Parosmia: Pathophysiology and Management.

Neuropeptide-Gated Perception of Appetitive Olfactory Inputs in Drosophila Larvae

Spatio–temporal dynamics of olfactory processing in the human brain: an event-related source imaging study

The entire olfactory system, except for the olfactory sensory neurons in the nasal cavity, is an intrinsic part of the limb system, conferring olfaction many rarely known functions including the regulation of emotion, memory, and physiological and psychological states, in addition to the general function of smell. Meanwhile, the innermost anatomical structures of the sensory system and the lacking of effective tools make the study of olfactory information coding, processing, transmission and perception processes extremely difficult. The functional magnetic resonance imaging (fMRI) has been broadly used in neuroscience research, because it can repeatedly and non-invasively monitor neuronal activity in any brain region with relatively high temporal and spatial resolutions. Its application has significantly advanced our understanding of olfactory information processing at higher olfactory centers in human brain. Olfactory bulb (OB), the information coding and processing center of the olfactory system, is dedicated to and essential for olfaction. However, the relative small size of human OB, in comparison with the spatial resolution of human fMRI, has been greatly hindering our study of the mechanisms of information coding and processing in the OB. Here the application of fMRI in the olfactory system was reviewed, and focused on the small animal fMRI, its advantages and some important progresses made in the past decade.

Olfactory Information Processing in Drosophila

The role of the Drosophila lateral horn in olfactory information processing and behavioral response

