Olfactory discrimination, reversal learning, and stimulus control in rats.

Conducted 3 experiments with a total of 21 Wistar rats. In Exp I Ss were trained to discriminate lights, tones, or odors and then given a series of discrimination reversals. Only Ss trained with odors showed positive transfer on the first reversal and acquisition of a reversal set. Other experiments demonstrated that (a) Ss preferentially attended to odors when presented in compound with lights or tones; (b) odors exerted more discriminative control than tones in tests using compound stimuli of competing sign; and (c) after pretraining on the positive stimulus, acquisition of an odor but not a light discrimination occurred with virtually no errors. These results demonstrate the importance of stimulus modality in the establishment of stimulus control and the need for more careful analysis of stimulus factors in cross-species comparisons of learning ability. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Diet preference in rats (Rattus norvegicus) as a function of odor exposure, odor concentration, and conspecific presence.

The relative contributions of social and stimulus factors in development of rat dietary preferences were examined. Investigation of odor-alone effects revealed that weak odors resulted in preference for familiar-odor diets, but only at longer exposure times. Shorter exposure to strong odors also produced differences in diet preference. When odor and conspecific presence were manipulated simultaneously, odors produced no diet preference at low intensities, whereas high-intensity odors did so regardless of conspecific presence. Medium-intensity odor concentrations produced differences only with conspecifics present, indicating social enhancement of stimuli that are ineffective in isolation. These results suggest the separate influence of social and stimulus factors on dietary preferences and explain contradictions in previous studies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention and habituation: Odor preferences, long-term memory, and multiple sensory cues of novel stimuli.

Investigation of and habituation to novel stimuli are part of exploratory behavior of rodents. They are necessary for assessing the environment in seeking food and sexual partners and in avoiding predators. Six experiments tested male and female Mongolian gerbils (Meriones unguiculatus) in a stimulus-elicited investigation paradigm. Findings indicate that (1) Ss initially showed preference for odors of strange male bedding and for odors of home cage bedding and then habituated. There was no preference between these 2 odors, although they could be discriminated. The complex odor stimulus elicited more response than any of the components tested. (2) Memory of an object or odor was demonstrated up to 4 wks later. (3) Sensory deprivation by blinding, anosmizing, or removing somatosensation of the upper snout made only small differences in investigation. The removal of any 2 of these sensory inputs produced more interference with the response, but all Ss investigated the stimulus. It is concluded that attention to novelty and habituation after repeated exposure are very robust behaviors and are mediated through multiple sensory channels. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential conditioning to a compound stimulus and its components in the terrestrial mollusc Limax maximus..

The neuronal mechanism of associative learning and memory storage operating in the central nervous system of the terrestrial mollusc Limax maximus has been modeled as a computer simulation called LIMAX (A. Gelperin et al [1985]). One test of the LIMAX model is to determine whether Limax can learn to avoid a compound stimulus composed of the mixture of two innately attractive odors without simultaneously learning an aversion to the individual odors comprising the mixture. We found that Limax can learn a strong aversion to odor A?+?B while odor A and odor B remain strongly attractive when presented individually. This result led us to reexamine the sensory coding scheme used in the LIMAX model to represent stimulus mixtures, and it suggests neurophysiological experiments to examine the actual chemosensory coding scheme used by Limax. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of rat anterior cingulate inactivation on cognitive flexibility.

The present experiment investigated the effects of muscimol injections into the rat dorsal anterior cingulate on the acquisition and reversal learning of a 4-choice odor discrimination. Long-Evans rats were trained to dig in cups that contained distinct odors. In the odor discrimination, one odor cup contained a cereal reinforcement in acquisition whereas a different odor cup contained a cereal reinforcement in reversal learning. The other 2 odor cups were never associated with reinforcement. Bilateral infusions of the gamma aminobutyric acid-A agonist muscimol did not impair acquisition of the odor discrimination but impaired reversal learning in a dose-dependent manner. During reversal learning, dorsal anterior cingulate inactivation did not lead to perseveration but selectively increased errors to the odor cups that were never reinforced. These findings suggest that the dorsal anterior cingulate supports learning when conditions require a shift in choice patterns and may enhance cognitive flexibility by decreasing interference of irrelevant stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cortico-hippocampal representations in simultaneous odor discrimination: A computational interpretation of Eichenbaum, Mathews, and Cohen (1989).

