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1. The Role of the Stimulus in Olfactory Plasticity

   https://doi.org/10.3390/brainsci13111553  

   Coppola, David M.; Reisert, Johannes (November 2023, Brain Sciences)

   Cheetham, Claire E. (Ed.)

   Plasticity, the term we use to describe the ability of a nervous system to change with experience, is the evolutionary adaptation that freed animal behavior from the confines of genetic determinism. This capacity, which increases with brain complexity, is nowhere more evident than in vertebrates, especially mammals. Though the scientific study of brain plasticity dates back at least to the mid-19th century, the last several decades have seen unprecedented advances in the field afforded by new technologies. Olfaction is one system that has garnered particular attention in this realm because it is the only sensory modality with a lifelong supply of new neurons, from two niches no less! Here, we review some of the classical and contemporary literature dealing with the role of the stimulus or lack thereof in olfactory plasticity. We have restricted our comments to studies in mammals that have used dual tools of the field: stimulus deprivation and stimulus enrichment. The former manipulation has been implemented most frequently by unilateral naris occlusion and, thus, we have limited our comments to research using this technique. The work reviewed on deprivation provides substantial evidence of activity-dependent processes in both developing and adult mammals at multiple levels of the system from olfactory sensory neurons through to olfactory cortical areas. However, more recent evidence on the effects of deprivation also establishes several compensatory processes with mechanisms at every level of the system, whose function seems to be the restoration of information flow in the face of an impoverished signal. The results of sensory enrichment are more tentative, not least because of the actual manipulation: What odor or odors? At what concentrations? On what schedule? All of these have frequently not been sufficiently rationalized or characterized. Perhaps it is not surprising, then, that discrepant results are common in sensory enrichment studies. Despite this problem, evidence has accumulated that even passively encountered odors can “teach” olfactory cortical areas to better detect, discriminate, and more efficiently encode them for future encounters. We discuss these and other less-established roles for the stimulus in olfactory plasticity, culminating in our recommended “aspirations” for the field going forward. 

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2. Effects of Wing Kinematics on Modulating Odor Plume Structures in the Odor Tracking Flight of Fruit Flies

   https://doi.org/10.1115/FEDSM2021-61832  

   Lei, Menglong; Li, Chengyu (August 2021, ASME 2021 Fluids Engineering Division Summer Meeting)

   Abstract Insects rely on their olfactory system to forage, prey, and mate. They can sense odorant plumes emitted from sources of their interests with their bilateral odorant antennae, and track down odor sources using their highly efficient flapping-wing mechanism. The odor-tracking process typically consists of two distinct behaviors: surging upwind and zigzagging crosswind. Despite the extensive numerical and experimental studies on the flying trajectories and wing flapping kinematics during odor tracking flight, we have limited understanding of how the flying trajectories and flapping wings modulate odor plume structures. In this study, a fully coupled three-way numerical solver is developed, which solves the 3D Navier-Stokes equations coupled with equations of motion for the passive flapping wings, and the odorant convection-diffusion equation. This numerical solver is applied to investigate the unsteady flow field and the odorant transport phenomena of a fruit fly model in both surging upwind and zigzagging crosswind cases. The unsteady flow generated by flapping wings perturbs the odor plume structure and significantly impacts the odor intensity at the olfactory receptors (i.e., antennae). During zigzagging crosswind flight, the differences in odor perception time and peak odor intensity at the receptors potentially help create stereo odorant mapping to track odor source. Our simulation results will provide new insights into the mechanism of how fruit flies perceive odor landscape and inspire the future design of odor-guided micro aerial vehicles (MAVs) for surveillance and detection missions. 

