Motion sickness

Symptoms commonly include nausea, vomiting, cold sweat, headache, dizziness, tiredness, loss of appetite, and increased salivation. Occasionally, tiredness can last for hours to days after an episode of motion sickness, known as "sopite syndrome". Rarely severe symptoms such as the inability to walk, ongoing vomiting, or social isolation may occur while rare complications may include dehydration, electrolyte problems, or a lower esophageal tear from severe vomiting. ==Cause==

Motion sickness can be divided into three categories: • Motion sickness caused by motion that is felt but not seen i.e. terrestrial motion sickness; • Motion sickness caused by motion that is seen but not felt i.e. space motion sickness; • Motion sickness caused when both systems detect motion but they do not correspond i.e. either terrestrial or space motion sickness. Motion felt but not seen In these cases, motion is sensed by the vestibular system and hence the motion is felt, but no motion or little motion is detected by the visual system, as in terrestrial motion sickness. Carsickness A specific form of terrestrial motion sickness, being carsick is quite common and evidenced by disorientation while reading a map, a book, or a small screen during travel. Carsickness results from the sensory conflict arising in the brain from differing sensory inputs. Motion sickness is caused by a conflict between signals arriving in the brain from the inner ear, which forms the base of the vestibular system, the sensory apparatus that deals with movement and balance, and which detects motion mechanically. If someone is looking at a stationary object within a vehicle, such as a magazine, their eyes will inform their brain that what they are viewing is not moving. Their inner ears, however, will contradict this by sensing the motion of the vehicle. Seasickness Seasickness is a form of terrestrial motion sickness characterized by a feeling of nausea and, in extreme cases, vertigo experienced after spending time on a boat. Adjusting to the craft's motion at sea is called "gaining one's sea legs"; it can take a significant portion of the time spent at sea after disembarking to regain a sense of stability "post-sea legs". Centrifuge motion sickness Rotating devices such as centrifuges used in astronaut training and amusement park rides such as the Rotor, Mission: Space and the Gravitron can cause motion sickness in many people. While the interior of the centrifuge does not appear to move, one will experience a sense of motion. In addition, centrifugal force can cause the vestibular system to give one the sense that downward is in the direction away from the center of the centrifuge rather than the true downward direction. Dizziness due to spinning When one spins and stops suddenly, fluid in the inner ear continues to rotate causing a sense of continued spinning while one's visual system no longer detects motion. Virtual reality Usually, VR programs would detect the motion of the user's head and adjust the rotation of vision to avoid dizziness. However, some cases such as system lagging or software crashing could cause lags in the screen updates. In such cases, even some small head motions could trigger the motion sickness by the defense mechanism mentioned below: the inner ear transmits to the brain that it senses motion, but the eyes tell the brain that everything is still. Virtual reality to reverse motion sickness Recent research has shown that virtual reality can also be used therapeutically to reverse seasickness by reintroducing visual cues that align more closely with the body's sense of motion. One effective approach involves simulating a stable artificial horizon within the headset while simultaneously introducing low-amplitude visual motion that matches the real movement of the vessel, such as pitch, roll, and heave. By restoring coherence between visual and vestibular input, this method can help the brain reestablish sensory integration, thereby reducing or even eliminating symptoms of motion sickness within minutes. Systems that synchronize VR environments with vessel dynamics have demonstrated significant promise in field trials. Motion seen but not felt In these cases, motion is detected by the visual system and hence the motion is seen, but no motion or little motion is sensed by the vestibular system. Motion sickness arising from such situations has been referred to as "visually induced motion sickness" (VIMS). Space motion sickness was effectively unknown during the earliest spaceflights because the very cramped conditions of the spacecraft allowed for only minimal bodily motion, especially head motion. Space motion sickness seems to be aggravated by being able to freely move around, and so is more common in larger spacecraft. Screen images This type of terrestrial motion sickness is particularly prevalent when susceptible people are watching films presented on very large screens such as IMAX, but may also occur in regular format theaters or even when watching TV or playing games. For the sake of novelty, IMAX and other panoramic type theaters often show dramatic motions such as flying over a landscape or riding a roller coaster. In regular-format theaters, an example of a movie that caused motion sickness in many people is The Blair Witch Project. Theaters warned patrons of its possible nauseating effects, cautioning pregnant women in particular. Blair Witch was filmed with a handheld camcorder, which was subjected to considerably more motion than the average movie camera, Virtual reality Motion sickness due to virtual reality is very similar to simulation sickness and motion sickness due to films. ==Pathophysiology==

