Personality and Olfactory Sensitivity

Even though perceptional abilities have repeatedly been found to be associated with certain personality styles (e.g., extraversion), such connections were reported sparsely for the olfactory modality. Two studies were carried out to investigate the relationship between olfactory sensitivity and 12 personality dimensions (including extraversion and neuroticism). In the first study, single olfactory measurements were compared to repeated measurements. In the second study, twins were recruited as subjects to also examine the heredity of olfactory sensitivity. The results indicate that neuroticism is a stronger predictor for olfactory sensitivity than extraversion. Repeated measurements seem to be necessary to obtain valid data on olfactory performance.     

The impact of mediodorsal thalamic lesions on olfactory attention and flavor perception

Olfactory attention may be important in generating odor-induced tastes - an arguably universal form of synesthesia - by ensuring that the taste concurrent is captured by the nose and olfaction, not by the mouth and gustation (oral-capture). To examine the role of olfactory attention in generating odor-induced tastes and oral capture we tested a small sample (n = 4) of participants with likely impairments in olfactory attention - individuals with mediodorsal thalamic nucleus (MDNT) lesions. These participants were compared to two sets of controls on tests of olfactory attention, oral capture, odor and flavor perception, and control tasks. MDNT participants demonstrated impaired olfactory attention and enhanced oral capture. Greater oral capture was associated with greater olfactory attentional impairment. These findings imply that olfactory attention may be important in attributing odor-induced tastes to the olfactory modality. However, unlike for visual binding and for the neurodevelopmental synesthesias, where attention may be necessary to demonstrate both phenomena, olfactory attention deficits did not impair flavor binding or the experience of odor-induced tastes.     

Inhibition of nitric oxide synthase impairs early olfactory associative learning in newborn rats

The present experiments examined the role of nitric oxide ( NO) in early associative olfactory learning in rats. A preference for peppermint odor was induced by pairing peppermint odor with tactile stimulation in Wistar rat pups, in either a repetitive training paradigm or in a one-trial olfactory learning paradigm. In a first experiment we studied the effect of nitric oxide synthase (NOs) inhibition on early olfactory learning in a repetitive paradigm, by systemic daily injections of NG-nitro-l-arginine methyl ester (l-NAME, 50 mg/kg, i.p.). In order to exclude possible deleterous effects of repeated injections of l-NAME, we explored in a second experiment the effect of a single inhibitor injection in a one-trial olfactory learning paradigm. Inhibition of NOs was performed by either administration of l-NAME (50 mg/kg, i.p.), or 7-nitroindazole (7-NI, 30 mg/kg, i.p.), a more selective inhibitor of the neuronal NOs. We showed that both l-NAME and 7-NI impaired early olfactory associative learning when given before training but not before subsequent testing. Considering that NOs neurons are already widespread in the central nervous system (the olfactory bulb included) during the first postnatal week, the sites where NO inhibition may have acted to impair olfactory learning are discussed. The mechanisms of action of NO in relation with other neurotransmitters known to be necessary for olfactory conditioning in rat pups remain to be established. Impairment by NO synthesis inhibition of the acquisition during the first postnatal week of an olfactory conditioning, but not its recall, suggests a role for NO at synapses involved in that learning.     

Adrenergic modulation of olfactory bulb circuitry affects odor discrimination

A rodent's survival depends upon its ability to perceive odor cues necessary to guide mate selection, sexual behavior, foraging, territorial formation, and predator avoidance. Arguably, the need to discriminate odor cues in a complex olfactory environment requires a highly adaptable olfactory system. Indeed, it has been proposed that context-dependent modulation of the initial sensory relay could alter olfactory perception. Interestingly, 40% of the adrenergic innervation from the locus coeruleus, fibers that are activated by contextual cues, innervates the first relay station in the olfactory system (the main olfactory bulb). Here we utilize restricted pharmacological inhibition of olfactory bulb noradrenergic receptors in awake-behaving animals. We show that combined blockade of alpha and beta adrenergic receptors does not impair two-odor discrimination behavior per se but does impair the ability to discriminate perceptually similar odors. Thus, contextual cues conveyed by noradrenergic fibers alter processing before the second synapse in the olfactory cortex, resulting in tuning of the ability to discriminate between similar odors.     