A previous model of hippocampal region function in classical conditioning is generalized to H. Eichenbaum, A. Fagan, P. Mathews, and N. J. Cohen's (see record 1988-28895-001) and H. Eichenbaum, A. Fagan, and N. J. Cohen's (see record 1990-09261-001) simultaneous odor discrimination studies in rats. The model assumes that the hippocampal region forms new stimulus representations that compress redundant information while differentiating predictive information; the piriform (olfactory) cortex meanwhile clusters similar and co-occurring odors. Hippocampal damage interrupts the ability to differentiate odor representations, while leaving piriform-mediated odor clustering unchecked. The result is a net tendency to overcompress in the lesioned model. Behavior in the model is very similar to that of the rats, including lesion deficits, facilitation of successively learned tasks, and transfer performance. The computational mechanisms underlying model performance are consistent with the qualitative interpretations suggested by Eichenbaum et al to explain their empirical data. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning in the Africanized honey bee: Apis mellifera L

Several series of experiments are reported that investigate learning in the Africanized honey bee. In the first series, classical conditioning of proboscis extension was studied by confining bees to small metal tubes where they received pairings of an odor with a 3-s feeding of sucrose. After a number of odor-sucrose pairings, the bees began to extend their proboscis to the odor. Controls include Unpaired, Discrimination, and Pseudoconditioning Groups. This technique was used to look at conditioning to a light CS, and to the odors of beeswax, geraniol, citral, and hexanal. The results indicate that acquisition was best when sucrose was paired with the odor of beeswax. Conditioning to the remaining odors was roughly similar, but acquisition did not occur using a light. In a second series of experiments, odors were no longer followed by sucrose feedings and the conditioned response slowly disappeared. With the exception of geraniol as a CS, this extinction effect did not occur if the animals continued to be fed on an unpaired schedule. In a third series of experiments, conditioned inhibition was demonstrated when geraniol was used as conditioned stimuli, but no effect was found when the odors of hexanal, citral and wax were used. In a fourth series of experiments, unrestrained bees flew back and forth from the laboratory to the hive, where they were taught to distinguish targets based on color and odor. With this technique, color and odor discrimination in the Africanized bees was demonstrated. In addition, it was found that more intruder bees visited the experimental station when the stimuli used were olfactory rather than visual.     

Olfaction and the "data" memory system in rats.

Conducted studies to characterize the memory system involved in successive olfactory discrimination learning in rats. Two odors emanated from different arms of a radical maze; 1 of the arms contained a water reward. After training on 4 to 5 pairs of odors Ss learned to discriminate the members of a new pair in 5–20 trials. Experiments in which either member of the pair was compared with a novel cue indicated that the Ss learn both positive and negative odors, rather than ignoring the negative cue. The memories for the odors were apparently persistent, and no evidence for retroactive interference from subsequent training was obtained. Animals trained on 3 component odors with 2 in common did not recognize the elements that were unshared when these were presented by themselves. Even when 1 of the 2 shared components was combined with the differentiating component into a cue the new cue was treated as a novel odor. Inclusion of a previously learned simple odor in a complex odor did affect the learning of that odor. Findings, combined with those of previous studies in which lesions were used, suggest that learning that a series of odor discriminations involves a version of the "data" memory system described by cognitive psychologists. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory repeated discrimination reversal in rats: Effects of chlordiazepoxide, dizocilpine, and morphine.

