Olfactory Domain Research Articles

Wireless monitoring of respiration with EEG reveals relationships between respiration, behavior, and brain activity in freely moving mice.

Active sampling in the olfactory domain is a fundamental aspect of mouse behavior, and there is increasing evidence that respiration-entrained neural activity outside of the olfactory system sets an important global brain rhythm. It is therefore crucial to accurately measure breathing during natural behaviors. We develop a new approach to do this in freely moving animals, by implanting a telemetry-based pressure sensor into the right jugular vein, which allows for wireless monitoring of thoracic pressure. After verifying this technique against standard head-fixed respiration measurements, we combined it with EEG and EMG recording and used evolving partial coherence analysis to investigate the relationship between respiration and brain activity across a range of experiments in which the mice could move freely. During voluntary exploration of odors and objects, we found that the association between respiration and cortical activity in the delta and theta frequency range decreased, whereas the association between respiration and cortical activity in the alpha range increased. During sleep, however, the presentation of an odor was able to cause a transient increase in sniffing without changing dominant sleep rhythms (delta and theta) in the cortex. Our data align with the emerging idea that the respiration rhythm could act as a synchronizing scaffold for specific brain rhythms during wakefulness and exploration, but suggest that respiratory changes are less able to impact brain activity during sleep. Combining wireless respiration monitoring with different types of brain recording across a variety of behaviors will further increase our understanding of the important links between active sampling, passive respiration, and neural activity.NEW & NOTEWORTHY Animals can alter their respiration rate to actively sample their environment, and increasing evidence suggests that neurons across the brain align their firing to this changing rhythm. We developed a new approach to measure sniffing in freely moving mice while simultaneously recording brain activity, and uncovered how specific cortical rhythms changed their coherence with respiration rhythm during natural behaviors and across arousal states.

An experimental paradigm for studying EEG correlates of olfactory discrimination.

Electroencephalography (EEG) correlates of olfaction are of fundamental and practical interest for many reasons. In the field of neural technologies, olfactory-based brain-computer interfaces (BCIs) represent an approach that could be useful for neurorehabilitation of anosmia, dysosmia and hyposmia. While the idea of a BCI that decodes neural responses to different odors and/or enables odor-based neurofeedback is appealing, the results of previous EEG investigations into the olfactory domain are rather inconsistent, particularly when non-primary processing of olfactory signals is concerned. Here we developed an experimental paradigm where EEG recordings are conducted while a participant executes an olfaction-based instructed-delay task. We utilized an olfactory display and a sensor of respiration to deliver odors in a strictly controlled fashion. We showed that with this approach spatial and spectral EEG properties could be analyzed to assess neural processing of olfactory stimuli and their conversion into a motor response. We conclude that EEG recordings are suitable for detecting active processing of odors. As such they could be integrated in a BCI that strives to rehabilitate olfactory disabilities or uses odors for hedonistic purposes.

Ongoing semantic change in a modernising society: a look at some adjectives from the olfactory domain in the Corpus of Historical American English

As a diachronic corpus-based investigation into onomasiological variation, this study has two main objectives. First, the paper analyses the evolution of the concept of sweet-smelling as a whole – that is, as instantiated by the three near-synonymous adjectives, fragrant, perfumed and scented, with a focus on language-external pressures for distributional changes. There seems to exist variation over time in the nouns that the concept typically collocates with, going from nouns referring to entities with a natural, pleasant smell to entities with an artificial agreeable aroma. It is here argued that this change is motivated by the social and technological transformations experienced by American society after the First and Second Industrial Revolutions, a claim that finds preliminary empirical support in the distribution from 1820 to 2009 of a series of lexical indicators from the semantic domains of cleaning, cosmetics and textile & clothing. Second, the distribution over time of the three adjectives is examined. The data point to a reorganisation concerning the internal semantic structure of the synonym set, with scented gaining ground at the expense of fragrant and perfumed in several contexts of use. Furthermore, the adjectives exhibit highly idiosyncratic collocational preferences, which go a long way towards explaining the alternation between them.

