Mechanism and circuitry for clustering and fine discrimination of odors in insects.

Odor recognition encompasses both clustering and fine discrimination. Clustering joins together sets of odors, and fine discrimination distinguishes between odors belonging to the same cluster. We hypothesize that these two aspects of odor recognition are encoded in parallel by two brain areas of the insect olfactory system. Population activity of neurons in the lateral horn encodes the odor cluster, and population activity of neurons in the mushroom body encodes the fine identity of the odor. Our mechanism is based on the hypothesis that the underlying network of the insect olfactory system consists of a repetitive, hard-wired substructure whose anatomy we describe. We show that these suggested mechanisms and circuitry explain not only the observed numbers and connections of neurons in the system, but also the observed activity of these neurons, and why oscillations are critical for fine discrimination but not for clustering of odors.