Saturday, February 11, 2017

Olfacoception - a brief overview. (or, "How does smell work, neurologically?")

In the field of neurology, smell is such an interesting anomaly. To adults, having smell does clearly serve purposes--allow us to smell food, alerts us that something may be burning, or tells us that we need to change a diaper. So why does smell start out as one of the (if not the single) most important senses that we then allow to regress?  The answer to that is simple--the degree to which we depend on it. While at birth we are relying upon smell to find milk, by the time our eyes have learned to focus, we find it much more easy to visually identify milk instead of smelling for it. (Not to mention that the smell may be somewhat sealed when in a bottle.)

The olfactory lobe (or olfactory bulb), the area of the brain where we process smell, and is a small area on the underside of the frontal lobe. The olfactory receptor cells line the upper side of the nasal cavity and then transmit to the olfactory lobe via the olfactory nerve. Enough with the technicalities; here are some of the areas of research in this realm of the brain you may find interesting:

  • Research done in the 1920's created a generalization that we can detect about 10 000 different odours. This was challenged in 2014 by research in France in which a team led by Caroline Bushdid found that 90% of humans can detect roughly 1 trillion different odours.
  • Unlike many neurons, olfactory neurons can regenerate. This ability by the olfactory nerves is one reason they are currently being researched so extensively, so that one day that ability could be applied to other types of neurons and nerve cells.
  • Roughly 3% of our human genome code is commited to olfactory receptors, neurons, and the lobe (bulb). This high percentage of our DNA not only shows links to our genetic ancestry, when we were likely far more dependent upon smell, but also to its incredible complexity.
  • Smell and memory can often have a strong correlation. The olfactory lobe is right beside the hippocampus (responsible for storing memories) and not far from the amygdala. For this reason, specific smells that strongly relate to specific memories can also be strong triggers for emotions. 
  • Olfactory hallucinations can play a part in many neurological disorders. People with epilepsy, tumours, with a history of strokes or experiencing a stroke all may experience hallucinations in which they claim to be smelling something while the olfactory receptors are not chemically receiving that smell (the smell is not physically existing). 
  • Olfactory hallucinations and olfactory illusions are two different forms of neurodeception. Hallucinations are when the receptors are actually not receiving any chemical reaction, but the olfactory lobe is acting as though the olfactory nerve is telling it the chemical is present. Illusions are when the receptors have a chemical reaction, but misinterpret it as a different smell. Research in 2001 looked at how easily we can fall for illusions with similar odours.  
Where can this come into play in the classroom, that is a bit of a difficult question. In a class where there odour usually takes a very small role, maybe it could begin to be experimented with. An example I will use is that of the degree to which the various components in grade 11 biology where they are learning about cellular respiration and then photosynthesis, all at a cellular/molecular level. Is there a chance that you could be burning one candle while teaching cellular respiration and then a candle with a very different odour when teaching photosynthesis? This is something I may put to the test this year.

To hear interviews with Dr. Keller, the lead researcher in the study that theorized we smell over 1 trillion different odours, click on this link:


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