汉･韩语“嗅、闻”和“맡다”的隐喻分析对比

The nose is an important organ responsible for the sense of smell, which is the most primitive sense of human beings. This feeling plays a very important role in people"s cognition of the external world. The corresponding words for smell in Chinese and Korean are “嗅”，“闻” and “맡다” respectively. The metaphorical expressions of the three words are analyzed through the corpus, and the similarities and differences between the three words ard found. At the same time, the connection between the sense of smell and the other senses is the contained in this paper. First, the origin domain of the three words is the same, which is the olfactory domain that uses the nose to identify smells. From this common origin domain, “嗅” and “闻” are mapped to two common target domains of “discovery” and “perception, feeling” respectively. Furthermore “嗅” also maps to the two target domains of “discrimination” and “exploration”. The Korean “맡다” only maps to the target domain of “perception, feeling”. The reason why the three words produce such a mapping is that they are all based on the most elemental function of smell. The reason for the difference between “嗅” and “闻” is that at the beginning of is creation, “闻” was just an action of listening to the sound with the ear, and in the process of semantic evolution, the meaning of the nose to distinguish odors was gradually generated. And “맡다” is because the lexicalizatin function has been complemented by the cognitive means of metaphor, and Korean is accustomed to using other expressions in language use. In addition, the olfactory domain of Chinese is mapped to the visual domain, the auditory domain and the integrated sensory domain, while the Korean language is only mapped to the integrated sensory domain. This shows that the sense of smell in Korean is not closely linked to vision and hearing, which also results in relatively few metaphorical expressions of “맡다”. 鼻子是承担嗅觉功能的一个重要器官，而嗅觉是人类最原始的一种感觉。这种感觉对于人们认知外部世界有着非常重要的作用。在汉语和韩语中嗅觉所对应的词语分别是“嗅”、“闻”以及“맡다”。通过语料库对三个词的隐喻表现进行分析，从而发现三者之间的异同，同时对发现嗅觉和其它感觉之间的联系是本文所要研究的内容。 首先，三个词的始源域是相同的，都是用鼻子辨别气味的嗅觉域。而从这个共同的始源域出发，“嗅”和“闻”分别向“发现”和“察觉、感觉”两个共同的目标域进行了映射。除此之外，“嗅”还向“分辨”、“探察”二个目标域进行了映射。而韩语“맡다"只向“察觉、感觉”这一个目标域进行了映 射。三个词语之所以会产生这样的映射是因为都是基于嗅觉最基本的功能。 “嗅”和“闻”之间产生这样的差异的原因在于，“闻”在被创造之初只是一个表示用耳朵听声音的动作，在语义演变过程中逐渐生成了鼻子辨别气味的意义。而“맡다”则是因为已经通过隐喻这种认知手段完成了词汇化的功能，在语言使用上韩语又习惯于使用别的表达方式。另外，汉语的嗅觉域向视觉域、听觉域和综合感觉域进行了映射，而韩语只向综合感觉域进行了映射。说明韩语中嗅觉和视觉、听觉的联系不紧密，这也造成了“맡다”的隐喻表现相对较少。

Smells Like Simile: Olfactory Expressions and their Figurative Potential in the Bosnian Language

This paper analyzes expressions that use the olfactory domain as a figurative source in the Bosnian language. Authentic texts retrieved from the Sketch Engine web application were used as the corpus for the study. The web corpus includes blogs, news portals, and other web pages that use olfactory expressions either in the main text or in the respective comment sections. Two basic smell expressions were found to have the greatest figurative potential and therefore examined in this study. The results of the two basic smell expressions indicate that they are mainly used figuratively with simile being the main focus. Another finding is that olfactory expressions are used for anticipatory purposes.

Olfactory perceptual decision-making is biased by motivational state.

