Charting plasticity in the regenerating maps of the mammalian olfactory bulb

The anatomical organization of a neural system can offer a glimpse into its functional logic. The basic premise is that by understanding how something is put together one can figure out how it works. Unfortunately, organization is not always represented purely at an anatomical level and is sometimes best revealed through molecular or functional studies. The mammalian olfactory system exhibits organizational features at all these levels including 1) anatomically distinct structural layers in the olfactory bulb, 2) molecular maps based upon odorant receptor expression, and 3) functional local circuits giving rise to odor columns that provide a contextual logic for an intrabulbar map. In addition, various forms of cellular plasticity have been shown to play an integral role in shaping the structural properties of most neural systems and must be considered when assessing each system's anatomical organization. Interestingly, the olfactory system invokes an added level of complexity for understanding organization in that it regenerates both at the peripheral and the central levels. Thus, olfaction offers a rare opportunity to study both the structural and the functional properties of a regenerating sensory system in direct response to environmental stimuli. In this review, we discuss neural organization in the form of maps and explore the relationship between regeneration and plasticity.