Effects of a benzodiazepine (chlordiazepoxide), an N-methyl-D-aspartate receptor antagonist (dizocilpine), and an opiate agonist (morphine) were studied with a procedure designed to assess effects of drugs and other manipulations on nonspatial learning in rats. In each session, rats were exposed to 2 different 2-choice odor-discrimination problems with food reinforcement for correct responses. One problem (performance discrimination) remained the same throughout the study. That is, 1 odor was always correct (S+) and the other was never correct (S-). For the other problem (reversal discrimination), stimuli changed every session. Six different odors were used to program the reversal discrimination; on any given session, S+ was a stimulus that had served as S- the last time it had appeared, S- was a stimulus that had been S+ on its last appearance. Thus, in each session, learning a discrimination reversal could be studied along with the performance of a comparable, but previously learned, discrimination. Chlordiazepoxide interfered with reversal learning at doses that had no effect on the performance discrimination. Morphine and dizocilpine also impaired reversal learning but only at doses that also affected performance of the well-learned performance discrimination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory recognition of conspecifics by domestic Norway rats

In order to learn more about their ability to recognize one another via olfaction, domestic male rats were given a series of preference tests in which pairs of odors from male conspecifics were presented. Both immature and mature males prefer (p less than .05) the odor from immature strangers over that from immature cage mates but are indifferent to the ordors from mature strangers versus cage mates. Both immature and mature males prefer (p less than .05) the odor from mature novel cage mates over that from mature cage mates to which they are temporarily habituated but are indifferent to the odors from immature novel versus familial cage mates. Mature males prefer (p less than .08) the odor from a cage mate over the subject's own odor, and they prefer (p less than .01) their own odor over no odor. Under certain conditions, male rats can discriminate between the odors from (a) strangers versus cage mates, (b) two cage mates, and (c) their own body versus a cage mate.     

Representations of odors in the rat orbitofrontal cortex change during and after learning.

Cells in the orbitofrontal cortex (OF) respond to odors and their associated rewards. To determine how these responses are acquired and maintained, the authors recorded single OF units in rats performing an odor discrimination task. Approximately 64% of all cells differentiated between rewarded and nonrewarded odors. These odor valence responses changed during learning in 26% of all cells, and these changes were positively correlated with improving performance, supporting the idea that the information provided by these cells is used in learning the task. However, changes in odor valence responses were also observed after learning, and included not only increases in odor discrimination, but also decreases or mixed increases and decreases. Thus, only some of the changes in firing reflected acquisition of the task. The results suggest that learning triggers a continuing reorganization of OF neural ensembles representing odors and their rewards. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Further studies of hippocampal representation during odor discrimination learning.

The contribution of hippocampal and nonhippocampal memory processing to simultaneous-cue odor discrimination learning was assessed. In this task rats with hippocampal system damage consequent to fornix lesions (fornix rats) were severely and persistently impaired in discrimination learning, acquisition of learning set, and concurrent discrimination, although they occasionally solved some problems at a normal rate. By using those problems on which fornix rats succeeded, to permit comparisons of performance strategies with normal rats, differences between groups were shown on response latency measures and on probe trials involving the novel pairing of familiar odors. Normal rats had a bimodal distribution of response latencies, and their latency depended on where the S+ was presented. Fornix rats had short response latencies and responded equally quickly wherever the S+ was presented. Furthermore, when the representation of familiar S+ and S– odor pairs was challenged in probe trials, normal rats responded appropriately to the correct stimulus, whereas fornix rats behaved as if presented with a new odor pair. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory stimulation induces filial preferences for huddling in rat pups.

Rat pups of all ages huddle with conspecifics, but the sensory control of contact behavior changes ontogenetically. Thermal cues control huddling until about Day 15, at which time species' odors become the dominant stimulus. The present 2 experiments with 150 Sprague-Dawley rat pups indicate that the filial response to conspecifics is dependent on olfactory experience. A synthetic chemical scent was added to the smells of the dam from Day 1 to Day 20 postpartum. Standardized videographic tests were used to assess the development of huddling preference. Preferences for nest-typical smells emerged by Day 15 in Ss from both scented and nonscented litters. Ss from scented nests preferred to huddle with a scented stimulus rat, whereas control Ss preferred a nonadulterated rat stimulus. Additional testing indicated that the affirmative preferences were specific to rearing odor and were not based on decreased aversion to test scents or on disrupted olfactory discrimination. The ontogeny of species-typical contact behavior is discussed in terms of the induction of a perceptual preference that is based on early odor stimulation. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned discrimination of airborne odorants by garter snakes (Thamnophis radis and T. sirtalis sirtalis).

