-------------------------------------------------------- CH4 0% -------------------------------------------------------- CH2O 0% -------------------------------------------------------- CH3OH 0% -------------------------------------------------------- N2 0%
-------------------------------------------------------- NO 0%
-------------------------------------------------------- NO2 0%
-------------------------------------------------------- N2O 0%
-------------------------------------------------------- Ar 0% -------------------------------------------------------- NaCl, Na2SO4, NaHCO3 -------------------------------------------------------- H2S 0%
-------------------------------------------------------- H2SO4 0%
-------------------------------------------------------- Cu??
-------------------------------------------------------- Zn??
-------------------------------------------------------- pH 0 _Acontium velatum_ _Thiobacillus thioodixans_
-------------------------------------------------------- Eh -450 mV Sulfate-reducing bacteria at pH 9.5 --------------------------------------------------------
Table VI.-_Extremes of Chemical Environmental Factors Permitting Growth or Activity_
---------------------------------------------------------------------- Chemical Maximum Pressure, Time, Organism Activity factor atm days ---------------------------------------------------------------------- O2 100% 1 Plants, Growth animals ---------------------------------------------------------------------- O3 100 ppm 5 _Armillaria Growth (ozone) --------------------------- mellea_ ----------------- 500 ppm 5 Light emission ---------------------------------------------------------------------- H2 100% Various Germination plants ---------------------------------------------------------------------- H2O Aw 1.0 1 Various Growth aquatic organisms
---------------------------------------------------------------------- H2O2 0.34% Rye Germination enhanced ---------------------------------------------------------------------- He 100% Wheat, rye, Germination rice ---------------------------------------------------------------------- CO 100% Rye Germination -------------------------------------------------------------- 80% 1.1 4 _Hydrogenomonas_ Growth ---------------------------------------------------------------------- CO2 100% 1.1 4 Rye Growth and germination ---------------------------------------------------------------------- CH4 100% 1.1 4 Rye Germination ---------------------------------------------------------------------- CH2O 50% Rye Germination ---------------------------------------------------------------------- CH3OH 50% Rye Germination ---------------------------------------------------------------------- N2 100% .1 10 Various plants Germination and root growth ---------------------------------------------------------------------- NO 18% .018 10 Sorghum, rice Germination and root growth ---------------------------------------------------------------------- NO2 18% .018 10 Rye, rice Germination and root growth ---------------------------------------------------------------------- N2O 100% 1.2 4 Rye Germination -------------------------------------------------------------- 96.5% 1.7 Rye Germination ------------------------------------ _Tenebrio Survival molitor_ ---------------------------------------------------------------------- Ar 100% 1.2 2 Rye Germination ---------------------------------------------------------------------- NaCl, 67% Photosynthetic Growth Na2SO4, bacteria NaHCO3 ---------------------------------------------------------------------- H2S 0.96 _Desulfovibrio Growth g/liter desulfuricans_ ---------------------------------------------------------------------- H2SO4 7% _Acontium Growth velatum_ ------------------------------- Thiobacilli Growth, reproduction ---------------------------------------------------------------------- Cu?? 12 _Thiobacillus Growth g/liter ferrooxidans_ ---------------------------------------------------------------------- Zn?? 17 _Thiobacillus Growth g/liter ferrooxidans_ ---------------------------------------------------------------------- pH 13 _Plectonema Growth nostocorum_ ------------------------------- _Nitrobacter_ Growth ------------------------------- _Nitrosomonas_ Growth ---------------------------------------------------------------------- Eh 850 mV Iron bacteria Growth at pH 3 ----------------------------------------------------------------------
chapter 4
_Behavioral Biology_
EFFECTS OF THE s.p.a.cE ENVIRONMENT ON BEHAVIOR
NASA was established in 1958, shortly after the Russian launching of the second Earth satellite Sputnik II, the first vehicle to carry life into orbit around the Earth. This accomplishment was preceded by the pioneering work of Henry et al. ([ref.77]), in which animals were exposed briefly to low-gravity states in Aerobee rockets. A motion-picture camera photographed the behavior of two white mice in rotating drums during this series of flights, which marked the first time that simple psychological tests were made on animals in the weightless condition. While this behavioral experiment was relatively simple, it provided the basic concepts for recent studies which involved rotation of animals during the weightless state. Subsequent flights such as Project MIA (Mouse-in-Able) reflected a preoccupation with physiologic measures (refs. [ref.78] and [ref.79]), although the flights of Baker and Able included preflight and postflight performance studies ([ref.80]). Able"s behavior was recorded in detail on in-flight film, but none of the behavior was programed or under experimental control.
