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Olfaction facilitates a large variety of animal behaviors such as feeding, mating, and communication. Recent work has begun to reveal the logic of odor transformations that occur throughout the olfactory system to form the odor percept. In this review, we describe the coding principles and mechanisms by which the piriform cortex and other olfactory areas encode three key odor features: odor identity, intensity, and valence. We argue that the piriform cortex produces a multiplexed odor code that allows non-interfering representations of distinct features of the odor stimulus to facilitate odor recognition and learning, which ultimately drives behavior.

本研究では、12 名の大学生を対象に日本人に馴染みの薄い、におい刺激に対して情報付与を行うという認知的操作が、一過性運動後の心理的および心臓血管反応に及す影響について検討した。対象者は、教示内容によってポジティブ教示群（6 名）と中立教示群（6 名）に振り分けられ、15 分間の運動後同じにおい刺激を吸入した。心理的反応では、情報内容は異なるもののポジティブな情報を提供したことによって、におい刺激に対するネガティブな印象が低減し、馴染み度が高まった。また、におい刺激に関するポジティブな情報は運動前と比較して運動後の落ち着き感を促進させた。心臓血管反応では、におい刺激に関するポジティブな情報は、運動後の心臓迷走神経活動の回復に影響を与えることが示された。以上のことから、におい刺激に対するポジティブな情報付与が運動後の落ち着き感の増大および心臓迷走神経活動の回復に影響することが示された。

The olfactory bulb (OB) transforms sensory input into spatially and temporally organized patterns of activity in principal mitral (MC) and middle tufted (mTC) cells. Thus far, the mechanisms underlying odor representations in the OB have been mainly investigated in MCs. However, experimental findings suggest that MC and mTC may encode parallel and complementary odor representations. We have analyzed the functional roles of these pathways by using a morphologically and physiologically realistic three-dimensional model to explore the MC and mTC microcircuits in the glomerular layer and deeper plexiform layer. The model makes several predictions. MCs and mTCs are controlled by similar computations in the glomerular layer but are differentially modulated in deeper layers. The intrinsic properties of mTCs promote their synchronization through a common granule cell input. Finally, the MC and mTC pathways can be coordinated through the deep short-axon cells in providing input to the olfactory cortex. The results suggest how these mechanisms can dynamically select the functional network connectivity to create the overall output of the OB and promote the dynamic synchronization of glomerular units for any given odor stimulus.

The effects of exposure to high concentrations of hydrogen sulfide (H2S) on human health are well known. However, the potential human health hazards posed by low-level chronic environmental H2S exposure are being debated. Accordingly, we reviewed the literature regarding the effects of chronic, environmentally-relevant H2S exposures on human health. All human observational studies using an analytical study design (e.g. cohort, cross-sectional, case-control) to evaluate chronic-duration low-level H2S exposure (approximately ≤ 10 ppm on average, for 1 year or more), were evaluated for a range of health outcomes. Respiratory symptoms in both adults and children were the most consistently reported symptoms on the increase. When reported, such effects appear to be temporary, given that there is no consistent evidence of pulmonary function deficit in either age group, among those chronically exposed to low H2S concentrations. While sparse, some data also suggest potential ocular symptoms and disorders associated with chronic ambient level H2S exposure in adults (not children), but the limited data on H2S exposures, co-exposures and/or strong odor stimulus of H2S, temper interpretation. Neurological symptoms and deficits have been reported in some studies, but the highest quality evidence, obtained using objective outcome measures and a reasonably detailed assessment of exposure, does not support a neurological-related risk in adults (only one study in children). For the other endpoints assessed (cardiovascular, reproductive and developmental, and carcinogenicity), the results were mixed and/or conflicting, but did not indicate a potential health hazard, although this literature has several major limitations, particularly with regard to exposure estimation and the ability to assess exposure-response.

