Olfactory processing: maps, time and codes.

Natural odors are complex, multidimensional stimuli. Yet, they are learned and recognized by the brain with a great deal of specificity and accuracy. This implies that central olfactory circuits are optimized to encode these complex chemical patterns and to store and recognize their neural representations. What shape this optimization takes remains somewhat mysterious. Recent results from studies focusing on odor representation in the first olfactory relay (i.e. one synapse downstream of the receptor neurons) suggest a great deal of order and precision in the spatial and temporal features of odor representation. Whether these spatio-temporal features of neural activity are an essential part of the code for odors (i.e. whether these features are essential for the downstream decoding circuits) remains a central issue.