control are evocative of motion sickness. This observation has explanatory significance both for space motion sickness and the re-entry disturbances that occur after prolonged spaceflight.

Gravitation↗

PubMed1987

Asymmetric otolith function and increased susceptibility to motion sickness during exposure to variations in gravitoinertial acceleration level.

Von Baumgarten and his colleagues (23,24) have suggested that asymmetries in otolith function between the left and right labyrinths may result from differences in otoconial mass and could play a role in space motion sickness. Such asymmetries would be centrally compensated for under terrestrial conditions but on exposure to weightlessness the persisting central compensation would produce a central imbalance that could lead to motion sickness. We have used ocular counterrolling as a way of measuring the relative "efficiency" of the left and right otoliths and have compared the ocular counterrolling scores of individuals with their susceptibility to motion sickness during passive exposure to variations in Gz in parabolic flight maneuvers. The experimental findings indicate that large asymmetries in counterrolling for leftward and rightward body tilts are associated with greater susceptibility to motion sickness in parabolic flight.

Acceleration↗

PubMed1987

Treatment of severe motion sickness with antimotion sickness drug injections.

This report concerns the use of intramuscular injections of scopolamine, promethazine, and dramamine to treat severely motion sick individuals participating in parabolic flight experiments. The findings indicate that a majority of individuals received benefit from 50-mg injections of promethazine or 0.5mg-injections of scopolamine. By contrast, 50-mg injections of dramamine and 25-mg injections of promethazine were nonbeneficial. The use of antimotion drug injections for treating space motion sickness is discussed.

Dimenhydrinate↗

PubMed1987

Head movements in low and high gravitoinertial force environments elicit motion sickness: implications for space motion sickness.

Astronauts report that head movements in flight tend to bring on symptoms of space motion sickness (SMS). We evaluated how head movements in pitch, yaw, and roll--made both with normal vision and eyes-occluded--affect susceptibility to motion sickness in the zero G phase of parabolic flight maneuvers. The findings are clearcut: pitch head movements are most provocative, yaw least provocative, and roll intermediate. Susceptibility is greater with normal vision than with eyes occluded. The same susceptibility pattern emerged for head movements in the 1.8-2.0 G phase of parabolic flight. These experiments suggest that SMS is not a unique nosological entity but, rather, is the consequence of exposure to nonterrestrial force levels. Head movements during departures in either direction from 1 G elicit symptoms. This implies that, rather than speaking of "space motion sickness," it would be more appropriate to think in terms of "nonterrestrial motion sickness."

Gravitation↗

PubMed1986

The effective intensity of Coriolis, cross-coupling stimulation is gravitoinertial force dependent: implications for space motion sickness.

Coriolis, cross-coupled angular acceleration stimulation readily induces motion sickness under terrestrial conditions. Nevertheless, the Skylab astronauts, when tested with such stimulation in-flight, were insusceptible even though each had been susceptible pre-flight. It is unclear whether this decreased susceptibility was the consequence of in-flight adaptation or in part the result of immediate changes in sensory-motor and vestibulo-motor function that occur during exposure to microgravity conditions. To evaluate this issue, we have tested individuals both in the high and low force phases of parabolic flight maneuvers using constant levels of Coriolis, cross-coupled stimulation. Our findings indicate that 1.) subjects are less susceptible when tested in 0 G than +2 Gz; 2.) the perceived intensity and provocativeness of Coriolis stimulation decreases in 0 G and increases in +2 Gz relative to +1 Gz baseline values; and 3.) changes in the apparent intensity of Coriolis stimulation occur virtually immediately when background gravitoinertial force level is varied. These findings explain in large part why the Skylab astronauts were refractory to motion sickness during Coriolis stimulation in-flight. The general implications for space motion sickness are discussed.

Coriolis Force↗

PubMed1986

Sudden emesis following parabolic flight maneuvers: implications for space motion sickness.

Episodes of emesis unaccompanied by the usual prodromal signs of motion sickness have been reported by astronauts in the space shuttle program (10). Such reports have raised the issue whether space motion sickness has different characteristics from terrestrial motion sickness. We present evidence here from parabolic flight experiments that sudden vomiting can occur in response to a provocative vestibular stimulus even when no premonitory symptoms are being experienced. Accordingly, in chronic exposure conditions, the absence of prominent signs or symptoms of motion sickness does not necessarily mean an absence of sensitization.