Animals encounter fine-scale temporal patterns of odorant mixtures that contain information about the distance and number of odorant sources. To study the role of such temporal cues for odorant detection and source localization, one needs odorant delivery devices that are capable of mimicking the temporal stimulus statistics of natural odor plumes. However, current odorant delivery devices either lack temporal resolution or are limited to a single odorant channel. Here, we present an olfactory stimulator that features precise control of high-bandwidth stimulus dynamics, which allows generating arbitrary fluctuating binary odorant mixtures. We provide a comprehensive characterization of the stimulator's performance and use it to demonstrate that odor background affects the temporal resolution of insect olfactory receptor neurons, and we present a hitherto unknown odor pulse-tracking capability of up to 60 Hz in Kenyon cells, which are higher order olfactory neurons of the insect brain. This stimulator might help investigating whether and how animals use temporal stimulus cues for odor detection and source localization. Because the stimulator is easy to replicate it can facilitate generating the same odor stimulus dynamics at different experimental setups and across different labs. published

Previous studies have confirmed that both honeybee and Drosophila are capable of learning and memory. This study aimed to investigate whether the house fly ( Aldrichina grahami ), with strong instincts to adapt their living environment, have the learning ability to associate odor stimulus to avoid electric shock in free flying state using a device developed by the authors. The result showed the learning ability of A. grahami at the electric shock voltages of 5 V, 25 V and 45 V AC. When 60 V was used, the flies were frequently injured. Our results indicate that A. grahami is a good model to study the neural mechanism of learning and memory. The paradigm in this study has some advantages that can be used in future studies of free insects.

Olfactory signals, a major means of communication in insects, travel in the form of turbulent odor plumes. In terrestrial environments, an odor blend emitted from a single point source exists in every strand of the plume, whereas, in confluent plumes from two different odor sources, the strands have some chance of being coincident and comprising a new third odor in those strands. Insects have the ability to detect and interpret necessary olfactory information from individual filamentous odor strands in complex multifilament odor plumes. However, behaviorists have had no way to measure the stimulus situations they are presenting to their temporally acute insect subjects when performing Y-tube olfactometer or confluent pheromone plume wind tunnel assays. We have successfully measured the degree of plume-strand mixing in confluent plumes in a wind tunnel by using a multichannel insect-antenna-based chemosensor. A PC-based computer algorithm to analyze antennal signals from the probe portion of the system performed real-time signal processing and, following a short training session, classified individual odorant/mixture strands at sub-second temporal resolution and a few tens of millimeters of spatial resolution. In our studies, the chemosensor classified a higher frequency of strands of two different odorants emitted from two closely spaced filter papers as being "mixed" when the sources were located only 1 or 2 cm apart than when the sources were 5 or 10 cm apart. These experiments demonstrate the chemosensor's potential to be used for measuring odor stimulus situations in more complex multiple-plume environments.

The aim of the present study was to determine the impact of aging on learning and retrieval of taste-potentiated odor aversion (TPOA). TPOA, which involves processing of odor, gustatory, and visceral cues, is a particular form of learning important to food selection. The experiment was carried out on young (1.5 month), adult (12 months), and old (20-24 months) rats. To determine whether the possible effects of aging on TPOA were related or not to general memory alterations, mnesic abilities of the rats were previously evaluated by submitting the animals to object recognition, olfactory discrimination, and spatial homing task. It was noted that the young, the adult, and the old rats were able to learn and to retrieve TPOA whatever the stimulus - either odor or taste - used to elicit retrieval. Interestingly, it can be underlined that the rejection of the odor stimulus only was even slightly increasing with the rat age. Thus, TPOA which is important in food selection and in animal survival is spared during aging while mnesic deficits were observed in the other behavioral tasks tested according to the task requirement.

Since the 1970s, human subjects that have undergone corpus callosotomy have provided important insights into neural mechanisms of perception, memory, and cognition. The ability to test the function of each hemisphere independently of the other offers unique advantages for investigating systems that are thought to underlie cognition. However, such approaches have been limited to mammals. Here we describe comparable experiments on an insect brain to demonstrate learning-associated changes within one brain hemisphere. After training one half of their bisected brains, cockroaches learn to extend the antenna supplying that brain hemisphere towards an illuminated diode after this has been paired with an odor stimulus. The antenna supplying the naive hemisphere shows no response. Cockroaches retain this ability for up to 24 h, during which, shortly after training, the mushroom body of the trained hemisphere alone undergoes specific post-translational alterations of microglomerular synaptic complexes in its calyces. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007.

