Generalization of conditioned food aversions in grazing sheep and its implications for food categorization

When grazing on heterogeneous pastures, herbivores may rely on food item generalization and categorization processes for reducing information processing while selecting their diet. The objective of this study was to assess the generalization of an aversion by grazing sheep for items differing by one or two criteria from an item against which they were negatively conditioned. Four items cultivated in pots were offered to the animals, resulting from the combination of an intrinsic criterion, i.e. grass species (ryegrass and fescue) and a transitory criterion, i.e. sward height (tall and short). We assessed the generalization process by comparing binary choices between the initially preferred tall ryegrass and the three other items, before and after animals had been partially conditioned against tall ryegrass. This method proved useful in assessing the generalization of an aversion. Sheep did not generalize their aversion on the basis of sward height but rather on species: they increased their preference for tall fescue and decreased their instantaneous preference for short ryegrass after having been conditioned against tall ryegrass. The generalization of an aversion through different states of a same species could indicate the possibility of a species-based categorization by grazing herbivores.     

Phenylthiocarbamide produces conditioned taste aversions in mice

Previous work has demonstrated that SWR/J (SW) mice avoid phenylthiocarbamide (PTC) to a greater degree than C3HeB/FeJ mice in 48 h, two-bottle preference tests given in ascending series. The authors hypothesized, based also on previous work, that SW mice might form a conditioned taste aversion over time due to the toxic properties of PTC. We directly tested this hypothesis by attempting to condition a taste aversion to sucrose by injections of PTC. In experiment 1, PTC was nearly as effective as a strong dose of LiCl in reducing sucrose drinking. In experiment 2, the sucrose aversions were parametrically modified by both sucrose concentration and PTC dose, a hallmark of conditioned taste aversion. We conclude that PTC can cause a conditioned taste aversion and discuss the importance of considering toxic effects of aversive tastants when analyzing behavioral strain differences.     

Using conditioned food aversions to protect blueberries from birds: Comparison of two carbamate repellents

This study compared the effectiveness of two carbamate repellents (trimethacarb and methiocarb) in protecting blueberry fields from fruit loss caused by birds (primarily Northern Mockingbirds, European Starlings and Northern Orioles). Methiocarb and trimethacarb reduced berry loss significantly in the treated plots by 25 and 52%, respectively, during the first week after application. Differences between the two repellents in effectiviness, however, were not statistically significant. Moreover, neither repellent reduced berry loss significantly in adjacent untreated plots. These results indicate that both repellants caused birds to avert only from treated berries, and not from the taste or sight of blueberries themselves.     

Generalization of conditioned taste aversions in hamsters: evidence for multiple bitter receptor sites

Multiple bitter receptor sites appear to exist within the hamstergustatory system supporting the data of other investigatorson humans, rats and frogs. The sodium salts of four anions,m-nitrobenzene sulfonate (NBSA), picrate, m-nitrobenzoate (NBA)and cholate, were tested in two-bottle preference tests andfor generalization to a variety of stimuli in a conditionedtaste aversion (CTA) paradigm. All four of these anions arebitter to humans. One, NBSA, generalized to sucrose suggestinga sweet taste, while the remaining three appear to be bitterwith varying degrees of saltiness. The bitterness of these threeanions to hamsters appears to be perceptually different froma quinine-type bitterness. Separate bitter receptor sites areindicated for quinine and urea, plus a third site acceptingNBA, picrate and cholate. More bitter sites are plausible. Separatesites for quinine and urea appear to occur across species. Itwas also concluded that quinine does not serve as a prototypicbitter stimulus for all bitters in the CTA test.     

The dependence of hippocampal electrical activity on the probability of the reinforcement of a conditioned food stimulus

In three dogs the dynamics was studied of changes in the number of instrumental motor reactions, the heart rate and the hippocampus theta rhythm was studied at the change of constant reinforcement to various regimes of probable reinforcement of alimentary conditioned stimulus. At 70 and 50% levels of the reinforcement the instrumental reflex appeared in response to all presentations of the signal stimulus. The greatest decrease in the number of reactions took place at 5% probability. The heart rate both in the intersignal period and at getting of empty feeder depended on the used probability of reinforcement and individual characteristics of animals. The frequency of the theta rhythm in all dogs was the highest at the 30% level and the lowest values were found at the 5% level of reinforcement. The obtained facts testify once more to complex genesis of emotional excitation, the value of which depends both on informational (uncertainty) and motivational (significance of reinforcement) factors.     