Aerospace Medicine↗

PubMed1986

Head movements in non-terrestrial force environments elicit motion sickness: implications for the etiology of space motion sickness.

Space motion sickness has become an operational concern in manned space flight. Considerable evidence exists that head movements in free fall, especially pitch movements, are provocative until adaptation occurs (3,4,8,9,11,17,18,22,26). The question arises whether space motion sickness is an unique nosological entity or is due to body movements in a nonterrestrial force environment, a force environment for which the body's dynamic sensory-motor adaptions to 1 G are no longer appropriate (14,16,18-21). To evaluate this issue, we had subjects make controlled head movements during exposure to high gravitoinertial force levels, 1.8-2.0 G, in parabolic flight maneuvers. Head movements in pitch with eyes open were most evocative of motion sickness, yaw movements with eyes covered were least provocative. This pattern is identical to that which occurs when the same types of head movements are made in the free fall phase of parabolic maneuvers (17,18). It appears that space motion sickness is the consequence of prolonged exposure to a non-terrestrial force background rather than of exposure to free fall per se.

Adult↗

PubMed1986

Cardiovascular epidemiology, exercise, and health: 40-year followup of the U.S. Navy's "1000 aviators".

The interrelationship of aging, performance, and stress modification has been the subject of investigations in the U.S. Navy. Beginning in 1940, a study of 1,056 student and instructor pilots lowered previously high attrition rates in training by emphasizing both physical and psychological screening. After World War II, when 208 pilots in the group died, followup studies of the survivors were conducted in 1951, 1957, 1963, 1969-71, 1977, and 1980-81. In February 1981, 715 questionnaires were mailed to known survivors, with 500 replies subsequently analyzed. Additionally, 114 of the respondents who had previously been examined during 1969, were again examined in 1980-81; those individuals were markedly different in their lifestyle, particularly in exercising regularly, abstaining from cigarette smoking, and drinking alcoholic beverages moderately, as contrasted to 28 aviators also examined in 1969 who died in the interim. Healthy lifestyle may alter cardiovascular risk, preventing premature death.

Aerospace Medicine↗

PubMed1984

Perception of body weight and body mass at twice earth-gravity acceleration levels.

On Earth, when standing on two feet, we experience particular patterns of force and pressure on the soles of our feet. As we lift one foot and balance on the other, little or no increase in force or pressure is perceived on the sole of the stance foot even though the contact forces of support on that foot have doubled. The failure to perceive this increase is actually an illusion resulting from the operation of spatial constancy mechanisms serving to preserve feelings of near constant force and pressure on the support surface(s) of the body. On Earth, body weight and body mass are perceived as remaining constant regardless as to whether we are standing on two feet or one and whether we are carrying large objects. In the high force phase(2 g acceleration) of parabolic flight, body weight is perceived as doubling, and a great increase in force is perceived on the soles of our feet if we are standing. When shifting balance from two feet to one, an increase in force of approximately 0.5 mg is felt on the sole of the stance foot. The actual increase in force is 1.0 mg but perceptual compensation is only being made for a 0.5 mg increase such as would be characteristic of shifting balance on Earth; accordingly an additional 0.5 mg (1.0-0.5 mg) residue is perceived. These findings indicate that body weight is dependent on the magnitude of the gravitoinertial forces acting on the body. Variations in the contact forces supporting the body due to passive or active locomotion of the body or to objects that are being carried are monitored and disregarded in computing apparent body weight. When stepping up and down from a low platform during the high force phases of parabolic flight, aberrant motion of the body and the aircraft is experienced. These illusory motions result because the doubling of body weight in a 2 g force background alters the normal relationship between patterns of alpha and gamma activation of antigravity muscles, muscle spindle activity, and the movements of the body. Accordingly, sensory-motor control and perceptual and postural stability on Earth are dependent on an active calibration to a 1 g background force level.

Acceleration↗

PubMed1984

Elicitation of motion sickness by head movements in the microgravity phase of parabolic flight maneuvers.