Acetylcholine and olfactory perceptual learning

Olfactory perceptual learning is a relatively long-term, learned increase in perceptual acuity, and has been described in both humans and animals. Data from recent electrophysiological studies have indicated that olfactory perceptual learning may be correlated with changes in odorant receptive fields of neurons in the olfactory bulb and piriform cortex. These changes include enhanced representation of the molecular features of familiar odors by mitral cells in the olfactory bulb, and synthetic coding of multiple coincident odorant features into odor objects by cortical neurons. In this paper, data are reviewed that show the critical role of acetylcholine (Ach) in olfactory system function and plasticity, and cholinergic modulation of olfactory perceptual learning at both the behavioral and cortical level.     

Phenomenal and access consciousness in olfaction

Contemporary literature on consciousness, with some exceptions, rarely considers the olfactory system. In this article the characteristics of olfactory consciousness, viewed from the standpoint of the phenomenal (P)/access (A) distinction, are examined relative to the major senses. The review details several qualitative differences in both olfactory P consciousness (shifts in the felt location, universal synesthesia-like and affect-rich experiences, and misperceptions) and A consciousness (recovery from habituation, capacity for conscious processing, access to semantic and episodic memory, learning, attention, and in the serial-unitary nature of olfactory percepts). The basis for these differences is argued to arise from the functions that the olfactory system performs and from the unique neural architecture needed to instantiate them. These data suggest, at a minimum, that P and A consciousness are uniquely configured in olfaction and an argument can be made that the P and A distinction may not hold for this sensory system.     

Role of centrifugal projections to the olfactory bulb in olfactory processing

While there is evidence that feedback projections from cortical and neuromodulatory structures to the olfactory bulb are crucial for maintaining the oscillatory dynamics of olfactory bulb processing, it is not clear how changes in dynamics are related to odor perception. Using electrical lesions of the olfactory peduncle, sparing output from the olfactory bulb while decreasing feedback inputs to the olfactory bulb, we demonstrate here a role for feedback inputs to the olfactory bulb in the formation of odor-reward associations, but not for maintaining primary bulbar odor representations, as reflected by spontaneous odor discrimination.     

Olfaction in Persons with Alzheimer's Disease

The need for low cost, noninvasive procedures for aiding in the diagnosis and understanding of Alzheimer's Disease (AD) has led to theories and procedures examining the role of olfactory disorders because of the finding that the brains of AD patients invariably exhibit neuropathology hi the hippocampus and entorhinal cortex. This loss correlates with the increase in the number of plaques and tangles and with the severity of dementia. Considered together, these findings suggest that brain structures closely related to the olfactory system demonstrate significant histopathology in AD. A comprehensive review of the literature pertaining to olfaction in persons with AD revealed that the olfactory identification ability of patients with memory disorders is impaired relative to controls. Consistency is lacking, however, when olfactory detection thresholds are investigated. Also, there is inconsistency in regards to severity of illness and olfactory function. In addition to differentiating AD patients from normals, the olfactory paradigm has shown some limited usefulness in differentiating AD patients from some other demented patients.     

The mental context for the description of odors: a semantic space

The experiments conducted in this research aimed to increase our understanding of olfactory properties and classify them hierarchically through entailment. The research objective was to build an odor classification based on internal knowledge (i.e. mental context). Twelve floral scents were described freely by 60 participants. First, three sensory judges undertook a semantic analysis of the 1145 olfactory terms gathered. Secondly, a study of the entailment between olfactory properties was conducted using 42 subjects working on four lists of terms describing the characteristics of floral perfumes. The results confirmed the hypothesis that olfactory properties show tree-like structure. This allowed us to propose a classification system composed of two superordinate categories: First, objects, being olfactory sources, constitute the first category and are considered as olfactory properties themselves (i.e. civilization, food and natural sources). Second non-objects properties are those applicable to a diversity of objects: (i.e. properties, such as objects' physical state: sensory, intensity, space, time) and those related to the subject (as personal feelings and value judgments). Based on these results, it appears that olfactory properties can be organized as a semantic network in line with the general theory of categorization.     

