PMC

Neuronal microcircuits for behavioral choice. (a and b) Proposed neuronal circuits for behavioral competition. (c) A proposed neuronal circuit for stimulus and behavioral competition. Symbols are given in the key.

Evidence for spikelets in C. elegans neurons. (a) Whole-cell recording of membrane potential in a neuron identified by expressing green fluorescent protein under the control of the promoter for the gene sra-11, which is known to be expressed specifically in three neuron classes (2 neurons per class): AIY, AVB and AIA; the recorded neuron is a member of one of these classes. Six current pulses (upper trace, 3 pA, 10 ms) were injected at 0.5 Hz. (b) A train of spikelets evoked in the same neuron by a longer current pulse (3 pA, 1.125 s). The recording pipette contained (mM): 125 KGlu, 18 KCl, 4 NaCl, 1 MgCl₂, 3 CaCl₂, 10 HEPES, and 20 BAPTA. The bath solution contained (mM): 5 KCl, 143 NaCl, 8 CaCl₂, 30 glucose, and 10 HEPES.

The neuronal circuit for klinokinesis in C. elegans. The circuit is depicted in schematic form as a cascade for four subcircuits, as labeled on the left. The overall function of each subcircuit is shown on the right. Groups of neurons of similar function are indicated by rectangles in some cases. Symbols are given in the key. Feedback connections from command neurons to sensory interneurons, and from sensory interneurons to sensory neurons, have been omitted for clarity; inhibitory motor neurons have been omitted for the same reason. The main anatomically defined classes of neurons summarized in this diagram are as follows. ON cells (8 classes, 13 neurons): Salts (ASEL, ADF); temperature (AFD, AWC); oxygen (AQR, PQR, URX); CO₂ (BAG). OFF cells (5 classes, 8 neurons): Salts (ASER, ASH); odors (AWC); O₂ (BAG); CO₂ (AFD). Hub neurons: RMG, RIH. Run interneurons (6 classes, 24 neurons): RMD, SMD, AIY, RIM, SMB, AIA. Turn interneurons (6 classes, 14 neurons): RIA, RIV, RIB, SIB, AIZ, AIB. Command neurons, forward locomotion (2 classes, 4 neurons): AVB, PVC. Command neurons, reverse locomotion (3 classes, 6 neurons): AVA, AVD, AVE. Excitatory motor neurons, forward locomotion (2 classes, 19 neurons): DB, VB. Excitatory motor neurons, reverse locomotion (3 classes, 32 neurons): DA, VA, AS. The number of sensory interneurons was estimated from Refs. [,,].

Experimental paradigms of behavioral choice in C. elegans. (a–d) The top and bottom rows show paradigms involving one or two stimuli (S₁, S₂), respectively; the left and right columns show paradigms involving one or two behaviors (B₁, B₂). Each panel contains a schematic illustration of a typical application of the paradigm, together with a simple electrical circuit that represents the switching logic entailed by the behavior. In the circuit diagrams, the ΔS switches close only when the stimulus is increasing; behaviors are symbolized by lamps which can be turned on by closing particular switches. The dashed line in c means that when one ΔS switch is closed the other is open, because the stimulus gradients rise in opposite directions. The ‘state’ switches in the yellow boxes are sensitive to the animal's internal state. In c and d, the circuits are more complex to allow for the correct behaviors when one or both stimuli are presented. Here the state switches serve the function of removing one of the resistors (R) from the circuit, thereby increasing the behavioral effect of one stimulus relative to the other (c) or causing one behavior to be more strongly activated than the other (d).