Neuroscience In Space
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Space neuroscience or astroneuroscience is the scientific study of the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...
(CNS) functions during
spaceflight Spaceflight (or space flight) is an application of astronautics to fly objects, usually spacecraft, into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such ...
.
Living systems Living systems are life forms (or, more colloquially known as living things) treated as a system. They are said to be open self-organizing and said to interact with their environment. These systems are maintained by flows of information, energy an ...
can integrate the inputs from the
senses A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of stimuli. Although, in some cultures, five human senses were traditionally identified as su ...
to navigate in their environment and to coordinate
posture Posture or posturing may refer to: Medicine * List of human positions ** Abnormal posturing, in neurotrauma **Spinal posture * Posturography, in neurology Other uses * Posture (psychology) * Political posturing Political posturing, also known a ...
, locomotion, and
eye movements Eye movement includes the voluntary or involuntary movement of the eyes. Eye movements are used by a number of organisms (e.g. primates, rodents, flies, birds, fish, cats, crabs, octopus) to fixate, inspect and track visual objects of i ...
.
Gravity In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...
has a fundamental role in controlling these functions. In
weightlessness Weightlessness is the complete or near-complete absence of the sensation of weight, i.e., zero apparent weight. It is also termed zero g-force, or zero-g (named after the g-force) or, incorrectly, zero gravity. Weight is a measurement of the fo ...
during spaceflight, integrating the sensory inputs and coordinating motor responses is harder to do because gravity is no longer sensed during
free-fall In classical mechanics, free fall is any motion of a body where gravity is the only force acting upon it. A freely falling object may not necessarily be falling down in the vertical direction. If the common definition of the word "fall" is used, ...
. For example, the
otolith An otolith (, ' ear + , ', a stone), also called otoconium, statolith, or statoconium, is a calcium carbonate structure in the saccule or utricle (ear), utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule ...
organs of the
vestibular system The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating motor coordination, movement with balance. Together with the cochlea, a part of the auditory sys ...
no longer signal head tilt relative to gravity when
standing Standing, also referred to as orthostasis, is a position in which the body is held in an upright (orthostatic) position and supported only by the feet. Although seemingly static, the body rocks slightly back and forth from the ankle in the ...
. However, they can still sense head translation during body motion. Ambiguities and changes in how the gravitational input is processed can lead to potential errors in
perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous syste ...
, which affects
spatial orientation In geometry, the orientation, attitude, bearing, direction, or angular position of an object – such as a line, plane or rigid body – is part of the description of how it is placed in the space it occupies. More specifically, it refers to t ...
and
mental representation A mental representation (or cognitive representation), in philosophy of mind, cognitive psychology, neuroscience, and cognitive science, is a hypothetical internal cognitive symbol that represents external reality or its abstractions. Mental re ...
. Dysfunctions of the
vestibular system The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating motor coordination, movement with balance. Together with the cochlea, a part of the auditory sys ...
are common during and immediately after spaceflight, such as space motion sickness in orbit and
balance disorder A balance disorder is a disturbance that causes an individual to feel unsteady, for example when standing or walking. It may be accompanied by feelings of giddiness, or wooziness, or having a sensation of movement, spinning, or floating. Equilibr ...
s after return to Earth. Adaptation to
weightlessness Weightlessness is the complete or near-complete absence of the sensation of weight, i.e., zero apparent weight. It is also termed zero g-force, or zero-g (named after the g-force) or, incorrectly, zero gravity. Weight is a measurement of the fo ...
involves not just the
Sensory-motor coupling Sensory-motor coupling is the coupling or integration of the sensory system and motor system. For a given stimulus, there is no one single motor command. "Neural responses at almost every stage of a sensorimotor pathway are modified at short and l ...
functions, but some
autonomic nervous system The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates viscera, internal organs, smooth muscle and glands. The autonomic nervo ...
functions as well.
Sleep disorders A sleep disorder, or somnipathy, is a medical disorder affecting an individual's sleep patterns, sometimes impacting physical, mental, social, and emotional functioning. Polysomnography and actigraphy are tests commonly ordered for diagnosing sle ...
and
orthostatic intolerance Orthostatic intolerance (OI) is the development of symptoms when standing upright that are relieved when reclining. There are many types of orthostatic intolerance. OI can be a subcategory of dysautonomia, a disorder of the autonomic nervous ...
are also common during and after spaceflight. There is no
hydrostatic pressure Hydrostatics is the branch of fluid mechanics that studies fluids at hydrostatic equilibrium and "the pressure in a fluid or exerted by a fluid on an immersed body". The word "hydrostatics" is sometimes used to refer specifically to water and o ...
in a weightless environment. As a result, the redistribution of body fluids toward the upper body causes a decrease in leg volume, which may affect
muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...
viscosity Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...
and compliance. An increase in
intracranial pressure Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury ( mmHg) and at rest, is normally 7–15 mmHg for a supine adu ...
may also be responsible for a decrease in near
visual acuity Visual acuity (VA) commonly refers to the clarity of visual perception, vision, but technically rates an animal's ability to recognize small details with precision. Visual acuity depends on optical and neural factors. Optical factors of the eye ...
. In addition, muscle mass and strength both decrease as a result of the reduced loading in
weightlessness Weightlessness is the complete or near-complete absence of the sensation of weight, i.e., zero apparent weight. It is also termed zero g-force, or zero-g (named after the g-force) or, incorrectly, zero gravity. Weight is a measurement of the fo ...
. Moreover, approximately 70% of astronauts experience space motion sickness to some degree during the first days. The drugs commonly used to combat motion sickness, such as
scopolamine Scopolamine, also known as hyoscine, or Devil's Breath, is a medication used to treat motion sickness and postoperative nausea and vomiting. It is also sometimes used before surgery to decrease saliva. When used by injection, effects begin a ...
and
promethazine Promethazine, sold under the brand name Phenergan among others, is a first-generation antihistamine, sedative, and antiemetic used to treat allergies, insomnia, and nausea. It may also help with some symptoms associated with the common cold a ...
, have soporific effects. These factors can lead to chronic
fatigue Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...
. The challenge of integrative
space medicine Space Medicine is a subspecialty of Emergency Medicine (Fellowship Training Pathway) which evolved from the Aerospace Medicine specialty. Space Medicine is dedicated to the prevention and treatment of medical conditions that would limit success in ...
and physiology is to investigate the adaptation of the human body to spaceflight as a whole, and not just as the sum of body parts because all body functions are connected and interact with each other.


