Why one person's good smell is another person's stinkS

Ever wonder if what you smell is what everyone else smells? Science does, too. And the answer could be no.

Hold up a blue t-shirt and ask people what color it is, and you'll probably always get the right answer. But is that because everyone sees pretty much the same color or is it because everyone has been trained to see a certain stimulus as blue? Red/Green color blindness can hide out in people for years before they realize that what they see of the world is not what anyone else does. Smells are even more subtle. Although it's uncommon for people to misidentify common sights and sounds, people often mix up smells when they scent them. What seems like orange to one person can smell like lime, or honey, or pineapple to another. These differences could be because people aren't used to navigating by smell, but they could also be because the same smell has trouble navigating through different people's brains.

The receptors in a person's nose are triggered by specific chemicals. When they come into contact with those chemicals, they activate neurons that head up to the olfactory bulb. Inside the bulb, each signal ends up in a little ball of nerves called the glomerulus. Certain glomeruli are paired with certain smells. So far, everyone is the same. Scientists observing mice can tell what the mouse is sniffing by looking at which glomerulus is stimulated.

Once stimulated, the glomerulus passes the signals to the olfactory cortex via specific mitral and tufted neurons (MTs). In insects, strict observance of protocol is observed. Each scent follows a certain path up from the glomerulus through a specific MT and to a certain area of the olfactory cortex, no matter which member of an insect species is doing the sniffing. When scientists marked MT pathways in mice, however, they found that there was no hammered-out protocol at all. Although the same scents were passed to the same glomerulus, they took different MTs to different parts olfactory cortex. In fact, if two mice had the same glomerulus stimulated, the resulting two signals were no more likely to land in the same place in the olfactory cortex than signals from two different glomeruli. The same scent stimulated different parts of the higher brain in different mice. There's no current way to tell if those different pathways added up to the same experience of if they didn't. If they did not, it may explain the extreme different responses to the same taste and smell that different humans have. The same chemicals may smell completely different to different people.

Via Science Daily.

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