Attenuation of radiation- and drug-induced conditioned taste aversions following area postrema lesions in the rat

The effects of lesions of the area postrema on the acquisition of radiation- and drug-induced (histamine and lithium chloride) conditioned taste aversions were investigated. The results indicated that area postrema lesions caused a significant attenuation of the aversion produced by pairing a novel sucrose solution with radiation (100 rad) or drug injection. Further, the area postrema lesions produced a similar level of attenuation of the taste aversion in all three treatment conditions. The results are discussed in terms of the implications of this finding for defining the mechanisms by which exposure to ionizing radiation can lead to the acquisition of a conditioned taste aversion.     

Presence of kynurenic acid in food and honeybee products

Kynurenic acid (KYNA) is an endogenous antagonist of ionotropic glutamate receptors and the α7 nicotinic acetylcholine receptor, showing anticonvulsant and neuroprotective activity. In this study, the presence of KYNA in food and honeybee products was investigated. KYNA was found in all 37 tested samples of food and honeybee products. The highest concentration of KYNA was obtained from honeybee products’ samples, propolis (9.6 nmol/g), honey (1.0–4.8 nmol/g) and bee pollen (3.4 nmol/g). A high concentration was detected in fresh broccoli (2.2 nmol/g) and potato (0.7 nmol/g). Only traces of KYNA were found in some commercial baby products. KYNA administered intragastrically in rats was absorbed from the intestine into the blood stream and transported to the liver and to the kidney. In conclusion, we provide evidence that KYNA is a constituent of food and that it can be easily absorbed from the digestive system.     

Effect of tryptophan and its metabolites on the conditioned reflex activity of the honeybee

The effect of tryptophane and its derivatives on the rate of elaboration and transformation of conditioned reflexes (CR) to odour, with alimentary reinforcement, was studied in wild bees under two conditions: free movement of the bee or its immobilization (stress situation), by means of genetic models (mutations, successive blocking stages of kynurenin path of tryptophane metabolism). It was shown that mutations eliciting accumulation of free tryptophane and serotonin in the hemolymph of the bees and creating a deficit of kynurenins accelerate the transformation of conditioned reflexes and aggravate the depression of conditioned activity usually elicited in wild bees by monotonous prolonged presentation of conditioned signal. The injections of tryptophane and serotonin (5 mg) produce the same action. Mutations, eliciting accumulation in the hemolymph of the kynurenins (kynurenin and 3-hydroxikynurenin) accelerate, in conditions of immobilization, the formation of conditioned reflexes and delay the process of their transformation, and also contribute to maintainance of a higher (in comparison with the norm) level of the conditioned activity under monotonous presentation of the signal. The same action is produced by the injection of 1 mcg kynurenin.     

Parallel thalamic pathways for whisking and touch signals in the rat

In active sensation, sensory information is acquired via movements of sensory organs; rats move their whiskers repetitively to scan the environment, thus detecting, localizing, and identifying objects. Sensory information, in turn, affects future motor movements. How this motor-sensory-motor functional loop is implemented across anatomical loops of the whisker system is not yet known. While inducing artificial whisking in anesthetized rats, we recorded the activity of individual neurons from three thalamic nuclei of the whisker system, each belonging to a different major afferent pathway: paralemniscal, extralemniscal (a recently discovered pathway), or lemniscal. We found that different sensory signals related to active touch are conveyed separately via the thalamus by these three parallel afferent pathways. The paralemniscal pathway conveys sensor motion (whisking) signals, the extralemniscal conveys contact (touch) signals, and the lemniscal pathway conveys combined whisking–touch signals. This functional segregation of anatomical pathways raises the possibility that different sensory-motor processes, such as those related to motion control, object localization, and object identification, are implemented along different motor-sensory-motor loops.     

Differences in the taste quality of maltose and sucrose in rats: issues involving the generalization of conditioned taste aversions

