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1. Plasticity in inhibitory networks improves pattern separation in early olfactory processing

   https://doi.org/10.1038/s42003-025-07879-2  

   Joshi, Shruti; Haney, Seth; Wang, Zhenyu; Locatelli, Fernando; Lei, Hong; Cao, Yu; Smith, Brian; Bazhenov, Maxim (December 2025, Communications Biology)

   Abstract Distinguishing between nectar and non-nectar odors is challenging for animals due to shared compounds and varying ratios in complex mixtures. Changes in nectar production throughout the day and over the animal’s lifetime add to the complexity. The honeybee olfactory system, containing fewer than 1000 principal neurons in the early olfactory relay, the antennal lobe (AL), must learn to associate diverse volatile blends with rewards. Previous studies identified plasticity in the AL circuits, but its role in odor learning remains poorly understood. Using a biophysical computational model, tuned by in vivo electrophysiological data, and live imaging of the honeybee’s AL, we explored the neural mechanisms of plasticity in the AL. Our findings revealed that when trained with a set of rewarded and unrewarded odors, the AL inhibitory network suppresses responses to shared chemical compounds while enhancing responses to distinct compounds. This results in improved pattern separation and a more concise neural code. Our calcium imaging data support these predictions. Analysis of a graph convolutional neural network performing an odor categorization task revealed a similar mechanism for contrast enhancement. Our study provides insights into how inhibitory plasticity in the early olfactory network reshapes the coding for efficient learning of complex odors. 

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2. Olfactory navigation in arthropods

   https://doi.org/10.1007/s00359-022-01611-9  

   Steele, Theresa J.; Lanz, Aaron J.; Nagel, Katherine I. (January 2023, Journal of Comparative Physiology A)

   Abstract Using odors to find food and mates is one of the most ancient and highly conserved behaviors. Arthropods from flies to moths to crabs use broadly similar strategies to navigate toward odor sources—such as integrating flow information with odor information, comparing odor concentration across sensors, and integrating odor information over time. Because arthropods share many homologous brain structures—antennal lobes for processing olfactory information, mechanosensors for processing flow, mushroom bodies (or hemi-ellipsoid bodies) for associative learning, and central complexes for navigation, it is likely that these closely related behaviors are mediated by conserved neural circuits. However, differences in the types of odors they seek, the physics of odor dispersal, and the physics of locomotion in water, air, and on substrates mean that these circuits must have adapted to generate a wide diversity of odor-seeking behaviors. In this review, we discuss common strategies and specializations observed in olfactory navigation behavior across arthropods, and review our current knowledge about the neural circuits subserving this behavior. We propose that a comparative study of arthropod nervous systems may provide insight into how a set of basic circuit structures has diversified to generate behavior adapted to different environments. 

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3. Spectral preferences of mosquitos are altered by odors

   https://doi.org/10.1242/jeb.250318  

   Blake, Adam J; Riffell, Jeffrey A (July 2025, Journal of Experimental Biology)

   ABSTRACT Vision underlies many important behaviors in insects generally and in mosquitos specifically. Mosquito vision plays a role in predator avoidance, mate finding, oviposition, locating vertebrate hosts and vectoring disease. Recent work has shown that when sensitized to CO2, the visual responses of Aedes aegypti are wavelength dependent, but little is known about how other olfactory stimuli can modulate visual responses. The visual cues associated with flowers, vertebrate hosts or oviposition sites differ substantially and it is possible that odors might prime the mosquito visual system to respond to these different resources. To investigate the interplay of olfactory and visual cues, we adapted previously used wind tunnel bioassays to use quasi-monochromatic targets (390–740 nm) created with novel LED synthesizers. We coupled these visual targets with CO2 and the odors representative of vertebrate hosts, floral nectar or oviposition sites and assessed responses via 3D tracking of female mosquitos. When CO2 alone was present, we observed a lower preference for wavelengths in the green portion of the visible spectrum with a gradual increase as wavelengths moved towards the violet and red ends of the spectrum. However, when odors associated with both flowers and oviposition sites were present, we observed significant increases in mosquito preference for green (475–575 nm) stimuli. In contrast, when vertebrate host odor was present, we saw increased preference for stimuli across the entire visible spectrum. These odor shifts in mosquito spectral preferences suggest these preferences are not fixed and shift depending on the behavioral context. 

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4. Effect of Temperature on Mosquito Olfaction

   https://doi.org/10.1093/icb/icad066  

   Lahondère, Chloé; Vinauger, Clément; Liaw, Jessica E; Tobin, Kennedy K; Joiner, Jillian M; Riffell, Jeffrey A (June 2023, Integrative And Comparative Biology)

   Synopsis Mosquitoes use a wide range of cues to find a host to feed on, eventually leading to the transmission of pathogens. Among them, olfactory cues (e.g., host-emitted odors, including CO2, and skin volatiles) play a central role in mediating host-seeking behaviors. While mosquito olfaction can be impacted by many factors, such as the physiological state of the insect (e.g., age, reproductive state), the impact of environmental temperature on the olfactory system remains unknown. In this study, we quantified the behavioral responses of Aedes aegypti mosquitoes, vectors of dengue, yellow fever, and Zika viruses, among other pathogens, to host and plant-related odors under different environmental temperatures. 

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5. Effects of stochastic coding on olfactory discrimination in flies and mice

   https://doi.org/10.1371/journal.pbio.3002206  

   Srinivasan, Shyam; Daste, Simon; Modi, Mehrab N.; Turner, Glenn C.; Fleischmann, Alexander; Navlakha, Saket (October 2023, PLOS Biology)

   Benton, Richard (Ed.)

   Sparse coding can improve discrimination of sensory stimuli by reducing overlap between their representations. Two factors, however, can offset sparse coding’s benefits: similar sensory stimuli have significant overlap and responses vary across trials. To elucidate the effects of these 2 factors, we analyzed odor responses in the fly and mouse olfactory regions implicated in learning and discrimination—the mushroom body (MB) and the piriform cortex (PCx). We found that neuronal responses fall along a continuum from extremely reliable across trials to extremely variable or stochastic. Computationally, we show that the observed variability arises from noise within central circuits rather than sensory noise. We propose this coding scheme to be advantageous for coarse- and fine-odor discrimination. More reliable cells enable quick discrimination between dissimilar odors. For similar odors, however, these cells overlap and do not provide distinguishing information. By contrast, more unreliable cells are decorrelated for similar odors, providing distinguishing information, though these benefits only accrue with extended training with more trials. Overall, we have uncovered a conserved, stochastic coding scheme in vertebrates and invertebrates, and we identify a candidate mechanism, based on variability in a winner-take-all (WTA) inhibitory circuit, that improves discrimination with training. 

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