Can you read in the car? If so, consider yourself pretty lucky. For one-third of the population, looking at a book while moving along in a car or a boat or train or plane quickly makes them sick to their stomach. But why do we get motion sickness in the first place? Well, believe it or not, scientists aren't exactly sure. The most common theory has to do with mismatched sensory signals. When you travel in a car, your body gets two different messages. Your eyes are seeing the inside of a vehicle, which doesn't seem to be moving. Meanwhile, your ear is telling your brain you're accelerating. Wait, your ear? Your ear has another important function besides hearing. In its innermost part lies a group of structures known as the vestibular system, which gives us our sense of balance and movement. Inside there are three semicircular tubules that can sense rotation, one for each dimension of space. And there are also two hair-lined sacks filled with fluid. When you move, the fluid shifts and tickles the hairs, telling your brain if you're moving horizontally or vertically. All this tells your body which direction you're moving in, how much you've accelerated, even at what angle. In a car, your vestibular system correctly senses your movement, but your eyes don't see it, especially when glued to a book. The opposite can happen. You're at the movies, and the camera makes a sweeping move. This time, your eyes think you're moving while your ear knows you're sitting still. But why does this conflicting information make us feel so terrible? Scientists aren't sure, but they think there's an evolutionary explanation. Fast moving vehicles and video recordings have only existed in the last couple of centuries, a blink in evolutionary time. For most of our history, there wasn't that much that could cause this sensory mix-up, except for poisons. And because poisons are not the best thing for survival, our bodies evolved a direct but unpleasant way to get rid of what we ate that was causing the confusion. It's a pretty reasonable theory, but it leaves things unexplained, like why women are more affected by motion sickness than men, or why passengers get more nauseous than drivers. Another theory suggests that the cause is more about the way some unfamiliar situations make it harder to maintain our natural body posture. Studies show that being immersed in water or just changing your stance can greatly reduce the effects of motion sickness. But we don't really know what's going on. We know the more common remedies for car queasiness -- looking at the horizon, over-the-counter pills, chewing gum, but none are totally reliable nor can they handle intense motion sickness and sometimes the stakes are far higher than just not being bored during a long car ride. At NASA, where astronauts are hurled into space at 17,000 miles per hour, motion sickness is a serious problem. In addition to researching the latest space-age technologies, NASA also spends a lot of time figuring out how to keep astronauts from vomiting up their space rations. Like understanding the mysteries of sleep or curing the common cold, motion sickness is one of those seemingly simple problems that, despite amazing scientific progress, we still know very little about. Perhaps one day the exact cause of motion sickness will be found, and with it, a completely effective way to prevent it, but that day is still on the horizon.
Bisa membaca di dalam mobil? Jika iya, kamu cukup beruntung. Bagi sepertiga populasi, membaca buku saat di dalam mobil yang bergerak atau di kapal, kereta, pesawat, akan langsung membuat mereka mual. Tapi kenapa kita bisa terkena mabuk perjalanan? Percaya atau tidak, ilmuwan belum paham betul. Teori paling umum adalah sinyal indra yang bertolak belakang. Saat naik mobil, tubuhmu mendapat dua pesan berbeda. Matamu melihat bagian dalam kendaraan, yang kelihatannya tidak bergerak. Sementara telingamu memberi tahu otakmu bahwa kamu sedang melaju. Tunggu, kupingmu? Kupingmu punya fungsi lain yang penting selain untuk mendengar. Di bagian terdalam, ada struktur yang disebut sistem vestibula, yang memberi kita rasa seimbang dan gerak. Di dalamnya ada tiga pipa setengah lingkaran yang bisa merasakan rotasi, satu untuk tiap dimensi ruang. Di sana pula ada dua kantong berambut berisi cairan. Saat bergerak, cairan bergeser dan mengitik rambut agar otakmu tahu jika kamu bergerak horizontal atau vertikal. Semua ini membuat tubuhmu tahu ke mana kamu bergerak, seberapa cepatnya kamu, bahkan di sudut mana. Di mobil, sistem vestibula merasakan pergerakanmu dengan benar, tapi matamu tak melihatnya, terutama saat terpaku ke buku. Kebalikannya bisa terjadi. Misal kamu di bioskop dan kamera bergeser secara luas. Kali ini, matamu pikir kau bergerak sementara telingamu tahu kau sedang duduk. Tapi kenapa informasi berlainan ini membuat kita tak nyaman? Ilmuwan belum tahu, tapi mereka pikir ada penjelasan dari sisi evolusi. Kendaraan cepat dan perekaman video baru ada beberapa abad terakhir, waktu yang singkat untuk masa evolusi. Di hampir seluruh sejarah kita, tak banyak penyebab kekacauan indra, kecuali racun. Karena racun bukan hal baik untuk bertahan hidup tubuh kita mengembangkan cara langsung tapi tak nyaman untuk membuang yang kita telan dan menyebabkan kekacauan. Teori ini cukup beralasan, tapi menyisakan banyak tanda tanya. Misal kenapa wanita mudah mabuk perjalanan dari pria atau kenapa penumpang mudah mual ketimbang pengemudi. Teori lain menyebut alasannya lebih kepada bagaimana kondisi asing menyulitkan menjaga posisi tubuh alami kita. Studi menunjukkan berada di air atau mengubah cara berdiri saja bisa sangat mengurangi dampak mabuk perjalanan. Namun, kita tak tahu pasti yang terjadi. Kita tahu pengobatan umum untuk mabuk di mobil -- melihat langit, kunyah permen karet, minum obat bebas, tapi tak satu pun bisa diandalkan atau bisa mengatasi mabuk perjalanan hebat. Kadang masalah ini lebih gawat daripada merasa bosan selama perjalanan panjang. Di NASA, saat astronot meluncur ke angkasa dengan kecepatan 17.000 mil per jam mabuk perjalanan jadi isu genting. Di samping meneliti teknologi era antariksawan terbaru, NASA juga mengisi banyak waktu mencari cara agar astronot tak memuntahkan ransumnya. Sama halnya memahami misteri tidur atau menyembuhkan selesma, mabuk perjalanan jadi salah satu masalah sederhana, yang meski dengan kemajuan sains, kita belum banyak mengetahuinya. Mungkin penyebab pasti mabuk perjalanan akan ditemukan, bersama dengan cara efektif untuk mencegahnya, tapi hari itu masih jauh.