The first flights in which behavior or performance was explicitly programed were those of Sam and Miss Sam in flights of the Little Joe rocket with the Mercury capsule, launched from Wallops Island in 1959 and 1960 ([ref.81]). The first major s.p.a.ce achievement in the behavioral sciences was the successful in-flight measurement of the behavior of the chimpanzee Ham in early 1961, in which the pretrained animal performed throughout the flight. The second achievement along these lines was in 1962 when the chimpanzee Enos made several orbits around Earth and performed continuously on a complex behavioral task. The tasks which the animals performed during these flights have been described in detail by Belleville et al. ([ref.82]), and the results of the in-flight performance have been presented by Henry and Mosely ([ref.83]). These early flights provided much of the technological framework on which current biological experiments on organisms during flights of extended duration are based. Due largely to the efforts of Grunzke (refs.
[ref.84] and [ref.85]), the apparatus needed to sustain animals during s.p.a.ce flight, such as zero-g watering and feeding devices, are now commonplace ([ref.86]). Advanced systems of programing stimulus presentations and recording responses, developed for Project Mercury, may now be seen in many basic research laboratories throughout the country.
Several other noteworthy advances have been made as an outgrowth of the Mercury animal flights. Immediately before the orbital flight MA-5, in which the chimpanzee Enos was employed, it was unexpectedly found that this 5-year-old animal was hypertensive. Subsequent centrifuge studies showed that its vascular responses exceeded those of a control group.
Consideration of the animal"s preflight experience led to speculation concerning the origin of this hypertension. An explanation of the high-blood-pressure responses detected in Enos has been pursued by Meehan et al. ([ref.87]). Persistent hypertension has been produced in other laboratory chimpanzees restrained in the same manner as those partic.i.p.ating in s.p.a.ce flight and exposed to demanding performance tasks, a demonstration which has important implications for prolonged manned s.p.a.ce flight and for cardiovascular medicine in general.
Studies more directly concerned with behavior and performance have been extended from those of Project Mercury. These extensions have been in the following directions: (1) the establishment and maintenance of complex behavioral repertoires under conditions of full environmental control, (2) the refinement of behavioral techniques for a.s.sessing sensory and motor processes, and (3) the maintenance of sustained performance under conditions of long-term isolation and confinement and preliminary extension of such experimental a.n.a.lysis to man.
Numerous studies with primate subjects, including several at Ames Research Center, have been devoted to developing methods for maintaining optimum performance in environments with limited sources of stimulation.
Monkeys, baboons, and chimpanzees, for example, have been isolated for periods of longer than 2 years with no decrement in performance on complicated behavioral tasks ([ref.88]). The behavioral techniques used in these studies are closely related to those employed on human subjects under NASA sponsorship at the University of Maryland ([ref.89]). The essence of these techniques is in the proper programing of environmental stimuli ([ref.90]). It is not sufficient to provide the subject with his physiological requirements for survival, but he must be given the psychological motivation for using these provisions. This statement, of course, is an oversimplification of the problem, but it serves to ill.u.s.trate the essence of these experimental programs.
Gravity has long been known as one of the major factors influencing various life processes and the orientation of both plants and animals.
One of the most challenging problems of s.p.a.ce research has been to define this influence more precisely. Related to the effect of gravity on living processes is the problem of the effects of weightlessness. Of particular interest to psychologists are the possible modifications an altered gravitational environment might produce in behavioral patterns basic to the animal"s maintenance and survival, such as eating, sensory and discriminative processes, development and maturation, and learning capacity ([ref.91]).
One prominent method of studying gravitational effects is to simulate an increase in gravity by centrifugation. Smith et al. ([ref.92]) and Winget et al. ([ref.93]) have investigated the effects of long-term acceleration on birds, primarily chickens, while Wunder (refs. [ref.94]
and [ref.95]) and his coworkers (refs. [ref.96]-[ref.99]) have used fruit flies, mice, rats, hamsters, and turtles. The general findings are that, when animals are subjected to a prolonged period of acceleration of moderate intensity, they exhibit decreased growth, delayed maturation, and an increase in the size of certain muscles and organs, dependent on the species. With regard to the decreased growth effect, the data of these investigators show some exceptions. When the gravitational increase is kept below a certain limit, growth was greater than that of controls in the fruit fly, turtle, mouse, and chicken. The limit below which enhancement of growth was observed varied with the species studied.
The data on food intake do not present a consistent picture. Wunder ([ref.94]) found that food intake in accelerated mice was markedly reduced from that of nonaccelerated control animals. Smith, however, found that in chickens, food intake increased up to 36 percent over controls and has derived an exponential relation between food intake and acceleration. After six generations of selective breeding, Smith has produced a strain of chickens better adapted to prolonged exposure to high g.
A very relevant finding of their research with birds was that exposure to chronic acceleration in some way appears to interfere with habituation to rotatory stimulation. Chickens who were being subjected to chronic acceleration were given repeated rotatory stimulation tests to estimate their labyrinthine sensitivity. This study revealed that centrifuged animals showed a marked reduction in labyrinthine sensitivity. This result appeared to persist after the acceleration was terminated. In animals who developed gait or postural difficulties as a result of acceleration, there was no evidence of a postnystagmus in response to the rotatory stimulation test, which the investigators point out may be evidence of a lesion in the labyrinth or its neural pathways.
