**9. Intracellular recording methods**

ORCs in the antenna send olfactory information as trains of action potentials to the ipsilateral ALs of the insect brain where the axon terminals of ORCs synapse onto central neurons in neural structures known as olfactory glomeruli. Central neurons in the ALs, such as projection neurons and local interneurons, can be characterized by intracellular recordings with sharp electrodes. These glass electrodes are filled with a physiological solution that mimics the intracellular fluid of the recorded neuron. In addition, the electrodes can contain intracellular markers such as fluorescent dyes. The development of new intracellular markers provides the basis for rapid and complete reconstruction of individual neurons with little or no toxicity to the neuron. For examples, central neurons are injected iontophoretically with Lucifer yellow, neurobiotin, or biocytin. Brains are then dissected and fixed overnight in formaldehyde with sucrose in phosphate buffer. To visualize biocytin-injected neurons, brains are incubated with, e.g., Cy3-conjugated streptavidin. After subsequent histological processing, neurons are further investigated by laser-scanning confocal microscopy. This approach allows the study of both the physiological as well as morphological properties of the recorded neuron in a relatively undisturbed *in vivo* preparation as described below.