History of space neuroscience

To date, only three countries, the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
,
Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
, and
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
, have the capability to launch humans into orbit. However, 520
astronaut An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a List of human spaceflight programs, human spaceflight program to serve as a commander or crew member of a spa ...
s from more than thirty different countries have flown in space and many of them have participated in space neuroscience research. The launch of the first living animal in orbit on
Sputnik Sputnik 1 (, , ''Satellite 1''), sometimes referred to as simply Sputnik, was the first artificial Earth satellite. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957 as part of the Soviet space progra ...
on November 3, 1957 marked the beginning of a rich history of unique scientific and technological achievements in space
life sciences This list of life sciences comprises the branches of science that involve the scientific study of life – such as microorganisms, plants, and animals including human beings. This science is one of the two major branches of natural science, ...
that have spanned more than fifty years to date. The first documented space neuroscience experiments were performed during the third human mission on board the Russian
Vostok Vostok () refers to east in Russian but may also refer to: Spaceflight * Vostok programme, Soviet human spaceflight project * Vostok (spacecraft), a type of spacecraft built by the Soviet Union * Vostok (rocket family), family of rockets derived ...
spacecraft. These experiments began after the crew from previous missions complained from
nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. It can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the throat. Over 30 d ...
and
spatial disorientation Spatial disorientation is the inability to determine position or relative motion, commonly occurring during periods of challenging visibility, since visual system, vision is the dominant sense for orientation. The auditory system, vestibular system ...
in
weightlessness Weightlessness is the complete or near-complete absence of the sensation of weight, i.e., zero apparent weight. It is also termed zero g-force, or zero-g (named after the g-force) or, incorrectly, zero gravity. Weight is a measurement of the fo ...
. Space neuroscience experiments typically addressed these operational issues until the
Skylab Skylab was the United States' first space station, launched by NASA, occupied for about 24 weeks between May 1973 and February 1974. It was operated by three trios of astronaut crews: Skylab 2, Skylab 3, and Skylab 4. Skylab was constructe ...
and
Salyut The ''Salyut'' programme (, , meaning "salute" or "fireworks") was the first space station programme, undertaken by the Soviet Union. It involved a series of four crewed scientific research space stations and two crewed military reconnaissa ...
space stations were made available for more fundamental research on the effect of gravity on CNS functions. Approximately 400 space neuroscience experiments have been performed from Vostok-3 in August 1962 to the Expedition-15 on board the
International Space Station The International Space Station (ISS) is a large space station that was Assembly of the International Space Station, assembled and is maintained in low Earth orbit by a collaboration of five space agencies and their contractors: NASA (United ...
in October 2007.


