Spontaneous Firing of Sensory Neurons Modulates the Gain in the Downstream Circuit of a Simple Olfactory System PDF Download
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Author: Matthew Justin O'Neill
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 63
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Book Description
In locusts and other insects, odorants are transduced into electrical signal by the olfactory receptor neurons and transmitted to central circuits for further processing. Previous studies have shown that exogenous variables (e.g., flow rates, humidity, temperature, odor mixtures, etc.) can influence the responses of the sensory neurons and therefore modulate the central circuits. However, how the sensory neuron activity is manipulated to achieve adaptive gain control in the following circuit is yet to be understood. It is possible that the magnitude of the stimulus-evoked response in the receptor neurons, their spontaneous activity, or both of these factors can change how information about a chemical cue is processed downstream. To this end, I studied the effects of modulating two different factors on the olfactory system (flow rate and relative humidity) at four levels of the olfactory system: individual olfactory receptor neurons (first-order neurons), the whole antenna (electroantennogram recordings), individual projection neurons in the antennal lobe of the brain (second-order neurons), and population antennal lobe activity as assayed by local field potential recordings in the mushroom body. We found that flow rate changes altered the magnitude of the stimulus-evoked responses in the antenna without altering the spontaneous activity levels. Whereas, changes in the relative humidity elicited a decrease in both response magnitude and baseline activity. Intriguingly, only the humidity modulation experiments brought about significant compensatory change in the spontaneous and odor-evoked activity of the second-order neurons in the antennal lobe. Therefore, our data and analysis suggest that baseline activity of receptor neurons seems to play a key role in adapting the gain of the locust brain's central circuit.
Author: Matthew Justin O'Neill
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 63
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Book Description
In locusts and other insects, odorants are transduced into electrical signal by the olfactory receptor neurons and transmitted to central circuits for further processing. Previous studies have shown that exogenous variables (e.g., flow rates, humidity, temperature, odor mixtures, etc.) can influence the responses of the sensory neurons and therefore modulate the central circuits. However, how the sensory neuron activity is manipulated to achieve adaptive gain control in the following circuit is yet to be understood. It is possible that the magnitude of the stimulus-evoked response in the receptor neurons, their spontaneous activity, or both of these factors can change how information about a chemical cue is processed downstream. To this end, I studied the effects of modulating two different factors on the olfactory system (flow rate and relative humidity) at four levels of the olfactory system: individual olfactory receptor neurons (first-order neurons), the whole antenna (electroantennogram recordings), individual projection neurons in the antennal lobe of the brain (second-order neurons), and population antennal lobe activity as assayed by local field potential recordings in the mushroom body. We found that flow rate changes altered the magnitude of the stimulus-evoked responses in the antenna without altering the spontaneous activity levels. Whereas, changes in the relative humidity elicited a decrease in both response magnitude and baseline activity. Intriguingly, only the humidity modulation experiments brought about significant compensatory change in the spontaneous and odor-evoked activity of the second-order neurons in the antennal lobe. Therefore, our data and analysis suggest that baseline activity of receptor neurons seems to play a key role in adapting the gain of the locust brain's central circuit.
Author: Kazuo Imaizumi
Publisher: Frontiers Media SA
ISBN: 2889454789
Category :
Languages : en
Pages : 152
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Book Description
Spontaneous activity in the nervous system is defined as neural activity that is not driven by an external stimulus and is considered a problem for sensory processing and computation. However, spontaneous activity is not completely random and often has unique spatiotemporal patterns that instruct neural circuit development in the developing brain. Moreover, normal and aberrant patterns of spontaneous activity underlie behavioral states and diseased conditions in the adult brain. The recent technological development has shed light on these unique questions in spontaneous activity. This eBook provides both original and review articles in the propensity, mechanisms, and functions of spontaneous activity in the sensory system. Our goal is to define the state of knowledge in the field, the current challenges, and the future directions for research.