The present study employed a conditioned taste aversion generalizationparadigm to test the hypothesis that maltose produces tastesensations in the rat which are qualitatively distinguishablefrom sucrose. Since stimulus generalization can occur in boththe quality and intensity domains, an intrachemical (acrossconcentration) generalization gradient was established to aidin the interpretation of the interchemical (across molecules)generalization gradient. Moreover, since the commonly used intaketest is vulnerable to nontaste post-ingestional influences,the present study measured immediate responses to 100 µlstimulus samples, thus increasing our confidence that the behaviorwas under orosensory control. In Experiment 1, naive water deprivedrats were trained in a specially designed gustometer to maintaindrinking-spout contact for intermittent water reinforcement.Following this, rats in the experimental group were given threeexposures to 0.1 M sucrose on separate days, with the firsttwo exposures immediately preceding an injection of LiCl. Acontrol group was treated identically but received distilledwater instead of sucrose. Rats were then tested in the gustometerfor their avoidance of three equimolar concentrations of sucroseand maltose. Rats received ten trials of each stimulus quasi-randomlypresented in two sessions. Results indicated that all sucroseconcentrations were avoided (in experimental group only), butonly the 0.3 M concentration of maltose was avoided. The lowestsucrose concentration was significantly less avoided than thehigher concentrations. Intensity generalization gradients aresuch that intensities weaker than the conditioned stimulus (CS)produce just as much or less of a conditioned response (CR)and intensities stronger than the CS produce just as much ora greater CR than that elicited by the CS itself. Therefore,based on the results of Experimental, it was predicted thatif 0.1 M maltose served as the CS, the order of avoidance shouldbe: 0.3 M sucrose 0.1 M sucrose 0.03 M sucrose 0.3 M maltose 0.1 M maltose 0.03 M maltose, if it were true that maltoseand sucrose produce identical sensations that differ only inintensity. Experiment 2 explicitly tested this prediction usingthe same procedure as Experiment 1 except that 0.1 M maltoseserved as the CS. The observed order of avoidance was 0.3 Mmaltose > 0.1 M maltose > 0.03 M maltose = 0.3 M sucrose= 0.1 M sucrose = 0.03 M sucrose. In both experiments the intrachemicalgeneralization gradient broadened and the interchemical generalizationgradient steepened upon retesting. In conclusion, qualitativedifferences between maltose and sucrose explain the outcomesof these experiments better than differences in the relativeintensity of these sugars at isomolar concentrations.     

Parallel pathways for habituation in repetitively stimulated PC12 cells

Habituation was investigated in neuronally differentiated PC12 cells by measuring the decrease in cellular secretion of norepinephrine with repetitive stimulation by either membrane depolarization or acetylcholine. When these two types of repetitive stimulation were applied to the same cells, habituation occurred independently to each, showing that two pathways for habituation can be utilized simultaneously in single cells. The two pathways apparently process stimuli in parallel, without competition between common intermediates.     

Parallel reinforcement learning for weighted multi-criteria model with adaptive margin

Reinforcement learning (RL) for a linear family of tasks is described in this paper. The key of our discussion is nonlinearity of the optimal solution even if the task family is linear; we cannot obtain the optimal policy using a naive approach. Although an algorithm exists for calculating the equivalent result to Q-learning for each task simultaneously, it presents the problem of explosion of set sizes. We therefore introduce adaptive margins to overcome this difficulty.     

Ontogenetic development of conditioned food aversion in chickens

Development of conditioned food aversion (CFA) was studied in 25-, 35-, and 45-day Leghorn chicks. Food-deprived birds had 10-min access to normal food on days 1 and 2, and to green coloured food CS on day 3. Injection of LiCl (0.15 M, 3–4% body weight) administered 10 min after CS on day 3 served as the US. Control groups were injected with the same volume of saline. Retention was tested on day 4 in three 3-min presentations of normal food alternating with two presentations of green food. Number of pecks and amount of food consumed were measured. Significant neophobic rejection of green food was observed in 25- but not in 35- and 45-day-old control birds. Neophobia in the youngest chicks was further accentuated by CFA which could be observed in pure form in the 45-day-old experimental group. Comparison of pecking rate and food intake showed that CFA in younger birds was accomplished predominantly by inhibition of pecking, and in older birds also by reduction of peck volume. It is concluded that protection against poisoning in chickens shifts between 25 and 45 days of posthatching age from neophobia to CFA.     

Parallel processing in the honeybee olfactory pathway: structure, function, and evolution

Animals face highly complex and dynamic olfactory stimuli in their natural environments, which require fast and reliable olfactory processing. Parallel processing is a common principle of sensory systems supporting this task, for example in visual and auditory systems, but its role in olfaction remained unclear. Studies in the honeybee focused on a dual olfactory pathway. Two sets of projection neurons connect glomeruli in two antennal-lobe hemilobes via lateral and medial tracts in opposite sequence with the mushroom bodies and lateral horn. Comparative studies suggest that this dual-tract circuit represents a unique adaptation in Hymenoptera. Imaging studies indicate that glomeruli in both hemilobes receive redundant sensory input. Recent simultaneous multi-unit recordings from projection neurons of both tracts revealed widely overlapping response profiles strongly indicating parallel olfactory processing. Whereas lateral-tract neurons respond fast with broad (generalistic) profiles, medial-tract neurons are odorant specific and respond slower. In analogy to “what-” and “where” subsystems in visual pathways, this suggests two parallel olfactory subsystems providing “what-” (quality) and “when” (temporal) information. Temporal response properties may support across-tract coincidence coding in higher centers. Parallel olfactory processing likely enhances perception of complex odorant mixtures to decode the diverse and dynamic olfactory world of a social insect.