During parabolic flight maneuvers in a Boeing KC-135 aircraft 44 college students were tested for motion sickness susceptibility. These subjects were categorized as 1) insusceptible, 2) moderately susceptible, or 3) highly susceptible to motion sickness during exposure to varying gravitoinertial force levels. After categorization, they were tested in the microgravity phase of parabolic flight to see how three types of head movements affected their baseline susceptibility. The head movements evaluated included side-to-side swivel, shoulder-to-shoulder roll, and front-up head and trunk movements; each type of head movement was used on a separate test day for eyes-open and eyes-covered conditions. Ten cycles of head movements were made in each parabola until a motion sickness endpoint, nausea, was reached or 40 parabolas had been completed. All types of head movements significantly increased susceptibility for subjects in all categories; eyes-open conditions were always more stressful than eyes-closed for each kind of head movement. These findings show unequivocally that natural head movements in microgravity can elicit symptoms of motion sickness. They suggest that head movements play an important etiological role in space motion sickness. In ground based studies where head movements are necessary to elicit symptoms, they are also necessary to elicit adaptation. We describe the use of paced and incremented head movement schedules as a possible way of partially alleviating space motion sickness.

Aerospace Medicine↗

PubMed1984

Clinical testing of the otoliths: a critical assessment of ocular counterrolling.

A test procedure which measures the amount of ocular counterrolling (OCR) of the eyes in response to lateral tilt of the body is considered a means of obtaining objective responses to stimulation of the otolithic receptors in the non-auditory labyrinth of the inner ear. OCR is thought to be the result of changing the orientation of the otolithic maculae relative to the gravitational vector. A special optical system (goniometer) has been devised which enables the observer to obtain a clear image of the subject's eye and to measure OCR responses in degrees and minutes of arc. Although attempts have been made elsewhere to evaluate the clinical significance of such responses, the results have been controversial, and clearly indicate the need for further study in order that OCR may be utilized as a reliable diagnostic tool. Accordingly, a review of the literature is presented, together with preliminary findings at St. Michael's Hospital and recommendations for further research.

Adult↗

PubMed1983

Etiological factors in space motion sickness.

We compared susceptibility to motion sickness during exposure to sudden-stop stimulation as a function of gravitoinertial force level. Our findings show that susceptibility is greatly enhanced, both with eyes-closed and eyes-open, for zero-g and 2-g conditions in parabolic flight compared with 1-g test conditions. The change in susceptibility is likely related to three factors: alterations in vestibulo-ocular function which result from variations in gravitoinertial force level (28,29); the altered pattern of otolithic activity resulting during variations in gravitoinertial force level; and the altered canal-otolith response synergies that result during exposure to gravitoinertial force levels greater or less than terrestrial levels. These factors are shown to be related to the etiology of space motion sickness and to the alterations in performance and vestibular function that are experienced by astronauts during reentry. An explanation is also proposed for the decrease in susceptibility to motion sickness exhibited by the Skylab astronauts inflight and for some period postflight during exposure to cross-coupled angular accelerations.

Adult↗

PubMed1983

Perceived orientation in free-fall depends on visual, postural, and architectural factors.

In orbital flight and in the free-fall phase of parabolic flight, feelings of inversion of self and spacecraft, or aircraft, are often experienced (2,3). We show here that perceived orientation in free-fall is dependent on the position of one's body in relation to the aircraft, the architectural features of the aircraft, and one's visual appreciation of the relative configurations of his body and the aircraft. Compelling changes in the apparent orientation of one's body and of the aircraft can be reliably and systematically induced by manipulating this relationship. Moreover, while free-floating in the absence of visual, touch, and pressure stimulation, all sense of orientation to the surroundings may be lost with only an awareness of the relative configuration of the body preserved (7). The absence of falling sensations during weightlessness points to the importance of visual and cognitive factors in eliciting such sensations.

Aerospace Medicine↗

PubMed1983

Motion sickness: acquisition and retention of adaptation effects compared in three motion environments.

A sharp distinction should be made between symptoms of motion-sickness per se and phenomena inferred from the symptomatology, which include rates of acquisition and decay of adaptation effects. Foreknowledge of these "derived phenomena" are valuable if it can be shown that they hold true for virtually any motion environment. Recently, we have developed a sudden-stop vestibulovisual interaction test for measuring susceptibility to motion sickness (1). The test procedure involves four successive assessments that provide not only an index of susceptibility to motion sickness but also the rates of acquisition and decay of adaptation effects. The 14 subjects participating in this test had previously served as subjects in parabolic flight experiments and seven of them had also taken part in the assessment of antimotion-sickness remedies in a slow rotation room. The present report examines whether their rates of acquisition and decay of adaptation to stressful motion represent consistent general features of their responses across motion environments. From these comparisons, it appears that an individual's rates of acquiring and losing adaptation are quite consistent in very different situations. The pattern of results also suggests modifications of the sudden-stop vestibulovisual test that should increase its effectiveness as a motion-sickness screening procedure, both for orbital flight and for terrestrial conditions.

