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PubMed2004

Functional characteristics of the associative areas of the cortex involved in visual information discrimination learning processes in monkeys.

Experiments on three groups of rhesus macaques (intact and with bilateral removal of field 7 and the sulcus principalis) were performed to study the functional characteristics of the associative areas of the cortex while the monkeys learned visual discrimination. Significant differences in learning processes associated with removal of structures and the properties of the stimuli were seen in all animals, in the form of different types of learning curves. As compared with intact monkeys, removal of field 7 had no effect on learning processes for images with properties such as spatial frequency, color, and animal images, though there was a significant worsening in the characteristics of learning during visual discrimination of spatial relationships between objects. Learning processes became unstable, the number of peaks and troughs on learning curves increased, and as a result the training periods were significantly lengthened and 85% of the animals were unable to achieve the learning criterion. Removal of the sulcus principalis significantly worsened the characteristics of discrimination of the sizes of geometric objects, the spatial relationships between them, and stimuli of different colors. The stable reaction time and the probability of refusal in most cases also increased for monkeys of both these groups. Cluster analysis based on the quantitative characteristics of learning processes, despite individual differences between the monkeys, demonstrated a tendency for stimuli to be separated into classes corresponding to different types of information. These data show that the result of sensory processing is that several (at least three) functional visual information flows are generated and that different areas of the cortex deal with these different flows.

Animals↗
PubMed2003

Impaired visual discrimination learning in anorexia nervosa.

The primate dopamine system is involved in appetitively motivated behaviours, including certain forms of learning, for example, visual discrimination learning. Furthermore, food restriction in animals and anorexia in humans is associated with impaired dopamine signaling. Based on this, we hypothesized that patients with anorexia nervosa (AN) would show a deficit in visual discrimination learning. In a dynamic categorization task involving the learning of a series of two-alternative forced-choice visual discriminations, conceptually identical to one shown to activate dopamine neurons in primates, and sensitive to dopaminergic manipulations in humans, patients with AN showed a deficit in learning that was most pronounced in the early stages of acquisition. In contrast, AN showed spared performance on a pattern recognition memory test sensitive to medial temporal lobe lesions, but insensitive to dopaminergic manipulations. We conclude that impaired appetitive function in patients with AN extends to include deficits in visual discrimination learning, and that this deficit represents indirect evidence for altered dopaminergic neurotransmission in AN.

Adult↗
PubMed1994

Role of the amygdala in picture discrimination learning with 24-h intertrial intervals.

Six monkeys (Macaca mulatta) learned to discriminate visually between pictures of objects. Each pair of pictures was presented only once per day (24-h intervals between successive trials with the same pair). Choice of the correct picture of a pair produced immediate food reward. One set of 20 pairs was learned before operation and a second set of 20 different pairs was learned after the amygdala had been removed bilaterally in three of the monkeys. The amygdalectomized animals were severely retarded in learning the second set. These results confirm earlier results indicating that amygdalectomy impairs visual discrimination learning in tasks where the discriminanda are directly associated with the incentive value of a primary reward, and they show that, contrary to the indication of some previous results, this impairment extends to the case where each picture is seen only once per day.

Amygdala↗
PubMed1995

Operant discrimination learning in detelencephalated pigeons (Columba livia).

Operant discrimination learning was analyzed in pigeons after massive telencephalic lesions. Twenty-one pigeons were divided into three groups: non-lesioned (N = 6), sham-lesioned (N = 5) and telencephalon lesioned (N = 10). Lesion surgeries were carried out before any experimental training. Learning procedures were run in the same sequence for all groups and under a food deprivation of 80% of the ad libitum weight. Successive discrimination was programmed by the alteration of red and yellow lights in the right key of a standard operant chamber: the red key was correlated with variable-ratio reinforcement; the yellow key was correlated with extinction. Session were run until steady-state key peck rates were obtained. The following results demonstrate discrimination learning by detelencephalated birds. Response shaping and steady-state rates required a larger number of sessions for lesioned pigeons (P < 0.05). They showed increased response rates in red (26.43 +/- 2.59) and yellow (11.17 +/- 2.86) components as compared to the non-lesioned (red: 16.51 +/- 2.0; yellow: 2.02 +/- 0.64) and sham-lesioned (red: 22.84 +/- 1.77; yellow: 4.72 +/- 1.99) groups (P < 0.05). These data show that telencephalic systems are not essential for operant discrimination learning but play a role in the modulation of discriminative behavior. Subtelencephalic systems appear to be functionally important for the organization and storage of learning.