Sensory systems must represent stimuli in manners dependent upon a wealth of factors, including stimulus intensity and duration. One way the brain might handle these complex functions is to assign the tasks throughout distributed nodes, each contributing to information processing. We sought to explore this important aspect of sensory network function in the mammalian olfactory system, wherein the intensity and duration of odor exposure are critical contributors to odor perception. This is a quintessential model for exploring processing schemes given the distribution of odor information by olfactory bulb mitral and tufted cells into several anatomically distinct secondary processing stages, including the piriform cortex (PCX) and olfactory tubercle (OT), whose unique contributions to odor coding are unresolved. We explored the coding of PCX and OT neuron responses to odor intensity and duration. We found that both structures similarly partake in representing descending intensities of odors by reduced recruitment and modulation of neurons. Additionally, while neurons in the OT adapt to odor exposure, they display reduced capacity to adapt to either repeated presentations of odor or a single prolonged odor presentation compared with neurons in the PCX. These results provide insights into manners whereby secondary olfactory structures may, at least in some cases, uniquely represent stimulus features.

More than 50 years have passed since the first recording of neuronal responses to an odor stimulus from the primary olfactory brain area, the main olfactory bulb. During this time very little progress has been achieved in understanding neuronal dynamics in the olfactory bulb in awake behaving animals, which is very different from that in anesthetized preparations. In this paper we formulate a new framework containing the main reasons for studying olfactory neuronal dynamics in awake animals and review advances in the field within this new framework.

SUMMARYBenthic crustaceans rely on chemical stimuli to mediate a diversity of behaviors ranging from food localization and predator avoidance to den selection, conspecific interactions and grooming. To accomplish these tasks,Caribbean spiny lobsters (Panulirus argus) rely on a complex chemosensory system that is organized into two parallel chemosensory pathways originating in diverse populations of antennular sensilla and projecting to distinct neuropils within the brain. Chemosensory neurons associated with aesthetasc sensilla project to the glomerular olfactory lobes (the aesthetasc pathway), whereas those associated with non-aesthetasc sensilla project to the stratified lateral antennular neuropils and the unstructured median antennular neuropil (the non-aesthetasc pathway). Although the pathways differ anatomically, unique roles for each in odor-mediated behaviors have not been established. This study investigates the importance of each pathway for orientation by determining whether aesthetasc or non-aesthetasc sensilla are necessary and sufficient for a lobster to locate the source of a 2 m-distant food odor stimulus in a 5000-liter seawater flume under controlled flow conditions. To assess the importance of each pathway for this task, we selectively ablated specific populations of sensilla on the antennular flagella and compared the searching behavior of ablated animals to that of intact controls. Our results show that either the aesthetasc or the non-aesthetasc pathway alone is sufficient to mediate the behavior and that neither pathway alone is necessary. Under the current experimental conditions,there appears to be a high degree of functional overlap between the pathways for food localization behavior.

The lateral septum (LS) is implicated in behavioral defense. We tested whether bilateral infusions of the GABAA receptor agonist muscimol into the LS suppress rats' defensive responses to cat odor. Rats received intra-LS infusions of either saline or muscimol (40 ng/rat) and were exposed to either a piece of a cat collar that had been previously worn by a cat or to a control (cat odor free) collar. Rats exposed to the cat odor collar displayed more head-out postures, while intra-LS application of muscimol reduced the number of head-out postures. However, this reduction was also present in rats exposed to a control (cat odor free) collar. This latter finding suggests that despite its involvement in other defensive behaviors (e.g., open arm avoidance in the elevated plus maze), the LS does not selectively regulate rats' receptor defensive responding to the olfactory cues present in our cat odor stimulus.

Honeybees (Apis mellifera) can be trained to associate an odor stimulus with a sucrose reward. The neural structures involved in the detection and integration of olfactory stimuli are represented bilaterally in the brain. Little is known about the respective roles of the two sides of the brain in olfactory learning. Does each side learn independently of the other, or do they communicate, and if so, to what extent and at what level of neural integration? We addressed these questions using the proboscis extension response (PER) conditioning paradigm applied in a preparation that allows the separation of the two input sides during olfactory stimulations. Bees conditioned to two odorants A and B, one being learned on each side (A+/B+ training), showed in extinction tests rather unspecific responses: They responded to both odorants on both sides. This could be attributable to either a transfer of the learned information between sides, or to a generalization between odorants on each side. By subjecting bees to conditioning on one side only (A+/0 training), we found that the learned information is indeed transferred between sides. However, when bees were trained explicitly to give opposite values to the two odorants on the two sides (A+B−/B+A− training), they showed clear side-specific response patterns to these odorants. These results are used in the elaboration of a functional model of laterality of olfactory learning and memory processing in the honeybee brain.