Growing evidence suggests that internal factors influence how we perceive the world. However, it remains unclear whether and how motivational states, such as hunger and satiety, regulate perceptual decision-making in the olfactory domain. Here, we developed a novel behavioral task involving mixtures of food and nonfood odors (i.e., cinnamon bun and cedar; pizza and pine) to assess olfactory perceptual decision-making in humans. Participants completed the task before and after eating a meal that matched one of the food odors, allowing us to compare perception of meal-matched and non-matched odors across fasted and sated states. We found that participants were less likely to perceive meal-matched, but not non-matched, odors as food dominant in the sated state. Moreover, functional magnetic resonance imaging (fMRI) data revealed neural changes that paralleled these behavioral effects. Namely, odor-evoked fMRI responses in olfactory/limbic brain regions were altered after the meal, such that neural patterns for meal-matched odor pairs were less discriminable and less food-like than their non-matched counterparts. Our findings demonstrate that olfactory perceptual decision-making is biased by motivational state in an odor-specific manner and highlight a potential brain mechanism underlying this adaptive behavior.

Event-Based Sensing and Signal Processing in the Visual, Auditory, and Olfactory Domain: A Review.

The nervous systems converts the physical quantities sensed by its primary receptors into trains of events that are then processed in the brain. The unmatched efficiency in information processing has long inspired engineers to seek brain-like approaches to sensing and signal processing. The key principle pursued in neuromorphic sensing is to shed the traditional approach of periodic sampling in favor of an event-driven scheme that mimicks sampling as it occurs in the nervous system, where events are preferably emitted upon the change of the sensed stimulus. In this paper we highlight the advantages and challenges of event-based sensing and signal processing in the visual, auditory and olfactory domains. We also provide a survey of the literature covering neuromorphic sensing and signal processing in all three modalities. Our aim is to facilitate research in event-based sensing and signal processing by providing a comprehensive overview of the research performed previously as well as highlighting conceptual advantages, current progress and future challenges in the field.

The effect of traditional Chinese medicine treatment for post-viral olfactory dysfunction

Background:Post-viral olfactory dysfunction (PVOD) have been reported in infections caused by several respiratory viruses, especially in COVID-19 which influence severely the quality of life of affected subjects. Few study has been published on the treatment of PVOD. Traditional Chinese medicine (TCM) is an effective method for PVOD which effects and safety have been confirmed. Therefore, this study is aim to evaluate the effects of TCM on PVOD.Methods:A searching strategy will be carried out mainly in the following databases in English and Chinese, PubMed, EMBASE, Cochrane Central Register of Controlled Trials, China Network Knowledge Infrastructure (CNKI), Chinese Scientific Journal Database (VIP), Chinese Biomedical and Medical Database (CBM), and Wanfang Database. Only randomized controlled trials related to TCM for PVOD will be included to enhance effectiveness. The primary outcome is the effective rate of PVOD. The secondary outcomes are included olfactory domain value examination, visual analogue scale (VAS), questionnaires of olfactory disorders (QOD), T&T olfactometer test, Sniffin ticks test, and any other clinical assessments. Two authors will independently perform study selection, data extraction, and quality assessment to ensure the quality of the systematic evaluation. Every disagreement will be deal with by the third author. Data synthesis and subgroup analysis will be performed in the Review Manager V 5.3.3.Results:This study is aim to evaluate the efficacy and safety of TCM in PVOD.Conclusion: This meta-analysis may provide more reliable evidence-based medical evidence for clinical practice to assist patient in relieving PVOD.Ethics and dissemination:There is no need to acquire ethical approval for individuals come from literatures instead of recruiting directly. The findings of this review will be reported in peer-reviewed publications and/or presented at relevant conferences.Prospero registration number:CRD42021238977.

Childhood Maltreatment Alters the Neural Processing of Chemosensory Stress Signals.