Author: Srinath Nizampatnam
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Sensory stimuli evoke spiking activities that are patterned across neurons and time in the early processing stages of olfactory systems. What features of these spatiotemporal neural response patterns encode stimulus-specific information (i.e. 'neural code'), and how they are translated to generate behavioral output are fundamental questions in systems neuroscience. The objective of this dissertation is to examine this issue in the locust olfactory system. In the locust antennal lobe (analogous to the vertebrate olfactory bulb), a neural circuit directly downstream to the olfactory sensory neurons, even simple stimuli evoke neural responses that are complex and dynamic. We found each odorant activated a distinct neural ensemble during stimulus presentation (ON response) and following its termination (OFF response). Our results indicate that the ON and OFF ensemble neural activities differed in their ability to recruit recurrent inhibition, entrain field-potential oscillations, and more importantly in their relevance to behavior (initiate versus reset conditioned responses). Furthermore, when the same stimulus was encountered in a multitude of ways, we found that the neural response patterns in individual neurons varied unpredictably. Intriguingly, a simple, linear logical classifier (OR-of-ANDs) that can decode information distributed in flexible subsets of ON neurons was sufficient to achieve robust recognition. We found that the incorporation of OFF neurons could enhance pattern discriminability and reduce false positives thereby further improving performance. These results indicate that a trade-off between stability and flexibility in sensory coding can be achieved using a simple computational logic. Lastly, we examined how the ON and OFF neural ensembles varied with stimulus intensity. We found that neurons that were ON responsive at low intensity switched and became OFF responsive at higher intensities. Similarly, OFF responsive neurons at low intensity were recruited and responded during odor stimulation at higher intensities. We found a competitive network involving two sub-categories of GABAergic local neurons can mediate this switch between ON and OFF responsive ensembles and how they vary as a function of stimulus intensity. In sum, our results provide a comprehensive understanding of how a relatively simple invertebrate olfactory system could perform complex adaptive computations with very simple individual components.
Author: Marley Deena Kass
Publisher:
ISBN:
Category : Neuroplasticity
Languages : en
Pages : 318
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Book Description
Conventional wisdom suggests that the body's sensory systems should be consistent, so that a given sensory stimulus always produces more-or-less the same signal to the brain, which can then retrieve related memories or information. However, using optical neurophysiological tools to observe the earliest parts of the mouse olfactory system, we have found that actually these signals are highly flexible, such that different sensory experiences and previously learned information radically affect the way sensory stimuli are processed in the brain. The first stage of sensory processing in the olfactory system takes place in the olfactory bulb, where axons from olfactory sensory neurons (OSNs) in the nose segregate by receptor type and converge into one or two glomeruli on the surface of the bulb. The brain's initial (primary) neural code for the identity of an odor in the nose is thus the spatiotemporal pattern of olfactory bulb glomeruli receiving synaptic input from OSNs, which can be modulated by local circuits in the glomerular layer of the bulb. Here, we demonstrate that these primary odor representations are changed in vivo through simple environmental manipulations, such as olfactory sensory deprivation or odor exposure. Subsequent experiments show that passive odor exposure leads to changes in temporal patterns of OSN synaptic output that are correlated with perceptual changes in odor quality. We move on from simple environmental manipulations to explore how emotional learning can influence early sensory processing, and surprisingly find that discriminative olfactory fear conditioning can selectively enhance the synaptic output of OSNs during the presentation of threat-predictive odorants. By contrast, when conditioned fear generalizes across olfactory stimuli that are quite different from a threat-predictive odor, there is a corresponding facilitation of odor-evoked activity in inhibitory interneurons in the olfactory bulb that generalizes across threatening and non-threatening odors. These experience-dependent effects may be further modulated by individual differences in endogenous factors such as the expression of certain transduction proteins or circulating levels of sex hormones that can independently shape primary sensory odor representations. Collectively, the results from these experiments demonstrate that early neural representations of odors are highly malleable on the basis of prior sensory experience and learning, even as early as the primary sensory input to the brain. Such plasticity presumably maximizes the detection and discrimination of meaningful sensory stimuli in a constantly changing olfactory environment, and is of broad importance for downstream brain regions that receive input from the bulb.