To understand the perception of an odor mixture by the slug Limax marginatus, a mixture of two odors (carrot and cucumber) was used to condition the slugs, and internal representation of the odor mixture and its components was determined by cooling-induced retrograde amnesia. Slugs conditioned with the odor mixture showed aversive behavior, not only towards the mixture, but also towards the individual odor components. When the conditioned slugs were cooled after presentation of one of the odor components, odor preferences for both components recovered, suggesting that the slugs perceived the odor mixture as an entity. However, when the slugs were exposed to the components of the odor mixture after conditioning with the mixture, cooling treatment resulted in amnesia, which was specific towards the odor presented before the cooling treatment. This suggests that slugs exposed to odor components after conditioning were able to recognize the odor components individually. Thus, slugs learn a binary mix...

リラクゼーション効果をもつ化粧品を開発するには, 心理作用を客観的に評価する必要がある。従来から, その評価手法として脳波解析が行われており, 安静時の脳波と刺激呈示時の脳波を比較することで, 刺激の効果を定性的に評価している。しかし, 脳波は安静時においても情動や環境などの影響を受け大きく変化することから, 定量的な評価を行うためには環境などの影響を分離する必要がある。そこで, 本論文では刺激に依存する成分のみを抽出する新しい手法を提案し, 実際にペパーミント, およびスペアミントの周期的香料刺激を呈示した場合に計測される脳波を解析した。その結果ペパーミントでは4-6Hz近辺, スペアミントでは9-11Hz近辺の脳波成分の増加をとらえることができた。これらのことから提案した手法は, 脳波解析に有用な手法であることが示唆された。

Adult female Tabanus nigrovittatus Macquart (Diptera: Tabanidae) were field collected from a salt marsh in Essex County, Massachusetts. The horse flies were transported back to and tested in the laboratory to determine the effects of octenol (1-octen-3-ol) on engorgement. Flies exposed to octenol strips had a significantly higher engorgement response compared with control flies. To our knowledge, this is the first study to demonstrate an important link between an odor stimulus and the feeding response in Tabanidae. Research examining the link between odor attractants and repellents on the engorgement response is lacking or limited in most hematophagous Diptera. Understanding the role odors have on ingestion is essential to knowing how to interrupt feeding behavior of blood-feeding arthropods, especially for important vectors.

Sensory testing to determine odor thresholds has produced very variable values (literature values can vary by two to three orders of magnitude). Some of this variation is due to interperson genetic and physiological differences, but variation in odor delivery during such tests is also likely to have a significant impact. Olfactometers deliver odor reliably, but are relatively expensive and usually deliver to a single panelist, making testing of the full panel time-consuming. Simpler ways of delivering odors were tested using online APCI-MS to determine the variability in the delivered odor concentration over periods of time associated with sensory panel testing.

Many animals find distant unseen resources by guiding their locomotion through fluid media, using olfactory information acquired from plumes of odorant molecules issuing from the resource of interest. This behavior occurs in birds and fish, but much of our knowledge of it derives from flying insects, especially moths. It is a highly integrative behavior, requiring not only the integration of olfactory information with a behavioral strategy to maintain contact with the odor plume, but also an ability to detect the direction of fluid flow that is carrying the odor cue. The temporal-spatial structure of the odor plume is determined by the fluid dynamics of the environment, and it profoundly affects the behavior. Thus, the success of animals (or artificial agents) is determined by an interaction between sensory input and internally generated behaviors. We have implemented behavioral-level simulations of odor-modulated moth flight to understand how the properties of the odor stimulus and the behavioral system interact to result in successful source location. Even simple reflexive models can track predictable, laminar-flow plumes, but only models with internally generated behaviors can track unpredictable, turbulent plumes. The "best" behavioral strategy depends on both the structure of the odor stimulus and an agent's performance limits.

