- Email: [email protected]
Neurosciences research in space Future directions
Acta Astronautica Vol. 23, pp. 289-293, 1991 Printed in Great Britain
0094-5765/91 $3.00+ 0.00 Pergamon Press plc
Neurosciences Research in Space: Future Directions
Frank M. Sulzman, Ph.D. Chief, Space Medicine and Biology Branch NASA Headquarters Washington, D.C. James W. Wolfe, Ph.D. Visiting Senior Scientist NASA Headquarters Washington, D.C. ABSTRACT Future research in the neurosciences can best be understood in the context of NASA's life sciences goals in the near term (1990-95), mid term (1995-2000), and long term (2000 and beyond). Since NASA is planning short-duration Spacelab and International Microgravity Laboratory (IML) flights for many years to come, the acute effects of exposure to microgravity will continue to be of experimental and operational interest in the near term. To this end, major new areas of research will be devoted to ground-based studies of preflight adaptation trainers and their efficacy in preventing or reducing the incidence of space motion sickness. In addition, an extensive series of studies of the vestibular system will be conducted inflight on the IML-1 mission The IML-2 mission will emphasize behavior and performance, biological rhythms, and further vestibular studies. In the mid-term period, Spacelab missions will employ new technology such as magnetic recording techniques in order to evaluate changes in the processing of sensory and motor inputs at the brainstem and cortical level during exposure to microgravity. Two Space Life Sciences (SLS) missions planned for the mid to late 1990's, SLS-4 and SLS-5, will utilize an onboard centrifuge facility that will enable investigators to study the effects of partial gravity on sensory and motor function. In the long term (2000 and beyond), Space Station Freedom and long-duration missions will provide opportunities to explore new options in the neurosciences, such as sensory substitution and augmentation, through the use of physical sensors to provide three-dimensional tactile-visual, tactile-auditory and tactile-somatosensory inputs. The use of this technology will be extremely important in the area of robotic telepresence. Finally, Space Station Freedom and proposed LifeSat missions will provide neuroscientists the opportunity to study the effects of partial gravity and microgravity on neuronal plasticity. NEAR-TERM (199Q-1995~ In the area of neurosciences, near-term research will be directed at a further understanding of the acute effects of microgravity and the so-called "space adaptation syndrome." On Spacelab Life Sciences 1, scheduled for launch in June 1990, experiments designed to evaluate changes in the visual, vestibular and proprioceptive systems will be conducted. An extensive sedes of experiments, collectively termed Microgravity Vestibular Investigations (MVI) and related to these same areas, is planned for the IML-1 mission to be flown in 1992.
289
290
FRANK M. SULZMANand JAMESW. WOLFE
Microoravitv Vestibular Investioations The MVI, under the direction of Dr. M. Reschke of Johnson Space Center, will be guided by seven major functional objectives, which will be accomplished by the crew during the 8- to 9-day mission. Experiment hardware consisting of a humanrated DC torque motor turntable, optokinetic stimulator, video and electro-oculographic eye recording systems, and software for analyzing vestibulo-ocular responses will be flown. Although there have been numerous vestibular studies on Soviet and American space missions, it is still not clear, from a quantitative standpoint, what changes occur in the vestibular and visual oculomotor system during adaptation to microgravity. One of the major objectives of these studies will be to evaluate changes in semicircular canal dynamics using a pseudorandom profile to drive the rotator over a decade of discrete frequencies between 0.1 and 1.0 Hz. The subjects will be stimulated in both the pitch and yaw orientations; eye movements will be recorded with eyes open in the dark with simultaneous horizontal and vertical electro-oculography and video camera. These data will be analyzed to determine changes in the phase, gain, and coherence of the VOR during adaptation to microgravity. Additional experiments will evaluate vestibulo-ocular reflex suppression, pre-rotatory and postrotatory time constants, optokinetic and optokinetic after-nystagmus, responses to voluntarily paced head movements, visual-vestibular interactions during sinusoidal oscillation, and formal reporting of motion-sickness symptoms. Preflight Adaotation Trainer (PAT~ A major question that still remains unanswered is whether individuals can be pre-adapted to some of the visual-vestibular conflicts that occur in the weightless environment. Since it appears that changes in otolithic input and subsequent reinterpretation of responses to head tilt lead to changes in visual perception and play a role in the space adaptation syndrome (Parker et al., 1985), the question arises as to whether these sensory rearrangements can be simulated in a 1-g environment. Furthermore, is it possible to demonstrate these phenomena and, through training, modify sensorimotor reflexes prior to space flight? In this regard, NASA has initiated a Preflight Adaptation Trainer (PAT) project, which has as its goal the development and validation of a series of trainers to simulate the rearrangement of stimuli in weightlessness. MID-TERM (1995-2000) Centrifuge Research Facilitv The Centrifuge Facility comprises a suite of equipment designed to support living specimens for long-term life sciences research in space on Space Station Freedom. It is well known that exposure to microgravity produces an array of biochemical and physiological changes in plants and animals, and that these changes extend