Olfactory awareness is positively associated to odour memory

We investigated the relationship between olfactory awareness and olfactory proficiency as determined by a set of standardised olfactory tasks. Olfactory awareness was indexed by scores in questionnaires focusing on odour interest, imagery ability, and prevalence of olfactory dreams. Nineteen subjects with high and 20 subjects with low odour awareness were presented with a set of standardised olfactory tasks: odour threshold, episodic odour recognition, and odour identification. The results showed that individuals with high odour awareness excelled in odour memory and identified more odours as compared with the low awareness group. Interestingly, odour naming ability exerted no influence on odour memory. Furthermore, high odour awareness was not related to a more sensitive olfactory sensory system as determined by olfactory threshold measurements.     

Recovery of structure and function following transection of the primary olfactory nerves in pigeons.

Preliminary experimentation on ring doves to ascertain whether they might regulate any aspects of their reproductive behavior in terms of olfactory cues was vitiated by the discovery that their sectioned olfactory nerves had apparently regenerated. Concurrent work on frogs has shown that the olfactory receptors degenerate after axotomy and are replaced by new ones. This phenomenon was studied in pigeons. All transected nerves were found to be healed. Electrical recording from the regenerated nerves revealed apparently normal receptor function and, indirectly, autonomic reflex responsiveness. Previously untrained pigeons learned an olfactory discrimination after reconstitution of the peripheral olfactory system using a conditioned suppression procedure. The olfactory nerves of trained pigeons were sectioned and the behavioral response recovered within 16-82 days. The gross sizes of primary olfactory nerves and olfactory bulbs were frequently much less than those of controls, but on the ultrastructural level there was no recognizable morphological deficiency in the receptor cellular organelles or terminal synaptic contacts in bulbar glomeruli. Recent results by other workers indicate that pigeons utilize olfactory cues in homing performance.     

An investigation on the olfactory capabilities of domestic dogs (Canis lupus familiaris)

Animal Cognition - The extraordinary olfactory capabilities in detection and rescue dogs are well-known. However, the olfactory performance varies by breed and search environment (Jezierski...     

The relationship between metacognitive awareness of olfactory ability and age in people reporting chemosensory disturbances

When determining how much to rely on olfactory information, accurate estimates of olfactory ability are important. Nevertheless, metacognitive errors regarding olfactory ability are common in the normal population. Are older adults less accurate at estimating olfactory ability, or do they simply tend to make a particular type of estimation error? We examined data from 203 patients, all of whom self-rated olfactory ability and then were tested with the Odorant Confusion Matrix. The patients' self-reports did not match the objective measure of olfactory ability in 42% of the cases, thus demonstrating a high level of impairment in metacognitive knowledge. Neither the cause of loss nor the patient's age was related to the inability to accurately estimate olfactory loss, but both contributed to the type of metacognitive errors patients made. Younger patients tended to underestimate their olfactory ability, thus behaving similarly to patients with "blindsight" who demonstrate residual visual function in the absence of awareness. Older patients tended to overestimate their olfactory ability, thus making the metacognitive error of deficit unawareness that is observed in a number of other clinical syndromes. These findings indicate that older patients are not necessarily more likely to make errors in estimating their olfactory ability; rather, they are more prone to a particular type of metacognitive error than are younger patients.     

Inhibitory neurotransmission and olfactory memory in honeybees

In insects, gamma-aminobutyric acid (GABA) and glutamate mediate fast inhibitory neurotransmission through ligand-gated chloride channel receptors. Both GABA and glutamate have been identified in the olfactory circuit of the honeybee. Here we investigated the role of inhibitory transmission mediated by GABA and glutamate-gated chloride channels (GluCls) in olfactory learning and memory in honeybees. We combined olfactory conditioning with injection of ivermectin, an agonist of GluCl receptors. We also injected a blocker of glutamate transporters (L-trans-PDC) or a GABA analog (TACA). We measured acquisition and retention 1, 24 and 48 h after the last acquisition trial. A low dose of ivermectin (0.01 ng/bee) impaired long-term olfactory memory (48 h) while a higher dose (0.05 ng/bee) had no effect. Double injections of ivermectin and L-trans-PDC or TACA had different effects on memory retention, depending on the doses and agents combined. When the low dose of ivermectin was injected after Ringer, long-term memory was again impaired (48 h). Such an effect was rescued by injection of both TACA and L-trans-PDC. A combination of the higher dose of ivermectin and TACA decreased retention at 48 h. We interpret these results as reflecting the involvement of both GluCl and GABA receptors in the impairment of olfactory long-term memory induced by ivermectin. These results illustrate the diversity of inhibitory transmission and its implication in long-term olfactory memory in honeybees.     

