Redundant neural circuits regulate olfactory masking

Olfactory masking is a complex olfactory response found in humans. However, the mechanisms whereby the presence of one odorant masks the sensory and behavioral responses elicited by another odorant are poorly understood. Here, we report that Caenorhabditis elegans displays olfactory masking and that the presence of a repulsive odorant, 2-nonanone, that signals threat strongly masks the attraction of other odorants, such as isoamyl alcohol (IAA) or benzaldehyde that signals food. Using a forward genetic screen, we found that several genes, osm-5, osm-1, and dyf-7, known to regulate the structure and function of sensory neurons played a critical role in olfactory masking. Loss of these genes mildly reduces the response to 2-nonanone and disrupts the masking effect of 2-nonanone. Restoring the function of OSM-5 in either AWB or ASH, two sensory neurons known to mediate 2-nonanone-evoked avoidance, is sufficient to rescue olfactory masking. AWB is activated by the removal of 2-nonanone stimulation or the onset of IAA; however, the mixture of 2-nonanone and IAA stimulates AWB similarly as 2-nonanone alone, masking the cellular effect of IAA. The latency of the AWB response is critical for the masking effect. Thus, our results identify redundant neural circuits that regulate the robust masking effect of a repulsive odorant and uncover the neuronal and cellular basis for this complex olfactory task. AUTHOR SUMMARYIn their natural environment, animals, including humans, encounter complex olfactory stimuli. However, regardless how complex the stimuli are, the behavioral output can only be one. Thus, how the brain processes multiple sensory cues to generate a coherent behavioral output is critical for the survival of the animal. In the present study, we combined molecular cellular genetics, optical physiology and behavioral analysis to study olfactory masking, a common olfactory phenomenon in which the presence of one odorant masks the stimulation of another odorant. Our results show that olfactory masking is regulated by redundant neuronal circuits, a mechanism that likely ensures the robust behavioral response to the sensory cue representing information critical for the survival.