The Sense of Smell, the Sense of SelfFor this article, I would like to revisit some of the questions left unanswered in my last article regarding the sense of smell. In that article, I outlined some of what we now know about how smells are identified and the initial levels of how that information is encoded in the brain; for this article I would like to retrace that path (as far as possible) up to my experience of smell and then see if my experience corresponds to the proposed models. From this perspective, I would like to take one last look at the equation "brain = behavior" and the notion of "ego-function" and see if I can make definitive sense of it all in a way that is not entirely dissonant with my experiences. Let's consider smell again, then. My last article ended with the following conclusions regarding the olfactory system. There are between 500 and 1000 unique protein receptor genes expressed only in the olfactory epithelium. Each of these receptors responds to a unique odorant or a unique characteristic of 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 type of odorant. Each type of neuron is randomly distributed in 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 and spatially organized map of activity across the several hundred receptor types. The gap between 1000 receptor neuron types and discrimination between 10,000 odors is bridged in the interpretation of activity level ratios and relationships in the population. The olfactory bulb was compared to an operator's switchboard, and the process of identifying odors was compared 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? Which parts of the brain assign meaning and identity to each stimulation pattern, and then choose an appropriate response? Some of these questions have been addressed by Walter Freeman in his research, and he has several useful insights into the process of preattentive perception, or the almost instantaneous recognition of the familiar.