The Sense of Scents, the Sense of Self

The Sense of Scents, the Sense of Self

For this paper, I'd like to revisit some of the questions left unanswered in my last paper regarding the sense of smell. In that paper, I outlined some of what is now understood about how smells are identified and the initial levels of how that information is coded in the brain; for this paper I would like to trace that path (as much as possible) through to my experience of smell and then to see if my experience matches the proposed models. From this perspective, I'd like to take a last look at the "brain = behavior" equation and the notion of the "I - function" and see if I can't make some final sense of it all in a way which is not utterly dissonant with my own experiences.

Let's look at smell again, then. My last paper left off with the following conclusions regarding the olfactory system. There are between 500 and 1000 unique protein receptor genes which are expressed only in the olfactory epithelium. These receptors each respond to a unique odorant or to a unique feature on an odorant molecule (epitopes). It is suggested that there is a one - to - one relationship between a specific odorant, its protein receptor, and the sensory neuron: that is, any given sensory neuron expresses only one type of receptor and is therefore responsive to only one kind of odorant. Each type of neuron is randomly distributed across one of four zones within the olfactory epithelium. The information from this population coding is then reorganized, as these axons leave the epithelium and travel to the olfactory bulb, into a very specific, spatially organized map of activity across the several hundred kinds of receptors. The span between the 1000 types of receptor neurons, and discrimination amongst 10,000 odors, is bridged in the interpretation of the ratios and relationships of activity level across the population. The olfactory bulb was compared to an operators switchboard, and the process of odor identification was likened to determining which switchboard lights were flashing. The obvious question then becomes, what parts of the brain watch over the olfactory bulb, monitor its activity and interpret that activity? What parts of the brain assign meaning and identity to each pattern of stimulation, and then choose an appropriate response?

Some of these questions have been addressed by Walter Freeman in his investigations, and he has several useful insights into the process of preattentive perception, or the almost instantaneous recognition of the familiar.