Tag Archives: neuroscience

Organized Odor

I was once told that “all knowledge can be distilled into two parts, identity and function”. It is a common parameter for effective research.  In order to know how one drug is more effective than another, which ingredient can accent your dish or how to pull the bow across your violin for that magical sound; you need to know what was different and how the outcome contributes to your desired goal.

Many items can seem similar and yet have much different functional properties even when applied similarly. You take Tylenol or ibuprofen for a headache. Both are medicines treating headaches, but I prefer ibuprofen because it consistently and quickly relieves my symptoms. They appear different and they both address pain, yet ibuprofen is functionally more effective for me.

I have an identical twin brother. He has a job in designing software and computer operations.  I studied medicine and enjoy philosophy and the Psychology of mind and behavior. It seems interesting that he likes to write programs for machines that make them mimic the behavior of an intelligent being. While I enjoy exploring brain science and human behavior through the schema of technical maps and diagrams.  I enjoy a metaphorical method of approaching the mind as if it followed a wiring diagram.  I would not be able to do his job nor would he be able to do mine.  Our functions are different.

In the article which will follow, identity and function are again implied. I will introduce this page by clarifying some particular points that I wish to emphasize and reference later when I discuss a topic on anxiety disorders.

Here in this image you will see as plain as the nose on your face. I made a copy of the same image and imprinted the underlying anatomy to discuss it further.






The odors we perceive in our environment are often actual particles that originate from a particular source. Depending on the type of odor, we can already know a few things about the makeup. In chemistry, I learned that similar aromas of objects imply that they are usually similar in molecular structure.  If something smells like rotten eggs, it is because the geometric structure is likely related to that of sulfur dioxide (O-S-O).

We even have labels for peculiar foul odors.  “Rancid” is usually from a sugar based source that is spoiled. “Putrid” is usually from a protein or meat based source. An interesting rule of thumb to remember is “if you can smell it, it must have some water soluble component in the structure. This is because much of what we can taste and smell must be be at least slightly dissolved in our saliva.  Often when the substance breaks down it releases smaller byproducts of itself in the air.  Other times, the odors you may be smell are actually from the gases released from bacteria that consume an eroding substance.  Bacteria after all, enjoy starches and sugars for fuel sources and release gases as the substance is digested.

As gases or particles strike our olfactory senses, they activate particular electrical patterns which our brain associates with its activation signal.  This will then become tagged by our judgement center and appropriately labelled.

Now imagine that we were in a contest and asked to push a button when we smell a unique odor. Having a unique scent pattern activated would be much like olfactory nerves activating as this single hand gesture represented.


Single Odor in Olfaction

However, if we have many overlapping olfactory nerves stimulating, it is just like many hand gestures occurring at the same time.  When we have many similar odors presented within the same environment, it could be very difficult to discern when a target odor is included. A good example is when you are buying a fragrance at a store. I remember a time when I tried different colognes at a men’s cologne store. After about the third cologne, I found it difficult to distinguish one trial cologne with another. This is because many receptors which shared activation patterns became amplified and masked the unique pattern which I most recently tried to evaluate. The noise was too great to identify the single characteristic scent.  In other words, when you experience a great forest it is too difficult to single out a tree.



Over stimulation of Olfaction

This seems to be a repeating phenomenon in biology.  In fact any of our senses can become saturated with stimulation diminishing the capability to identify unique objects.  It is the same principle behind that red dot you see after a flash photograph. After a strong sensation impacts the cones of your eyes, unique color signal chemicals are released from special color sense cones in the neuro-receptors for the red color perception. It will then take a short time to replenish the cones neurochemically for an appropriate background squelch, as the annoying dot disappears.

I hope this is helpful as you enjoy this article.

Making sense of scents

Study shows that mice can identify specific odors amid complex olfactory environments

For many animals, making sense of the clutter of sensory stimuli is often a matter or literal life or death.

Exactly how animals separate objects of interest, such as food sources or the scent of predators, from background information, however, remains largely unknown. Even the extent to which animals can make such distinctions, and how differences between scents might affect the process were largely a mystery – until now.

A new study, described in an August 3 paper in Nature Neuroscience, a team of researchers led by Venkatesh Murthy, Professor of Molecular and Cellular Biology, showed that while mice can be trained to detect specific odorants embedded in random mixtures,their performance drops steadily with increasing background components. The team included Dan Rokni, Vikrant Kapoor and Vivian Hemmelder, all from Harvard University.

“There is a continuous stream of information constantly arriving at our senses, coming from many different sources,” Murthy said. “The classic example would be a cocktail party – though it may be noisy, and there may be many people talking, we are able to focus our attention on one person, while ignoring the background noise.

“Is the same also true for smells?” he continued. “We are bombarded with many smells all jumbled up. Can we pick out one smell “object” – the smell of jasmine, for example, amidst a riot of other smells? Our experience tells us indeed we can, but how do we pick out the ones that we need to pay attention to, and what are the limitations?”

To find answers to those, and other, questions, Murthy and colleagues turned to mice.

After training mice to detect specific scents, researchers presented the animals with a combination of smells – sometimes including the “target” scent, sometimes not. Though previous studies had suggested animals are poor at individual smells, and instead perceived the mixture as a single smell, their findings showed that mice were able to identify when a target scent was present with 85 percent accuracy or better.

“Although the mice do well overall, they perform progressively poorer when the number of background odors increases,” Murthy explained.

Understanding why, however, meant first overcoming a problem particular to olfaction.

While the relationship between visual stimuli is relatively easy to understand – differences in color can be easily described as differences in the wavelength of light – no such system exists to describe how two odors relate to each other. Instead, the researchers sought to describe scents according to how they activated neurons in the brain.

Using fluorescent proteins, they created images that show how each of 14 different odors stimulated neurons in the olfactory bulb. What they found, Murthy said, was that the ability of mice to identify a particular smell was markedly diminished if background smells activated the same neurons as the target odor.

“Each odor gives rise to a particular spatial pattern of neural responses,” Murthy said. “When the spatial pattern of the background odors overlapped with the target odor, the mice did much more poorly at detecting the target. Therefore, the difficulty of picking out a particular smell among a jumble of other odors, depends on how much the background interferes with your target smell. So, we were able to give a neural explanation for how well you can solve the cocktail party problem.

“This study is interesting because it first shows that smells are not always perceived as one whole object – they can be broken down into their pieces,” he added. “This is perhaps not a surprise – there are in fact coffee or wine specialists that can detect faint whiffs of particular elements within the complex mixture of flavors in each coffee or wine. But by doing these studies in mice, we can now get a better understanding of how the brain does this. One can also imagine that understanding how this is done may also allow us to build artificial olfactory systems that can detect specific chemicals in the air that are buried amidst a plethora of other odors.”






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Posted by on August 5, 2014 in Interesting Items, Neuroscience


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