The ability to smell coffee immaterial of the presence of other interfering smells or the environment remains the same in humans. In effect, other smells or different environmental factors do not get in the way of our ability to experience the smell of individual odours. Researchers at Washington University in St. Louis found the answer as to why this happens by studying locusts (Proceedings of the National Academy of Sciences).
Like Pavlov's dogs, locusts were trained to associate an odour with food, their preference being a blade of grass. After going a day without food, a locust was exposed to a puff of odour (a puff of hexanol or isoamyl acetate), then given a blade of grass. In as few as six presentations, the locust learned to open its sensory appendages close to the mouth in expectation of a snack after simply smelling the ‘training odourant’.
The researchers studied which neurons were fired when the locust was exposed to the odour under different conditions, be it the presence of other smells, different environment, or when they were starved or fully fed.
Under different circumstances, they found highly inconsistent patterns of neurons were activated even though the locust appendage close to the mouth opened every time. The neural responses were highly variable with what the locusts were doing, behaviourally.
They turned to machine-learning algorithms to understand how variable neural responses continued to produce consistent or stable behaviour. It turned out that the locust exploited two functional types of neurons: those that are activated when an odourant is present, and those which are silenced when an odourant is present but become activated after the odour presentation ends, says the university press release.
To recognise an odourant's presence, researchers simply needed to add evidence for the odourant being present and subtract evidence against that odour being present. If the result was above a certain threshold, machine learning would predict the locust smelled the odour.
