Sister,aunt-niece,and cousin recognition by social wasps

In blind laboratory observations, gynes (potential queens) of the social waspPolistes fuscatus discriminated nestmate sisters from unrelated nonnestmate gynes but failed to discriminate between nestmate sisters and nonnestmate aunts and nieces. Gynes treat nonnestmate aunts and nieces as nestmate sisters, indicating that gynes recognize kin other than nestmates (i.e., aunts and nieces) by using genetic odors. In blind field observations, femaleP. fuscatus discriminated between nestmate sisters and nonnestmate first cousins and unrelated nonnestmates. However, females failed to discriminate between nonnestmate first cousins and unrelated nonnestmates. The results of the laboratory and field studies provide additional support for the cue similarity threshold model of recognition, which has important sociobiological implications for social wasps.This research was supported by NSF Grant BNS 86-06817.     

Role of inhibition for temporal and spatial odor representation in olfactory output neurons: a calcium imaging study

The primary olfactory brain center, the antennal lobe (AL) in insects or the olfactory bulb in vertebrates, is a notable example of a neural network for sensory processing. While physiological properties of the input, the olfactory receptor neurons, have become clearer, the operation of the network itself remains cryptic. Therefore we measured spatio-temporal odor-response patterns in the output neurons of the olfactory glomeruli using optical imaging in the honeybee Apis mellifera. We mapped these responses to identified glomeruli, which are the structural and functional units of the AL. Each odor evoked a complex spatio-temporal activity pattern of excited and inhibited glomeruli. These properties were odor- and glomerulus-specific and were conserved across individuals. We compared the spatial pattern of excited glomeruli to previously published signals, which derived mainly from the receptor neurons, and found that they appeared more confined, showing that inhibitory connections enhance the contrast between glomeruli in the AL. To investigate the underlying mechanisms, we applied GABA and the GABA-receptor antagonist picrotoxin (PTX). The results show the presence of two separate inhibitory networks: one is GABAergic and modulates overall AL activity, the other is PTX-insensitive and glomerulus-specific. Inhibitory connections of the latter network selectively inhibit glomeruli with overlapping response profiles, in a way akin to "lateral" inhibition in other sensory systems. Selectively inhibited glomeruli need not be spatial neighbors. The net result is a globally modulated, contrast-enhanced and predictable representation of odors in the olfactory output neurons.     

Impairment of olfactory discrimination by blockade of GABA and nitric oxide activity in the honey bee antennal lobes

Honey bees readily associate an odor with sucrose reinforcement, and the response generalizes to other odors as a function of structural similarity to the conditioned odor. Recent studies have shown that a portion of odor memory is consolidated in the antennal lobes (AL), where first-order synaptic processing of sensory information takes place. The AL and/or the sensory afferents that project into them show staining patterns for the enzyme nitric oxide synthase, which catalyzes the release of the gaseous transmitter nitric oxide (NO). The results show that pharmacological blockade of NO release impairs olfactory discrimination only when release is blocked before conditioning. Blockade of GABAergic transmission disrupts discrimination of similar but not dissimilar odorants, and does so when the block occurs before condition or before testing. These results show that GABA and NO regulate the specificity of associative olfactory memory in the AL.     

The glomerular code for odor representation is species specific in the honeybee Apis mellifera.

Odors are coded by glomerular activity patterns in the insect antennal lobe (AL) and in the mammalian olfactory bulb. We measured glomerular responses to 30 different odors in the AL of honeybees using calcium-sensitive dyes. By subsequently staining glomeruli and identifying individual glomerular outlines, we were able to compare the patterns between animals. Regardless of whether the odors were mixtures or pure substances, environmental odors or pheromones, their representations were highly conserved among individuals. Therefore, it may be possible to create a functional atlas of the AL in which particular molecular receptive ranges are attributed to each glomerulus.     