Accumulating evidence suggests that childhood maltreatment (CM) confers risk for psychopathology later in life by inducing hypervigilance to social threat cues such as fearful faces. However, it remains unclear whether the modulatory impact of CM extents to the olfactory domain of social communication in humans. To address this question, we examined whether CM modulates the neural processing of chemosensory threat signals in sweat and whether CM affects the stress-reducing effects of oxytocin (OXT) in this context. In a randomized, double-blind within-subject functional MRI study design, 58 healthy participants (30 females) received intranasal OXT (40 IU) or placebo (PLC) and completed a forced-choice emotion recognition task with faces of varying emotion intensities (neutral to fearful) while exposed to sweat stimuli and a non-social control odor. Axillary sweat samples were collected from 30 healthy male donors undergoing an acute psychosocial stressor (stress) and ergometer training (sport) as control in a pre-study. CM was assessed by the 25-item Childhood Trauma Questionnaire (CTQ). The final fMRI analysis included 50 healthy participants (26 females). Regression analysis showed a stress-specific association of CTQ scores with amygdala hyperreactivity, hippocampal deactivation, and increased functional connectivity between the amygdala and the hippocampus, medial orbitofrontal cortex, and the anterior cingulate cortex (ACC) under PLC. Furthermore, we observed a positive association of CTQ scores and the dampening effects of OXT on stress-related amygdala responses. Our findings suggest that CM may induce hypervigilance to chemosensory threat cues in a healthy sample due to inefficient frontolimbic inhibition of amygdala activation. Future studies should investigate whether increased recruitment of the intralimbic amygdala-hippocampus complex reflects a compensatory mechanism that prevents the development of psychopathology in those who have experienced CM. Furthermore, the results reveal that the stress-specific effects of OXT in the olfactory domain are more pronounced in participants with increasing levels of CM exposure.

Higher-order discrimination learning by honeybees in a virtual environment.

Non-elemental learning constitutes a cognitive challenge because events to be learned are usually ambiguous in terms of reinforcement outcome, contrary to elemental learning, which relies on unambiguous associations. Negative patterning (NP) constitutes a paradigmatic case of non-elemental learning, as subjects have to learn that single elements are reinforced while their simultaneous presentation is not reinforced (A+, B+ vs. AB-). Solving NP requires treating AB as being different from the linear sum of its components in order to overcome the ambiguity of stimulus reinforcement (i.e. A and B are as often reinforced as not reinforced). The honeybee is currently the only insect mastering NP as shown by studies restricted mainly to the olfactory domain. Here, we tested the bees' capacity to solve a NP discrimination in the visual domain and used to this end a virtual reality (VR) environment in which a tethered bee walking stationary on a spherical treadmill faces visual stimuli projected on a semicircular screen. We show that bees learn a composite grating made of alternated green and blue bars in an elemental way, and generalize their response to both a blue and a green grating. Yet, after NP training, one-quarter of the bees inhibited elemental processing and responded significantly more to the single-coloured gratings than to the composite grating. Alternative strategies were used by the other bees, which achieved partial NP learning. These results offer attractive perspectives to study different forms of visual learning in a controlled VR environment, and dissect their underlying mechanisms.

Externalization Errors of Olfactory Source Monitoring in Healthy Controls—An fMRI Study

Using a combined approach of functional magnetic resonance imaging (fMRI) and noninvasive brain stimulation (transcranial direct current stimulation [tDCS]), the present study investigated source memory and its link to mental imagery in the olfactory domain, as well as in the auditory domain. Source memory refers to the knowledge of the origin of mental experiences, differentiating events that have occurred and memories of imagined events. Because of a confusion between internally generated and externally perceived information, patients that are prone to hallucinations show decreased source memory accuracy; also, vivid mental imagery can lead to similar results in healthy controls. We tested source memory following cathodal tDCS stimulation using a mental imagery task, which required participants to perceive or imagine a set of the same olfactory and auditory stimuli during fMRI. The supplementary motor area (SMA) is involved in mental imagery across different modalities and potentially linked to source memory. Therefore, we attempted to modulate participants' SMA activation before entering the scanner using tDCS to influence source memory accuracy in healthy participants. Our results showed the same source memory accuracy between the olfactory and auditory modalities with no effects of stimulation. Finally, we found SMA's subregions differentially involved in olfactory and auditory imagery, with activation of dorsal SMA correlated with auditory source memory.

