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Nature Oct 2021Mounting evidence shows that dopamine in the striatum is critically involved in reward-based reinforcement learning. However, it remains unclear how dopamine reward...
Mounting evidence shows that dopamine in the striatum is critically involved in reward-based reinforcement learning. However, it remains unclear how dopamine reward signals influence the entorhinal-hippocampal circuit, another brain network that is crucial for learning and memory. Here, using cell-type-specific electrophysiological recording, we show that dopamine signals from the ventral tegmental area and substantia nigra control the encoding of cue-reward association rules in layer 2a fan cells of the lateral entorhinal cortex (LEC). When mice learned novel olfactory cue-reward associations using a pre-learned association rule, spike representations of LEC fan cells grouped newly learned rewarded cues with a pre-learned rewarded cue, but separated them from a pre-learned unrewarded cue. Optogenetic inhibition of fan cells impaired the learning of new associations while sparing the retrieval of pre-learned memory. Using fibre photometry, we found that dopamine sends novelty-induced reward expectation signals to the LEC. Inhibition of LEC dopamine signals disrupted the associative encoding of fan cells and impaired learning performance. These results suggest that LEC fan cells represent a cognitive map of abstract task rules, and that LEC dopamine facilitates the incorporation of new memories into this map.
Topics: Animals; Anticipation, Psychological; Cues; Dopamine; Entorhinal Cortex; Female; Male; Memory; Mice; Mice, Inbred C57BL; Pyramidal Cells; Reward
PubMed: 34552245
DOI: 10.1038/s41586-021-03948-8 -
Neuropsychology Review Mar 2024Olfactory training (OT), or smell training,consists of repeated exposure to odorants over time with the intended neuroplastic effect of improving or remediating... (Review)
Review
Olfactory training (OT), or smell training,consists of repeated exposure to odorants over time with the intended neuroplastic effect of improving or remediating olfactory functioning. Declines in olfaction parallel declines in cognition in various pathological conditions and aging. Research suggests a dynamic neural connection exists between olfaction and cognition. Thus, if OT can improve olfaction, could OT also improve cognition and support brain function? To answer this question, we conducted a systematic review of the literature to determine whether there is evidence that OT translates to improved cognition or altered brain morphology and connectivity that supports cognition. Across three databases (MEDLINE, Scopus, & Embase), 18 articles were identified in this systematic review. Overall, the reviewed studies provided emerging evidence that OT is associated with improved global cognition, and in particular, verbal fluency and verbal learning/memory. OT is also associated with increases in the volume/size of olfactory-related brain regions, including the olfactory bulb and hippocampus, and altered functional connectivity. Interestingly, these positive effects were not limited to patients with smell loss (i.e., hyposmia & anosmia) but normosmic (i.e., normal ability to smell) participants benefitted as well. Implications for practice and research are provided.
Topics: Humans; Brain; Cognition; Olfaction Disorders; Olfactory Training; Smell
PubMed: 36725781
DOI: 10.1007/s11065-022-09573-0 -
Current Opinion in Neurobiology Oct 2022Volatile chemicals in the environment provide ethologically important information to many animals. However, how animals learn to use this information is only beginning... (Review)
Review
Volatile chemicals in the environment provide ethologically important information to many animals. However, how animals learn to use this information is only beginning to be understood. This review highlights recent experimental advances elucidating olfactory learning in rodents, ranging from adaptations to the environment to task-dependent refinement and multisensory associations. The broad range of phenomena, mechanisms, and brain areas involved demonstrate the complex and multifaceted nature of olfactory learning.
Topics: Animals; Brain; Conditioning, Classical; Learning; Smell
PubMed: 35998474
DOI: 10.1016/j.conb.2022.102623 -
Nature Jul 2020Animals coexist in commensal, pathogenic or mutualistic relationships with complex communities of diverse organisms, including microorganisms. Some bacteria produce...