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3. Effects of flapping kinematics on odor plume dynamics in low Reynolds number settings

   https://doi.org/10.1063/5.0255476  

   Lei, Menglong; Li, Chengyu (March 2025, Physics of Fluids)

   Insects rely on their olfactory systems to detect odors and locate odor sources through highly efficient flapping-wing mechanisms. While previous studies on bio-inspired unsteady flows have primarily examined the aerodynamic functions of flapping wings, they have largely overlooked the effects of wing-induced unsteady flows on airborne odor stimuli. This study aims to explore how flapping kinematics influence odorant transport. Computational fluid dynamics simulations were employed to investigate unsteady flow fields and odorant transport by solving the Navier–Stokes and odor advection–diffusion equations. Both two-dimensional (2D) and three-dimensional (3D) simulations were conducted to visualize the flow fields and odor concentration distributions generated by pitching–plunging airfoils. Our findings reveal that higher Strouhal numbers, characterized by increased flapping frequency, produce stronger flow jets that enhance odor advection and dissipation downstream, while reducing odor concentration on the airfoil surface. In 2D simulations, symmetry breaking at high Strouhal numbers causes oblique advection of vortices and odor plumes. In contrast, 3D simulations exhibit bifurcated horseshoe-like vortex rings and corresponding odor plume bifurcations. These findings highlight the intricate coupling between unsteady aerodynamics and odor transport, offering valuable insights for bio-inspired designs and advanced olfactory navigation systems. 

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4. Respiratory Modulation by Phototransduction Demonstrates Time-Dependence in Male Mice

   Halick, SR; Marino, GM; Arble, DM (March 2026, ASBMB Annual Meeting)

   The transduction of light energy at the retina goes on to affect a range of non-image forming processes, most notably circadian photoentrainment, mood, and the pupillary light reflex. Our lab has previously demonstrated that retinal phototransduction can also modulate an animal’s breathing. However, it remains unknown how the timing of a light stimulus alters phototransduction and resulting behavior. Here, we investigate how unpredictable light stimuli affect respiratory frequency and tidal volume in mice. Male C57BL/6J mice (n = 8) were maintained on a 12:12 light–dark cycle, and breathing was assessed using whole-body plethysmography. All light stimuli were presented during the animals’ dark phase, either 1 hour after lights off (“early” dark phase, ZT13 to ZT16) or 5 hours after lights off (“late” dark phase, ZT17 to ZT20). As supported by our prior research, early light stimuli immediately suppressed breathing and, later, led to an increase in breathing after stimuli offset. However, late dark phase stimuli failed to affect respiration, even when spectral composition of the light was modified. These data demonstrate that the timing of light has differential effects on breathing. These data may implicate time-dependent differences in phototransduction and/or time-dependent differences in signal processing which go on to affect fundamental physiological processes. 

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5. The functional logic of odor information processing in the Drosophila antennal lobe

   https://doi.org/10.1371/journal.pcbi.1011043  

   Lazar, Aurel A.; Liu, Tingkai; Yeh, Chung-Heng (April 2023, PLOS Computational Biology)

   Morozov, Alexandre V. (Ed.)

   Recent advances in molecular transduction of odorants in the Olfactory Sensory Neurons (OSNs) of theDrosophilaAntenna have shown that theodorant object identityis multiplicatively coupled with theodorant concentration waveform. The resulting combinatorial neural code is a confounding representation of odorant semantic information (identity) and syntactic information (concentration). To distill the functional logic of odor information processing in the Antennal Lobe (AL) a number of challenges need to be addressed including 1) how is the odorantsemantic informationdecoupled from thesyntactic informationat the level of the AL, 2) how are these two information streams processed by the diverse AL Local Neurons (LNs) and 3) what is the end-to-end functional logic of the AL? By analyzing single-channel physiology recordings at the output of the AL, we found that the Projection Neuron responses can be decomposed into aconcentration-invariantcomponent, and two transient components boosting the positive/negative concentration contrast that indicate onset/offset timing information of the odorant object. We hypothesized that the concentration-invariant component, in the multi-channel context, is the recovered odorant identity vector presented between onset/offset timing events. We developed a model of LN pathways in the Antennal Lobe termed the differential Divisive Normalization Processors (DNPs), which robustly extract thesemantics(the identity of the odorant object) and the ON/OFF semantic timing events indicating the presence/absence of an odorant object. For real-time processing with spiking PN models, we showed that the phase-space of the biological spike generator of the PN offers an intuit perspective for the representation of recovered odorant semantics and examined the dynamics induced by the odorant semantic timing events. Finally, we provided theoretical and computational evidence for the functional logic of the AL as a robustON-OFF odorant object identity recovery processoracross odorant identities, concentration amplitudes and waveform profiles. 

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