**1. Introduction**

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The aim of this chapter is to discuss current electrophysiological recording techniques used to study the processing of olfactory and gustatory information in insects. More specifically, we will describe methods employed (a) to determine the physiological properties of gustatory (GRCs) and olfactory receptor cells (ORCs) in the peripheral nervous systems and (b) to physiologically characterize identifiable olfactory neurons in the central nervous system.

In studying the structural and functional organization of the nervous system, it is at times advantageous to use animal models, such as insects, for experimentation. Key factors that make insect nervous systems excellent models for analyzing gustatory and olfactory mechanisms are that they possess a relatively simple peripheral and central nervous system compared with their vertebrate counterparts. They also bear easily accessible sensory organs (sensilla) and individually identifiable neural structures. The number of receptor cells mediating mechanisms involved in olfaction and gustation is relatively small. Interestingly, some brain regions in invertebrates and vertebrates show remarkable morphological and physiological similarity and, therefore, the insect nervous system provides insights into general principles underlying taste and odor coding that occur in higher vertebrates.

Gustatory and olfactory cues play vital roles in shaping insect behavior. Insects rely on these senses in the sampling and selection of food sources, avoidance of noxious or toxic compounds, mating, and locating egg-laying sites. These chemical cues are detected by GRCs and ORCs housed in sensilla located mainly on the mouthparts, legs, and antennae and are converted into a neural code of action potentials, which is sent to the central nervous system for processing. GRCs and ORCs constitute sensory filters for environmental taste and smell signals in insects. They form the first layer of a decision making process and transfer information directly to centers in the brain.
