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Glomerular Modules

A number of observations suggest that glomeruli of related, but distinct, molecular specificity are clustered together within the olfactory bulb. Odorants sharing molecular features activate overlapping regions of the glomerular layer, but the glomeruli stimulated within these areas are often different even for closely related odorants (24,27,28). Most odorants activate clusters of adjacent glomeruli within their primary response regions rather than activating individual glomeruli, and the number of glomeruli in a cluster that are activated to any given extent increases with increasing odorant concentration (23). Along a homologous series of straight-chained odorants possessing the same functional group but increasing numbers of carbon atoms, the activated glomeruli shift gradually and systematically in location within the glomerular region that was responsive to molecules containing that functional group (28,30). 

By comparing activity patterns of odorants differing in chemical structure by small increments, and by outlining the new glomerular clusters associated with these changes, boundaries can be derived that enclose glomeruli responding to related features (23,29). These areas, termed "glomerular modules", have proven useful in testing predictions regarding the activity patterns that would be evoked by previously untested odorants (29,30,31). The specificity of these domains has been replicated with the use of optical imaging of endogenous signals from the glomerular layer of the olfactory bulb (68,70). The boundaries of proposed glomerular modules can be used to reduce the complexity of data matrices for statistical analyses (30,31,32,36). On this website, these modular boundaries are offered as overlays on activity patterns. However, despite their usefulness, the modules are works-in-progress, and boundaries will be altered as additional activity patterns are collected. For example, certain modules easily can be divided into sub-modules while certain odorants stimulate activity centered on the borders between adjacent modules as they are drawn currently (31). Furthermore, interdigitated glomeruli within certain modules appear to respond to odorants not obviously sharing molecular features (e.g., modules "c" and "C" stimulated by ketones and aromatic odorants in 32). While most of the original designations remain consistent, these modular designations as ongoing hypotheses that will be revised as new data become available.  

Current working definitions of glomerular modules used in analyses of bulbar activity patterns.

 
 
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Mapping Data
Background
Combinatorial Coding
Molecular Features
Glomerular Modules
Chemotopic Progressions
Global Chemotopy
Feature Interactions
Predictive Value
Odorant Concentration
Odorant Contaminants
Effects of Experience
Literature Cited
 
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This Human Brain Project/Neuroinformatics project is funded by the National Institute on Deafness and Other Communication Disorders and the National Institute of Mental Health