Operational aspects

Sensory and sensorimotor disturbances when arriving in low Earth orbit are well documented, the most known of these being space motion sickness (SMS). Individual differences, spacecraft size, and body movements cause SMS symptoms. Typically lasting the first three or four days of weightlessness, symptoms range from
headaches A headache, also known as cephalalgia, is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Head ...
and
fatigue Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...
to
nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. It can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the throat. Over 30 d ...
and
vomiting Vomiting (also known as emesis, puking and throwing up) is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenteritis, pre ...
. The consequences vary from simple discomfort to possible incapacitation, creating potential problems during
extra-vehicular activity Extravehicular activity (EVA) is any activity done by an astronaut in outer space outside a spacecraft. In the absence of a breathable Earthlike atmosphere, the astronaut is completely reliant on a space suit for environmental support. EVA i ...
, re-entry, and emergency egress from the spacecraft. The body receives a variety of conflicting signals from the visual, somato-sensory, and vestibular organs in weightlessness. These conflicting inputs are thought to be the primary cause of SMS, but the precise mechanisms of the conflict are not well understood. Medications currently used to alleviate the symptoms produce undesirable side effects. Astronauts must remain alert and vigilant while operating complicated equipment. Therefore, getting enough
sleep Sleep is a state of reduced mental and physical activity in which consciousness is altered and certain Sensory nervous system, sensory activity is inhibited. During sleep, there is a marked decrease in muscle activity and interactions with th ...
is a crucial factor of mission success. Weightlessness, a confined and isolated environment, and busy schedules coupled with the absence of a regular 24-hour day make
sleep Sleep is a state of reduced mental and physical activity in which consciousness is altered and certain Sensory nervous system, sensory activity is inhibited. During sleep, there is a marked decrease in muscle activity and interactions with th ...
difficult in space. Astronauts typically average only about six hours of sleep each night. Cumulative sleep loss and sleep disruption could lead to performance errors and accidents that pose significant
risk In simple terms, risk is the possibility of something bad happening. Risk involves uncertainty about the effects/implications of an activity with respect to something that humans value (such as health, well-being, wealth, property or the environ ...
to mission success. Sleep and circadian cycles also temporally modulate a broad range of physiological, hormonal, behavioral, and cognitive functions. Methods to prevent sleep loss, reduce
human error Human error is an action that has been done but that was "not intended by the actor; not desired by a set of rules or an external observer; or that led the task or system outside its acceptable limits".Senders, J.W. and Moray, N.P. (1991) Human Er ...
, and optimize mental and physical performance during long-duration spaceflight are being investigated. Particular concerns include the effect of the space environment on higher-order cognitive processes like
decision-making In psychology, decision-making (also spelled decision making and decisionmaking) is regarded as the Cognition, cognitive process resulting in the selection of a belief or a course of action among several possible alternative options. It could be ...
and the impact of changing gravity on mental functions, which will be important if
artificial gravity Artificial gravity is the creation of an inertial force that mimics the effects of a gravitational force, usually by rotation. Artificial gravity, or rotational gravity, is thus the appearance of a centrifugal force in a rotating frame of ...
is considered as a
countermeasure A countermeasure is a measure or action taken to counter or offset another one. As a general concept, it implies precision and is any technological or tactical solution or system designed to prevent an undesirable outcome in the process. The fi ...
for future interplanetary space missions. It is also necessary to develop human-response measurement technologies to assess the crew's ability to perform flight-management tasks effectively. Simple and reliable behavioral and psycho-physiological response measurement systems are needed to assess mental loading, stress, task engagement, and
situation awareness Situational awareness or situation awareness, often abbreviated as SA is the understanding of an environment, its elements, and how it changes with respect to time or other factors. It is also defined as the perception of the elements in the envi ...
during spaceflight.