Significant insights into the dynamics of neuronal populations have been gained in the olfactory system where rich spatio-temporal dynamics is observed during, and following, exposure to odours. It is now widely accepted that odour identity is represented in terms of stimulus-specific rate patterning observed in the cells of the antennal lobe (AL). Here we describe a nonlinear dynamical framework inspired by recent experimental findings which provides a compelling account of both the origin and the function of these dynamics. We start by analytically reducing a biologically plausible conductance based model of the AL to a quantitatively equivalent rate model and construct conditions such that the rate dynamics are well described by a single globally stable fixed point (FP). We then describe the AL's response to an odour stimulus as rich transient trajectories between this stable baseline state (the single FP in absence of odour stimulation) and the odour-specific position of the single FP during odour stimulation. We show how this framework can account for three phenomena that are observed experimentally. First, for an inhibitory period often observed immediately after an odour stimulus is removed. Second, for the qualitative differences between the dynamics in the presence and the absence of odour. Lastly, we show how it can account for the invariance of a representation of odour identity to both the duration and intensity of an odour stimulus. We compare and contrast this framework with the currently prevalent nonlinear dynamical framework of 'winnerless competition' which describes AL dynamics in terms of heteroclinic orbits. This article is part of a Special Issue entitled "Neural Coding".

Magnetoreception is a sophisticated orientation mechanism, involving a magnetoreceptor connected to the nervous system with signal amplification. The molluskTritonia diomedeais a good model to investigate the behavioral and neural responses to the magnetic field. The mollusk inhibits all unnecessary activities and focuses on an available cue during orientation. Although Pd7 cells are inhibited by magnetic pathway, it was excited by another stimulus, water streams plus food odor. Two sensory pathways connected to Pd7 through the same or different circuits were tested. The action potential activity through Pd7 was compared in these different stimulations. The changes in Pd7 activity indicate a response of enhanced electrical activity to water streams plus food odor stimulus, and Pd7 activity can be excited by at least one of these stimuli. These results indicate an inverse relationship between magnetic orientation and feeding.

Efficiency level of work in a factory or an office is influenced by the physiological and psychological factors. These factors seem to be reflected in emotional aspect of human behavior. The emotion is ultimately judged from the view point of pleasantness or unpleasantness. In this study, odor stimulus, which easily induce pleasant or unpleasant feeling, was used for the experimental environment. Psychophysiological evaluation of the emotional aspect was tried to be assessed by using Event-related potentials(ERPs) evoked by S1–S2 and S1–S2+R paradigm. Multivariate analysis was used to the single trial ERP wave forms as samples in order to estimate component wave forms(basis waves). The area of the largest basis waves in the both paradigms were measured. Increase ratio of the mean of these basis waves on each hemisphere were compared and Rt/Lt ratio was obtained. It is revealed that the Rt/Lt ratio was less in the favorite than in both control and unfavorable conditions, and that unfavorable one was larger than the control. These results assumed that ERP measurements and analysis might reveal the subjective conditions in favorite and unfavorable environments.

This study investigated cued odor identification performance with a set of 64 natural common odors (half of edible and half of nonedible stimuli) in three groups of participants: one group of 30 young adults (mean age 25.3 years, range 18–30, SD 3.1) and two groups of older adults—20 young-old (mean age 64.4 years, range 60–69, SD 2.8) and 21 old-old (mean age 74.6 years, range 70–79, SD 2.5). The results showed that 49 of the 64 odors were correctly identified by over 70% of the participants in all groups. The odor identification performance of the young-old adults did not differ from that of the young adults. However, the oldest group showed a significant loss of performance in the task. Women in the young-old group performed better than men, whereas no gender differences were found in the other two age groups. The data obtained in this study will be useful for further perceptual and memory studies conducted in the olfactory modality with young as well as with older participants.