from the cellular to the whole organism level. SLS-4 and SLS-5 will provide opportunities for extensive studies in these areas prior to the launch of Space Station Freedom. In order to manipulate gravity as an experimental variable and separate the effects of weightlessness from the other variables in space flight, it is essential to provide a 1-g control environment through the use of an on-board centrifuge. The Centrifuge Facility, as it is currently being developed, consists of a 1.8- to 2.4-meter diameter centrifuge capable of housing a variety of specimens from plants to small primates, habitat modules for housing the specimens both on and off the centrifuge, and a special glovebox and workstation that can be used for experimental purposes as well as transferring specimens between habitats. In the neurosciences, early studies will emphasize research in such areas as biological rhythms and behavior that can be monitored by implanted and totally isolated devices. It is anticipated that advances in miniaturization will eventually make it possible to obtain chronic neural recordings from single cells within the central nervous system in the intact animal. The Centrifuge Facility will also allow investigators to study the effects of varying gravity levels on the morphology and development of central nervous system structures.
8th IAA Man in Space Symposium
Magnetic Recor~lina of Evoked Potentials Superconducting quantum interference devices (SQUID) allow for localizing neuronal activity within the brain through the recording of extracranial magnetic field patterns which are generated discreetly in response to controlled stimuli. Localizing neuronal activity within the brain through the recording of extracranial magnetic fields offers an advantage in that noninvasive recordings from subcortical and cortical structures can be obtained simultaneously. Presently, commercially available systems have a position accuracy better than 3 mm for a current dipole 3 cm beneath the surface of the brain. SQUIDs have evolved from large single-channel recording devices to multiple detection systems with up to 26 channels. In the past few years, Los Alamos National Laboratory has developed a new gradiometer design that automatically provides shielding from external background fields by a factor of 100,000 or more. This advance in SQUID technology means that the requirement for a magnetically shielded room is eliminated. Photolithography techniques may be used to make the coils, eliminating the need to individually balance gradiometer coils. It is also anticipated that advances in high temperature superconductors will make it possible to eliminate the helium cooling requirement. Thus, it is highly probable that a low-cost and portable system will be available for research in space. The application of this technology will be extremely powerful in the evaluation of changes in the processing of sensory and motor information during long-term exposure to microgravity. Such studies will lead to a clearer understanding of how the central nervous system adapts to unique stimuli and the role that gravity plays in modifying sensorimotor responses. LONG-TERM (2000 -->) Neuronal Plasticity It has been known for many years that sensory deprivation and the loss of afferent input can lead to dramatic changes in the density of neurons and synaptic connections. Early studies using visual deprivation (Fifkova, 1970) demonstrated that the size of synaptic contacts could be modified by changes in the visual environment. In 1972, West and Greenough were able to show that an enriched environment led to an increase in the size of synaptic specializations. Based on these and numerous other studies, Hiilman and Chen (1985, p. 40) proposed that "functional recovery following perturbations appears to be due mainly to compensations in circuitry that improve the efficacy of remaining neuronal elements. Sprouting of axons and the formation of new synapses may achieve this end, yet numerous other factors potentially also modulate the efficacy of synaptic transmission." In an extensive series of studies of deafferentation of the cerebellum, Hillman and Chen (1981a; 1981b; 1981c; 1984) were able to show that changes in the size of the synapses could occur within hours after interruption of the inputs and were visible after 24 hours. However, functional deficits due to lesions of the cerebellum were not seen until there was a marked reduction (40 percent) in neurons, and the effects were not obvious until the deficit went beyond 65 percent. Based on this evidence, the question arises as to the possible effects of microgravity on synaptic and neuronal plasticity. Since microgravity leads to a loss of normal afferent input to the vestibular, proprioceptive and somatosensory systems, can long-term exposure to microgravity lead to neuronal degenertion and synap~ic rearrangement within these systems? This question may also be relevant for organisms living in a partial gravity environment such as on the Moon or a Mars base. It is also of concern that the compensation that occurs in response to stimulus deprivation masks the loss of function until a critical number of cells are lost. These observations are somewhat similar to the development of Alzheimer's disease or senility, or even mild strokes. The deficit is masked until a critical level of neuronal loss can no longer be compensated for. Since neuronal loss is a normal consequence of aging, it will become very important to determine if exposure to microgravity may accelerate this process for those sensory and motor systems deprived of a normal afferent input. Therefore, future studies using both ground-based simulations and Spacelab experiments will need to address the effects of long-duration exposure to microgravity on neuronal plasticity.