Sensory functions in space

All living organisms on Earth have the ability to sense and respond to changes in their internal and external environment. Organisms, including humans, must accurately sense before they can react, thus ensuring
survival Survival or survivorship, the act of surviving, is the propensity of something to continue existing, particularly when this is done despite conditions that might kill or destroy it. The concept can be applied to humans and other living things ...
. The body senses the environment by specialized sensory organs. The CNS utilizes these sensations in order to coordinate and organize muscle activities, shift from uncomfortable positions, and adjust
balance Balance may refer to: Common meanings * Balance (ability) in biomechanics * Balance (accounting) * Balance or weighing scale * Balance, as in equality (mathematics) or equilibrium Arts and entertainment Film * Balance (1983 film), ''Balance'' ( ...
properly. In common speech, five different
senses A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of stimuli. Although, in some cultures, five human senses were traditionally identified as su ...
are usually recognized:
vision Vision, Visions, or The Vision may refer to: Perception Optical perception * Visual perception, the sense of sight * Visual system, the physical mechanism of eyesight * Computer vision, a field dealing with how computers can be made to gain und ...
,
hearing Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is auditory sci ...
, smell,
taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste. Taste is the perception stimulated when a substance in the mouth biochemistry, reacts chemically with taste receptor cells l ...
, and
touch The somatosensory system, or somatic sensory system is a subset of the sensory nervous system. The main functions of the somatosensory system are the perception of external stimuli, the perception of internal stimuli, and the regulation of bo ...
. All these senses are somewhat affected by weightlessness. In fact, the human body has seven sensory systems – not five. The sixth and seventh systems are the senses of motion located in the inner ear. The former signals the beginning and end of rotation and the latter signals body tilt relative to gravity as well as body translation. The seventh system no longer provides tilt information in weightlessness; however, it does continue to signal translation, so the afferent signals to the CNS are confusing. The experience of living and working in space alters the way the CNS interprets the otolith organ signals during
linear acceleration In mechanics, acceleration is the Rate (mathematics), rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are Euclidean vector, vector ...
. Although the perception is fairly accurate when subjects are exposed to angular acceleration in yaw in-flight, there are disturbances during angular rotation in pitch and roll, and during linear acceleration along the body transversal and longitudinal axes. Perception of body motion is also altered during the same motion immediately after landing. There is an adaptation to weightlessness in orbit that carries over to post-flight reactions to linear acceleration.