Evidence for impaired olfactory function and structural brain integrity in a disorder of ciliary function, Usher syndrome.

Diseases involving cilia dysfunction, such as Usher Syndrome (USH), often involve visual and auditory loss. Psychophysical evidence has suggested that this may also hold true for the peripheral olfactory domain. Here we aimed to go a step further by attempting to establish relations between the integrity of cortical structures and olfactory function in this condition. We investigated olfactory function for USH types 1 (USH1) and 2 (USH2). Bilateral olfactory bulb (OB) volume and olfactory sulcus (OS) depth were also analysed.Thirty-three controls with no previous olfactory deficits were age, sex and handedness-matched to 32 USH patients (11 USH1, 21 USH2). A butanol detection threshold test was performed to measure olfactory function. For OB volume and OS depth, morphometric measurements were performed using magnetic resonance imaging (MRI) based on detailed segmentation by three independent operators. Averaged values across these were used for the statistical analyses. Total intracranial volume was estimated using Freesurfer to account for head size variability.Olfactory threshold was significantly lower in controls when compared to USH, USH1, and USH2. OS depth was found to be shallower in both hemispheres in USH patients when compared with the control group. OB volume was not significantly different between control and USH groups, or respective subgroups. Nevertheless, butanol threshold was negatively correlated with the left OB volume for the USH type 1 subgroup. The main effect of OS depth reduction was found to be mainly due to the comparison between USH2 and controls.Our results provide evidence for morphometric changes and olfactory dysfunction in patients with USH. This correlated with a reduction in left OB volume in the USH1 subgroup, the most severe USH phenotype. The main effect of reduced OS depth was found to stem mainly from USH2 raising questions regarding a possible complex interaction between sensory olfactory loss and central cortical changes in this disease.

Oxytocin reduces a chemosensory-induced stress bias in social perception

Social transmission of fear is not restricted to visual or auditory cues, but extends to the phylogenetically more ancient olfactory domain. Anxious individuals exhibit heightened sensitivity towards chemosensory stress signals in sweat; however,it is still unknown whether endogenous neuromodulators such as the peptide hormone oxytocin (OXT) influence the chemosensory communication of stress. Here, we investigated whether OXT selectively diminishes behavioral and neural responses to social chemosensory stress cues utilizing a randomized, double-blind, placebo (PLC)-controlled, within-subject functional MRI study design. Axillary sweat was obtained from 30 healthy male donors undergoing the Trier Social Stress Test (stress) and bicycle ergometer training (sport). Subsequently, 58 healthy participants (30 females) completed a forced-choice emotional face recognition task with stimuli of varying intensities (neutral to fearful) while they were exposed to both sweat stimuli and a non-social control odor following intranasal OXT or PLC administration, respectively. OXT diminished stress-induced recognition accuracy and response time biases towards fear. On the neural level, OXT reduced stress-evoked responses in the amygdala in both sexes, the anterior cingulate cortex (ACC) in females, and the hippocampus in males. Furthermore, OXT reinstated the functional connectivity between the ACC and the fusiform face area that was disrupted by stress odors under PLC. Our findings reveal a new role for OXT signaling in the modulation of chemosensory communication of stress in humans. Mechanistically, this effect appears to be rooted in a downregulation of stress-induced limbic activations and concomitant strengthening of top-down control descending from the ACC to the fusiform face area.