52 ref. doi: 10.1101/lm.81504; In honeybees, the proboscis extension response (PER) can be conditioned by associating an odor stimulus (CS) to a sucrose reward (US). Conditioned responses to the CS, which are acquired by most bees after a single CS-US pairing, disappear after repeated unrewarded presentations of the CS, a process called extinction. Extinction is usually thought to be based either on (1) the disruption of the stored CS-US association, or (2) the formation of an inhibitory "CS-no US" association that is better retrieved than the initial CS-US association. The observation of spontaneous recovery, i.e., the reappearance of responses to the CS after time passes following extinction, is traditionally interpreted as a proof for the formation of a transient inhibitory association. To provide a better understanding of extinction in honeybees, we examined whether time intervals during training and extinction or the number of conditioning and extinction trials have an effect on the occurrence of spontaneous recovery. We found that spontaneous recovery mostly occurs when conditioning and testing took place in a massed fashion (1-min intertrial intervals). Moreover, spontaneous recovery depended on the time elapsed since extinction, 1 h being an optimum. Increasing the number of conditioning trials improved the spontaneous recovery level, whereas increasing the number of extinction trials reduced it. Lastly, we show that after single-trial conditioning, spontaneous recovery appears only once after extinction. These elements suggest that in honeybees extinction of the PER actually reflects the impairment of the CS-US association, but that depending on training parameters different memory substrates are affected.

Odor identification is one of the main tasks of the olfactory system. It is performed almost independently from the concentration of the odor providing a robust recognition. This capacity to ignore concentration information does not preclude the olfactory system from estimating concentration itself. Significant experimental evidence has indicated that the olfactory system is able to infer simultaneously odor identity and intensity. However, it is still unclear at what level or levels of the olfactory pathway this segregation of information occurs. In this work, we study whether this odor information segregation is performed at the input stage of the olfactory bulb: the glomerular layer. To this end, we built a detailed neural model of the glomerular layer based on its known anatomical connections and conducted two simulated odor experiments. In the first experiment, the model was exposed to an odor stimulus dataset composed of six different odorants, each one dosed at six different concentrations. In the second experiment, we conducted an odor morphing experiment where a sequence of binary mixtures going from one odor to another through intermediate mixtures was presented to the model. The results of the experiments were visualized using principal components analysis and analyzed with hierarchical clustering to unveil the structure of the high-dimensional output space. Additionally, Fisher's discriminant ratio and Pearson's correlation coefficient were used to quantify odor identity and odor concentration information respectively. Our results showed that the architecture of the glomerular layer was able to mediate the segregation of odor information obtaining output spiking sequences of the principal neurons, namely the mitral and external tufted cells, strongly correlated with odor identity and concentration, respectively. An important conclusion is also that the morphological difference between the principal neurons is not key to achieve odor information segregation.

It is known empirically that scented environments induced by favored or unfavorable odor stimuli affect the emotional aspects of human behavior. These effects seem to be reflected in such psychological factors as mood and feeling. Several studies have addressed the effects of odors on human psychological function by using event-related potentials (ERPs) [1,2]. In our previous studies, also [3,4], we found that both favored and unfavorable odor stimuli affected the basis waves of ERPs extracted by multivariate analysis. In this study, right/left (rt/lt) ratios measured from basis waves of ERPs obtained from 20 subjects were examined in different “feeling” profiles induced by the same odor stimulus.

Neonatal rats acquire an olfactory preference following daily exposure to an odor that is accompanied by tactile stimulation. In the present study, we determined the neurobehavioral responses of pups trained and tested with odors of either the same or different concentration. On postnatal day (PND) 1–18, all animals were exposed for 10 min/day to either peppermint or air while receiving perineal tactile stimulation. On PND 19, pups trained with a low odor concentration preferred that concentration to either air or a high odor concentration. However, rat pups trained with the high odor concentration preferred that odor to air, regardless of its concentration and showed equal preference between odor concentrations. These results suggest both that pups can learn to prefer a specific odor concentration and that they can learn to recognize odor quality across concentrations. To determine the neural responses to such stimuli, trained and control pups were exposed to either low or high peppermint odor concentrations following an injection of 14 C-labelled 2-deoxyglucose (2-DG). Early experience with the high odor concentration resulted in the 2-DG uptake response to both test odor concentrations which was higher than that of pups that had previous experience with either the low odor concentration or with clean air. Though the 2-DG density did not increase with test odor concentration, the size of the 2-DG foci did, regardless of previous experience. The 2-DG response to odor concentration is, therefore, influenced by both previous experience and immediate odor stimulus characteristics that are revealed in parallel responses within the olfactory bulb.