Adaptation, Biological↗

PubMed1982

Rapid perceptual adaptation to high gravitoinertial force levels: evidence for context-specific adaptation.

Subjects exposed to periodic variations in gravitoinertial force (2-G peak) in parabolic flight maneuvers quickly come to perceive the peak force level as having decreased in intensity. By the end of a 40-parabola flight, the decrease in apparent force is approximately 40%. On successive flight days, the apparent intensity of the force loads seems to decrease as well, indicating a cumulative adaptive effect. None of the subjects reported feeling abnormally "flight" for more than a minute or two after return to 1-G background force levels. The pattern of findings suggests a context-specific adaptation to high-force levels.

Adaptation, Physiological↗

PubMed1982

Antimotion-sickness efficacy of scopolamine 12 and 72 hours after transdermal administration.

The antimotion sickness remedy, transdermal therapeutic system-scopolamine, administered in this experiment was scheduled to deliver 1.0 mg of scopolamine over a period of 3 d, and this paper compares its efficacy 12 and 72 h after administration. In a double-blind study, six male college students were individually exposed to a standardized provocative test in a slow rotation room after six apparently identical treatments comprising four placebos and two medications. Efficacy was categorized as beneficial, inconsequential, or detrimental. None of the responses was detrimental. Following the first administration of the therapeutic system, there were four beneficial responses after 12 h but none was beneficial after 72 h. Following the second treatment regimen, there were four beneficial responses after 12 h and three beneficial responses after 72 h. Great individual differences were demonstrated, two subjects accounting for six beneficial responses and two accounting for only one beneficial response. The difference in efficacy after 12 and 72 h has practical and theoretical significance.

Adult↗

PubMed1981

Mechanisms underlying modulations of thermal nystagmic responses in parabolic flight.

In six subjects nystagmography was used to compare the responses to cold calorization of one horizontal semicircular canal under ground-based and parabolic flight conditions. On the ground the expected individual differences in primary nystagmic responses were observed; only one subject manifested a brief weak secondary nystagmus. Aloft, the irrigation was carried out in straight-and-level flight prior to a pushover (half-parabola) that initiated a series of four to nine typical parabolas in a modified KC-135 aircraft. Thereafter, the free-fall phases of the parabolas furnished a zero baseline for measuring weight differences in endolymph due to changes in gravitoinertial force. In all subjects a secondary nystagmus was generated in addition to the primary nystagmus during the course of the parabolic maneuvers. The slow phase of the secondary nystagmus rarely exceeded 10 mm per sec. Evidence is presented that secondary nystagmus arises as a direction-specific adaptation effect countering the primary nystagmic response. Three stages were recognizable: first, when primary and secondary nystagmus alternated in step with the high and low force phases of the parabolas; second, after disappearance of primary nystagmus when secondary nystagmus appeared alone and was modulated by the changes in force; and third, when the secondary nystagmus present became independent of the highest gravitoinertial forces generated. Great individual differences were observed, suggesting that with large departures of the cupula from its functional rest position there are large individual variations in rate of restoration.

Adult↗

PubMed1981

Variations in gravitoinertial force level affect the gain of the vestibulo-ocular reflex: implications for the etiology of space motion sickness.

Recordings of horizontal nystagmus were obtained on 16 male subjects exposed to repeated patterns of horizontal angular acceleration, constant velocity rotation, and sudden-stop deceleration in the laboratory and in the free-fall and high-force periods of parabolic flight. Nystagmus intensity was a clear function of gravitoinertial force level: slow phase velocity and beat frequency increased during exposure to high force levels and decreased in free-fall compared to values obtained at I G. These findings indicate that the gain of the vestibulo-ocular reflex decreases in free-fall. This fact likely accounts for the disorientation and dizziness sometimes experienced by astronauts when moving their heads in the early phases of orbital flight and again after splashdown. The implications of the present findings, both for the etiology and for the treatment of space motion sickness, are discussed.

Acceleration↗