Posture, movement, and locomotions

Exposure to weightlessness causes changes to the signals from the receptors to
touch The somatosensory system, or somatic sensory system is a subset of the sensory nervous system. The main functions of the somatosensory system are the perception of external stimuli, the perception of internal stimuli, and the regulation of bo ...
,
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...
, and
gravity In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...
, i.e., all information necessary for postural stability. Adaptive modifications in the central processing of sensory information take place to produce motor responses that are appropriate for the new gravitational environment. As a result, terrestrial motor strategies are progressively abandoned in weightlessness, as astronauts adapt to the weightless environment. This is particularly true for the major postural
muscles Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...
found in the lower legs. The modifications in posture, movement, and locomotion acquired in reduced gravity are then inappropriate for Earth's gravity upon return. After landing,
postural instability A balance disorder is a disturbance that causes an individual to feel unsteady, for example when standing or walking. It may be accompanied by feelings of giddiness, or wooziness, or having a sensation of movement, spinning, or floating. Balance ...
approaching clinical
ataxia Ataxia (from Greek α- negative prefix+ -τάξις rder= "lack of order") is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in e ...
is manifested as a result of this in-flight neural reorganization. Difficulties with
standing Standing, also referred to as orthostasis, is a position in which the body is held in an upright (orthostatic) position and supported only by the feet. Although seemingly static, the body rocks slightly back and forth from the ankle in the ...
,
walking Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined as an " inverted pendulum" gait in which the body vaults o ...
, turning corners, climbing stairs, and a slowing of
gait Gait is the pattern of Motion (physics), movement of the limb (anatomy), limbs of animals, including Gait (human), humans, during Animal locomotion, locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on s ...
are experienced as astronauts re-adapt to Earth's gravity, until terrestrial motor strategies are fully re-acquired. Adaptation to spaceflight also induces a significant increase in the time required to traverse an obstacle course on landing day, and recovery of functional mobility takes an average of two weeks. These difficulties can have adverse consequences for an astronauts’ ability to stand up or escape from the vehicle during emergencies and to function effectively immediately after leaving the spacecraft after flight. Thus it is important to understand the cause of these profound impairments of posture and locomotion stability, and develop countermeasures. The most significant sensorimotor problems astronauts will face during a stay on the Moon and Mars are likely to occur when walking around in their
space suits A space suit (or spacesuit) is an environmental suit used for protection from the harsh environment of outer space, mainly from its vacuum as a highly specialized pressure suit, but also its temperature extremes, as well as radiation and ...
. The suits are big and bulky and change the body's
center of gravity In physics, the center of mass of a distribution of mass in space (sometimes referred to as the barycenter or balance point) is the unique point at any given time where the weighted relative position of the distributed mass sums to zero. For ...
. This along with the uneven terrain and limited field of view makes locomotion challenging.


Compensatory eye movements

The function of the
vestibular system The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating motor coordination, movement with balance. Together with the cochlea, a part of the auditory sys ...
during spaceflight is by far the most carefully studied of all. This is especially true of the gravity-sensing
otolith organs An otolith (, ' ear + , ', a stone), also called otoconium, statolith, or statoconium, is a calcium carbonate structure in the saccule or utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule and utricle, i ...
and their relationship to
eye movement Eye movement includes the voluntary or involuntary movement of the eyes. Eye movements are used by a number of organisms (e.g. primates, rodents, flies, birds, fish, cats, crabs, octopus) to fixate, inspect and track visual objects of inte ...
s. The vestibular
semicircular canal The semicircular canals are three semicircular interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the lateral, anterior and posterior semicircular canals. They are the part of the bony labyrinth, ...
function seems unchanged in weightlessness because the horizontal eye movements that compensated for head yaw rotation are not affected by spaceflight. The absence of gravity stimulation of the otoliths reduces the torsional
vestibulo-ocular reflex The vestibulo-ocular reflex (VOR) is a reflex that acts to stabilize Gaze (physiology), gaze during head movement, with eye movement due to activation of the vestibular system, it is also known as the cervico-ocular reflex. The reflex acts to im ...
during head roll rotation in microgravity. This deficit is absent when astronauts are exposed to
centrifugal force Centrifugal force is a fictitious force in Newtonian mechanics (also called an "inertial" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It appears to be directed radially away from the axi ...
s, suggesting that the adaptive CNS changes are taking place centrally rather than peripherally. During the first days in orbit, the asymmetry of vertical eye movements in response to moving visual scenes is inverted. A return to symmetry of the vestibulo-ocular and
optokinetic reflex The optokinetic reflex (OKR), also referred to as the optokinetic response, or optokinetic nystagmus (OKN), is a compensatory reflex that supports visual image stabilization. The purpose of OKR is to prevent motion blur on the retina that would o ...
es is then observed. Some studies have shown increased latencies and decreased peak velocities of
saccade In vision science, a saccade ( ; ; ) is a quick, simultaneous movement of both Eye movement (sensory), eyes between two or more phases of focal points in the same direction. In contrast, in Smooth pursuit, smooth-pursuit movements, the eyes mov ...
s, while others have found just the opposite. It is possible that these conflicting results depend on when the measures were obtained during the mission. There is also a serious disruption of
smooth pursuit In the scientific study of vision, smooth pursuit describes a type of eye movement in which the eyes remain fixated on a moving object. It is one of two ways that visual animals can voluntarily shift gaze, the other being saccadic eye movement ...
eye movements, especially in the vertical plane.
Human missions to Mars The idea of sending humans to Mars has been the subject of aerospace engineering and scientific studies since the late 1940s as part of the broader exploration of Mars. Long-term proposals have included sending settlers and terraforming the p ...
will include several transitions between different gravitational environments. These changes will eventually affect the reflex eye movements. A key question is whether astronauts can have different sets of reflexes among which they can rapidly switch based on the gravitational environment. Determination of the dual-adaptive capabilities of reflex eye movements in such circumstances is vitally important so that it can be determined to what extent the
Sensory-motor coupling Sensory-motor coupling is the coupling or integration of the sensory system and motor system. For a given stimulus, there is no one single motor command. "Neural responses at almost every stage of a sensorimotor pathway are modified at short and l ...
skills acquired in one-g environment will transfer to others.