291
292
FRANK M. SULZMANand JAMESW. WOLFE
Sensorv Substitution. Auementation. and Robotic Teleoresence Sensory substitution is related to the fact that higher organisms, through neuronal plasticity, can integrate and interpret information provided to one sensory modality to represent another sensory input. Specific examples include sign language for the deaf and Braille for the blind. During the past two decades, extensive research has been conducted by Bach-y-Rita et al. (1969; 1972; 1985) in the development of tactile vision substitution systems for the blind. These systems employ an optical display which is transduced to a form of stimulation that can activate the skin receptors. Due to the plasticity of the nervous system, "the subjective localization of the information obtained through the television camera is not on the skin; it is accurately located in the three-dimensional space in front of the camera, whether the skin stimulation matrix is placed on the back, on the abdomen, on the thigh, or changed from one of these body locations to another" (Bach-y-Rita et al., p. 51-52, 1987). Subsequently, a tactile-auditory substitution system was developed and is now available commercially (Tacticon). More recently, Bach-y-Rita and Collins (1982) developed a tactile somatosensory substitution system that provides tactile information to leprosy patients with insensate hands. "Within a few hours of training, it was possible to locate the sensation on the fingertips, and it was possible to identify various textures. As with the tactile vision substitution system, correct subjective localization (in this case to the fingertips) required active control of movement by the subject" (Bach-y-Rita et. al., 1987, p. 52). Based on the success of this line of research with clinical patients, NASA has funded research directed at the development of a space suit glove sensory substitution system and the application of this technology to space robots. Development of the space suit glove is based on the hypothesis that sensory information in response to active hand movement would be subjectively located in the hand, even though the information arrives at another location on the body, such as the skin of the abdomen or arm. In the area of robotic telepresence, "when a robot's hand closes on an object, the astronaut's hand inside the controlling glove would feel the same mechanical resistance through proprioception...The astronaut would receive direct position feedback of robot joint angles from his own joint receptors. He would receive direct force feedback of robot forces from his own muscle and tendon receptors." (Bach-yRita et al., 1987, p. 56). The potential for further refinement and application of this technology to future space missions is extremely promising. The development of more sophisticated transducers and software to control input-output relationships will make it possible to achieve Orwell's world of "feelies"; the capability of being able to provide proprioceptive and somatosensory information through sensory substitution would undoubtedly enhance one's capability to endure long-duration space missions. In conclusion, to gain a better understanding of the effects of long-duration missions on the central nervous system, it is imperative that both ground-based studies and studies in microgravity be conducted using the latest technology available to the neuroscientists. REFERENCES Bach-y-Rita, P., C.C. Collins, F. Saunders, B. White and L. Scadden. Vision substitution by tactile image projection. Nature, 221:963-964, 1969. Bach-y-Rita, P., Brain Mechanisms In Sensorv Substitution. New York, Academic Press, 1972. Bach-y-Rita, P., and B. Hughes. Tactile vision substitution: Some instrumentation and perceptual considerations. In: Warren, C., and Strelow, E. editors: . ~ ( t ~ l g ~ , , _ ~ Sensina for the Blind. Dordrecht, The Netherlands, 1985. Bach-y-Rita, P., J.G. Webster, W.J. Tompkins and T. Crabb. Sensory substitution for space gloves and for space robots, proceedings of the Workshoo on Soace TQlerobotics. Vol. II, 51-57, 1987. Fifkova, E. The effect of monocular deprivation on the synaptic contacts of the visual cortex. J. Neurobiol., 1:285-295, 1970.
