Perceptual learning in olfaction: professional wine tasters versus controls

By having professional wine tasters and controls perform olfactory tasks of absolute detection (1-butanol), discrimination (lemon and cloves), and identification (common household odors), the present two experiments studied (a) if perceptual odor learning takes place from odor experience acquired under nonlaboratory conditions, (b) if this learning generalizes to odors for which experience is limited, and (c) if generalized learning can be referred to increased general interest for odors that increases attention to odorous features. The results showed that whereas wine tasters were not better than controls on detection, they were superior to controls on discrimination and identification, the latter due to only a few odors. Ratings of experience with certain odors during professional evaluation suggest that generalized perceptual learning may take place in discrimination but not in identification. Wine tasters did not show more general interest for odorous features than did controls. The nonsuperiority in detection may be explained by the fact wine tasters have no professional experience of a detection task per se, implying that perceptual odor learning does not generalize from the olfactory tasks of discrimination and identification to detection.     

Automated study of simultaneous-cue olfactory discrimination learning in adult mice.

Adult C57BL/6J mice were trained in a fully automated operant task to discriminate between 2 simultaneously presented odors for water reward. Each mouse was trained on 16 different discrimination problems to a criterion of 90% correct in a block of 20 trials for each problem. Each of the mice tested reached criterion on all discriminations; the number of errors made before reaching criterion was greatest for the first few problems and decreased substantially thereafter. Acquisition performance on early trials of novel discriminations suggested that mice form learning sets for olfactory cues. The mice were trained on 4 additional problems and tested for memory with probe trials at retention intervals of 1, 2, 4, and 8 weeks. Good retention of olfactory cues was seen even at the longest memory delay. Automated testing of olfactory discriminations should be useful for assessing learning and memory abilities in genetically modified mice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The olfactory thalamocortical system and odor reversal learning examined using an asymmetrical lesion paradigm in rats.

The olfactory thalamocortical system was disrupted bilaterally in rats using (a) unilateral mediodorsal thalamic (MD) lesions plus contralateral bulbectomy and transection of the anterior commissure (AC), (b) unilateral MD lesions plus contralateral lesions of the frontal cortex, or (c) bilateral MD lesions. Rats were trained on an odor discrimination task and on the reversal of that task. Experimental groups performed as well as controls on the initial discrimination tasks but made more errors on the reversal problem. Rats with asymmetrical disruption of the olfactory thalamocortical system performed as poorly as those with bilateral MD lesions. These outcomes indicate that odor reversal learning deficits in rats with bilateral MD lesions stem from interruption of the olfactory thalamic-neocortical system and also provide evidence that the AC mediates significant interhemispheric transfer of olfactory information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Benzodiazepines impair the acquisition and reversal of olfactory go/no-go discriminations in rats.

The present study assessed whether benzodiazepines impair the acquisition, performance, and reversal of olfactory and auditory go/no-go discriminations in rats. Experiment 1 showed that midazolam (0.5-2 mg/kg sc) did not affect the performance of a well-learned two-odor olfactory discrimination and moderately facilitated performance of a go/no-go auditory discrimination. Experiment 2 found that midazolam (1 mg/kg) increased the number of errors made in the acquisition of a novel go/no-go olfactory discrimination task and in the reversal of a previously well-learned olfactory discrimination. However, midazolam did not affect the acquisition and reversal of an equivalent auditory discrimination task. Experiment 3 showed that diazepam (1 mg/kg) also impaired the acquisition and reversal of a novel olfactory discrimination task. Taken together, these results indicate that benzodiazepines cause a selective impairment of olfactory discrimination learning. This may reflect an effect of benzodiazepines in the glomerular circuitry of the olfactory bulb and at downstream olfactory processing sites such as the piriform cortex and orbitofrontal cortex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of nucleus basalis magnocellularis lesions in Long-Evans hooded rats on two learning set formation tasks, delayed matching-to-sample learning, and open-field activity.