Neural correlates of social odor recognition and the representation of individual distinctive social odors within entorhinal cortex and ventral subiculum

Recognition of individual conspecifics is important for social behavior and requires the formation of memories for individually distinctive social signals. Individual recognition is often mediated by olfactory cues in mammals, especially nocturnal rodents such as golden hamsters. In hamsters, this form of recognition requires main olfactory system input to the lateral entorhinal cortex (LEnt). Here, we tested whether neurons in LEnt and the nearby ventral subiculum (VS) would show cellular correlates of this natural form of recognition memory. Two hundred ninety single neurons were recorded from both superficial (SE) and deep layers of LEnt (DE) and VS while male hamsters investigated volatile odorants from female vaginal secretions. Many neurons encoded differences between female's odors with many discriminating between odors from different individual females but not between different odor samples from the same female. Other neurons discriminated between odor samples from one female and generalized across collections from other females. LEnt and VS neurons showed enhanced or suppressed cellular activity during investigation of previously presented odors and in response to novel odors. A majority of SE neurons decreased firing to odor repetition and increased activity to novel odors. In contrast, DE neurons often showed suppressed activity in response to novel odors. Thus, neurons in LEnt and VS of male hamsters encode information that is critical for the identification and recognition of individual females by odor cues. This study reveals cellular mechanisms in LEnt and VS that may mediate a natural form of recognition memory in hamsters. These neuronal responses were similar to those observed in rats and monkeys during performance in standard recognition memory tasks. Consequently, the present data extend our understanding of the cellular basis for recognition memory and suggest that individual recognition requires similar neural mechanisms as those employed in laboratory tests of recognition memory.     

Relation of olfactory EEG to behavior: factor analysis

Rabbits were conditioned to lick (CR+) in response to one odor (CS+); another odor (CS-) served as a discriminative control (CR-). Electroencephalograms (EEGs) were recorded from arrays of 64 electrodes on the olfactory bulb in three stages, each with six sessions: in Stage I, odors A+ and B-; in Stage II, odors C+ and B-; and in Stage III, odors C+ and A-. Spatial EEG amplitude patterns were measured for multiple control (C), CS+, and CS- EEG bursts in each trial. Data were transformed via factor analysis and expressed by factor scores as spatial patterns specified by factor loadings. In discriminant analysis of the factor scores, we correctly classified the C and CS bursts on the average by 65-80% from all trials for each subject and session and by 75-90% for trials with correct CRs. The latter was confirmed with a stepwise linear discriminant analysis of the original 64-variable data. Factor patterns were relatively invariant within but changed between stages. The results implied that stable spatial patterns of bulbar activity emerged in respect to CSs under reinforcement and persisted until the stimulus-response contingencies were changed.     

Field potential response changes in the rabbit olfactory bulb accompany behavioral habituation during the repeated presentation of unreinforced odors

Summary Experiments were performed on waking rabbits to investigate the changes in both sniffing behavior and local field potential responses in the olfactory bulb during repeated exposure to unreinforced odors. Six rabbits were each implanted with 2 pairs of electrodes for differential recording of the bulbar extracellular field potential. Each animal was given 3 sequential sessions to each of 2 separate odors on 6 consecutive days, while monitoring the bulbar field potential activity and sniffing behavior. Behavioral sniffing responses exhibited rapid within-session decrement in amplitude and long term decrement across sessions. The within-session decrement showed spontaneous recovery between sessions. Both decremental changes in sniffing behavior were accompanied by changes in the bulbar field potential responses. The responses to novel odors were characterized by a reduction in amplitude of high frequency activity (40–80 Hz) and a corresponding increase in amplitude of low frequency activity (15–25 Hz). The high frequency component of the responses showed an initial increase in frequency to a novel odor on the first 3 presentations followed by a rapid decrease in frequency on subsequent trials in the first session which stabilized thereafter. No change in frequency or relative amplitude was observed for the low frequency component. The absolute difference between the odor evoked activity and the preceeding control activity measured on each trial showed a significant decrement across sessions with no evidence for spontaneous recovery. The results demonstrate that olfactory bulb responses to novel unreinforced odors show both rapid and long-term changes which parallel changes in sniffing behavior. These changes, which have been predicted by a theoretical model of the olfactory bulb (Freeman 1979a, b), are postulated to reduce the spatial specificity of the response pattern to unreinforced odors.     

Spatial EEG correlates of nonassociative and associative olfactory learning in rabbits

Recent studies have shown that spatially distributed olfactory bulbar activity correlates with odor-specific behavioral responding (Coopersmith & Leon, 1984; Freeman & Grajski, 1987; Freeman & Schneider, 1982; Freeman & Viana di Prisco, 1986; Grajski, Breiman, Viana di Prisco, & Freeman, 1986; Gray, Freeman, & Skinner, 1986; Sullivan & Leon, 1986; Viana di Prisco & Freeman, 1985). The present studies established olfactory bulbar spatial electroencephalogram (EEG) correlates of nonassociative and associative learning in odorant stimulation in rabbits. Behavior was quantified by measuring magnitude and probability of the sniff response. It was shown that (a) olfactory bulbar spatial EEG amplitude patterns do not simply reflect odor (peripheral) stimulation, (b) repeated presentations of a nonreinforced odor initially reveal a transient EEG pattern change but the pattern change does not recur after the subject has habituated to the odor, and (c) repeated presentations of a reinforced odor (mild cutaneous shock), with a second nonreinforced odor serving as a control, reveal that coexisting, odor-specific spatial EEG amplitude patterns emerge with the acquisition of differential behavioral responding.     