8th IAA Man in Space Symposium
Hillman, D.E., and Chen, S. Plasticity of synaptic size with constancy of total synaptic contact area on Purkinje cells in the cerebellum. In: Vidrio, F.A., and. Galina, M.A. (editors), 8vmoosia Proceedings of the 11th International Conaress of Anatomy (pp. 229-245). New York: Alan R. Liss, 1981a. Hillman, D.E., and Chen, S. Vulnerability of cerebellar development in malnutrition. I. Quantitation of layer volume and neuron numbers. Neuroscience. 6:1249-1262. 1981b. Hillman, D.E., and Chen. S. Vulnerability of cerebellar development in malnutrition. II. Intrinsic determination of total synaptic areas on Purkinje cell spines. Neuroscience, 6:1263-1275 1981 c. Hillman, D.E., and Chen, S. Reciprocal relationship between size of postsynaptic densities and their number: constancy in contact area. Brain Research. 295:325-343, 1984. Hillman, D.E., and Chen, S. Plasticity in the size of presynaptic and postsynaptic membrane specializations. In: C.W. Cotman, editor: Svnaotic Plasticitv. Guilford Press, New York, NY, 1985. Parker, D.E., Reschke, M.F., Arrott, A.P., Homick, J.L. and Lichtenberg, B.K.. Otolith tilttranslation reinterpretation following prolonged weightlessness: Implications for preflight training, Aviat. Soace Environ. Med., 56:601, 1985. West, R.W. and Greenough, W.T. Effects of environmental complexity on cortical synapse of rats: Preliminary results. Behav. Biol., 7:279-284, 1972. ACKNOWLEDGEMENTS The authors thank Drs. Flynn, Hillman, Parker, and Reschke and Ms. Vitcenda for providing information and materials for this presentation, and Mr. Ron Teeter for editing and Ms. Kim Walker for typing the manuscript.
293
0094-5765/91 $3.00+ 0.00 Pergamon Press plc
Neurosciences Research in Space: Future Directions
Frank M. Sulzman, Ph.D. Chief, Space Medicine and Biology Branch NASA Headquarters Washington, D.C. James W. Wolfe, Ph.D. Visiting Senior Scientist NASA Headquarters Washington, D.C. ABSTRACT Future research in the neurosciences can best be understood in the context of NASA's life sciences goals in the near term (1990-95), mid term (1995-2000), and long term (2000 and beyond). Since NASA is planning short-duration Spacelab and International Microgravity Laboratory (IML) flights for many years to come, the acute effects of exposure to microgravity will continue to be of experimental and operational interest in the near term. To this end, major new areas of research will be devoted to ground-based studies of preflight adaptation trainers and their efficacy in preventing or reducing the incidence of space motion sickness. In addition, an extensive series of studies of the vestibular system will be conducted inflight on the IML-1 mission The IML-2 mission will emphasize behavior and performance, biological rhythms, and further vestibular studies. In the mid-term period, Spacelab missions will employ new technology such as magnetic recording techniques in order to evaluate changes in the processing of sensory and motor inputs at the brainstem and cortical level during exposure to microgravity. Two Space Life Sciences (SLS) missions planned for the mid to late 1990's, SLS-4 and SLS-5, will utilize an onboard centrifuge facility that will enable investigators to study the effects of partial gravity on sensory and motor function. In the long term (2000 and beyond), Space Station Freedom and long-duration missions will provide opportunities to explore new options in the neurosciences, such as sensory substitution and augmentation, through the use of physical sensors to provide three-dimensional tactile-visual, tactile-auditory and tactile-somatosensory inputs. The use of this technology will be extremely important in the area of robotic telepresence. Finally, Space Station Freedom and proposed LifeSat missions will provide neuroscientists the opportunity to study the effects of partial gravity and microgravity on neuronal plasticity. NEAR-TERM (199Q-1995~ In the area of neurosciences, near-term research will be directed at a further understanding of the acute effects of microgravity and the so-called "space adaptation syndrome." On Spacelab Life Sciences 1, scheduled for launch in June 1990, experiments designed to evaluate changes in the visual, vestibular and proprioceptive systems will be conducted. An extensive sedes of experiments, collectively termed Microgravity Vestibular Investigations (MVI) and related to these same areas, is planned for the IML-1 mission to be flown in 1992.