Author: Anna Menini
Publisher: CRC Press
ISBN: 1420071998
Category : Science
Languages : en
Pages : 438
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Book Description
Comprehensive Overview of Advances in OlfactionThe common belief is that human smell perception is much reduced compared with other mammals, so that whatever abilities are uncovered and investigated in animal research would have little significance for humans. However, new evidence from a variety of sources indicates this traditional view is likely
Author: Chao Li
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 139
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Book Description
Sensory stimuli often evoke temporal patterns of spiking activity across a population of neurons in the early processing stages. What features of these spatiotemporal responses encode behaviorally relevant information, and how dynamic processing of sensory signals facilitates information processing are fundamental problems in sensory neuroscience that remain to be understood. In this thesis, I have investigated these issues using a relatively simple invertebrate model (locusts; Schistocerca americana). In locusts, odorants are transduced into electrical signals by olfactory sensory neurons in the antenna and are subsequently relayed to the downstream neural circuit in the antennal lobe (analogous to the olfactory bulb in vertebrates). We found that the sensory input evoked by an odorant could vary depending on whether the stimulus was presented solitarily or in an overlapping sequence following another cue. These inconsistent sensory inputs triggered dynamic reorganization of ensemble activity in the downstream antennal lobe. As a result, we found that the neural activities evoked by an odorant pattern-matched across conditions, thereby providing a basis for invariant stimulus recognition. Notably, we found that only the combination of neurons activated by an odorant was conserved across conditions. The temporal structure of the ensemble neural responses, on the other hand, varied depending on stimulus history: synchronous ensemble firings when stimulated by a novel odorant compared to asynchronous activities induced by a redundant stimulus. Furthermore, these neural responses were refined on a slower timescale (on the order of minutes, i.e. happening over trials) such that the same information about odorant identity and intensity was represented with fewer spikes. We validated these interpretations of our physiological data using results from multiple quantitative behavioral assays. In sum, this thesis work provides fundamental insights regarding behaviorally important features of olfactory signal processing in a relatively simple biological olfactory system.
Author: Hannah Ada Arnson
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 120
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Book Description
Understanding how sensory systems encode stimuli is a fundamental question of neuroscience. The role of every sensory system is to encode information about the identity and quantity of stimuli in the environment. Primary sensory neurons in the periphery are faced with the task of representing all relevant information for further processing by downstream circuits, ultimately leading to detection, classification and potential response. However, environmental variability potentially alters stimulus properties in non-relevant ways. Here, we address these problems using the mouse accessory olfactory system (AOS) as a model. The AOS is an independent olfactory system possessed by most terrestrial vertebrates, although not humans, and is specialized to detect social cues. It mediates behaviors such as reproduction, aggression, and individual identification. Non-volatile compounds found in urine, including sulfated steroids, are the main source of AOS stimuli. Vomeronasal sensory neurons (VSNs), the primary sensory neurons of the AOS, are located in the base of the nasal cavity, and they detect the identity and quantity of stimuli. However, like other sensory cues, urine is subject to environmental modulation through mechanisms such as evaporation and dilution that affect the concentrations of ligands in non-biologically relevant ways. Ideally, the AOS represents stimuli in ways that are stable across condition. In the scope of this thesis, I explore how the AOS represents concentration at the levels of the individual neuron, the circuit and the whole animal. Using extracellular recordings of explanted tissue, we characterized how VSNs encode stimuli. VSNs fired predominantly in trains of action potentials with similar structure during spontaneous and stimulus-driven activity. Using pharmacological and genetic tools, we demonstrated that the signal transduction cascade influences the structure of both spontaneous and stimulus-driven activity. Then, we explored the representation of concentration of sulfated steroids by VSNs and the circuit mechanisms by which the AOS can represent concentration information in a manner invariant to environmental uncertainties. We identified ratio-coding as a means for stable concentration representation. The ratio of the concentrations of non-volatile ligands found in urine will not change following urine evaporation or dilution, while the individual concentrations will. This property allows for both insensitivity to changes in absolute concentration and sensitivity to changes in relative concentration. Using extracellular recording and computational modeling, we have demonstrated that VSN activity can be used to robustly encode concentration using ratios. Finally, we attempted to develop a novel behavioral assay to investigate how mice detect AOS stimuli.
