Conditioned Odor Research Articles

Visualizing mushroom body response to a conditioned odor in honeybees.

Combining differential conditioning with optophysiological recordings of bee brain activity allows the investigation of learning-related changes in complex neural systems. In this study we focused on the mushroom bodies of the bee brain. Presenting different odors to the animal leads to significant activation of the mushroom body lips. After differential conditioning, the rewarded odor leads to stronger activation than it did before training. Activation by the unrewarded odor remains unchanged. These results resemble findings in the bee's antennal lobes, which are the first olfactory relay station in the insect brain. As an integrative neural network, enhanced activation of the mushroom body lip may carry additional information, i.e., for processing odor concentrations.

Morphometric modeling of olfactory circuits in the insect antennal lobe: I. Simulations of spiking local interneurons

Inhibitory local interneurons (LNs) play a critical role in shaping the output of olfactory glomeruli in both the olfactory bulb of vertebrates and the antennal lobe of insects and other invertebrates. In order to examine how the complex geometry of LNs may affect signaling in the antennal lobe, we constructed detailed multi-compartmental models of single LNs from the sphinx moth, Manduca sexta, using morphometric data from confocal-microscopic images. Simulations clearly revealed a directionality in LNs that impeded the propagation of injected currents from the sub-micron-diameter glomerular dendrites toward the much larger-diameter integrating segment (IS) in the coarse neuropil. Furthermore, the addition of randomly-firing synapses distributed across the LN dendrites (simulating the noisy baseline activity of afferent input recorded from LNs in the odor-free state) led to a significant depolarization of the LN. Thus the background activity typically recorded from LNs in vivo could influence synaptic integration and spike transformation in LNs through voltage-dependent mechanisms. Other model manipulations showed that active currents inserted into the IS can help synchronize the activation of inhibitory synapses in glomeruli across the antennal lobe. These data, therefore, support experimental findings suggesting that spiking inhibitory LNs can operate as multifunctional units under different ambient odor conditions. At low odor intensities, (i.e. subthreshold for IS spiking), they participate in local, mostly intra-glomerular processing. When activated by elevated odor concentrations, however, the same neurons will fire overshooting action potentials, resulting in the spread of inhibition more globally across the antennal lobe. Modulation of the passive and active properties of LNs may, therefore, be a deciding factor in defining the multi-glomerular representations of odors in the brain.

Enhancing Athletic Performance through the Administration of Peppermint Odor

Previous research has indicated that odorant presentations can have both positive and negative effects on psychological perceptions of athletic task performance. The present study extends past research by assessing how the administration of peppermint odor affects actual athletic task performance. Forty athletes undertook a series of physical tasks under conditions of no-odor or peppermint odor. The peppermint odor condition resulted in increases in running speed, hand grip strength, and number of push-ups, but had no effect on skill related tasks such as basketball free-throw shots. The implications are particularly salient in regard to enhancing athletic performance using a nonpharmacological aid and as an adjunct to athletic training and physical therapy.

Searching for the memory trace in a mini-brain, the honeybee.

To determine general or species-specific properties in neural systems, it is necessary to use comparative data in evaluating experimental findings. Presented here are data on associative learning and memory formation in honeybees, emphasizing a comparative approach. We focus on four aspects: (1) the role of an identified neuron, VUM(mx1), as a neural substrate of appetitive reinforcement; (2) the sequences of molecular events as they correlate with five forms of memory stages; (3) the localization of the memory traces following appetitive olfactory learning; and (4) the brief description of several forms of complex learning in bees (configuration in olfactory conditioning, categorization in visual feature learning, delayed matching-to-sample learning, and latent learning in navigation). VUM(mx1) activity following the conditioned stimulus odor is sufficient to replace the unconditioned stimulus, and VUM(mx1) changes its response properties during learning similarly to what is known from dopamine neurons in the basal ganglia of the mammalian brain. The transition from short- to mid- and long-term forms of memory can be related to specific activation of second messenger cascades (involving NOS, PKA, PKC, and PKM) resembling general features of neural plasticity at the cellular level. The particular time course of the various memory traces may be adapted to the behavioral context in which they are used; here, the foraging cycle of the bee. Memory traces for even such a simple form of learning as olfactory conditioning are multiple and distributed, involving first- and second-order sensory neuropils (antennal lobe and mushroom bodies), but with distinctly different properties. The wealth of complex forms of learning in the context of foraging indicates basic cognitive capacities based on rule extraction and context-dependent learning. It is believed that bees might be a useful model for studying cognitive faculties at a middle level of complexity.

