Figure 1.

Recording and stimulation. A, Schematic cross section of a leech midbody segment and overview of the local bend circuitry. Four sensory neurons, bilateral P_D and P_V, respond to pressure applied to the body wall (illustrated by hands). The “P” cells project to a set of interneurons (yellow) that in turn project to a set of excitatory and inhibitory motor neurons (green) that innervate the musculature in the body wall. B, Overview of recording and stimulation. A P_D cell and a contralateral P_V cell (labeled P_V^c) are impaled with sharp electrodes used to deliver spike-evoking stimuli. A selection of four nerves is targeted with suction electrodes for simultaneous extracellular recording from the axons of multiple motor neurons. Naming of nerves follows Ort et al. (1974).