Lipids in Eating and Appetite Regulation – A Neuro‐Cognitive Perspective

Foods high in dietary fat provide a particularly energy‐rich source of nutrition. A preferred food choice in humans, their intake is thought to contribute substantially to the current obesity epidemic. Fat has recently been proposed to constitute a basic taste; yet, its diverse sensory properties in the olfactory and somatosensory domain, as well as its postingestive effects have made the exact attributes that make its consumption so appealing difficult to disentangle. Recent scientific advances have shed light on the different molecular mechanisms underlying the sensory detection of fat in the periphery, and described their relevance for perceptual experience and eating behavior. However, these different analysis levels are to date poorly integrated, both within each sensory modality, and from a multisensory perspective.The current Highlight Article aims to integrate current knowledge concerning the molecular mechanisms of the different sensory modalities contributing to fat perception, as well as their cortical neuroanatomical correlates and their behavioral and clinical relevance for fat intake. In doing so, we would like to highlight the evidence for cortical integration among the different sensory domains as a driving mechanism for the emotional evaluation of fatty foods, and point out gaps in the current literature, which should be addressed to complete the picture of fat perception from a cognitive neuroscience perspective.

Animals can assign novel odours to a known category

The ability to identify a novel stimulus as a member of a known category allows an organism to respond appropriately towards it. Categorisation is thus a fundamental component of cognition and an essential tool for processing and responding to unknown stimuli. Therefore, one might expect to observe it throughout the animal kingdom and across sensory domains. There is much evidence of visual categorisation in non-human animals, but we currently know little about this process in other modalities. In this experiment, we investigated categorisation in the olfactory domain. Dogs were trained to discriminate between 40 odours; the presence or absence of accelerants formed the categorical rule. Those in the experimental group were rewarded for responding to substrates with accelerants (either burnt or un-burnt) and inhibit responses to the same substrates (either burnt or un-burnt) without accelerants (S+ counterbalanced). The pseudocategory control group was trained on the same stimuli without the categorical rule. The experimental group learned the discrimination and animals were able to generalise to novel stimuli from the same category. None of the control animals were able to learn the discrimination within the maximum number of trials. This study provides the first evidence that non-human animals can learn to categorise non-biologically relevant odour information.

Altered olfactory processing and increased insula activity in patients with obsessive-compulsive disorder: An fMRI study

Obsessive-compulsive disorder (OCD) patients show increased insula activation to disgust-inducing images compared to healthy controls (HC). We explored whether this disgust reactivity was also present in the olfactory domain by conducting the first fMRI study of olfaction in OCD. Neural activation in response to pleasant and unpleasant odors (vs. unscented air) was investigated in 15 OCD and 15 HC participants using fMRI. OCD participants (vs. HC) had increased left anterior insula activation to unpleasant odors (vs. unscented air), which positively correlated with their disgust sensitivity and ratings of the unpleasantness and intensity of those odors. OCD participants (vs. HC) showed increased activation of caudate nucleus and left anterior and posterior insula to pleasant odors (vs. unscented air), which positively correlated with their OCD symptom severity, trait anxiety, frequency of feeling disgust, and odor intensity ratings. OCD participants had increased anterior insula activation to both pleasant and unpleasant odors, which correlated with their OCD symptoms, anxiety, disgust sensitivity, and frequency of feeling disgust. OCD patients might have a negative cognitive bias and experience all stimuli, regardless of valence, as being more unpleasant than healthy people. These findings further elucidate the neural underpinnings of OCD and may contribute to more effective treatments.

The role of piriform associative connections in odor categorization

Distributed neural activity patterns are widely proposed to underlie object identification and categorization in the brain. In the olfactory domain, pattern-based representations of odor objects are encoded in piriform cortex. This region receives both afferent and associative inputs, though their relative contributions to odor perception are poorly understood. Here, we combined a placebo-controlled pharmacological fMRI paradigm with multivariate pattern analyses to test the role of associative connections in sustaining olfactory categorical representations. Administration of baclofen, a GABA(B) agonist known to attenuate piriform associative inputs, interfered with within-category pattern separation in piriform cortex, and the magnitude of this drug-induced change predicted perceptual alterations in fine-odor discrimination performance. Comparatively, baclofen reduced pattern separation between odor categories in orbitofrontal cortex, and impeded within-category generalization in hippocampus. Our findings suggest that odor categorization is a dynamic process concurrently engaging stimulus discrimination and generalization at different stages of olfactory information processing, and highlight the importance of associative networks in maintaining categorical boundaries.