Responses of 75 single units in the goldfish olfactory bulb were analyzed in detail for their relationship to the time-course of the change in odor concentration during each odor stimulus. Odor stimuli were controlled for rise time, duration, and peak concentration by an apparatus developed for the purpose. This apparatus enabled aqueous odor stimuli to be interposed into a constant water stream without changes in flow rate. The time-course of the concentration change within the olfactory sac was inferred from conductivity measurements at the incurrent and excurrent nostrils. Temporal patterns of firing rate elicited by stimuli with relatively slow rising and falling phases could be quite complex combinations of excitation and suppression. Different temporal patterns were produced by different substances at a single concentration in most units. Statistical measures of the temporal pattern of response for a small number of cells at a given concentration were more characteristic of the stimulus substance than any of three measures of magnitude of response. The temporal patterns change when the peak concentration, duration, and rise time of the stimuli are varied. The nature of these changes suggests that the different patterns are due primarily to the combined influence of two factors: (a) a stimulus whose concentration varies over time and (b) a relationship between concentration and impulse frequency which varies from unit to unit. Some units produce patterns suggestive of influence by neural events of long time constant. The importance of temporal patterns in odor quality and odor intensity coding is discussed.

The fire salamanderSalamandra salamandra (L.) exhibits prey-catching responses to stationary visual patterns if it has previously been stimulated by a moved dummy prey. When presented with two stationary objects, salamanders choose circular patterns over rectangles, regardless of the orientation of the latter. By contrast, when the pattern is moved horizontally, horizontally-oriented rectangles are preferred (Fig. 2). If an odor stimulus is associated with a stationary visual pattern the choice behavior may be altered, but visual stimuli play the greater role. Visual detection of stationary patterns can be explained by involuntary tremor-like eye movements.

Although cis-11-tetradecenyl acetate is a sex attractant for males of several species of moths these species responded selectively to subtle quantitative or qualitative changes in the composition of the odor stimulus. It is plausible, based on the odor-discrimination capability of the moths, that moths of many species could use pheromones of identical chemical structure and avoid interspecific pheromonal confusion by responding only to specific concentrations and/or blends of chemicals characteristic of their own species.

The scope of this work is the evaluation of the non-carcinogenic occupational risk related to foundry emissions, focusing on the category of workers involved in olfactometric assessments. Odor pollution from industrial activities such as foundries is a serious environmental concern. Sensorial techniques (e.g. dynamic olfactometry, EN13725:2003) currently represent the preferred method for odor emission characterization. During olfactometric analyses, human assessors are directly exposed to the odor at increasing concentrations, thus requiring the assessment of the associated exposure risk to guarantee workers' safety. This paper presents an investigation aiming to produce an inventory of compounds emitted from foundries together with their odor thresholds and toxicological limits (TLVs), with the final objective to propose a procedure for ensuring workers' safety during olfactometric analyses. Looking at the database resulting from this study, among the >100 compounds emitted by foundries, 8 have a maximum concentration above their TLV. Among those, ammonia, H2S, phenol, toluene and trimethylamine, produce an odor stimulus before they reach a toxic concentration, thus not representing a risk for olfactometric workers. Benzene, formaldehyde and SO2 are identified as the most critical compounds because they may reach toxic concentrations in foundry emissions, and they start being perceived by humans above their TLV. The proposed procedure entails a minimum dilution factor of 27'000 to be applied to odor samples analyzed by olfactometry, which however might result inapplicable in practical cases, thus pointing out the necessity to adopt chemical measurements to investigate specifically the concentration of the most critical compounds identified in this study.

Certain male moths flying upwind toward a scent-producing female appear to be guided anemotactically by optomotor reactions to the ground pattern. Loss of the odor stimulus changes the anemotactic angle from into wind to across wind with left-right reversals.