Rats with quisqualic acid lesions of the nucleus basalis magnocellularis (nBM) and control rats were compared in discrimination reversal learning set (DRLS) and olfactory discrimination learning set (ODLS) tasks, a delayed matching-to-sample task (DMTS), and open-field activity. Evidence of learning set formation was seen to control rats but not in nBM-lesioned rats in the DRLS and ODLS tasks. Better-than-chance performances were seen for both groups in open-field activity. These findings suggest that the nBM is important for higher cognitive processing such as "learning to learn" and thus is important for a complex form of reference memory. In addition, perseverational, working memory, and attentional deficits could not explain learning set impariment after nBM lesions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory discrimination in rats with anterior amygdala lesions.

In Exp I, 12 male rats with posterior lateral olfactory tract/anterior amygdala lesions or with control neocortical lesions were tested for retention of a preoperatively learned odor detection task and for learning on new odor discrimination problems. All Ss had perfect or near-perfect retention of the detection task, and there were no discernible differences between groups in learning on the new odor discrimination problems. In Exp II, an intensity-difference threshold for olfaction was determined in 4 male Long-Evans rats before and after similar lesions. There were no apparent differences between pre- and postoperative performances on this psychophysical test. Results indicate that lateral olfactory tract projections to the amygdala and posterior olfactory cortex are not essential for normal performance on simple olfactory discrimination tasks, although the more caudal projections of the olfactory bulb play an important role in the arousal and maintenance of certain species-typical behaviors. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Promoter/repressor system of Lactobacillus plantarum phage og1e: characterization of the promoters pR49-pR-pL and overproduction of the cro-like protein cng in Escherichia coli

Previous studies have shown that extensive damage to the medial prefrontal cortex (mPFC) of rats causes reversal learning deficits. The mPFC of rats, however, consists of several subareas that are different from each other in both cytoarchitecture and neural connectivity, suggesting a functional dissociation among the mPFC subareas. In the present study, selective lesions of the mPFC of rats were made with a specially designed microknife whose intracranial placement could be controlled stereotaxically. Restricted lesions were made to each of the 3 parts of the mPFC: the anterior cingulate area (AC) (including the medial precentral area, PrCm), the prelimbic area (PL), and the infralimbic area (IL). One week after surgery, rats were trained in an aversively motivated visual discrimination task in a novel rotating T-maze. After reaching the acquisition criterion, rats were trained in a reversal task in the same maze. No difference was found in acquisition between control and mPFC lesioned rats. However, lesions of either the PL or the IL produced a marked deficit in the reversal task. This behavioral deficit was not found in rats with lesions of the AC. The results indicate that the mPFC of rats is not essential for discrimination learning, but that each of the 2 ventral subareas of the mPFC, PL, and IL, plays a critical role in reversal learning.     

Effects of nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester on spatial and cued leaning

An investigation was made of the effects of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) on the acquisition and retention of two operantly conditioned discrimination tasks. Twenty Long-Evans rats were conditioned to approach one of two spatial locations that was either held constant across trials (spatial task) or was associated with a visual cue (illuminated lamp) that was randomly assigned to one of the locations on each trial (cued task). Rats were assigned to one of two treatment groups in which they received intraperitoneal injections of either NG-nitro-L-arginine methyl ester or saline approximately 2 h before sessions on each day of training. Analysis was made of the trial-by-trial performance in order to identify the characteristics of learning under each condition. Assessment of learning acquisition was based on the number of trials required to reach a criterion of 80% correct responses, whereas retention was assessed by the number of trials to criterion on each day after the criterion was initially reached. Analysis indicated that treatment groups did not differ significantly on acquisition or retention of either the spatial or cued task. These results indicate that inhibition of nitric oxide synthase does not interfere with the learning or retention of basic operant tasks that involve simple spatial or visual analysis. Whereas results from biochemical and physiological investigations have suggested an impact of nitric oxide synthase on behavioural function, behavioural investigations indicate a limited impact of nitric oxide synthase inhibition on learning and memory. Although these results do not discount the role of nitric oxide synthase in a hippocampal mechanism, they illustrate that behavioural analysis should be made in the context of multiple interacting neural systems. Viewed with previous behavioural research on the effects of NG-nitro-L-arginine methyl ester, these results indicate that nitric oxide synthase inhibition results in impairment of certain forms of learning whereas other forms are preserved.     