Spatial orientation

In
weightlessness Weightlessness is the complete or near-complete absence of the sensation of weight, i.e., zero apparent weight. It is also termed zero g-force, or zero-g (named after the g-force) or, incorrectly, zero gravity. Weight is a measurement of the fo ...
, astronauts must rely much more on vision to maintain their
spatial orientation In geometry, the orientation, attitude, bearing, direction, or angular position of an object – such as a line, plane or rigid body – is part of the description of how it is placed in the space it occupies. More specifically, it refers to t ...
, because the
otolith An otolith (, ' ear + , ', a stone), also called otoconium, statolith, or statoconium, is a calcium carbonate structure in the saccule or utricle (ear), utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule ...
organs can no longer signal the “down” direction. During prolonged exposure, however, reliance seems to shift toward an intrinsic, body vertical reference. The erroneous illusions of self-motion during head movements performed during and after return to Earth gravity are presumably due to a re-interpretation of vestibular inputs. Ground-based studies suggest that the CNS resolves the “tilt-translation”
ambiguity Ambiguity is the type of meaning (linguistics), meaning in which a phrase, statement, or resolution is not explicitly defined, making for several interpretations; others describe it as a concept or statement that has no real reference. A com ...
based on the frequency content of the
linear acceleration In mechanics, acceleration is the Rate (mathematics), rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are Euclidean vector, vector ...
detected by the
otolith An otolith (, ' ear + , ', a stone), also called otoconium, statolith, or statoconium, is a calcium carbonate structure in the saccule or utricle (ear), utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule ...
organs, with low frequency indicating “tilt” and high frequency indicating “translation”. A crossover exists at about 0.3 Hz where the otolith signals are then ambiguous. Exposure to weightlessness presumably results in a shift of this crossover frequency, which could then contribute to
spatial disorientation Spatial disorientation is the inability to determine position or relative motion, commonly occurring during periods of challenging visibility, since visual system, vision is the dominant sense for orientation. The auditory system, vestibular system ...
and SMS. Although investigations of higher cognitive processes, such as
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the motion, movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navig ...
and
mental rotation Mental rotation is the ability to rotate mental representations of two-dimensional and three-dimensional objects as it is related to the visual representation of such rotation within the human mind. There is a relationship between areas of the b ...
are limited, the astronauts frequently report that the spacecraft interiors look longer and higher than they actually are, and a reduction in the perceived height of three-dimensional objects is observed in-flight compared with pre-flight, suggesting an alteration in the
mental representation A mental representation (or cognitive representation), in philosophy of mind, cognitive psychology, neuroscience, and cognitive science, is a hypothetical internal cognitive symbol that represents external reality or its abstractions. Mental re ...
of three-dimensional cues in weightlessness.
Perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous syste ...
is a model of the brain, a hypothesis about the world that presupposes the
Newton's laws of motion Newton's laws of motion are three physical laws that describe the relationship between the motion of an object and the forces acting on it. These laws, which provide the basis for Newtonian mechanics, can be paraphrased as follows: # A body re ...
. These laws change in weightlessness and, therefore, one could expect changes in the mental representation of objects’ shape and distance during spaceflight. The rare investigations carried out in space so far have not demonstrated drastic changes, probably because the CNS continues to use an internal model of gravity, at least for a short while. It can be speculated that the way of processing three dimensions will be more developed after a long absence of a gravitational reference. Further investigations carried out in space will perhaps reveal that other higher cortical functions are impaired in weightless conditions. The combination of
virtual reality Virtual reality (VR) is a Simulation, simulated experience that employs 3D near-eye displays and pose tracking to give the user an immersive feel of a virtual world. Applications of virtual reality include entertainment (particularly video gam ...
with the measurement of
evoked potentials An evoked potential or evoked response is an electrical potential in a specific pattern recorded from a specific part of the nervous system, especially the brain, of a human or other animals following presentation of a stimulus such as a light fl ...
and
brain mapping Brain mapping is a set of neuroscience techniques predicated on the mapping of (biological) quantities or properties onto spatial representations of the (human or non-human) brain resulting in maps. According to the definition established in 2 ...
on board the International Space Station should provide exciting results on the adaptive mechanisms of cerebral functions in weightlessness.


