Meeting Abstract

S1.4  Tuesday, Jan. 4  Passing Phases: Structure of a neural circuit that couples modular neural oscillators MULLONEY, B.*; SMARANDACHE, C.R.; Mulloney bcmulloney@ucdavis.edu

Many behavioral tasks require synchronization of distributed neural circuits, but the neural mechanisms that synchronize them are largely unknown. In the crayfish CNS, the modular local circuits that control swimmerets are distributed in four segments, but when the swimmeret system is active the outputs of these modules are synchronized with a stable intersegmental phase-difference of 0.25, an example of metachronal synchronization. In each module, coordinating neurons encode detailed information about each cycle of the module’s motor output as bursts of spikes, and export this information to modules in other segments. This information is both necessary and sufficient for normal intersegmental coordination. In a comprehensive set of recordings, we mapped the synaptic connections of two types of coordinating neurons onto their common target neurons in other segments. In these target neurons, both types of coordinating axons caused large, brief excitatory postsynaptic potentials (EPSPs). Each axon made its strongest synapse onto the target neuron in the nearest neighboring segment. Its synapses onto homologous targets in more remote segments were progressively weaker, a segmental gradient of synaptic strength. The shape-indices of these EPSPs are tuned to transmit the coordinating information from each axon precisely. In each target neuron’s own module, these bursts of EPSPs modified the phase of the module’s motor output. Each target neuron decodes information from several coordinating axons, and the strengths of their synapses differ systematically. These differences in synaptic strength weight information from each segment differently, which we postulate can account for features of the system’s characteristic metachronal synchronization.