Lateral horn of insect brain

The lateral horn (lateral protocerebrum) is one of the two areas of the insect brain where projection neurons of the antennal lobe send their axons. The other area is the mushroom body. Several morphological classes of neurons in the lateral horn receive olfactory information through the projection neurons.

In lateral horn, axons of pheromone-sensitive projection neurons are segregated from the axons of plant odor-sensitive projection neurons. In addition, the dendrites of lateral horn neurons are restricted to one of these two zones, suggesting that pheromones and plant odors are processed separately in the lateral horn.

Lateral horn neurons responsive to non-pheromonal odors arborize widely in the lateral horn, possibly integrating information from a large number of projection neurons (even if the projection neurons themselves project only to specific regions of the lateral horn). Intracellular recordings from lateral horn neurons show that many of these neurons respond broadly to odors. Responses in these neurons are synchronized to odor-evoked oscillations, and depend on odor concentration.

The olfactory receptor neurons in the antenna and maxillary palps project into the olfactory lobes of the insect brain, which in turn project the higher order processing centers, the lateral horn or the mushroom bodies. The lateral horn has vague boundaries in the brain but is bordered by the ends of the branching of projecting neurons in the lateral protocerebrum. There are at least 10 morphological classes of lateral horn neurons. This system is highly conserved throughout the insect world.

Insects need an area that integrates olfactory information because they use olfaction as their primary means of gaining information about their world. They must assign a "valence" (attraction or aversion behavior) to important odors like poisonous food (aversion), mates (attraction) or colony members (situational). This response is usually base on if the scent is pleasant or unpleasant to the animal. The lateral horn is the brain region that accomplishes this olfactory information integration. It coordinates behaviors innate (instinctual) behaviors with certain odors.

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