March 22, 2012
Brain Handles Odors In A Different Way
Researchers from the Stowers institute for Medical Research have traced individual odor molecules in the brain to create a new model of how our sense of smell works. While once thought to cluster related smells, researchers have know discovered that the brain reacts to smells in a broader sense.
Previous research has shown that the brain handles the senses in a very orderly way.
Things that we touch were thought to be mapped together in the somatosensory cortex, things that we heard were mapped together in the auditory system, and things that we taste were mapped together in the gustatory cortex. The olfactory cortex handles things that we smell, but new research suggests that this system may react to smells differently than previously thought.
Rather than group chemically-related smells together in the olfactory system, the smells were mapped everywhere in the system.
“When we mapped the individual chemical features of different odorants, they mapped all over the olfactory bulb, which processes incoming olfactory information,” says Associate Investigator C. Ron Yu, PhD, who led the study published in this week´s online edition of the Proceedings of the National Academy of Sciences (PNAS).
“From the animal´s perspective that makes perfect sense. The chemical structure of an odor molecule is not what´s important to them. They really just want to learn about their environment and associate olfactory information with food or other relevant information.”
As we smell things, nasal receptors send an electrical signal up to glomeruli in the olfactory bulb. The pattern with which these glomeruli send and receive signals to the olfactory system was thought to represent specific odors.
This hypothesis on how the brain handles odor had been widely accepted, but it had never been accurately mapped. Recent research and available technologies have shown that this process breaks down at a very fine level, thus requiring a more fine-tuned and up close look at the olfactory map.
Yu and his team generated a line of super sensitive transgenic mice and equipment sophisticated enough to deliver hundreds of odor stimuli to a single mouse.
In their tests, the researchers discovered that certain odors did activate within a specific and distinct area of the olfactory bulb. Other odors, however, signaled glomeruli in various areas of the bulb. Some odors even intermingled in the olfactory bulb, suggesting that the glomeruli haven´t yet evolved to detect the specific chemical shapes of certain odors.
This finding did not surprise lead author of the study Limei Ma, PhD, as there are thousands of odors.
“Many of them could be really novel to the organism, something they never encountered before,” she says. “The system must have the capability to recognize and encode anything.”
The research suggests that the “chemotopic” hypothesis on how the brain responds to different odors may not be completely accurate. The team has now devised a “Tunotopic” hypothesis on the olfactory system. This means individual glomeruli are “tuned” to receive certain odor chemical molecules, and therefore can send them to different areas of the olfactory bulb. The team believes that this sort of hypothesis can be used to describe how the brain handles the other senses as well.
“When you have a new chemical synthesized, like new perfumes and food flavors, you don´t have to create new brain regions to react to it,” Ma said in the press release. “What you do is use the existing receptors to sense all these chemicals and then tell your brain whether this is novel, whether it´s similar, or whether it´s something really strange.”