Repeated formaldehyde effects in an animal model for multiple chemical sensitivity.

Chemical intolerance is a phenomenon observed in multiple chemical sensitivity (MCS) syndrome, an ill-defined disorder in humans attributed to exposure to volatile organic compounds. Amplification of symptoms in individuals with MCS resembles the phenomenon of psychostimulant- and stress-induced sensitization in rodents. We have recently tested in rats the hypothesis that repeated chemical exposure produces sensitization of central nervous system (CNS) circuitry. A rat model of MCS in our laboratory has employed several endpoints of CNS function after repeated formaldehyde (Form) exposure (1 h/day x 5 days/week x 4 weeks). Repeated Form exposure produced behavioral sensitization to later cocaine injection, suggesting altered dopaminergic sensitivity in mesolimbic pathways. Rats given repeated Form also demonstrated increased fear conditioning to odor paired with footshock, implicating amplification of neural circuitry guiding fear responding to a conditioned odor cue. Recent studies examining the effects of repeated Form on locomotor activity during each daily exposure showed a decrease in rearing activity after 12-15 days of Form exposure compared to air-exposed controls. EEG recordings taken 1 week after withdrawal from daily Form revealed altered sleep architecture. Some of the differences in sleep disappeared after subsequent brief (15 min) challenge with Form the next day. Overall, the findings indicate that repeated low-level chemical exposure produces behavioral changes that may be akin to those observed in individuals with MCS, such as greater sensitivity to chemicals manifest as increased anxiety upon chemical exposure and altered sleep and/or fatigue. Study of the underlying CNS changes will provide a basis for mechanistically based animal models for MCS.

Enantioselectivity of odor perception in honeybees (Apis mellifera carnica).

The authors tested the ability of 60 free-flying honeybees (Apis mellifera carnica) to discriminate a conditioning odor from an array of 26 simultaneously presented substances. The stimuli included 10 pairs of enantiomers and 6 essential oils. The bees (a) significantly distinguished between 98% of the 540 odor pairs tested, thus showing an excellent overall discrimination performance, and (b) were able to discriminate between the optical isomers of limonene, alpha-pinene, beta-citronellol, menthol, and carvone but failed to distinguish between the (+)- and (-)-forms of alpha-terpineol, camphor, rose oxide, fenchone, and 2-butanol. The findings support the assumptions that enantioselective molecular odor receptors may exist only for some volatile enantiomers and that insects and mammals may share common principles of odor quality perception, irrespective of their completely differing repertoires of olfactory receptors.

Effects of pleasant and unpleasant ambient odors on human voice pitch

The perception of odors is well identified as having strong emotional correlates. It is also well known that the acoustic characteristics of the voice differ according to the emotional state. This study compared some acoustic features of the voice of 18 subjects reading the same text in pleasant (lavender) and unpleasant (pyridine) ambient odor conditions. The results revealed that the pitch of the voice was higher in the pleasant than in the unpleasant condition. These findings are consistent with the hypothesis of local and functional convergences of encoding vocal emotion and hedonic perception of odors.

Diazepam attenuates conditioned odor potentiation of startle in rats

Recently, Richardson, Vishney, and Lee (1999) described a simple protocol whereby conditioned odor potentiation of startle (OPS) could be observed in rats. The aim of the present study was to extend their findings by determining whether OPS is attenuated by pretest intraperitoneal injection of diazepam. The results showed that diazepam (0.6 mg/kg) markedly attenuated OPS at test (Experiment 1) and that this attenuation was not due to diazepam’s affecting either odor detection or mobility (Experiment 2). The results suggest not only that the OPS effect is mediated by fear, but also that it may be mediated by the same neural substrates that mediate conditioned tone and conditioned light potentiated startle.

