From what I've read in the medical literature (and this has been discussed before), the olfactory system is "ripe" for being "highjacked" by the dopaminergic system for it's ability to be transfomed into a dopamine producing area of the brain. In other words the cells of the olfactory system can be "turned on" by gene mechanisms to produce dopamine and develop dendrites to deliver the dopamine neurotransmitter to cells in the substantia nigra and other nearby structures in the immediate area in the forebrain. While this helps the dopaminergic system to function, it is a "last ditch effort" that the brain uses to get extra dopamine for the greater need of movement. Thus the sense of smell is "sacrificed" as it is considered by evolution to be "secondarily in neccessity" to the need for dopaminergic transmission. In this process the olfactory neurons lose their ability to function as they were designed for. I am surprised by this, as I would have thought smell to be more important than "taste". However, this may be a manifestation of the nature of the olfactoy bulb itself; it's ability to morph into a dopamine producing structure; it's abilities to produce outgrowths that reach the areas of dopamine uptake. cs