289
290
FRANK M. SULZMANand JAMESW. WOLFE
Microoravitv Vestibular Investioations The MVI, under the direction of Dr. M. Reschke of Johnson Space Center, will be guided by seven major functional objectives, which will be accomplished by the crew during the 8- to 9-day mission. Experiment hardware consisting of a humanrated DC torque motor turntable, optokinetic stimulator, video and electro-oculographic eye recording systems, and software for analyzing vestibulo-ocular responses will be flown. Although there have been numerous vestibular studies on Soviet and American space missions, it is still not clear, from a quantitative standpoint, what changes occur in the vestibular and visual oculomotor system during adaptation to microgravity. One of the major objectives of these studies will be to evaluate changes in semicircular canal dynamics using a pseudorandom profile to drive the rotator over a decade of discrete frequencies between 0.1 and 1.0 Hz. The subjects will be stimulated in both the pitch and yaw orientations; eye movements will be recorded with eyes open in the dark with simultaneous horizontal and vertical electro-oculography and video camera. These data will be analyzed to determine changes in the phase, gain, and coherence of the VOR during adaptation to microgravity. Additional experiments will evaluate vestibulo-ocular reflex suppression, pre-rotatory and postrotatory time constants, optokinetic and optokinetic after-nystagmus, responses to voluntarily paced head movements, visual-vestibular interactions during sinusoidal oscillation, and formal reporting of motion-sickness symptoms. Preflight Adaotation Trainer (PAT~ A major question that still remains unanswered is whether individuals can be pre-adapted to some of the visual-vestibular conflicts that occur in the weightless environment. Since it appears that changes in otolithic input and subsequent reinterpretation of responses to head tilt lead to changes in visual perception and play a role in the space adaptation syndrome (Parker et al., 1985), the question arises as to whether these sensory rearrangements can be simulated in a 1-g environment. Furthermore, is it possible to demonstrate these phenomena and, through training, modify sensorimotor reflexes prior to space flight? In this regard, NASA has initiated a Preflight Adaptation Trainer (PAT) project, which has as its goal the development and validation of a series of trainers to simulate the rearrangement of stimuli in weightlessness. MID-TERM (1995-2000) Centrifuge Research Facilitv The Centrifuge Facility comprises a suite of equipment designed to support living specimens for long-term life sciences research in space on Space Station Freedom. It is well known that exposure to microgravity produces an array of biochemical and physiological changes in plants and animals, and that these changes extend from the cellular to the whole organism level. SLS-4 and SLS-5 will provide opportunities for extensive studies in these areas prior to the launch of Space Station Freedom. In order to manipulate gravity as an experimental variable and separate the effects of weightlessness from the other variables in space flight, it is essential to provide a 1-g control environment through the use of an on-board centrifuge. The Centrifuge Facility, as it is currently being developed, consists of a 1.8- to 2.4-meter diameter centrifuge capable of housing a variety of specimens from plants to small primates, habitat modules for housing the specimens both on and off the centrifuge, and a special glovebox and workstation that can be used for experimental purposes as well as transferring specimens between habitats. In the neurosciences, early studies will emphasize research in such areas as biological rhythms and behavior that can be monitored by implanted and totally isolated devices. It is anticipated that advances in miniaturization will eventually make it possible to obtain chronic neural recordings from single cells within the central nervous system in the intact animal. The Centrifuge Facility will also allow investigators to study the effects of varying gravity levels on the morphology and development of central nervous system structures.
