Background: Multi-sensory integration is necessary for organisms to discriminate differentenvironmental stimuli and thus determine behavior. Caenorhabditis elegans has 12 pairs of amphidsensory neurons, which are involved in generating behaviors such as thermotaxis towardcultivation temperature, and chemotaxis toward chemical stimuli. This arrangement of knownsensory neurons and measurable behavioral output makes C. elegans suitable for addressingquestions of multi-sensory integration in the nervous system. Previous studies have suggested thatC. elegans can process different chemoattractants simultaneously. However, little is known abouthow these organisms can integrate information from stimuli of different modality, such as thermaland chemical stimuli.Results: We studied the behavior of a population of C. elegans during simultaneous presentationof thermal and chemical stimuli. First, we examined thermotaxis within the radial temperaturegradient produced by a feedback-controlled thermoregulator. Separately, we examined chemotaxistoward sodium chloride or isoamyl alcohol. Then, assays for simultaneous presentations of 15°C(colder temperature than 20°C room temperature) and chemoattractant were performed with15°C-cultivated wild-type worms. Unlike the sum of behavioral indices for each separate behavior,simultaneous presentation resulted in a biased migration to cold regions in the first 10 min of theassay, and sodium chloride-regions in the last 40 min. However, when sodium chloride wasreplaced with isoamyl alcohol in the simultaneous presentation, the behavioral index was verysimilar to the sum of separate single presentation indices. We then recorded tracks of single wormsand analyzed their behavior. For behavior toward sodium chloride, frequencies of forward andbackward movements in simultaneous presentation were significantly different from those in singlepresentation. Also, migration toward 15°C in simultaneous presentation was faster than that in15°C-single presentation.Conclusion: We conclude that worms preferred temperature to chemoattractant at first, butpreferred the chemoattractant sodium chloride thereafter. This preference was not seen forisoamyl alcohol presentation. We attribute this phase-dependent preference to the result ofintegration of thermosensory and chemosensory signals received by distinct sensory neurons.
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