Enhanced Fos expression within the primary olfactory and limbic pathways induced by an aversive conditioned odor stimulus

A central question in olfactory learning is how animals become tuned to odor stimuli that gain significance through conditioning. A leading view is that tuning to conditioned odor stimuli involves functional modifications within the primary olfactory pathways, themselves. 7 Here we studied this idea further by investigating responses within the olfactory system to an odor that had previously been paired with footshock in classical fear-conditioning trials in adult rats. Using the transcription factor Fos as a marker of odor-induced neuronal activation, 1,14 we found that in rats that had received forward pairings of odor and footshock during training, presentation of the conditioned odor stimulus, alone, produced an enhanced increase in levels of Fos in the main and accessory olfactory bulbs and anterior olfactory nucleus compared with that found in animals that had received backward presentations of the stimuli or of odor alone. These results demonstrate that Fos responses to an odor within the primary olfactory pathways can be modified through aversive conditioning, and are consistent with other evidence that olfactory conditioning can lead to functional changes within these pathways. 7

Pavlovian aversive and appetitive odor conditioning in humans: subjective, peripheral, and electrocortical changes.

Differential Pavlovian conditioning of aversive and appetitive odors was examined in 30 male healthy subjects. The appetitive conditioning group (n=15) received a pleasant odor (vanilla), the aversive conditioning group (n=15) an unpleasant odor (fermented yeast) as unconditioned stimulus. Slides of two different neutral faces that were easy to discriminate served as conditioned stimuli (CS). An EEG was recorded from nine electrodes. Electromyographic activity was measured bilaterally from the m. corrugator supercilii and m. zygomaticus. The startle response was obtained from the m. orbicularis oculi. Finally, heart rate and skin conductance response were assessed. The subjective data and the skin conductance response revealed successful differential aversive conditioning. By contrast, the pleasant odor failed to produce appetitive odor conditioning. The conditioned and unconditioned response of the corrugator muscles confirm previous reports on the m. corrugator being strongly involved in the expression of negative affect. Contrary to previous findings, magnitude of the startle reflex was not found to be modulated depending on the valence of the CS. Central psychophysiological parameters showed little change during differential conditioning. The presence of subjective-evaluative conditioning and contingency awareness without significant changes in cortical and cardiovascular correlates might be due to extremely localized cortical processing of conditioned olfactory cues or primarily subcortical processing. The latter interpretation is strengthened by the presence of differential conditioning in non-voluntary responses such as the corrugator muscles.

Lateralized memory storage and crossed inhibition during odor processing by Limax.

After odor conditioning intact Limax maximus and injecting LY into their haemocoel, labeled groups of neurons are found in either the right or left procerebral lobe but never in both procerebral lobes. This suggests that a competitive interaction occurs between right and left odor processing pathways of which the procerebral lobe is a part. We use the nerve discharge in the external peritentacular nerve evoked by applying a puff of conditioned odor to the nose to document crossed inhibition between left and right odor processing pathways. Responses in the external peritentacular nerve evoked by stimulating one superior nose with a conditioned odor are strongly lateralized as responses occur only on the stimulated side. Stimulating both superior noses simultaneously with the same conditioned odor yields responses in both external peritentacular nerves that resemble the sum of responses to unilateral stimulation. Simultaneously stimulating both superior noses, each with a different conditioned odor leads to strong inhibition of both external peritentacular nerve responses. The crossed inhibition is also evident if both superior and inferior noses on the same side are stimulated simultaneously. A lateral inhibitory mechanism, situated postsynaptic to odor recognition, appears to inhibit external peritentacular nerve responses if the two noses receive conflicting sensory inputs.

Effects of inhalation of essential oils on EEG activity and sensory evaluation.

The purpose of this study was to investigate EEG changes in subjects directly after inhalation of essential oils, and subsequently, to observe any effect on subjective evaluations. EEG and sensory evaluation were assessed in 13 healthy female subjects in four odor conditions. Four odor conditions (including lavender, chamomile, sandalwood and eugenol) were applied respectively for each subject in the experiment. The results were as follows. 1) Four basic factors were extracted from 22 adjective pairs by factor analysis of the sensory evaluation. The first factor was "comfortable feeling", the second "cheerful feeling", the third "natural feeling" and the fourth "feminine feeling". In the score of the first factor (comfortable feeling), the odors in order of high contribution are lavender, eugenol, chamomile and sandalwood. 2) Alpha 1 (8-10 Hz) of EEG at parietal and posterior temporal regions significantly decreased soon after the onset of inhalation of lavender oil (p < 0.01). Significant changes of alpha 1 were also observed after inhalation of eugenol or chamomile. The change after inhalation of sandalwood was not significant. These results showed that alpha 1 activity significantly decreased under odor conditions in which subjects felt comfortable, and showed no significant change under odor conditions in which subjects felt uncomfortable. These results suggest a possible correlation between alpha 1 activity and subjective evaluation.

