'Name the smell' brain game
doi:10.1038/nindia.2008.137 Published online 7 March 2008
A research team from Bangalore’s National Centre for Biological Sciences has tried to analyze the mechanism that the brain adopts to differentiate between two separate smells at one go.
It is known that at times the brain can not differentiate between two odors simultaneously. Instead, it gets an intermediate, completely new odor between the two. Earlier work had proposed theoretical models on how the circuitry of the olfactory bulb (OB) – the brain hub that processes odor information sent from the nose – segregates odors. These models believed that each odor would be represented by distinct stable firing patterns of the OB neurons, called attractor states.
"We have shown that this is not true," says one of the researchers Adil Ghani Khan. In fact, if one mixes two distinct odors then the firing pattern elicited by the mixture is intermediate between the two odors, he says. "Thus the OB does not use attractors states," he says.
The researchers have also come up with a new way of looking at the patterns of firing that these neurons show. Earlier research was unable to predict the brain response to a mixture of odors given the two original odors. The patterns did not simply add up in the mixtures.
"We show that the way of looking at the two original patterns in the first place was wrong. What we can see in these recordings is only the tip of the iceberg, we don’t see whats happening in the neurons when the firing rate falls to zero," Khan says.
The team developed an algorithm to predict the actual shape of the response pattern. This shows that one can predict the responses not only to mixtures of odors in different ratios, but also to odors at different concentrations.
The new model shows how two different patterns can add up to give a third completely new pattern. This may explain an observation in human studies, where sometimes a mixture of two odors smells like a completely new, third odor.
- Khan, A. G. et al. Odor Representations in the Rat Olfactory Bulb Change Smoothly with Morphing Stimuli. Neuron 57, 571-585 (2008)