Can rats acquire an olfactory learning set?

Experimental rats were trained on multiple 2-odor discrimination tasks, whereas controls were given repeated sessions on Task 1 and then were tested on a novel 2-odor task. Experimental rats showed strong positive transfer across problems and approached errorless or near-errorless learning. Control rats maintained near-perfect performance on Task 1 but performed at chance on initial trials when tested with novel odors. Thus, the near-errorless terminal performance of experimental rats was a function their having been trained on multiple problems and was not simply the result of eliminating "disruptive response tendencies' (I. C. Reid & R. G. M. Morris, 1992). Results support the view that when rats are trained on a series of 2-odor discrimination tasks, they acquire a strategy or rule that allows them to solve new problems with few or no errors. (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)     

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)     

The effects of aging on memory for sequentially presented objects in rats.

The current study investigated memory for sequentially presented objects in young rats 6 months old (n = 12) and aged rats 24 months old (n = 12). Rats were tested on a task involving three exploratory trials and one probe test. During the exploratory trials, the rat explored a set of three sequentially presented object pairs (A-A, B-B, and C-C) for 5 min per pair with a 3-min delay between each pair. Following the exploratory trials, a probe test was conducted where the rat was presented simultaneously with one object from the first exploratory trial (A) and one object from the third exploratory trial (C). Results from the exploratory trials showed no significant age-related differences in exploration, indicating that 24-month-old rats explored the object pairs as much as 6-month-old rats. The probe test demonstrated that 6-month-old rats spent significantly more time exploring object A compared to object C, indicating that young rats show intact temporal order memory for the exploratory trial objects. However, 24-month-old rats showed no preference for object A and spent a relatively equal amount of time exploring objects A and C. The results suggest that temporal order memory declines as a result of age-related changes in the rodent brain. The findings also may reflect differences in attraction to objects with different memory strengths. Since age-related differences were not detected during the exploratory trials, age-related differences on the probe trial were not due solely to decreased exploration, motivation, or locomotion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Quokkas ( Setonix brachyurus ) demonstrate tactile discrimination learning and serial-reversal learning.

Two male quokkas (Setonix brachyurus: a herbivorous macropod marsupial) were trained to discriminate pairs of stimuli in the laboratory. Quokkas indicated their choice by pulling on 1 of 2 simultaneously presented cords. The quokkas' discrimination abilities were tested on 6 tactile and 6 visual discrimination tasks. Correct responses were rewarded with food. For both quokkas, all tactile tasks were learned to a criterion of 75% correct in up to 4 20-trial sessions. No visual task maintained criterion performance in 4 sessions. One tactile discrimination was reversed 10 times. After the 1st reversal, the error rate declined sharply and fell to a level well below the initial discrimination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ventrolateral prefrontal cortex lesions in rats impair the acquisition and retention of a tactile-olfactory configural task.

Rats with aspirative lesions of the ventrolateral frontal cortex were tested on acquisition and postsurgical retention of an associative learning task that required that they learn a tactile–olfactory configural discrimination. The task required that they pull up a string to obtain attached food and that they identify the correct string using a compound of string size and odor. The rats were not impaired in initial learning or reversal of the olfactory elements of the discrimination. They were impaired in acquisition and retention of the compound, and their deficit was proportional to lesion size. The results confirm that the ventrolateral frontal cortex is involved in processing of olfactory information and imply that the prefrontal cortex is involved in at least certain types of cross-modal configural associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Location serves as a conditional cue when harp seals (Pagophilus groenlandicus) solve object discrimination reversal problems.