Odour and Proustian memory: reduction of context-dependent forgetting and multiple forms of memory

In Experiment 1, the reintroduction of the same ambient odour (lemon or lavender) improved performance four weeks later in both free recall and recognition of a word list. This was a cross-over design that allowed direct comparison between congruent and incongruent odour conditions. A further comparison with an additional group showed that memory was not improved by the presence of a different odour. Experiment 2 investigated the effect of two odour cues (lemon and lavender) in the same cross-over design using three learning and memory tests: (1) free recall of a word list; (2) problem solving; and (3) spatial learning. While recall of the word list and spatial learning were best when the same odour was present at both learning and test, there was no such context-dependent effect for the problem-solving task. However, the presence of the lavender odour at test improved performance in the problem-solving task, irrespective of the odour present at the first exposure. Thus although lavender had some effect on problem solving, we saw context-dependent retrieval only in free recall and spatial learning. We discuss the implications of this dissociation. Copyright © 2001 John Wiley & Sons, Ltd.

The ontogeny of conditioned odor potentiation of startle.

During development, conditioned responses usually occur first to olfactory, then to auditory, and finally to visual cues. The authors of the present study report that fear potentiation of startle to an olfactory conditioned stimulus emerges relatively late in development (i.e., at 23 days of age; Experiments 1 and 2). The failure to observe conditioned odor potentiation of startle (OPS) in younger rats was not due to a failure to either acquire or remember the odor-shock association (Experiment 3). Surprisingly, the authors also found that rats trained at 16 but tested at 23 days of age failed to exhibit the OPS effect even though they did exhibit pronounced odor avoidance (Experiment 4). The results are discussed in terms of (a) sensory-specific sequential emergence of learned fear, (b) the neural circuit involved in fear potentiation of startle, and (c) the concept that conditioned responding is appropriate to the animal's age at the time of training rather than its age at testing.

Expression of c-Fos in the main olfactory bulb of neonatal rabbits in response to garlic as a novel and conditioned odour

Expression of c-Fos was examined in the olfactory bulbs of 3-day-old rabbits after they had been presented with the odour of garlic as a novel stimulus, as a learned odour, or during conditioning, and this expression compared with baseline levels in non-stimulated controls. Exposure to garlic odour resulted in substantial and widespread increases in c-Fos expression in the olfactory bulbs of all animals. However, although conditioned pups showed a specific behavioural response to the learned garlic odour, neither the amount nor pattern of c-Fos expression differed compared to pups exposed to garlic as a novel odour. The odour-induced expression of c-Fos was not well localised, although there was a significant increase in the number of granule cells expressing c-Fos in the ventrolateral region of the bulb. These results support previous reports that the response to odours in the olfactory bulb of new-born animals is not as spatially distinct as that in adults. Nevertheless, the immature olfactory system of these young animals is clearly capable of very specific odour learning.

Biofiltration of asphalt emissions: Full‐scale operation treating off‐gases from polymer‐modified asphalt production

AbstractIn response to complaints from nearby residents, a biofilter was designed, installed, and tested for treating odors in one of three odorous emission streams from an asphalt plant producing polymer‐modified asphalt. Hydrogen sulfide (H2S) was determined to be the most prevalent gaseous reduced sulfur compound and was detected in the emission stream only when polymer material was being added to raw asphalt. Emission stream H2S concentrations we requite variable, ranging from 16 to approximately 30,000 ppm (v/v) and considered the likely compound contributing most to the plant's odor complaints.The biofilter was effective in controlling odor from the production process and removed an overall average of 65% of the H2S during polymer addition, and for H2S concentrations less than 400 ppmv, re m oval averaged 98%. These removal efficiencies reflect data from the biofilter operating at 2.5‐minute empty bed residence time in 1996 and a 6.1‐minute empty bed residence time in 1997.The biofilter's bed became increasingly acidified during the plant's 1997 operating season producing a pH gradient through the bed ranging from a high of 6.6 to a low of 3.1. The bed medium moisture content remained constant at about 60% (wet weight basis), but changes were observed in the water potential: no correlation to performance was determined. Changes in the microbial community reflected the bed acidification trend, with acidophiles becoming gene rally more numerous in the bed's deeper portions and in the mid to late season when the bed was most acidified. Bed acidification did not impact the biofilter's H2S removal efficiency.Nearby residents we resurveyed and roughly half of the respondents indicated that the odor conditions had improved, one‐third felt odor conditions were unchanged and the remaining 15% felt odor conditions were worse despite the fact that only one of three of the plant's odorous emission streams were treated by the biofilter. Plans are to implement biofiltration for odor control at all of the facility's emission points.

