14. Sensorimotor Adaptation, Including SMS

Sensorimotor adaptation refers to the capacity of the central nervous system to gradually update motor control to compensate for changes in sensory inputs from the environment or for changes in mechanical characteristics of the body. One example is learning to accommodate to the refraction of light in water when reaching for objects viewed through a diving mask. In the microgravity environment, somatosensory and vestibular inputs are quite different than they are on Earth. The body is unloaded, resulting in greater movement per unit of force. Moreover, on Earth the otoliths of the vestibular system signal angle of orientation of the head relative to a gravitational vector, which is absent in space. There is a resulting reinterpretation of head tilt as a linear acceleration which leads to motor control and perceptual disruptions on return to Earth. It is perhaps not surprising then that crewmembers report a high incidence of space motion sickness due to sensory conflict. In addition, once individuals adapt movement control for the microgravity environment, these new control processes and strategies are maladaptive for Earth’s gravitational field. Therefore, there is a period of readaptation of sensorimotor control upon return to Earth which can last for days to weeks depending upon the preceding flight duration.