Event Abstract Back to Event Information processing in the Drosophila Olfactory System: From Odors to Kenyon cells Faramarz Faghihi1*, Florentin Wörgötter1 and Christoph Kolodziejski1 1 Georg-August-University Goettingen, Drittes Physikalisches Institut, Germany Insect navigation in natural environments, for instance to seek food or to find a mate of the same species, relies on the efficiency of the insects’ olfactory system to detect, memorize, associate and retrieve olfactory information. The olfactory system of Drosophila (including Antennal Lobe and the Mushroom Body) consists only around 3000 neurons (Newquist, 2011) and is thus an ideal model to study the information processing of learning and memory (Masse et al. 2009). Although the system is very simple, experimentally assessing all parameters is still very difficult if not impossible. An important example for information processing is the threshold of coincidence detection in Mushroom Body neurons, the so called Kenyon cells. Here, coincidence detection means that a neuron can detect the occurrence of timely simultaneous but spatially separate input signals. In computational studies (Nowotny et al., 2003; Smith et al., 2008) the number of coincidentally active input neurons that suffice to trigger Kenyon cell firing (i.e. the threshold) is usually set arbitrarily and to our knowledge there exists only one study that addresses this question theoretically (Huerta and Garcia-Sanchez, 2003). As Kenyon cells are involved in associative odor learning (Galili et al., 2011), a detailed understanding of their function and parameters is advantageous for a better understanding of learning and memory in Drosophila. The quality of information processing in a computational model of the olfactory system can give us a lead on physiological and structural parameters of this system. For this purpose we use an information theoretical measure, the mutual information, which relates to the capacity of information transmission (Paninski, 2003). The greater the mutual information between, for instance, the presented odors and the Kenyon cells, the more information about the presented odor(s) is in the Kenyon cell firing and, thus, the more efficacious is the information processing. When we model the olfactory system with experimentally verified parameters and the environment in such a way that the system has to rely on the discrimination of distinct odors, we find, for instance, a clear optimum in mutual information for coincidence threshold values between 3 and 5. Additionally, non-synaptic modulatory input (Szyszka et al., 2008) modifies the optimal threshold values and can by this compensate dynamic environments or changing motivational states. This study shows the potential of using mutual information to extract basic structural and functional properties of such neuronal systems. Acknowledgements This research was supported by the BMBF-funded BCCN Goettingen with grant number 01GQ1005A, project B5. References Galili SD, Ludke A, Galizia CG, Szyszka P, Tanimoto H. Olfactory Trace Conditioning in Drosophila. Journal of Neuroscience 31(20): 7240-7248, 2011. Huerta R, Garcia-Sanchez M. Design parameters of the fan-out phase of sensory systems. Journal of Computational Neuroscience 15(1): 5-17, 2003. Masse NY, Turner GC, Jefferis GS. Olfactory information processing in Drosophila. Current Biology 19(16): R700-713, 2009. Newquist G. Brain organization and the roots of anticipation in Drosophila olfactory conditioning. Neuroscience Biobehavioral Review 35(5): 1166-1174, 2011. Nowotny T, Rabinovich MI, Huerta R, Abarbanel HD. Decoding temporal information through slow lateral excitation in the olfactory system of insects. Journal of Computational Neuroscience 15(2): 271-281, 2003. Paninski L. Estimation of Entropy and Mutual Information. Neural Computation 15: 1191–1253, 2003. Smith D, Wessnitzer J, Webb B. A model of associative learning in the mushroom body. Biological Cybernetics, 99(2): 89-103, 2008. Szyszka P, Galkin A, Menzel R. Associative and non-associative plasticity in Kenyon cells of the honeybee mushroom body. Frontiers in Systems Neuroscience, 2, 2008. Keywords: Drosophila Olfactory System, Information Processing, Kenyon cells, mutual information, Neuromodulatory Conference: Bernstein Conference 2012, Munich, Germany, 12 Sep - 14 Sep, 2012. Presentation Type: Poster Topic: Sensory processing and perception Citation: Faghihi F, Wörgötter F and Kolodziejski C (2012). Information processing in the Drosophila Olfactory System: From Odors to Kenyon cells. Front. Comput. Neurosci. Conference Abstract: Bernstein Conference 2012. doi: 10.3389/conf.fncom.2012.55.00189 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 11 May 2012; Published Online: 12 Sep 2012. * Correspondence: Mr. Faramarz Faghihi, Georg-August-University Goettingen, Drittes Physikalisches Institut, Goettingen, Niedersachsen, 37077, Germany, ffaghih2@gmu.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Faramarz Faghihi Florentin Wörgötter Christoph Kolodziejski Google Faramarz Faghihi Florentin Wörgötter Christoph Kolodziejski Google Scholar Faramarz Faghihi Florentin Wörgötter Christoph Kolodziejski PubMed Faramarz Faghihi Florentin Wörgötter Christoph Kolodziejski Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Generation of neuronal diversity is a biological strategy widely used in the brain to process complex information. The olfactory bulb is the first relay station of olfactory information in the vertebrate central nervous system. In the olfactory bulb, axons of the olfactory sensory neurons form synapses with dendrites of projection neurons that transmit the olfactory information to the olfactory cortex. Historically, the olfactory bulb projection neurons have been classified into two populations, mitral cells and tufted cells. The somata of these cells are distinctly segregated within the layers of the olfactory bulb; the mitral cells are located in the mitral cell layer while the tufted cells are found in the external plexiform layer. Although mitral and tufted cells share many morphological, biophysical, and molecular characteristics, they differ in soma size, projection patterns of their dendrites and axons, and odor responses. In addition, tufted cells are further subclassified based on the relative depth of their somata location in the external plexiform layer. Evidence suggests that different types of tufted cells have distinct cellular properties and play different roles in olfactory information processing. Therefore, mitral and different types of tufted cells are considered as starting points for parallel pathways of olfactory information processing in the brain. Moreover, recent studies suggest that mitral cells also consist of heterogeneous subpopulations with different cellular properties despite the fact that the mitral cell layer is a single-cell layer. In this review, we first compare the morphology of projection neurons in the olfactory bulb of different vertebrate species. Next, we explore the similarities and differences among subpopulations of projection neurons in the rodent olfactory bulb. We also discuss the timing of neurogenesis as a factor for the generation of projection neuron heterogeneity in the olfactory bulb. Knowledge about the subpopulations of olfactory bulb projection neurons will contribute to a better understanding of the complex olfactory information processing in higher brain regions.