Contributions of Superior and Inferior Tentacles to Learned Food-Avoidance Behavior in Limax marginatus

We investigated learned food-avoidance behavior of conditioned slugs in detail, and examined the effect of removing the inferior or superior tentacles (ITs and STs) on the avoidance behavior. The conditioning procedure significantly lowered the preference level of slugs to the conditioned odor, and the decrease of the preference was maintained for at least 48 hr. Video analysis experiments showed that change in the crawling direction during an aversion response occurred consistently accompanied by an average of 1.2 head swings. The first head swing was usually observed within 1 cm from the conditioned odor. Removal of the ITs after conditioning reversed the trend towards a lowered preference level. On the other hand, removal of the STs did not change the level. These results suggest that the IT inputs are needed to induce conditioned behavior. The contribution of STs to the conditioning behavior is indicated by the significant increase in the average number of head swings (3.6 swings) in a trial after their removal. In some trials, the slugs lacking STs avoided the odor source after crossing it. These observations indicate that removal of STs decreases the orientation ability of conditioned slugs.

Olfactory discrimination ability and odor structure-activity relationships in honeybees.

Using the training procedure introduced by von Frisch in 1919, we tested the ability of free-flying honeybees to discriminate a conditioning odor from an array of 44 simultaneously presented substances. The stimuli included homologous series of aliphatic alcohols, aldehydes and ketones, isomeric forms of some of these substances, as well as several terpenes and odor mixtures, and thus comprised stimuli of varying degrees of structural similarity to any conditioning odor. We found (i) that the honeybees significantly distinguished between 97.0% of the 1848 odor pairs tested, thus showing an excellent discrimination performance when tested in a free-flying situation with an array of structurally related substances; (ii) a significant negative correlation between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length with all aliphatic substance classes tested; (iii) that both the position and type of a functional group also affected discriminability of odorants in a substance class-specific manner; and (iv) striking similarities in odor structure-activity relationships between honeybees and human and nonhuman primates tested previously on a subset of substances employed here. Our findings demonstrate that the similarities found in the structural organization of the olfactory systems of insects and vertebrates are paralleled by striking similarities in relative discrimination abilities. This strongly suggests that similar mechanisms of odor coding and discrimination may underlie olfaction in vertebrates and insects.

Visual event related potentials modulated by contextually relevant and irrelevant olfactory primes.

Visual evoked potentials were recorded from 16 scalp locations on 10 young subjects during presentation of a series of high-quality photographs on a computer screen. The photographs consisted of equal numbers of pictures of fruit (citrus and non-citrus fruits), flowers (roses and other flowers) and objects (e.g. buildings, vehicles, animals etc.). Every picture was different in order to avoid repetition effects. The pictures were presented under four odour conditions: no odour, rose odour, jasmine odour and citrus odour. In order to keep the subjects alert they were asked to make categorizing decisions for the visual stimuli (e.g. flower or fruit). No decision was required concerning the relationship between the visual stimulus and the odour. As expected, the N400 peak was more negative when the picture stimulus did not match the odour. It is hypothesized that the N400 peak can be used as a measure of relatedness of a sensory stimulus to a previous or on-going prime, irrespective of the mode of the stimuli.

Olfactory oscillations augment odor discrimination not odor identification by Limax CNS.

There is great interest in the function of synchronous oscillations in olfactory centers, as documented in a wide variety of species. In Limax procerebral (PC) lobe, local field potential oscillations are ongoing and altered by odor stimulation. Recordings from external peritentacular nerves (ePTNs) reveal a neural correlate of tentacle positioning, a response signifying recognition of a conditioned odor. Using the odor-elicited ePTN response we found no clear difference in the dynamics of the PC oscillations which precedes and predicts the occurrence of ePTN responses. Reversibly blocking the oscillations did not impair recognition of conditioned odors but reduced the differential nerve response to related odors. PC oscillations may play a role in odor discrimination but are not necessary for odor recognition.