An inexpensive and automated method for presenting olfactory or tactile stimuli to rats in a two-choice discrimination task

An inexpensive and automated method for presentation of olfactory or tactile stimuli in a two-choice task for rats was implemented with the use of a computer-controlled bidirectional motor. The motor rotated a disk that presented two stimuli of different texture for tactile discrimination, or different odor for olfactory discrimination. Because the solid olfactory stimuli were placed outside the chamber in metal pods with a mesh at front for odor sampling, "washout" of odors between trials was not necessary. To avoid differential auditory cues from motor rotation, the stimuli were arranged such that on each trial the motor always rotated exactly one quarter revolution (in 1 s), left or right, to present the next stimulus at trial start. To illustrate the use of the equipment, 2 rats were trained on tactile discrimination and 2 rats on olfactory discrimination. The rats sampled the stimulus on the disk through a port on the back wall by sniffing at it (olfactory) or touching it (tactile). The task was a go-left/go-right discrimination with the stimulus on the disk being discriminative for which lever provided reinforcement. The rats reached a stable level above 90% correct after 21 and 32 training sessions for tactile and olfactory discrimination, respectively. The article outlines how the equipment was constructed from low-cost components. Inputs from and outputs to the equipment were implemented through the parallel port of a personal computer without the use of a commercial interface board. The method of automated and low-cost presentation of olfactory or tactile stimuli should be of use for a variety of experimental situations such as matching-to-sample and cross-modal discrimination.     

Identification of olfactory stimuli as reinforcers in individuals with autism: a preliminary investigation

Preference for six olfactory stimuli was assessed via paired preference assessments with three adults with autism. Using a combination multielement and reversal design, a reinforcer assessment was then conducted to determine the extent to which three (high preference, medium preference, and low preference) of the six olfactory stimuli evaluated in the preference assessment functioned as reinforcers for responding in the context of a sorting task. Relative to baseline, all of the participants exhibited increased responding for access to their high preference olfactory stimulus. The utility of olfactory stimuli as components of behavior intervention plans is discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Regional studies of brain biogenic amines in castrated muricidal and non-muricidal wistar rats

Castrated Wistar rats were isolated for 8 months and their muricidal behavior was investigated. Significantly fewer (35%) of such rats became muricidal (CM) compared to controls. The steady-state levels of 5-HT, 5-HIAA, DA, DOPAC, and NE, as well as the changes in synthesis or utilization rats of 5-HT and DA, were analyzed in 15 brain areas derived from CM rats and non-muricidal (CNM) control subjects. In CM rats, higher 5-HT levels were recorded in 5 areas considered to be involved in muricidal behavior: raphe, amygdala, olfactory tubercles, olfactory bulbs, and striatum. The alterations of serotonergic neurotransmission in castrated muricidal rats differ strikingly from those observed in non-castrated muricidal rats. An increase of 5-HT level and in the 5-HT synthesis index as well as a lower 5-HT utilization index were recorded in the raphe of CM rats. Our data suggest that the decrease of 5-HT levels generally said to be the main alteration in the muricidal rat's brain has to be reconsidered. Increased DA levels were observed in CM rats: raphe (50%), amygdala, olfactory tubercles, striatum, and septum (40%), while DA was decreased in cortical areas. There were slight increases of DA synthesis indices in the septum, olfactory tubercles and striatum with a decreased utilization index in the olfactory tubercles. Few alterations in NE levels were observed in CM rats: a decrease in the olfactory tubercles, superior colliculus, and striatum and an increase in temporal cortex. The monoaminergic alterations correlate with the modulation of muricidal behavior. Some areas (the olfactory tubercles, raphe, striatum, and temporal cortex) seem to be particularly involved. © 1992 Wiley-Liss, Inc.     