The two antennal lobes, the primary olfactory centers of the brain, of the moth Manduca sexta each contain one neuron that displays serotonin immunoreactivity. The neuron projects out of the antennal lobe and sends branches into ipsi- and contralateral protocerebral areas. An axon-like process extends from the contralateral protocerebrum to, and terminates in, the contralateral antennal lobe. In order to begin to investigate the possible role of this unique neuron in olfactory information processing, we have used laser scanning confocal microscopic and electron microscopic immunocytochemical techniques to study the ramification pattern, ultrastructural characteristics, and synaptic connections of the neuron in the antennal lobes of female adult Manduca sexta. The neuron ramifies extensively in the antennal lobe contralateral to the cell body. The ramifications, mainly in the base and center of each glomerulus, do not overlap with those of the sensory axons from the antenna. This finding suggests that the serotonin-immunoreactive neuron may not receive direct input from sensory neurons, and that it may modulate the activity of the neurons of the antennal lobe rather than that of the sensory neurons. In the electron microscope, the neuron exhibits large dense-cored vesicles and small, clear round vesicles. In the antennal lobe ipsilateral to the cell body, the primary neurite of the serotonin-immunoreactive neuron is unbranched and lacks detectable synaptic connections. The ramifications in the contralateral antennal lobe, however, participate in synaptic connections. At very low frequency, contralateral branches form synapses onto unlabeled processes and also receive synapses from unidentified neurons in the glomeruli, indicating that the neuron may participate directly in synaptic processing of olfactory information. The high ratio of output to input synapses made by the serotonin-immunoreactive processes in the contralateral antennal lobe is consistent with the idea that this neuron may receive synaptic input via its bilateral branches in the protocerebrum and then send information to the contralateral antennal lobe where the neuron may exert feedback or modulatory influences on olfactory information processing in the glomeruli.

Although numerous functional magnetic resonance imaging (FMRI) studies have been performed on the processing of olfactory information, the intranasal trigeminal system so far has not received much attention. In the present study, we sought to delineate the neural correlates of trigeminal stimulation using carbon dioxide (CO(2)) presented to the left or right nostril. Fifteen right-handed men underwent FMRI using single runs of 3 conditions (CO(2) in the right and the left nostrils and an olfactory stimulant-phenyl ethyl alcohol-in the right nostril). As expected, olfactory activations were located in the orbitofrontal cortex (OFC), amygdala, and rostral insula. For trigeminal stimulation, activations were found in "trigeminal" and "olfactory" regions including the pre- and postcentral gyrus, the cerebellum, the ventrolateral thalamus, the insula, the contralateral piriform cortex, and the OFC. Left compared with right side stimulations resulted in stronger cerebellar and brain stem activations; right versus left stimulation resulted in stronger activations of the superior temporal sulcus and OFC. These results suggest a trigeminal processing system that taps into similar cortical regions and yet is separate from that of the olfactory system. The overlapping pattern of cortical activation for trigeminal and olfactory stimuli is assumed to be due to the intimate connections in the processing of information from the 2 major intranasal chemosensory systems.

Olfaction and Depth of Word Processing: A Magnetoencephalographic Study

Olfactory receptor neurons in the nasal epithelium detect a huge variety of airborne chemicals (termed ‘odourants’) and encode information about these stimuli in the form of action potentials. This code is then transmitted to the brain, where spatiotemporal patterns of neural activity represent the identity, concentration and temporal dynamics of the odourants. Neural processing of olfactory information at multiple levels in the brain mediates odour recognition, synthetic olfactory perceptions and provides feedback control to the initial stages of the olfactory pathway. This article presents some of the challenges in olfactory information processing and then reviews our current knowledge of the mechanisms by which the olfactory bulb and olfactory cortex represent odours and analyse olfactory information. Key Concepts: The chemical identity of an odourant is represented by the set of ORNs it stimulates and determines the odour's perceived quality. The concentration of an odourant is represented jointly by the amplitude of the ORN response and the recruitment of ORNs expressing lower affinity receptors; this determines the odour's perceived intensity. Each olfactory bulb glomerulus receives axonal projections from a set of ORNs expressing the same odour receptor. An odour stimulates a subset of ORNs (based on their odour receptor expression) and thus drives activity in a corresponding subset of olfactory bulb glomeruli – this odour‐to‐glomerulus mapping is one of the most accessible codes in the nervous system. Activity in olfactory bulb glomeruli is determined by a complex set of interactions among ORN sensory inputs, interneurons within and between glomeruli and modulatory inputs from other brain regions. The set of mitral cells responding during odour presentation represents the chemical identity of the odour, whereas their firing frequency and timing provides additional information about the odour concentration. Activity in mitral cells is shaped by complex interactions with inhibitory granule cells that interconnect mitral cells receiving disparate sensory input. Neurons in piriform cortex respond to specific combinations of input from mitral cells in the olfactory bulb, thus selectively responding to certain odours or combinations of odours.