Animals coexist in commensal, pathogenic or mutualistic relationships with complex communities of diverse organisms, including microorganisms. Some bacteria produce bioactive neurotransmitters that have previously been proposed to modulate nervous system activity and behaviours of their hosts. However, the mechanistic basis of this microbiota-brain signalling and its physiological relevance are largely unknown. Here we show that in Caenorhabditis elegans, the neuromodulator tyramine produced by commensal Providencia bacteria, which colonize the gut, bypasses the requirement for host tyramine biosynthesis and manipulates a host sensory decision. Bacterially produced tyramine is probably converted to octopamine by the host tyramine β-hydroxylase enzyme. Octopamine, in turn, targets the OCTR-1 octopamine receptor on ASH nociceptive neurons to modulate an aversive olfactory response. We identify the genes that are required for tyramine biosynthesis in Providencia, and show that these genes are necessary for the modulation of host behaviour. We further find that C. elegans colonized by Providencia preferentially select these bacteria in food choice assays, and that this selection bias requires bacterially produced tyramine and host octopamine signalling. Our results demonstrate that a neurotransmitter produced by gut bacteria mimics the functions of the cognate host molecule to override host control of a sensory decision, and thereby promotes fitness of both the host and the microorganism.
Topics: Animals; Avoidance Learning; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Feeding Behavior; Gastrointestinal Microbiome; Intestines; Metabolomics; Mutation; Neurotransmitter Agents; Octanols; Octopamine; Providencia; Receptors, Biogenic Amine; Receptors, G-Protein-Coupled; Sensory Receptor Cells; Smell; Tyramine; Tyrosine Decarboxylase
PubMed: 32555456
DOI: 10.1038/s41586-020-2395-5 -
Journal of Comparative Physiology. A,... Jul 2023Using 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... (Review)
Review
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.
Topics: Animals; Arthropods; Olfactory Pathways; Smell; Odorants; Brain
PubMed: 36658447
DOI: 10.1007/s00359-022-01611-9 -
Neuron Apr 2023The coincidence between conditioned stimulus (CS) and unconditioned stimulus (US) is essential for associative learning; however, the mechanism regulating the duration...
The coincidence between conditioned stimulus (CS) and unconditioned stimulus (US) is essential for associative learning; however, the mechanism regulating the duration of this temporal window remains unclear. Here, we found that serotonin (5-HT) bi-directionally regulates the coincidence time window of olfactory learning in Drosophila and affects synaptic plasticity of Kenyon cells (KCs) in the mushroom body (MB). Utilizing GPCR-activation-based (GRAB) neurotransmitter sensors, we found that KC-released acetylcholine (ACh) activates a serotonergic dorsal paired medial (DPM) neuron, which in turn provides inhibitory feedback to KCs. Physiological stimuli induce spatially heterogeneous 5-HT signals, which proportionally gate the intrinsic coincidence time windows of different MB compartments. Artificially reducing or increasing the DPM neuron-released 5-HT shortens or prolongs the coincidence window, respectively. In a sequential trace conditioning paradigm, this serotonergic neuromodulation helps to bridge the CS-US temporal gap. Altogether, we report a model circuitry for perceiving the temporal coincidence and determining the causal relationship between environmental events.
Topics: Animals; Smell; Serotonin; Drosophila; Conditioning, Classical; Neurons; Mushroom Bodies
PubMed: 36706757
DOI: 10.1016/j.neuron.2022.12.034 -
Current Opinion in Insect Science Oct 2023Flowers present information to their insect visitors in multiple simultaneous sensory modalities. Research has commonly focussed on information presented in visual and... (Review)
Review
Flowers present information to their insect visitors in multiple simultaneous sensory modalities. Research has commonly focussed on information presented in visual and olfactory modalities. Recently, focus has shifted towards additional 'invisible' information, and whether information presented in multiple modalities enhances the interaction between flowers and their visitors. In this review, we highlight work that addresses how multimodality influences behaviour, focussing on work conducted on bumblebees (Bombus spp.), which are often used due to both their learning abilities and their ability to use multiple sensory modes to identify and differentiate between flowers. We review the evidence for bumblebees being able to use humidity, electrical potential, surface texture and temperature as additional modalities, and consider how multimodality enhances their performance. We consider mechanisms, including the cross-modal transfer of learning that occurs when bees are able to transfer patterns learnt in one modality to an additional modality without additional learning.