Rat fetuses were exposed to an odor stimulus on day 20 of gestation via amniotic injection and then injected with LiCl. In a CER paradigm, 10 day old pups were trained to approach an anesthetized dam in a runway for suckling reinforcement. When running speeds had stabilized the odor stimulus experienced in-utero was introduced into the test chamber. This odor took on aversive properties as a function of its pairing with LiCl, as evidenced by a decrease in running speed on CER trials and increases in the number of trials that were terminated because pups failed to traverse the runway. These data indicate that the fetal rat is capable of odor aversion learning.

Absolute odor thresholds for methyl isobutyl ketone were estimated under five conditions: odor sample-to-air blank ratios of 1:2, 1:1, 2:1, 4:1, and 9:1. Each of the five ratios was presented in two replicated balanced Latin square sequences to five adult human Ss. The results showed that significantly lower estimates of the threshold were obtained when the ratio of odor samples to air blanks was 1:1. These results are discussed in terms of possible adaptation effects, maintenance of an internal frame of reference as a basis for decisions, and response matching to pay-off expectancy.

Five experiments employed 2- and 10-day-old rat pups to examine the ontogeny of odor-aversion learning. When duration of exposure to the to-be-conditioned odor stimulus (CS) was long, Experiments 1 and 2 demonstrated substantial and similar aversions across the two ages regardless of whether the toxin unconditioned stimulus (US) occurred simultaneously with, immediately before, immediately after, or some time after the CS. These experiments, therefore, did not support the claim of Rudy and Cheatle ( Ontogeny of Learning and Memory . Hillsdale, N.J.: Erlbaum (1979)) that the 2-day old pup suffers a deficit in its learning about the relation between successively presented events. The remaining experiments showed, however, that the 2-day-old pups did not acquire an aversion to a briefly presented CS, that the failure to condition this CS was not due to its overshadowing by contextual cues, and that the 10-day-old pup did acquire an aversion to that CS. The experiments have revealed, therefore, that there are age-related differences in the rat pup's ability to learn about the relation between a briefly-presented CS and the effects of a US.

A new testing facility for research on canine olfaction was established. Instrumentation incorporates recent improvements in odor stimulus production and control techniques and provides a means -- through automated program control -- to obtain simultaneous measurements from up to four independent testing chambers. Enhancement of odor detection performance following systemic administration of the same odorant ('sensitization') generally occurs from 5 to 12 days after ingestion of a small measured quantity of the odorant. The maximum performance level subsequently achieved is seen as an elevation of scores roughly equivalent to that typical for a ten-fold higher test concentration. This performance elevation either declines back to baseline, within about one week, or is sustained for many weeks. The sensitization effect does not occur if the ingested odorant differs markedly in structure from the behavioral testing odorant, a finding that indicates relative specificity of the effect and suggests that its site of origin is at the receptor level. A comparison was made of the performance of German shepherds and Fox terriers during the initial acquisition phase of training on a forced-choice odor detection task. Handlers directly controlled the dogs by the use of a hand-held lead and voice commands.

A multistage dynamic flow dilution olfactometer allowing the delivery of precisely controlled stimuli over a wide concentration range is presented. Discrete concentration values, in the range 10(-6) to 5.6 X 10(-2) of the saturated vapor of an odorous compound, are obtained from two original concentration by combining 4 dilution stages. Short stimulus pulses, of a known and reproducible concentration and with short rising and falling times, are sampled from steady concentration levels. A programmable controller manages the olfactometer dilution stage selection, the odor stimulus switch and starts the peripheral devices required by the experiment. The programming of olfactometer function makes it an extremely flexible system for various experimental projects in olfaction.

Parameters of Lumbricus terrestris behavior and learning in a T-maze are explored by comparing the animals' use of odor as a cue with their use of more traditional stimuli. Available stimuli are a volatile odor, inclination of the maze, and light-shadow at the choice point—as well as kinesthetic-tactile stimuli. It is found that L. terrestris can use odor to choose a specified exit on the first trial. However, more than a taxis is involved. Behavior over trials is characterized by a rapid decrease in choice speed when the consequences of at least one alternative are noxious (saline), and by a rapid increase in choice speed when the consequence of neither alternative is noxious. Contrasting above and below threshold intensities of the odor stimulus, with and without noxious consequences, reveals that only odor permits rapid association of cue and consequence. The specificity and rapidity of the behavior changes found with odor suggests selective association must be considered as a factor in earthworm learning.