For snakes, the nasal chemical senses are critical in intraspecific communication and prey recognition. Although it is known that garter snakes can respond differentially to airborne odorants, no previous study has demonstrated that snakes can learn a task with airborne odors as discriminative stimuli. In Experiment 1, 7 plains garter snakes (Thamnophis radix) were trained in a two-choice apparatus to move into a compartment containing lemon-scented chips for a food reward. All 7 snakes improved performance when the first 10 and last 10 trials of the 100 trials of conditioning were compared. Four of the snakes were subsequently trained to move away from the scented compartment into the unscented compartment. The 4 snakes rapidly learned this reversal. In Experiment 2, 7 common garter snakes (T. sirtalis sirtalis) were trained to traverse a two-choice maze with the presence or absence of amyl acetate odor as the conditioned stimulus. The snakes were pretested for odor versus nonodor preference and were trained to go to the initially nonpreferred stimulus. Of the 7 snakes, 5 achieved a predetermined criterion (two training sessions with cumulative correct responding above the .05 confidence level) within 85 trials. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hedonic and sensory characteristics of odors conditioned by pairing with tastants in humans.

Animals readily acquire positive odor-taste hedonic associations, but evidence for this in humans remains weak and was explored further. Retronasal pairing of odors with sucrose or salty stimuli (Experiment 1) increased the rated sweetness of sucrose-paired odors without altering liking, although changes in odor pleasantness correlated with sucrose liking. Experience of odors with sucrose or quinine by sweet likers (Experiment 2) found increased pleasantness and sweetness for sucrose-paired odors, whereas quinine-paired odors became less liked and more bitter. Odor-sucrose pairings in sweet likers and dislikers (Experiment 3) found increased sweetness in both groups but increased odor liking only in likers. These data suggest that evaluative and sensory learning are dissociable and that evaluative changes are sensitive to individual differences in sweet liking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of cognitive and affective processing in a transgenic mouse model of cortical-limbic neuropotentiated compulsive behavior.

Obsessive compulsive disorder (OCD) may involve abnormal cortical-limbic processing or responsiveness. Mice with behaviors resembling the symptoms of OCD and related disorders were made by expression of a neuropotentiating cholera toxin (CT) transgene in cortical-limbic D1 receptor-expressing neurons. Because these D1CT mice express CT in the piriform cortex and amygdala (major cognitive and affective olfactory processing areas) it was tested whether abnormal odor perception, discrimination, or responsiveness facilitates their compulsion-like behavior. The mice exhibited normal olfactory discriminative capability. An anxiogenic odor potentiated their abnormal repetitive leaping, but novel or familiar nonthreatening odors did not. These data suggest that compulsions can be triggered not by impaired cortical-limbic processing but by increased cortical-limbic responsiveness, particularly to sensory or cognitive stimuli with affective properties. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Molecular cloning, characterization and expression of cDNA encoding phosphoserine aminotransferase involved in phosphorylated pathway of serine biosynthesis from spinach

The reactions elicited by nociceptive stimulations were studied in mice exposed to the presence of different odors: positive (attractive), negative (aversive), or neutral. In a first set of experiments, the animals were not habituated to the odors before the nociceptive stimuli were applied; in this case, the olfactory environment during experienced pain had essentially no effect on the nociceptive reactions, whatever the nature of the odors. In a second set of experiments, the animals were habituated to the same odor for 20 days. The control group consisted of mice habituated to and tested in the presence of the odor of the laboratory. In that case, compared to controls, the neutral odor had no influence on nociceptive reactions. By contrast, the positive odor decreased and the negative odor increased the reactions, especially when the intensity of the nociceptive stimulus was low. Moreover, it has been shown that the reactions elicited during a second nociceptive stimulation period depend on the perception of pain animals experience during the first stimulation, which depended, in turn, on the odor associated with it. Results are discussed in terms of opioid-mediated interactions between olfaction and pain.     