8th IAA Man in Space Symposium
Magnetic Recor~lina of Evoked Potentials Superconducting quantum interference devices (SQUID) allow for localizing neuronal activity within the brain through the recording of extracranial magnetic field patterns which are generated discreetly in response to controlled stimuli. Localizing neuronal activity within the brain through the recording of extracranial magnetic fields offers an advantage in that noninvasive recordings from subcortical and cortical structures can be obtained simultaneously. Presently, commercially available systems have a position accuracy better than 3 mm for a current dipole 3 cm beneath the surface of the brain. SQUIDs have evolved from large single-channel recording devices to multiple detection systems with up to 26 channels. In the past few years, Los Alamos National Laboratory has developed a new gradiometer design that automatically provides shielding from external background fields by a factor of 100,000 or more. This advance in SQUID technology means that the requirement for a magnetically shielded room is eliminated. Photolithography techniques may be used to make the coils, eliminating the need to individually balance gradiometer coils. It is also anticipated that advances in high temperature superconductors will make it possible to eliminate the helium cooling requirement. Thus, it is highly probable that a low-cost and portable system will be available for research in space. The application of this technology will be extremely powerful in the evaluation of changes in the processing of sensory and motor information during long-term exposure to microgravity. Such studies will lead to a clearer understanding of how the central nervous system adapts to unique stimuli and the role that gravity plays in modifying sensorimotor responses. LONG-TERM (2000 -->) Neuronal Plasticity It has been known for many years that sensory deprivation and the loss of afferent input can lead to dramatic changes in the density of neurons and synaptic connections. Early studies using visual deprivation (Fifkova, 1970) demonstrated that the size of synaptic contacts could be modified by changes in the visual environment. In 1972, West and Greenough were able to show that an enriched environment led to an increase in the size of synaptic specializations. Based on these and numerous other studies, Hiilman and Chen (1985, p. 40) proposed that "functional recovery following perturbations appears to be due mainly to compensations in circuitry that improve the efficacy of remaining neuronal elements. Sprouting of axons and the formation of new synapses may achieve this end, yet numerous other factors potentially also modulate the efficacy of synaptic transmission." In an extensive series of studies of deafferentation of the cerebellum, Hillman and Chen (1981a; 1981b; 1981c; 1984) were able to show that changes in the size of the synapses could occur within hours after interruption of the inputs and were visible after 24 hours. However, functional deficits due to lesions of the cerebellum were not seen until there was a marked reduction (40 percent) in neurons, and the effects were not obvious until the deficit went beyond 65 percent. Based on this evidence, the question arises as to the possible effects of microgravity on synaptic and neuronal plasticity. Since microgravity leads to a loss of normal afferent input to the vestibular, proprioceptive and somatosensory systems, can long-term exposure to microgravity lead to neuronal degenertion and synap~ic rearrangement within these systems? This question may also be relevant for organisms living in a partial gravity environment such as on the Moon or a Mars base. It is also of concern that the compensation that occurs in response to stimulus deprivation masks the loss of function until a critical number of cells are lost. These observations are somewhat similar to the development of Alzheimer's disease or senility, or even mild strokes. The deficit is masked until a critical level of neuronal loss can no longer be compensated for. Since neuronal loss is a normal consequence of aging, it will become very important to determine if exposure to microgravity may accelerate this process for those sensory and motor systems deprived of a normal afferent input. Therefore, future studies using both ground-based simulations and Spacelab experiments will need to address the effects of long-duration exposure to microgravity on neuronal plasticity.
