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What is the relationship between loss of balance and motion sickness? Eduardo Garcia [via e-mail]

DANIEL BUENOThe motion sickness that occurs when traveling by car or ship stems from the relationship between the vestibular system — which includes the organs of the inner ear (labyrinth), one of the mechanisms responsible for balance — and the autonomic nervous system, consisting of the sympathetic and parasympathetic nervous systems. Whenever there is a sensory conflict between the labyrinth, which is responsible for spatial orientation and for detecting the position and movement of the head, and the visual system, the balance between the two is affected, and the person begins to feel dizzy, that is, has a sensation of movement. The conflict is transferred to the autonomic nervous system  through the nucleus of the vagus nerve, located in the central nervous system. This may cause neurovegetative symptoms, the familiar nausea, vomiting, sweating, pallor, tachycardia, or in some cases, diarrhea. Discomfort may also be caused by other conflict situations between vision and the vestibular system, such as by watching 3D movies at the cinema. However, the phenomenon is not connected to human evolution. Although the autonomic nervous system works defensively, in this case nausea is only one symptom of a vestibular disorder.

Specialist consulted
Fernando Ganança, Department of Otorhinolaryngology and Head and Neck Surgery, Federal University of São Paulo (Unifesp)