Dynamics of olfactory bulb input and output activity during odor stimulation in zebrafish

The processing of odor-evoked activity in the olfactory bulb (OB) of zebrafish was studied by extracellular single unit recordings from the input and output neurons, i.e., olfactory receptor neurons (ORNs) and mitral cells (MCs), respectively. A panel of 16 natural amino acid odors was used as stimuli. Responses of MCs, but not ORNs, changed profoundly during the first few hundred milliseconds after response onset. In MCs, but not ORNs, the total evoked excitatory activity in the population was initially odor-dependent but subsequently converged to a common level. Hence, the overall population activity is regulated by network interactions in the OB. The tuning widths of both ORN and MC response profiles were similar and, on average, stable over time. However, when analyzed for individual neurons, MC response profiles could sharpen (excitatory response to fewer odors) or broaden (excitatory response to more odors), whereas ORN response profiles remained nearly unchanged. Several observations indicate that dynamic inhibition plays an important role in this remodeling. Finally, the reliability of odor identification based on MC population activity patterns improved over time, whereas odor identification based on ORN activity patterns was most reliable early in the odor response. These results demonstrate that several properties of MC, but not ORN, activity change during the initial phase of the odor response with important consequences for odor-encoding activity patterns. Furthermore, our data indicate that inhibitory interactions in the OB are important in dynamically shaping the activity of OB output neurons.     

Principal component analysis of odor coding at the level of third‐order olfactory neurons in Drosophila

Olfactory information in Drosophila is conveyed by projection neurons from olfactory sensory neurons to Kenyon cells (KCs) in the mushroom body (MB). A subset of KCs responds to a given odor molecule, and the combination of these KCs represents a part of the neuronal olfactory code. KCs are also thought to function as coincidence detectors for memory formation, associating odor information with a coincident punishment or reward stimulus. Associative conditioning has been shown to modify KC output. This plasticity occurs in the vertical lobes of MBs containing α/α' branches of KCs, which is shown by measuring the average Ca²⁺ levels in the branch of each lobe. We devised a method to quantitatively describe the population activity patterns recorded from axons of >1000 KCs at the α/α' branches using two‐photon Ca²⁺ imaging. Principal component analysis of the population activity patterns clearly differentiated the responses to distinct odors.     

Multi-unit recordings reveal context-dependent modulation of synchrony in odor-specific neural ensembles

We used neural ensemble recording to examine odor-evoked ensemble patterns in the moth antennal (olfactory) lobe. Different odors are thought to evoke unique spatiotemporal patterns of glomerular activity, but little is known about the population dynamics underlying formation of these patterns. Using a silicon multielectrode array, we observed dynamic network interactions within and between glomeruli. Whereas brief odor pulses repeatedly triggered activity in the same coding ensemble, the temporal pattern of synchronous activity superimposed on the ensemble was neither oscillatory nor odor specific. Rather, synchrony strongly depended on contextual variables such as odor intensity and intermittency. Also, because of emergent inhibitory circuit interactions, odor blends evoked temporal ensemble patterns that could not be predicted from the responses to the individual odorants. Thus even at this early stage of information processing, the timing of odor-evoked neural representations is modulated by key stimulus factors unrelated to the molecular identity of the odor.     

Spatial patterns of olfactory bulb single-unit responses to learned olfactory cues in young rats