291
292
FRANK M. SULZMANand JAMESW. WOLFE
Sensorv Substitution. Auementation. and Robotic Teleoresence Sensory substitution is related to the fact that higher organisms, through neuronal plasticity, can integrate and interpret information provided to one sensory modality to represent another sensory input. Specific examples include sign language for the deaf and Braille for the blind. During the past two decades, extensive research has been conducted by Bach-y-Rita et al. (1969; 1972; 1985) in the development of tactile vision substitution systems for the blind. These systems employ an optical display which is transduced to a form of stimulation that can activate the skin receptors. Due to the plasticity of the nervous system, "the subjective localization of the information obtained through the television camera is not on the skin; it is accurately located in the three-dimensional space in front of the camera, whether the skin stimulation matrix is placed on the back, on the abdomen, on the thigh, or changed from one of these body locations to another" (Bach-y-Rita et al., p. 51-52, 1987). Subsequently, a tactile-auditory substitution system was developed and is now available commercially (Tacticon). More recently, Bach-y-Rita and Collins (1982) developed a tactile somatosensory substitution system that provides tactile information to leprosy patients with insensate hands. "Within a few hours of training, it was possible to locate the sensation on the fingertips, and it was possible to identify various textures. As with the tactile vision substitution system, correct subjective localization (in this case to the fingertips) required active control of movement by the subject" (Bach-y-Rita et. al., 1987, p. 52). Based on the success of this line of research with clinical patients, NASA has funded research directed at the development of a space suit glove sensory substitution system and the application of this technology to space robots. Development of the space suit glove is based on the hypothesis that sensory information in response to active hand movement would be subjectively located in the hand, even though the information arrives at another location on the body, such as the skin of the abdomen or arm. In the area of robotic telepresence, "when a robot's hand closes on an object, the astronaut's hand inside the controlling glove would feel the same mechanical resistance through proprioception...The astronaut would receive direct position feedback of robot joint angles from his own joint receptors. He would receive direct force feedback of robot forces from his own muscle and tendon receptors." (Bach-yRita et al., 1987, p. 56). The potential for further refinement and application of this technology to future space missions is extremely promising. The development of more sophisticated transducers and software to control input-output relationships will make it possible to achieve Orwell's world of "feelies"; the capability of being able to provide proprioceptive and somatosensory information through sensory substitution would undoubtedly enhance one's capability to endure long-duration space missions. In conclusion, to gain a better understanding of the effects of long-duration missions on the central nervous system, it is imperative that both ground-based studies and studies in microgravity be conducted using the latest technology available to the neuroscientists. REFERENCES Bach-y-Rita, P., C.C. Collins, F. Saunders, B. White and L. Scadden. Vision substitution by tactile image projection. Nature, 221:963-964, 1969. Bach-y-Rita, P., Brain Mechanisms In Sensorv Substitution. New York, Academic Press, 1972. Bach-y-Rita, P., and B. Hughes. Tactile vision substitution: Some instrumentation and perceptual considerations. In: Warren, C., and Strelow, E. editors: . ~ ( t ~ l g ~ , , _ ~ Sensina for the Blind. Dordrecht, The Netherlands, 1985. Bach-y-Rita, P., J.G. Webster, W.J. Tompkins and T. Crabb. Sensory substitution for space gloves and for space robots, proceedings of the Workshoo on Soace TQlerobotics. Vol. II, 51-57, 1987. Fifkova, E. The effect of monocular deprivation on the synaptic contacts of the visual cortex. J. Neurobiol., 1:285-295, 1970.
8th IAA Man in Space Symposium
Hillman, D.E., and Chen, S. Plasticity of synaptic size with constancy of total synaptic contact area on Purkinje cells in the cerebellum. In: Vidrio, F.A., and. Galina, M.A. (editors), 8vmoosia Proceedings of the 11th International Conaress of Anatomy (pp. 229-245). New York: Alan R. Liss, 1981a. Hillman, D.E., and Chen, S. Vulnerability of cerebellar development in malnutrition. I. Quantitation of layer volume and neuron numbers. Neuroscience. 6:1249-1262. 1981b. Hillman, D.E., and Chen. S. Vulnerability of cerebellar development in malnutrition. II. Intrinsic determination of total synaptic areas on Purkinje cell spines. Neuroscience, 6:1263-1275 1981 c. Hillman, D.E., and Chen, S. Reciprocal relationship between size of postsynaptic densities and their number: constancy in contact area. Brain Research. 295:325-343, 1984. Hillman, D.E., and Chen, S. Plasticity in the size of presynaptic and postsynaptic membrane specializations. In: C.W. Cotman, editor: Svnaotic Plasticitv. Guilford Press, New York, NY, 1985. Parker, D.E., Reschke, M.F., Arrott, A.P., Homick, J.L. and Lichtenberg, B.K.. Otolith tilttranslation reinterpretation following prolonged weightlessness: Implications for preflight training, Aviat. Soace Environ. Med., 56:601, 1985. West, R.W. and Greenough, W.T. Effects of environmental complexity on cortical synapse of rats: Preliminary results. Behav. Biol., 7:279-284, 1972. ACKNOWLEDGEMENTS The authors thank Drs. Flynn, Hillman, Parker, and Reschke and Ms. Vitcenda for providing information and materials for this presentation, and Mr. Ron Teeter for editing and Ms. Kim Walker for typing the manuscript.
293