Selective hippocampal lesions in rats disrupt acquisition and retention of a positive patterning discrimination

To determine the contribution of the hippocampus in the processing of a configural positive patterning discrimination (PPD) task, discrimination between reinforced presentations of a tone plus light compound stimulus and nonreinforced presentations of each of its components (TL+/T-,L-) was examined using a conditioned-suppression paradigm. In the first experiment, rats demonstrated a rapid acquisition of the PPD with an appropriate discriminative responding. Rats submitted to posttraining hippocampal lesions (using multiple injections of ibotenic acid) were no longer able to master correctly the previously solved discrimination, demonstrating significant differences in their response rates during the 2 never-reinforced elemental stimulus presentations. In Experiment II, lesioned rats were not able to correctly learn the PPD, demonstrating the same pattern of responding as in Experiment I. These rats were also severely disrupted in a radial maze elimination task. Experiment IIIa indicated that, in a simple conditioning task (T+, L+), normal rats acquired a rapid conditioned suppression for both stimuli, with the tone being slightly more susceptible to conditioning than the light stimulus. In Experiment IIIb, conditioning to the compound tone plus light stimulus led to a clear conditioning to the tone and almost no conditioning to the light, suggesting an overshadowing from the tone to the light. Similar results were obtained in rats with hippocampal lesions. These results strongly suggest that the disruption showed by rats with hippocampal lesions in the PPD task cannot be due to an alteration of the relative salience of the stimulus. The inability of rats with hippocampal lesions to solve correctly the PPD is due to difficulties in eliminating responding to some unimportant events of the situation, reflecting a deficit in selective attention processes rather than in an ability to process configural stimuli. In the discussion, the putative role of the hippocampus in selective attentional processes is more fully discussed.     

Memory effects on symptom reporting in a respiratory learning paradigm.

With odors as conditioned stimuli (CSs) and CO?-enriched air as the unconditioned stimulus, participants learned to exhibit respiratory responses and somatic complaints on presentation of only the odor CS+. Studied was whether complaints during CS+-only trials were inferred from the conditioned somatic responses or were based on activated memory of the complaints during acquisition. Participants (N?=?56) were either attentionally directed away or not from the complaints during acquisition, and the effects on somatic complaints during test were studied. Respiratory responses, heart rate, and somatic complaints were measured. No physiological conditioning effects were found. However, more complaints were reported to the CS+ than to the CS– odor, but only when the CS+ was foul smelling. This effect was modulated by the attention manipulation, showing that the learned complaints during the test phase were based on memory of the acquisition complaints and not on physiological responses during the test. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Representation-mediated overshadowing and potentiation of conditioned aversions.

Examined the ability of CS-evoked representations of flavored substances to modulate the conditioning of LiCl-based aversions to simultaneously presented flavors or odors. In Exps I–III, 156 thirsty Sprague-Dawley rats first received pairings of an auditory CS with a flavored-water UCS; they then received pairings of a compound stimulus with a toxin. Exp IV examined the potentiation of aversion conditioning to a novel odor using 32 Ss. In Exp I, conditioning of a flavor was partially overshadowed when it was presented in compound with a tone that had been previously paired with another flavor. Exp II replicated that result and also found that conditioning to a flavor was not overshadowed when the flavor was presented in compound with a tone that had been paired with that same flavored substance. In Exps III and IV, conditioning to an odor stimulus was potentiated when it was presented in compound with either a tone or another odor that had been previously paired with a flavor stimulus. Results suggest that evoked representations of stimuli may substitute for those events themselves in a variety of associative functions. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)