1. Neonatal rat pups were classically conditioned to an odor stimulus from postnatal day 1 (PN1) to PN18. Tactile stimulation (stroking) was used as the unconditioned stimulus. On PN19, mitral/tufted cell single-unit responses to the conditioned odor were examined in both conditioned and control pups. Recordings were made from mitral/tufted cells in two regions of the olfactory bulb: 1) an area typically associated with focal [14C]2-deoxyglucose (2-DG) uptake in response to the conditioned odor and 2) an area distant from focal 2-DG uptake to the conditioned odor. Animals were anesthetized with urethane and were naturally respiring during the single-unit recording procedure. 2. Changes in mitral/tufted cell firing rate in response to odors in both bulbar regions and all training groups were classified as either excitatory, suppressive, or no response. This response classification was used to compare response patterns to the conditioned odor between bulbar regions and training groups. 3. Classical conditioning selectively modified the response patterns of mitral/tufted cells to the conditioned odor when those cells were associated with regions of focal 2-DG uptake for that odor. Mitral/tufted cells demonstrated significantly more suppressive and fewer excitatory responses to the conditioned odor than cells in control pups. Response patterns to a novel odor were not similarly modified. 4. Response patterns of mitral/tufted cells distant from the focal region of 2-DG uptake to the conditioned odor were not modified by conditioning compared with control pups. 5. The difference in response pattern between cells in the 2-DG focus and cells distant to the 2-DG focus was apparent within 500 ms of the stimulus onset. Given the respiratory rate of these pups (2 Hz), these data suggest that the modified response pattern occurred on the first inhalation of the learned odor. 6. These data demonstrate that both spatial and temporal patterns of olfactory bulb output neuron activity are used in the coding of olfactory information in the bulb. Furthermore, these spatial/temporal response patterns can be modified by early learning.     

Side-specific olfactory conditioning leads to more specific odor representation between sides but not within sides in the honeybee antennal lobes

Honeybees can be trained to associate odorants to sucrose reward by conditioning the proboscis extension response. Using this paradigm, we have recently shown that bees can solve a side-specific task: they learn simultaneously to discriminate a reinforced odor A from a non-reinforced odor B at one antenna (A+B−) and the reversed problem at the other antenna (A−B+). Side-specific (A+B−/B+A−) conditioning is an interesting tool to measure neurophysiological changes due to olfactory learning because the same odorant is excitatory (CS+) on one brain side and inhibitory (CS−) on the opposite side. In the bee brain, the antennal lobe (AL) is the first olfactory relay where the olfactory memory is established. Using calcium imaging, we compared odor-evoked activity in the functional units, the glomeruli, of the two ALs, both in naive and conditioned individuals. Each odor evoked a different pattern of glomerular activity, which was symmetrical between sides and highly conserved among naive animals. In conditioned bees, response patterns were overall symmetrical but showed more active glomeruli and topical differences between sides. By representing odor vectors in a virtual olfactory space whose dimensions are the responses of 23 identified glomeruli, we found that distances between odor representations on each brain side were significantly higher in conditioned than in naive bees, but only for CS+ and CS−. However, the distance between CS+ and CS− representations was equal to that of naive individuals. Our work suggests that side-specific conditioning decorrelates odor representations between AL sides but not between CS+ and CS− within one AL.     

Estrous odors and sexually conditioned neutral odors activate separate neural pathways in the male rat

Olfactory stimuli play important roles in sexual behavior. Previous studies have demonstrated that both estrous odors and initially neutral odors paired with copulation influence the sexual behavior of male rats. The present study examines the pattern of neural activation as revealed by Fos immunoreactivity (Fos-IR) following exposure to bedding scented with either a neutral odor (almond) paired previously with copulation, estrous odors or no odor. Following exposure to estrous odors Fos-IR increased in the accessory olfactory bulb, medial amygdala, medial bed nucleus of the stria terminalis, medial preoptic area, ventromedial hypothalamus, ventral tegmental area, and both the nucleus accumbens core and shell. Conversely, following exposure to the sexually conditioned odor Fos-IR increased in the piriform cortex, basolateral amygdala, nucleus accumbens core, and the anterior portion of the lateral hypothalamic area. In addition, following exposure to almond odor Fos-IR increased in the main olfactory bulb independent of its pairing with copulation. These patterns of Fos-IR following exposure to estrous or sexually conditioned odors were not influenced by either the addition or omission of the other type of odor. These findings demonstrate that estrous and sexually conditioned odors are processed by distinct neural pathways and converge in the nucleus accumbens core, suggesting that this structure has a unique role in processing sexual stimuli of both pheromonal and olfactory natures.     

Speed and accuracy of olfactory discrimination in the rat

The sense of smell is typically thought of as a 'slow' sense, but the true temporal constraints on the accuracy of olfactory perception are not known. It has been proposed that animals make finer odor discriminations at the expense of additional processing time. To test this idea, we measured the relationship between the speed and accuracy of olfactory discrimination in rats. We found that speed of discrimination was independent of odor similarity, as measured by overlap of glomerular activity patterns. Even when pushed to psychophysical limits using mixtures of two odors, rats needed to take only one sniff (<200 ms at theta frequency) to make a decision of maximum accuracy. These results show that, for the purpose of odor quality discrimination, a fully refined olfactory sensory representation can emerge within a single sensorimotor or theta cycle, suggesting that each sniff can be considered a snapshot of the olfactory world.     