Olfactory fear conditioning induces field potential potentiation in rat olfactory cortex and amygdala

The widely used Pavlovian fear-conditioning paradigms used for studying the neurobiology of learning and memory have mainly used auditory cues as conditioned stimuli (CS). The present work assessed the neural network involved in olfactory fear conditioning, using olfactory bulb stimulation-induced field potential signal (EFP) as a marker of plasticity in the olfactory pathway. Training consisted of a single training session including six pairings of an odor CS with a mild foot-shock unconditioned stimulus (US). Twenty-four hours later, the animals were tested for retention of the CS as assessed by the amount of freezing exhibited in the presence of the learned odor. Behavioral data showed that trained animals exhibited a significantly higher level of freezing in response to the CS than control animals. In the same animals, EFPs were recorded in parallel in the anterior piriform cortex (aPC), posterior piriform cortex (pPC), cortical nucleus of the amygdala (CoA), and basolateral nucleus of the amygdala (BLA) following electrical stimulation of the olfactory bulb. Specifically, EFPs recorded before (baseline) and after (during the retention test) training revealed that trained animals exhibited a lasting increase (present before and during presentation of the CS) in EFP amplitude in CoA, which is the first amygdaloid target of olfactory information. In addition, a transient increase was observed in pPC and BLA during presentation of the CS. These data indicate that the olfactory and auditory fear-conditioning neural networks have both similarities and differences, and suggest that the fear-related behaviors in each sensory system may have at least some distinct characteristics.     

The effect of similarity between elemental stimuli and compounds in olfactory patterning discriminations

We studied the ability of honeybees to discriminate between single odorants and binary olfactory mixtures. We analyzed the effect of the number of common elements between these two stimulus classes on olfactory discrimination. We used olfactory conditioning of the honeybees' proboscis extension reflex (PER), a paradigm in which odors can be associated with a reinforcement of sucrose solution. Bees were asked to discriminate reinforced from nonreinforced olfactory stimuli. They were trained with two elemental odors (A and B) versus a binary olfactory mixture. The mixture was either AB (group 2CE, two common elements), AC (group 1CE, one common element A), or CD (group 0CE, no common element). Three groups followed a positive patterning schedule (mixture reinforced and elements nonreinforced: groups 2CE+, 1CE+, and 0CE+) and three other groups a negative patterning schedule (mixture nonreinforced and elements reinforced: groups 2CE-, 1CE-, and 0CE-). We showed that a reduction of similarity (number of common elements) between elemental odors and compounds enhanced the ability to discriminate elements from compounds and that the kind of compound processing used by the bees supports theories that assume nonelemental compound processing (i.e., that exclude the mere summation of the elemental associative strengths upon compound presentation).     

Critical roles of mecamylamine-sensitive mushroom body neurons in insect olfactory learning

In insects, cholinergic neurons are thought to transmit olfactory conditioned stimulus (CS) to the sites for associating the CS with unconditioned stimulus (US), but the types of acetylcholine (ACh) receptor used by neurons participating in the association have not been determined. In cockroaches, a type of nicotinic ACh receptor specifically antagonized by mecamylamine (MEC) has been characterized. Here we investigated the roles of neurons possessing MEC-sensitive ACh receptors (MEC-sensitive neurons) in olfactory conditioning of salivation, monitored by changes in activities of salivary neurons, in cockroaches. Local and bilateral microinjection of MEC into each of the three olfactory centers, antennal lobes, calyces of the mushroom bodies and lateral protocerebra, impaired olfactory responses of salivary neurons, indicating that MEC-sensitive neurons in all olfactory centers participate in pathways mediating olfactory responses of salivary neurons. Conditioning of olfactory CS with sucrose US was impaired by injection of MEC into the antennal lobes or calyces, i.e., conditioned responses were absent even after recovery from MEC injection, suggesting that the CS-US association occurs in MEC-sensitive neurons in calyces (most probably Kenyon cells) or in neurons in downstream pathways. In contrast, conditioned responses appeared after recovery from MEC injection into the lateral protocerebra, suggesting that MEC-sensitive neurons in the lateral protocerebra are downstream of the association sites. Since lateral protocerebra are major termination areas of mushroom body efferent neurons, we suggest that input synapses of MEC-sensitive Kenyon cells, or their output synapses upon mushroom body efferent neurons, are the sites for CS-US association for conditioning of salivation.