Smith has implicated social factors as interfering with acceleration effects. His subjects were typically accelerated four or six to a cage.
When groups were mixed midway through the experiment, they exhibited a higher mortality rate and incidence of acceleration symptoms than did groups whose const.i.tuency remained unchanged.
At the U.S. Naval School of Aeros.p.a.ce Medicine, numerous studies have been conducted on the effects of slow rotation on the behavior and physiology of humans and animals ([ref.100]). Rotation initially produces decrements in performance, but adaptation to a rotating environment ensues quite rapidly (refs. [ref.101]-[ref.103]). Perceptual distortion, nystagmus, nausea, and other signs of discomfort are common responses to slow rotation. These symptoms are generally reduced with continued exposure (adaptation). Interestingly, however, adaptation is delayed when the subjects are exposed to a fixed reference outside their rotating environment.
At NASA-Ames, rodents have been used in experiments by Weissman and Seldeen to delimit the stimulus effects of rotation. In these experiments the subjects must discriminate between different speeds of rotation in order to obtain food reinforcement. The results thus far provide evidence that these animals are capable of discriminating between the different speeds at which they are being rotated. The range of speeds studied was 0-25 rpm, with tests of discrimination being made at intervals of less than 5 rpm. Experiments such as these will lead to the development of techniques for measuring rotational sensitivity in many species, including man.
The optimum configuration of manned s.p.a.cecraft will depend, in part, upon biomedical considerations. A voluminous literature now exists on the possible hazards to man of prolonged exposure to zero-g conditions.
Should prolonged weightlessness prove to be a serious detriment to health, consideration must be given to design concepts which provide artificial gravity.
No data exist on the minimum gravity requirements necessary to sustain basic biological functions for extended periods. A limit of 0.2 g has been given as the lower level at which man can walk unaided ([ref.104]).
It has also been recommended that angular velocity be maintained at the lowest possible level in order to minimize the occurrence of vestibular disturbances. These recommendations are based on human-factor requirements, rather than upon biological considerations, which may significantly modify these values. In recent studies, a technique has been devised which promises to provide reliable criteria for biological acceptability, since it is based on fundamental biological and behavioral principles.
As animals progress up the evolutionary stale, their survival depends less and less upon stereotyped physiological reactions which occur in reflex fashion, in response to environmental stimulation. In higher organisms, survival depends more upon the capacity of organisms to modify their behavior. At the highest levels of functional efficiency, the ultimate form of adaptation is seen-the manipulation of the environment by the organism. Developments in behavioral science now permit us to utilize the adaptive behavior of animals to investigate many problems of biological interest. Recent studies on the self-selection of gravity levels represent a further attempt to exploit the adaptive capacities of animals, in order to provide information relevant to problems of s.p.a.ce exploration.
One such project allows animals to select their own gravity environment in an apparatus designed to create g-forces through centrifugal action by rotation at 60 rpm ([ref.105]). The surface of this centrifuge is parabolic, so that the resultant of the centrifugal g and the Earth"s gravity is always normal to the surface. When the animal moves away from the center, increasing the radius of rotation, it is exposed to increasing gravity. Motion toward the center reduces the gravity level.
By this means, an animal is free to select its own gravity environment.
When the animal moves toward or away from the center, he is moving from one tangential velocity to another. He is therefore acted upon by a third force-due to Coriolis acceleration. The effects of Coriolis forces are a major problem difficult to eliminate in studies such as these, but they must be taken into account in the design of s.p.a.cecraft which produce artificial gravity by rotation. Motion of the head in any direction not parallel to the centrifugal force vector would result in bizarre stimulation of the semicircular ca.n.a.ls and consequent motion sickness. This effect is likely to become even more p.r.o.nounced if the sensitivity of these organs is increased by prolonged exposure to reduced gravity. Methods such as these are currently being developed for conducting a refined psychophysical a.n.a.lysis of gravity, including studies by Lange and Broderson on the perception of angular, linear, and Coriolis acceleration.
The results of animal studies such as these will be of great value in arriving at a decisive judgment concerning the need for artificial gravity in a manned orbiting s.p.a.ce station, or other vehicles designed for long-term occupancy.
To aid in the interpretation of in-flight data, other studies are underway to determine the functions of the vestibular system, as a princ.i.p.al brain center related to orientation in s.p.a.ce and to the physiology of posture and movement, as well as with the influences of acceleration, rotation, and weightlessness. Experiments are presently being conducted on monkeys and cats in order to trace these complex neurological connections and to determine their functional organization.
BIOLOGICAL INFORMATION SYSTEMS
The nature of memory has been the subject of considerable speculation in the past. It has long been felt intuitively that retention of information in the central nervous system involves either an alteration of preexisting material or structure, or, alternatively, synthesis of materials not present previously. The cellular site of operational alteration was unknown but, again intuitively, was felt to be closely a.s.sociated with the synapses. The problems faced by early investigators were great; but nevertheless much information relevant to the question of biological information storage was obtained. With the relatively recent advent of more refined tools and methodologies, there has been rapid progress.