We examined the capacity of harp seals (Pagophilus groenlandicus) to use spatial context (i.e., their tank) as a conditional cue to solve a two-choice visual discrimination reversal task. Seals were trained to touch one of two 3D objects. Two of four seals experienced a context shift that coincided with each of five reversals in the reward value of the two stimuli (i.e., a reversal of S+ and S-); these seals solved the six discriminations in significantly fewer trials than did seals that did not experience a context shift with the contingency reversal. Thus, harp seals use contextual cues when encoding information. The findings are discussed in terms of harp seals' adaptations to the pack-ice environment, the constraints of the learning tasks, and the nature of the subjects that were raised in captivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of frontal cortex in social odor discrimination and scent-marking in female golden hamsters (Mesocricetus auratus).

Orbital/agranular insular (ORB/AI) cortex has been implicated in traditional olfactory learning tasks and social behavior but its precise role in discriminating-learning social odors is not known. Female golden hamsters received aspiration lesions of ORB/AI or dorsomedial (DM) frontal cortex and were tested for their ability to (a) discriminate between odors of individual males in a habituation-discrimination task, (b) show preferences for male over female odors, and (c) scent-mark in response to male odors. Lesioned females readily discriminated between scents of individual males. Neither lesion altered female preferences for male odors. Females with DM lesions showed increased levels of scent marking to male odors, but those with ORB/AI cortex lesions did not differ from controls. Thus, ORB/AI cortex does not appear to be critical for discrimination of odors of individuals or sex or for scent-marking responses based on these discriminations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The hippocampus and transverse patterning guided by olfactory cues

Normal rats and rats with hippocampal system damage were trained on a novel, olfactory version of the transverse-patterning task that involved the concurrent learning and continued performance of 3 partially ambiguous discrimination problems (A+B-, B+C-, C+A-). Animals with lesions of the fornix or perirhinal-entorhinal cortex acquired at least as rapidly as normal rats these problems presented in sequential blocks of trials involving the same stimulus pair. All groups also performed well on an initial test session when the order of stimulus pair presentations was randomized. Normal rats continued to discriminate appropriately in additional testing sessions with trials presented in random order. By contrast, both groups with hippocampal system damage performed poorly in continued random-order testing. These results extend the generality of the deficit in transverse patterning to the olfactory modality and demonstrate that the deficit is equivalent in magnitude after fornix or perirhinal-entorhinal damage. Findings also suggest that the transverse-patterning problem can be acquired transiently without critical hippocampal involvement, although continued performance relies on hippocampal function.     

Taste-potentiated odor aversion learning: Role of the amygdaloid basolateral complex and central nucleus.

Examined the relative contributions of the amygdaloid basolateral complex (ABL) and central nucleus (CN) to taste-potentiated odor aversion (TPOA) learning, an associative learning task that is dependent on information processing in 2 sensory modalities. In Exp 1, rats with neurotoxic lesions of these systems were trained on the TPOA task by presenting a compound taste–odor conditioned stimulus (CS), which was followed by LiCl administration. Results showed that ABL damage caused an impairment in potentiated odor aversion learning but no deficit in the conditioned taste aversion. In contrast, rats with CN damage learned both tasks. Exp 2 examined the effects of ABL damage on TPOA and odor discrimination learning. The odor discrimination procedure used a place preference task to demonstrate normal processing of olfactory information. Results indicated that although ABL-lesioned animals were impaired on TPOA, there was no deficit in odor discrimination learning. (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)     

Object discrimination learning in aged Japanese monkeys.

The authors investigated the behavioral aging effects of Japanese macaques in 3-object discrimination learning tasks: learning-set (LS) formation, go/no-go discrimination learning, and multiple discrimination reversals. Aged monkeys showed deteriorated performance in these tasks compared with younger controls. Hypothesis analysis of LS showed that aged monkeys had difficulty learning the lose-shift component of the hypothesis win-stay-lose-shift with respect to object. Deficits in go/no-go successive discrimination were clear in no-go trials only in the first 2 pairs of 5 tasks. Performance of aged monkeys was severely disturbed from a chance to criterion level in discrimination reversals. These results are attributed not only to increased tendency for perseveration but also to difficulty in associating the reward and the object in aged monkeys and may be related to the decline in the functions of the ventral frontal cortex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)