There are various hypotheses that attempt to explain the cause of the condition. Sensory conflict theory Contemporary sensory conflict theory, referring to "a discontinuity between either visual, proprioceptive, and somatosensory input, or semicircular canal and otolith input", is probably the most thoroughly studied. According to this theory, when the brain presents the mind with two incongruous states of motion, the result is often nausea and other symptoms of disorientation known as motion sickness. Such conditions happen when the vestibular system and the visual system do not present a synchronized and unified representation of one's body and surroundings. According to sensory conflict theory, the cause of terrestrial motion sickness is the opposite of the cause of space motion sickness. The former occurs when one perceives visually that one's surroundings are relatively immobile while the vestibular system reports that one's body is in motion relative to its surroundings. Neural mismatch A variation of the sensory conflict theory is known as neural mismatch, implying a mismatch occurring between ongoing sensory experience and long-term memory rather than between components of the vestibular and visual systems. This theory emphasizes "the limbic system in the integration of sensory information and long-term memory, in the expression of the symptoms of motion sickness, and the impact of anti-motion-sickness drugs and stress hormones on limbic system function. The limbic system may be the neural mismatch center of the brain." Defense against poisoning It has also been proposed that motion sickness could function as a defense mechanism against neurotoxins. Nystagmus hypothesis Yet another theory, known as the nystagmus hypothesis, Exhausted Brain Theory The Exhausted Brain Theory (EBT) proposes that motion sickness and cybersickness originate from the metabolic cost of neural adaptation when the brain is forced to reconcile conflicting or unfamiliar sensory inputs. Instead of describing sickness purely as a sensory mismatch, EBT interprets it as a state of neural energy exhaustion in multisensory cortical networks responsible for perceptual coherence. According to the theory, continuous re-adaptation to inconsistent sensory information—such as visual–vestibular discordance in virtual or real motion—requires substantial metabolic energy to update predictive internal models. When the energetic demand of this process exceeds available resources, functional fatigue develops, leading to nausea, dizziness, and other sickness symptoms. EBT builds on predictive-coding and information-theoretic perspectives, viewing the brain as an energy-limited inference system. Under strong sensory conflicts, prediction-error minimization becomes metabolically unsustainable, resulting in temporary neural exhaustion. Physiological studies of cybersickness show changes consistent with this framework, including altered cerebral oxygenation, pupil dilation, and autonomic regulation during symptom onset. EBT complements earlier frameworks such as the sensory-conflict and postural-instability theories, framing them as behavioral outcomes of an underlying energetic limitation in the brain's adaptive processes. ==Diagnosis==

The diagnosis is based on symptoms. Other conditions that may present similarly include vestibular disorders such as benign paroxysmal positional vertigo and vestibular migraine and stroke. == Treatment ==

Treatment may include behavioral measures or medications. Medication Three types of medications are sometimes prescribed to improve symptoms of motion sickness: antimuscarinics such as scopolamine, H1 antihistamines such as dimenhydrinate, and amphetamines such as dexamphetamine. Scopolamine (antimuscarinic) Scopolamine is the most effective medication. It is available as a skin patch. Effective first generation antihistamines include doxylamine, diphenhydramine, promethazine, meclizine, cyclizine, and cinnarizine. Providing smells does not appear to have a significant effect on the rate of motion sickness. ==Epidemiology==

Roughly one-third of people are highly susceptible to motion sickness, and most of the rest get motion sick under extreme conditions. Around 80% of the general population is susceptible to cases of medium to high motion sickness. The rates of space motion sickness have been estimated at between forty and eighty percent of those who enter weightless orbit. Several factors influence susceptibility to motion sickness, including sleep deprivation and the cubic footage allocated to each space traveler. Studies indicate that women are more likely to be affected than men, and that the risk decreases with advancing age. There is some evidence that people with Asian ancestry may develop motion sickness more frequently than people of European ancestry, and there are situational and behavioral factors, such as whether a passenger has a view of the road ahead, and diet and eating behaviors. == See also ==