Topics: Bees; Animals; Learning; Flowers; Temperature
PubMed: 37468044
DOI: 10.1016/j.cois.2023.101086 -
Molecules (Basel, Switzerland) Jul 2020Taste processing is an adaptive mechanism involving complex physiological, motivational and cognitive processes. Animal models have provided relevant data about the... (Review)
Review
Taste processing is an adaptive mechanism involving complex physiological, motivational and cognitive processes. Animal models have provided relevant data about the neuroanatomical and neurobiological components of taste processing. From these models, two important domains of taste responses are described in this review. The first part focuses on the neuroanatomical and neurophysiological bases of olfactory and taste processing. The second part describes the biological and behavioral characteristics of taste learning, with an emphasis on conditioned taste aversion as a key process for the survival and health of many species, including humans.
Topics: Amygdala; Animals; Avoidance Learning; Brain Mapping; Conditioning, Psychological; Humans; Models, Neurological; Olfactory Perception; Taste Perception
PubMed: 32650432
DOI: 10.3390/molecules25143112 -
Frontiers in Neural Circuits 2022In the mouse olfactory system, odor signals detected in the olfactory epithelium are converted to a topographic map of activated glomeruli in the olfactory bulb. The map... (Review)
Review
In the mouse olfactory system, odor signals detected in the olfactory epithelium are converted to a topographic map of activated glomeruli in the olfactory bulb. The map information is then conveyed by projection neurons, mitral cells and tufted cells, to various areas in the olfactory cortex. An odor map is transmitted to the anterior olfactory nucleus by tufted cells for odor identification and recollection of associated memory for learned decisions. For instinct decisions, odor information is directly transmitted to the valence regions in the amygdala by specific subsets of mitral cells. Transmission of orthonasal odor signals through these two distinct pathways, innate and learned, are closely related with exhalation and inhalation, respectively. Furthermore, the retronasal/interoceptive and orthonasal/exteroceptive signals are differentially processed during the respiratory cycle, suggesting that these signals are processed in separate areas of the olfactory bulb and olfactory cortex. In this review article, the recent progress is summarized for our understanding of the olfactory circuitry and processing of odor signals during respiration.
Topics: Amygdala; Animals; Mice; Odorants; Olfactory Bulb; Olfactory Pathways; Respiration; Smell
PubMed: 35431818
DOI: 10.3389/fncir.2022.861800 -
Animal Cognition Nov 2020Animals travelling through the world receive input from multiple sensory modalities that could be important for the guidance of their journeys. Given the availability of... (Review)
Review
Animals travelling through the world receive input from multiple sensory modalities that could be important for the guidance of their journeys. Given the availability of a rich array of cues, from idiothetic information to input from sky compasses and visual information through to olfactory and other cues (e.g. gustatory, magnetic, anemotactic or thermal) it is no surprise to see multimodality in most aspects of navigation. In this review, we present the current knowledge of multimodal cue use during orientation and navigation in insects. Multimodal cue use is adapted to a species' sensory ecology and shapes navigation behaviour both during the learning of environmental cues and when performing complex foraging journeys. The simultaneous use of multiple cues is beneficial because it provides redundant navigational information, and in general, multimodality increases robustness, accuracy and overall foraging success. We use examples from sensorimotor behaviours in mosquitoes and flies as well as from large scale navigation in ants, bees and insects that migrate seasonally over large distances, asking at each stage how multiple cues are combined behaviourally and what insects gain from using different modalities.
Topics: Animals; Ants; Bees; Cues; Homing Behavior; Learning; Orientation
PubMed: 32323027
DOI: 10.1007/s10071-020-01383-2