Multisensory integration in C. elegans

Abstract

Multisensory integration is a neural process by which signals from two or more distinct sensory channels are simultaneously processed to form a more coherent representation of the environment. Multisensory integration, especially when combined with a survey of internal states, provides selective advantages for animals navigating complex environments. Despite appreciation of the importance of multisensory integration in behavior, the underlying molecular and cellular mechanisms remain poorly understood. Recent work looking at how Caenorhabditis elegans makes multisensory decisions has yielded mechanistic insights into how a relatively simple and well-defined nervous system employs circuit motifs of defined features, synaptic signals and extrasynaptic neurotransmission, as well as neuromodulators in processing and integrating multiple sensory inputs to generate flexible and adaptive behavioral outputs.

Figure 1. Different mechanisms of multisensory integration in C. elegans

(a) Different mechanisms by which multisensory inputs converge at cellular sites. (i) Polymodal sensory neurons are themselves capable of integrating multiple sensory stimuli; (ii) sensory neurons work with one another to form a more complete representation of the multisensory environment, then use that information to direct responses to specific sensory stimuli; (iii) sensory neurons recruit one another, even one not ordinarily sensitive to the sensory stimulus, as an interneuron to generate a more appropriate response to the sensory stimulus. Examples of sensory stimuli and neurons are provided. Arrows represent information flow, and depict known functional relationships between neurons indicated by genetic, anatomical, behavioral, or physiological analysis. (b) Different circuit motifs underlying multisensory decision making. (i) Interneurons direct behavioral responses to simultaneously presented multisensory stimuli by integrating inputs from sensory neurons that respond to distinct unisensory stimuli present in the environment; (ii) a “hub” interneuron interact with “spoke” sensory neurons to direct behavioral responses to stimuli detected by the sensory neurons; (iii) in a “top-down” fashion, an interneuron regulates a multisensory decision by tuning the sensitivity of a sensory neuron. Arrows in blue denote characterized transmitter signaling systems like glutamate, peptides, or monoamines.