Are you able to read a book in a car or a plane without the feeling of nausea? If so, consider yourself lucky, because for approximately one third of the population these situations develop a feeling of sickness in their stomach (Takov and Tadi, 2023). So why does this happen? The truth is no one really knows the neurobiological cause of motion sickness (MS), currently the leading hypothesis has to do with mismatched sensory signals, known as the “sensory conflict” theory (Paillard et al., 2014).
When travelling in a car, or any other form of transportation, your body is getting two very different forms of messages. The eyes are seeing the inside of the vehicle that does not appear to be moving, and at the same time your ears can detect that you are accelerating. The ears do this via the vestibular system that lies within the innermost part of the ear. This system provides a sense of movement and balance for the body (Bertolini and Straumann, 2016). Inside the vestibular system there are two hair-lined sacks (the utricle and the saccule) that contain fluids (Casale et al., 2024). When you are inside a car the fluids begin to shift due to acceleration thus stimulating the hairs. This stimulation gives feedback to the brain that tells you if you are moving horizontally, or vertically. The combination of those factors provides your brain with the ability to sense what angle, direction, and the magnitude of acceleration you are experiencing. Thus, when you are in a car the vestibular system is correctly sensing the acceleration you are experiencing, but your eyes are perceiving that you are not moving. The result of this sensory conflict malfunctions the process of the semicircular canals in the vestibular system, resulting in MS (Bertolini and Straumann, 2016).
As nearly two in three people experience MS in their lives it is vital to integrate new methods to alleviate MS, especially amidst the promise of self-driving cars that would exponentially increase the number of people experiencing carsickness (Schmidt et al., 2020). The three countermeasures that are possible for the alleviation of car induced motion sickness are sensory cues, in-car design, and vehicle centric adaptations (see Figure 1).
Figure. 1 Three countermeasure methods to combat MS. In each measure there is a sub measure that describes the method and mechanism used to combat the physical effects of MS (Pereira et al., 2024).
A particularly intriguing solution for MS that has recently arisen is the induced reduction of symptoms of nausea via olfaction (Branigan and Tadi, 2024). A study conducted tested visually induced MS by subjecting participants to a nauseating 15-minute video. This video previously had induced MS in participants that were tested earlier. The same video was introduced to a new group, with the addition of a smell of either roses, leather or no scent during the video. It was found that in the presence of roses the perceived amount of MS that was felt significantly decreased, while the participants that were subjected to the scent of leather sustained a smaller decrease in MS relative to the roses (Keshavarz et al., 2015) as seen in Figure 2 below.
Figure. 2 depicts the Fast Motion Sickness Scale (FMS) score which is a scalable measure used to quantify the perceived amount of MS over a period of time for four different variable scent groups- rose, leather, control, and the group where the scents being diffused into the room went unnoticed. The roses had the largest decrease in MS compared to the control group, while the leather decreased to a lesser degree. The results from the experiment show that scents that are perceived pleasantly can decrease the symptoms of MS.
MS is truly a deteriorating phenomenon that causes people throughout the world much suffering. By understanding the process and alleviation techniques such as olfaction for MS, those affected can have significantly less suffering as new treatments become apparent.
References
Bertolini, G. and Straumann, D., 2016. Moving in a Moving World: A Review on Vestibular Motion Sickness. Frontiers in Neurology, 7, p.14. https://doi.org/10.3389/fneur.2016.00014.
Branigan, B. and Tadi, P., 2024. Physiology, Olfactory. In: StatPearls. [online] Treasure Island (FL): StatPearls Publishing. Available at: <http://www.ncbi.nlm.nih.gov/books/NBK542239/> [Accessed 28 January 2024].
Casale, J., Browne, T., Murray, I.V. and Gupta, G., 2024. Physiology, Vestibular System. In: StatPearls. [online] Treasure Island (FL): StatPearls Publishing. Available at: <http://www.ncbi.nlm.nih.gov/books/NBK532978/> [Accessed 28 January 2024].
Keshavarz, B., Stelzmann, D., Paillard, A. and Hecht, H., 2015. Visually induced motion sickness can be alleviated by pleasant odors. Experimental Brain Research, 233(5), pp.1353–1364. https://doi.org/10.1007/s00221-015-4209-9.
Paillard, A.C., Lamôré, M., Etard, O., Millot, J.-L., Jacquot, L., Denise, P. and Quarck, G., 2014. Is there a relationship between odors and motion sickness? Neuroscience Letters, 566, pp.326–330. https://doi.org/10.1016/j.neulet.2014.02.049.
Schmidt, E.A., Kuiper, O.X., Wolter, S., Diels, C. and Bos, J.E., 2020. An international survey on the incidence and modulating factors of carsickness. Transportation Research Part F: Traffic Psychology and Behaviour, 71, pp.76–87. https://doi.org/10.1016/j.trf.2020.03.012.
Takov, V. and Tadi, P., 2023. Motion Sickness. In: StatPearls. [online] Treasure Island (FL): StatPearls Publishing. Available at: <http://www.ncbi.nlm.nih.gov/books/NBK539706/> [Accessed 16 January 2024].