Author: Gary Francis Hammen
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 127
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Book Description
A common challenge across sensory processing modalities is forming meaningful associations between the neural responses and the outside world. These neural representations of the world must then be integrated across different sensory systems contributing to each individuals perceptual experience. While there has been considerable study of sensory representations in the visual system of humans and multiple model organisms, other sensory domains, including olfaction, are less well understood. In this thesis, I set out to better understand the sensory representations of the mouse accessory olfactory system (AOS), a part of the olfactory system. The mouse AOS, our model chemosensory system, comprises peripheral vomeronasal sensory neurons (VSNs), the accessory olfactory bulb (AOB), and downstream effectors. Our work describes the neural representations of multiple sensory inputs in the AOS, specifically the representations of odorants in high dimensional chemical sensory space in the AOB, and how these representations are shaped by interactions within the circuit. Given the complex nature of olfactory chemosensory representations, the features of our model system may give new perspectives on the neural representation of the outside world. In a neural representation of olfactory information, both the interactions between each receptor and odor compounds as well as the circuit mediated interactions could potentially affect the neural representations of the outside world. The initial neural response comprises component interactions between each receptor and the odor; chemical signals must interact with physical receptors. However, chemosensory processing, such as olfaction, requires interpreting a large variety of potentially overlapping chemical cues from the environment with only a finite number of receptor types. This means that each chemical cue does not necessarily activate only one receptor type or region of the circuit, but rather the cue is likely to be represented by multiple receptor and odor component interactions. Also, the component parts of odors may be processed differently when presented in isolation versus in a more complex mixture, thus allowing the response to a particular odor to vary with chemical context. Moreover, once these component representations exist, interactions within the neural circuit may further shape these responses. For example, one might expect component parts of a complex odor to specifically inhibit other component parts. In the case of the accessory olfactory system this inhibition could be at the receptor level or at the level of the sensory representation in the accessory olfactory bulb (AOB). In Chapter 3, I describe the overall organization of chemosensory representations in the accessory olfactory bulb (AOB), which is found to be a modular map in which the primary associations of functional sensory responses are spatially organized relative to one another. I find these primary associations are condensations of the first order sensory neuron axon terminals, which form population response pooling structures called glomeruli. In these glomeruli, similar response types from those sensory neurons expressing one of the approximately 300 receptor types in the vomeronasal organ (VNO) co-converge. One purpose of converging inputs of neurons expressing the same receptor is likely to minimize noise, and I demonstrate that pooling of like receptor responses into glomeruli does increase neural signal relative to noise. However, I also observed a modular organization among and between glomeruli in which certain types or patterns of chemosensory responses are always spatially adjacent to one another, while others are much farther apart than would be expected by chance. I found this spatial modularity for both ethological stimuli (urine collected from conspecifics with widely divergent physiological endocrine status) and individual sulfated steroids. In Chapter 4, I explore the consequences of changing sensory context, specifically the presentation of multiple compounds, and the role that inhibition plays in the neural representation of the sensory stimuli. First, I tested whether the circuit responds differently to demands to represent a single odor than to demands to represent multiple odors by using odors that activate glomeruli both inside and outside of modules. I found that responses to mixtures rapidly diverge from the responses of individual component parts. Moreover, there was an effect of inhibition in modulating the response to preferred stimuli in all glomeruli. However, initial analysis of one type of pregnanolone responsive glomeruli demonstrated that the divergent response to mixtures in this type of glomerulus was not mediated by inhibition at the glomerular level, but was rather attributable to bottom-up effects from the interactions of multiple ligands with chemosensory receptors in the VNO. Nonetheless, I also demonstrated that in the AOB, the axon terminals of the same sensory neurons (glomeruli) are organized into modules that allow for feedback inhibition. Significant ionotropic glutamate receptor signal modulation was observed within modules, demonstrating that there are inhibition mediated effects in the representation of complex mixtures when glomeruli are co-locally arranged. Specifically, at both the level of the VSNs and also in AOB glomeruli, the response to allopregnanolone sulfate is inhibited by co-presentation with estradiol sulfate. This both significantly increases the relative representation of estradiol sulfate and shifts representation of allopregnanolone primarily within modules. These types of context dependent interactions depend on the spatial organization described in Chapter 3 as well as mixture context, and have the potential to optimize the representation of some chemical cues in a context specific manner.