Don Griffin, one of the foremost students of comparative cognition, offered the following definition of cognition: “The term cognition is ordinarily taken to mean information processing in human and nonhuman central nervous systems that often leads to choices and decisions” (Griffin and Speck, 2004). Clearly we can study cognition by analyzing animal information processing systems and the manner in which behavioral choices and decision making are altered by experience. The use of olfactory information for guiding a wide range of basic biological decisions is ubiquitous in animals, including humans (Gelperin, 2010). Chemosensory processing, and particularly olfactory information processing, is a particularly attractive modality within which to seek comparative insights into cognitive processes underlying learning and memory.

gamma-Aminobutyric acid (GABA)-gated chloride channel receptors are abundant in the CNS, where their physiological role is to mediate fast inhibitory neurotransmission. In insects, this inhibitory transmission plays a crucial role in olfactory information processing. In an effort to understand the nature and properties of the ionotropic receptors involved in these processes in the honeybee Apis mellifera, we performed a pharmacological and molecular characterization of GABA-gated channels in the primary olfactory neuropile of the honeybee brain-the antennal lobe (AL)-using whole cell patch-clamp recordings coupled with single-cell RT-PCR. Application of GABA onto AL cells at -110 mV elicited fast inward currents, demonstrating the existence of ionotropic GABA-gated chloride channels. Molecular analysis of the GABA-responding cells revealed that both subunits RDL and LCCH3 were expressed out of the three orthologs of Drosophila melanogaster GABA-receptor subunits encoded within the honeybee genome (RDL, resistant to dieldrin; GRD, GABA/glycine-like receptor of Drosophila; LCCH3, ligand-gated chloride channel homologue 3), opening the door to possible homo- and/or heteromeric associations. The resulting receptors were activated by insect GABA-receptor agonists muscimol and CACA and blocked by antagonists fipronil, dieldrin, and picrotoxin, but not bicuculline, displaying a typical RDL-like pharmacology. Interestingly, increasing the intracellular calcium concentration potentiated GABA-elicited currents, suggesting a modulating effect of calcium on GABA receptors possibly through phosphorylation processes that remain to be determined. These results indicate that adult honeybee AL cells express typical RDL-like GABA receptors whose properties support a major role in synaptic inhibitory transmission during olfactory information processing.

Olfactory system and emotion: Common substrates

Processing of olfactory information is modulated by centrifugal projections from cortical areas, yet their behavioral relevance and underlying neural mechanisms remain unclear in most cases. The anterior olfactory nucleus (AON) is part of the olfactory cortex, and its extensive connections to multiple upstream and downstream brain centers place it in a prime position to modulate early sensory information in the olfactory system. Here, we show that optogenetic activation of AON neurons in awake male and female mice was not perceived as an odorant equivalent cue. However, AON activation during odorant presentation reliably suppressed behavioral odor responses. This AON-mediated effect was fast and constant across odors and concentrations. Likewise, activation of glutamatergic AON projections to the olfactory bulb (OB) transiently inhibited the excitability of mitral/tufted cells (MTCs) that relay olfactory input to the cortex. Single-unit MTC recordings revealed that optogenetic activation of glutamatergic AON terminals in the OB transiently decreased sensory-evoked MTC spiking, regardless of the strength or polarity of the sensory response. The reduction in MTC firing during optogenetic stimulation was confirmed in recordings in awake mice. These findings suggest that glutamatergic AON projections to the OB impede early olfactory signaling by inhibiting OB output neurons, thereby dynamically gating sensory throughput to the cortex.SIGNIFICANCE STATEMENT The anterior olfactory nucleus (AON) as an olfactory information processing area sends extensive projections to multiple brain centers, but the behavioral consequences of its activation have been scarcely investigated. Using behavioral tests in combination with optogenetic manipulation, we show that, in contrast to what has been suggested previously, the AON does not seem to form odor percepts but instead suppresses behavioral odor responses across odorants and concentrations. Furthermore, this study shows that AON activation inhibits olfactory bulb output neurons in both anesthetized as well as awake mice, pointing to a potential mechanism by which the olfactory cortex can actively and dynamically gate sensory throughput to higher brain centers.