Children’s exposure to odors in everyday contexts predicts their odor awareness

A great degree of interindividual variability has been reported in measures of psychophysical olfactory performance and odor awareness in both children and adults. Previous studies have suggested the possibility that one of the factors that might contribute to this variability could be the degree of odor exposure experienced in everyday contexts. In the present study, we hypothesized that children exposed to a greater variety of odors on a more frequent basis exhibit higher odor identification, discrimination, and odor awareness scores. We have found an effect of odor exposure on one aspect of the children’s olfactory knowledge as reflected in their reports of olfactory behavior, but not olfactory abilities. In so doing, we have replicated some of the previous findings in the literature of the female advantage in the olfactory domain. Namely, we report that girls showed a more profound metacognitive understanding of their sense of smell and a greater degree of olfaction-oriented behavior, which was not accounted for by a gender difference in verbal fluency. Nevertheless, girls did not outperform boys on any of the olfactory tests. Semi-longitudinal and longitudinal studies in verbally proficient children, employing both self- and parental reports of children’s odor exposure and repeated olfactory testing, may provide insight into whether children exposed more frequently to a greater variety of odors over the longer term come to exhibit greater odor awareness and superior performance in olfactory tests.

Parallel Olfactory Processing in the Honey Bee Brain: Odor Learning and Generalization under Selective Lesion of a Projection Neuron Tract.

The function of parallel neural processing is a fundamental problem in Neuroscience, as it is found across sensory modalities and evolutionary lineages, from insects to humans. Recently, parallel processing has attracted increased attention in the olfactory domain, with the demonstration in both insects and mammals that different populations of second-order neurons encode and/or process odorant information differently. Among insects, Hymenoptera present a striking olfactory system with a clear neural dichotomy from the periphery to higher-order centers, based on two main tracts of second-order (projection) neurons: the medial and lateral antennal lobe tracts (m-ALT and l-ALT). To unravel the functional role of these two pathways, we combined specific lesions of the m-ALT tract with behavioral experiments, using the classical conditioning of the proboscis extension response (PER conditioning). Lesioned and intact bees had to learn to associate an odorant (1-nonanol) with sucrose. Then the bees were subjected to a generalization procedure with a range of odorants differing in terms of their carbon chain length or functional group. We show that m-ALT lesion strongly affects acquisition of an odor-sucrose association. However, lesioned bees that still learned the association showed a normal gradient of decreasing generalization responses to increasingly dissimilar odorants. Generalization responses could be predicted to some extent by in vivo calcium imaging recordings of l-ALT neurons. The m-ALT pathway therefore seems necessary for normal classical olfactory conditioning performance.

GABAergic feedback signaling into the calyces of the mushroom bodies enables olfactory reversal learning in honey bees.

In reversal learning, subjects first learn to respond to a reinforced stimulus A and not to a non-reinforced stimulus B (A+ vs. B−) and then have to learn the opposite when stimulus contingencies are reversed (A− vs. B+). This change in stimulus valence generates a transitory ambiguity at the level of stimulus outcome that needs to be overcome to solve the second discrimination. Honey bees (Apis mellifera) efficiently master reversal learning in the olfactory domain. The mushroom bodies (MBs), higher-order structures of the insect brain, are required to solve this task. Here we aimed at uncovering the neural circuits facilitating reversal learning in honey bees. We trained bees using the olfactory conditioning of the proboscis extension reflex (PER) coupled with localized pharmacological inhibition of Gamma-AminoButyric Acid (GABA)ergic signaling in the MBs. We show that inhibition of ionotropic but not metabotropic GABAergic signaling into the MB calyces impairs reversal learning, but leaves intact the capacity to perform two consecutive elemental olfactory discriminations with ambiguity of stimulus valence. On the contrary, inhibition of ionotropic GABAergic signaling into the MB lobes had no effect on reversal learning. Our results are thus consistent with a specific requirement of the feedback neurons (FNs) providing ionotropic GABAergic signaling from the MB lobes to the calyces for counteracting ambiguity of stimulus valence in reversal learning.