Author: Carla Mucignat-Caretta
Publisher: CRC Press
ISBN: 1466553413
Category : Medical
Languages : en
Pages : 614
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Book Description
Intraspecific communication involves the activation of chemoreceptors and subsequent activation of different central areas that coordinate the responses of the entire organism—ranging from behavioral modification to modulation of hormones release. Animals emit intraspecific chemical signals, often referred to as pheromones, to advertise their presence to members of the same species and to regulate interactions aimed at establishing and regulating social and reproductive bonds. In the last two decades, scientists have developed a greater understanding of the neural processing of these chemical signals. Neurobiology of Chemical Communication explores the role of the chemical senses in mediating intraspecific communication. Providing an up-to-date outline of the most recent advances in the field, it presents data from laboratory and wild species, ranging from invertebrates to vertebrates, from insects to humans. The book examines the structure, anatomy, electrophysiology, and molecular biology of pheromones. It discusses how chemical signals work on different mammalian and non-mammalian species and includes chapters on insects, Drosophila, honey bees, amphibians, mice, tigers, and cattle. It also explores the controversial topic of human pheromones. An essential reference for students and researchers in the field of pheromones, this is also an ideal resource for those working on behavioral phenotyping of animal models and persons interested in the biology/ecology of wild and domestic species.
Author: Haoyang Rong
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Sensory systems receive and process external stimuli to allow an organism to perceive and react to the environment. How is sensory information subsequently represented, transformed, and interpreted in the neural system? In this dissertation, I have investigated this fundamental question using the fruit fly (Drosophila melanogaster) olfactory system.Chemical cues are transduced into neural signals in the insect antenna by the olfactory receptor neurons (ORNs). The ORNs send their axons to the antennal lobe (AL), with each ORN type innervating a specific neuropil (glomerulus), where they synapse onto excitatory and inhibitory projection neurons (ePNs and iPNs). The ePNs project their axons to the 3rd order stages, the calyx (CL) and lateral horn (LH). On the other hand, the iPNs only innervate the LH. In this dissertation, I first examined how well the peripheral neural activities evoked by an odorant could predict the final behavioral output. As the stimulus intensity increases, a fly's preference for some odorants switch from attraction to aversion. Behavior assay suggested this phenomenon may help the fly evade harmful environment. Our results indicate that at the level of ORNs, increases in stimulus intensity could result in oscillatory extracellular field potentials that arise entirely due to abrupt changes in cell excitability. Notably, combining the activity of a few ORNs was sufficient to predict intensity-dependent preference changes with odor intensity. How is the sensory input organized in the downstream neural circuit, the insect antennal lobe? Odor-evoked signals from sensory neurons (ORNs) triggered neural responses that were patterned over space and time in cholinergic ePNs and GABAergic iPNs within the antennal lobe. The dendritic-axonal (I/O) response mapping was complex and diverse, and the axonal organization was region-specific (mushroom body vs. lateral horn). In the lateral horn, feed-forward excitatory and inhibitory axonal projections matched 'odor tuning' in a stereotyped, dorsal-lateral locus, but mismatched in most other locations. In the temporal dimension, ORN, ePN, and iPN odor-evoked responses had similar encoding features, such as information refinement over time and divergent ON and OFF responses. Notably, analogous spatial and temporal coding principles were observed in all flies, and the latter emerged from idiosyncratic neural processing approaches. In sum, these results provide key insights necessary for understanding how sensory information is organized along spatial and temporal dimensions.
