Space neuroscience or astroneuroscience is the scientific study of the central nervous system (CNS) functions during spaceflight. Living systems can integrate the inputs from the senses to navigate in their environment and to coordinate posture, locomotion, and eye movements. Gravity has a fundamental role in controlling these functions. In weightlessness during spaceflight, integrating the sensory inputs and coordinating motor responses is harder to do because gravity is no longer sensed during free-fall. For example, the otolith organs of the vestibular system no longer signal head tilt relative to gravity when standing. 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, which affects spatial orientation and mental representation. Dysfunctions of the vestibular system are common during and immediately after spaceflight, such as space motion sickness in orbit and balance disorders after return to Earth.[1]
Adaptation to weightlessness involves not just the Sensory-motor coupling functions, but some autonomic nervous system functions as well. Sleep disorders and orthostatic intolerance are also common during and after spaceflight. There is no hydrostatic pressure 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 viscosity and compliance. An increase in intracranial pressure may also be responsible for a decrease in near visual acuity.[2] In addition, muscle mass and strength both decrease as a result of the reduced loading in weightlessness. Moreover, approximately 70% of astronauts experience space motion sickness to some degree during the first days.[3] The drugs commonly used to combat motion sickness, such as scopolamine and promethazine, have soporific effects. These factors can lead to chronic fatigue. The challenge of integrative space medicine 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.