Neuroscience and space exploration

From Voskhod to the
International Space Station The International Space Station (ISS) is a large space station that was Assembly of the International Space Station, assembled and is maintained in low Earth orbit by a collaboration of five space agencies and their contractors: NASA (United ...
, spacecraft have improved in size and comfort and have allowed more and more people traveling into orbit. However, even with all of the human spaceflight experience gained over the past fifty years, no single completely effective countermeasure, or combination of countermeasures, exists against the negative effects of long-duration exposure to weightlessness. If a crew of astronauts were to embark on a six-month journey to Mars today, the countermeasures currently employed would presumably leave them less operational after landing. Many believe that physiological adaptation to Mars gravity (0.38 G) and re-adaptation to Earth gravity (1 G) would be enhanced by frequent exposure to
artificial gravity Artificial gravity is the creation of an inertial force that mimics the effects of a gravitational force, usually by rotation. Artificial gravity, or rotational gravity, is thus the appearance of a centrifugal force in a rotating frame of ...
on board the spacecraft en route to and from Mars. This would require an on-board human-rated
centrifuge A centrifuge is a device that uses centrifugal force to subject a specimen to a specified constant force - for example, to separate various components of a fluid. This is achieved by spinning the fluid at high speed within a container, thereby ...
or spacecraft rotation to produce a
centrifugal force Centrifugal force is a fictitious force in Newtonian mechanics (also called an "inertial" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It appears to be directed radially away from the axi ...
similar to gravity. This solution, while potentially effective, raises a number of operational, engineering, and physiological issues that will need to be addressed. The human physiological responses to long-duration exposure to anything other than zero-gravity or Earth's gravity are unknown. Research is needed to identify the minimum level, duration, and frequency of gravity level required to maintain normal CNS functions, as well as the importance of a gravity gradient across the body. The complex functioning of the CNS, even in the 1-G environment of Earth, has not revealed all its secrets. The most basic space neuroscience questions must be answered to minimize risks and optimize crew performance during transit and planetary operations. The results of this research will certainly find other applications in
medicine Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...
and
biotechnology Biotechnology is a multidisciplinary field that involves the integration of natural sciences and Engineering Science, engineering sciences in order to achieve the application of organisms and parts thereof for products and services. Specialists ...
. Our ability to understand how Earth's gravitational environment has shaped the evolution of sensory and motor systems can give us a clearer understanding of the fundamental mechanisms of CNS functions. Knowledge of the effects of gravity on CNS functions in humans, as well as elucidation of the basic mechanisms by which these effects occur, will be of direct benefit to understanding the impact of, and providing countermeasures for, long-term exposure of humans to the
weightlessness Weightlessness is the complete or near-complete absence of the sensation of weight, i.e., zero apparent weight. It is also termed zero g-force, or zero-g (named after the g-force) or, incorrectly, zero gravity. Weight is a measurement of the fo ...
of spaceflight and the partial gravity of
Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...
and
Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...
bases.


See also

*
Effect of spaceflight on the human body The effects of spaceflight on the human body are complex and largely harmful over both short and long term. Significant adverse effects of long-term weightlessness include muscle atrophy and deterioration of the skeleton ( spaceflight osteopeni ...


References


External links


Space Neuroscience Research



Human Physiology in Space
* {{DEFAULTSORT:Neuroscience Behavioral neuroscience Space medicine