Figure 5. Functional Circuits Involved in C. elegans’ Olfaction. (A) The RMG interneuron acts as a hub for olfactory input from four chemosensory neurons, the oxygen-carbon dioxide sensing URX neuron, and the IL2 neurons. Integrated input is them passed downstream onto the command interneuron. (B) The AWA and ASH neurons synapses onto the RIM interneuron to control initiation of forward and backwards locomotion. (C) Icas#9, an indolated ascaroside is sensed by three chemosensory neurons and two receptors to control roaming behavior. (D) The AWC-AIA-AIY circuit functions in an “Odor-OFF” fashion. When odor is present (left), the AWC neuron inhibits AIY, and is inhibited by AIA. When the odor is removed (right), the AWC neurons inhibit the inhibitory AIY, and activate AIB. The removal of AIY inhibition contributes to AIY activity as well. (E) Nociceptive avoidance is fine-tuned by ASI and ASH. A “reciprocal inhibition” is observed, with ASI activating ADF inhibition of ASH. Meanwhile, ASH activates RIC inhibition of ASI.