You may not
enjoy the smell of your dirty laundry, but your brain knows and appreciates that it’s yours. A new study reveals a key way we detect our own scent and distinguish that scent from others’.
Smell is a powerful thing. Many species use it to communicate (think dogs sniffing their introductions) or attract mates (the Stickleback fish is a good example of this one). Humans may not be as overtly smell-dependent, but our brains actually use this sense more than you might think.
Communication by smell comes down to a thing called the major histocompatibility complex, or MHC. Every creature with a backbone has MHC molecules on the surface of its cells. These molecules act like bouncers, carefully controlling the balance of proteins inside the cell. When new proteins come a-knocking, the MHC checks their IDs to determine if they are okay to enter the cell (recognized as self) or get kicked out (non-self). This keeps the riffraff at bay, but can also cause the body to reject unrecognized things like transplanted organs.
That’s not all these MHC molecules do, though. New research shows that a person’s brain will recognize his or her own scent based on an individual’s unique combination of MHC proteins. Scientists have long known that people are drawn to mates with a non-self MHC, but this is the first time that scientists have shown that people recognize (and like) their own smell.
Researchers genotyped participating women to determine if their MHCs were type A or B. The researchers then applied two synthetic MHC proteins to womens’ armpits, one that resembled their own and one that did not. Women, except for smokers and those with a cold, preferred the smell of their own type of MHC proteins. This proved preference, but the researchers wanted more solid evidence, so they pulled out the magnetic resonance imaging machine. The women’s brains showed a clear divide between the areas of the brain activated by self and non-self MHCs. The results of the study, published Wednesday in Proceedings of the Royal Society B, provide the first evidence of this neural difference in humans.
Scientists still need to figure out what receptors in the human nose are able to detect the MHC, and if our noses are picking up on other distinguishing factors in body odor aside from these particular proteins. But scientists are at least on the scent.