Influence of affective and cognitive judgments on autonomic parameters during inhalation of pleasant and unpleasant odors in humans

Hedonic tone is so salient in odor perception that several authors have used odors to induce affective states. Various studies have shown that the electrophysiological and psychophysiological response patterns induced by olfactory stimuli are different for pleasant and unpleasant odors, and that these types of odor activate brain structures differentially. These results suggest that odors are first categorized according to pleasantness. The objective of the present work was to study the possible existence of an involuntary affective categorization in olfaction. Given that certain variations in the autonomic system, such as skin conductance amplitude and heart rate, are not under the voluntary control of human subjects, we used such psychophysiological methods for this investigation. Our results indicate that unpleasant odors provoke heart-rate acceleration during both a smelling task (control condition: a task in which subjects had only to inhale odors) and a pleasantness judgment, but not during a familiarity judgment. These results suggest that subjects involuntarily categorize odors by their pleasantness.     

The fish is bad: Negative food odors elicit faster and more accurate reactions than other odors

Dissociating between ‘good’ or ‘bad’ odors is arguable of crucial value for human survival, since unpleasant odors often signal danger. Therefore, negative odors demand a faster response in order to quickly avoid or move away from negative situations. We know from other sensory systems that this effect is most evident for stimuli from ecologically-relevant categories. In the olfactory system the classification of odors into the food or non-food category is of eminent importance. We therefore aimed to explore the link between odor processing speed and accuracy and odor edibility and valence by assessing response time and detection accuracy. We observed that reaction time and detection accuracy are influenced by both pleasantness and edibility. Specifically, we showed that an unpleasant food odor is detected faster and more accurately than odors of other categories. These results suggest that the olfactory system reacts faster and more accurately to ecologically-relevant stimuli that signal a potential danger.     

Control of the rat olfactory bulb activity induced by biologically significant odors (author's transl)

In acute experiments, unitary activity was recorded from mitral cells of the rat olfactory bulb. The animals were stimulated with odors that have been shown in previous experiments to give a distinct emotional behavior. In curarized rats an odor giving alarm behavior evoked a greater number of inhibitory than excitatory responses was elicited by a neutral odor. In rats under Nembutal anesthesia an alarming odor evoked a greater number of inhibitory than excitatory responses; a reassuring odor evoked a greater number of excitatory than inhibititory responses; and equal number of inhibitory and excitatory responses; a reassuring or a neutral odor evoked an equal number of inhibitory and excitatory responses. After sectioning the olfactory peduncles, the difference in ratio between excitatory and inhibitory responses for alarming or reassuring odors was no longer present. The results are discussed in terms of a modulation of mitral cell activity by higher nervous centers in relation to the biological significance of the stimulating odors.     

Effects of odor familiarity on the development of systematic exploration in the spiny mouse, Acomys cahirinus

Developmental changes in patterns of exploration by infant spiny mice, Acomys cahirinus are described. These were investigated using an unbaited radial maze and under three odor conditions; that is, animals were tested in the presence of either familiar (own) odors, unfamiliar conspecific odors, or no odors (washed floor). Two hypotheses were tested. The first was based on the results of a pilot study, and was that adult animals would explore the radial maze in a systematic and predictable fashion tending to move from one arm to the next sequentially. It was hypothesized that infants would adopt this sequential strategy only gradually, as they matured. The second hypothesis was that such patterns of exploration would depend upon the olfactory environment; the presence of familiar odors might facilitate systematic patterns of exploration in very young Acomys. The results showed that both adults and juveniles were less likely to move sequentially when tested with no conspecific odor present; sequential patterns of movement were most likely in the presence of unfamiliar odor, however. The only significant change with age in infants was found for animals tested with unfamiliar odors; these animals showed a dramatic increase in sequential behavior between 3 and 7 days of age. Two additional experiments are reported, which investigated the preferences of infant Acomys for unfamiliar conspecific odors, and it was found that very young (about 3 days) animals exhibit a preference for odors derived from unfamiliar conspecific litters, even when tested in the physical presence of their own parents. The results are discussed with reference to the use of olfactory information as directional cues for animals exploring the radial maze.