Animals↗
PubMed1997

Effect of postweaning nutritional and environmental restrictions on discrimination learning in albino rats.

Charles Foster littermate albino rats (72) were randomized into 9 independent groups in a 3 x 3 factorial design by varying nutrition and environment each at three levels: normal nutrition, 25% nutritional restriction and 50% nutritional restriction; normal environment, 3-week environmental restriction and 6-week environmental restriction. The nutritional and environmental restrictions were imposed from the 30th day of life for 6 weeks. The animals were subsequently tested for black/white original learning followed by reversal discrimination learning in a T-maze. The results indicated significant main effects for nutrition and environment on indices of learning ability. However, the nutrition x environment interaction was not significant. Post hoc analysis revealed that moderate and severe nutritional restriction as well as long-term environmental restriction caused significant discrimination learning deficits. Short-term environmental restriction failed to produce significant effect on learning behaviour. The results are discussed in context of environmental stress effects, altered brain mechanisms and psychological changes such as increased drive level and emotionality of the animal.

Animal Nutritional Physiological Phenomena↗
PubMed2001

Finite mixture distribution models of simple discrimination learning.

Through the application of finite mixture distribution models, we investigated the existence of distinct modes of behavior in learning a simple discrimination. The data were obtained in a repeated measures study in which subjects aged 6 to 10 years carried out a simple discrimination learning task. In contrast to distribution models of exclusively rational learners or exclusively incremental learners, a mixture distribution model of rational learners and slow learners was found to fit the data of all measurement occasions and all age groups. Hence, the finite mixture distribution analysis provides strong support for the existence of distinct modes of learning behavior. The results of a second experiment support this conclusion by crossvalidation of the models that fit the data of the first experiment. The effect of verbally labeling the values on the relevant stimulus dimension and the consistency of behavior over measurement occasions are related to the mixture model estimates.

Bayes Theorem↗
PubMed2001

Impairments in visual discrimination learning and recognition memory produced by neurotoxic lesions of rhinal cortex in rhesus monkeys.

Much work on the cognitive functions of the primate rhinal (i.e. entorhinal plus perirhinal) cortex has been based on aspiration lesions of this structure, which might disrupt fibres passing nearby and through the rhinal cortex in addition to removing the cell bodies of the rhinal cortex itself. To determine whether damage limited to the cell bodies of the rhinal cortex is sufficient to impair visual learning and memory, four rhesus monkeys (Macaca mulatta) were preoperatively trained on a battery of visual learning and memory tasks, including single-pair discrimination learning for primary reinforcement, single-pair discrimination reversals, concurrent discrimination learning and reversal, and delayed matching-to-sample. Following acquisition of these tasks and a preoperative performance test, ibotenic acid was injected bilaterally into the rhinal cortex, and the monkeys were retested. Consistent with the results of studies using aspiration lesions, the monkeys were impaired on single-pair discrimination learning as well as recognition memory performance postoperatively, although reliable reversal learning impairments were not observed. The magnitude of postoperative impairment in discrimination learning was not correlated with the magnitude of postoperative impairment in recognition memory, suggesting a possible dissociation between these functions within the rhinal cortex. The correspondence of behavioural deficits following aspiration and neurotoxic lesions of the rhinal cortex validates the attribution of various cognitive functions to this structure, based on the results of studies with aspiration lesions.

Animals↗
PubMed1980

Tactile discrimination learning in the monkey: the effects of unilateral or bilateral removals of the second somatosensory cortex (area SII).

The tactile impairment in monkeys with unilateral removals of area SII is seen as possibly analogous to the rare condition of tactile agnosia. The lesions in a new series of animals with SII removals are described. The performance of 3 groups of monkeys is compared: no group differences were obtained on visual tasks (except retrieval of a moving target); minimal if any differences were obtained on inter-manual transfer of tactile learning; significant differences were found between animals with unilateral or bilateral removals of SII relative to unoperated animals at re-learning tactile discrimination tasks, irrespective of the hand being used. These findings suggest that area SII projects to a further neural system involved in somatosensory performance; and that a unilateral removal has its effect through the functional disruption of the intact SII.

Agnosia↗
PubMedDate not supplied

Effects of two ACTH analogs on successive odor discrimination learning in rats.

Olfactory discrimination learning has been shown to provide a powerful tool to investigate the mechanisms involved in the formation, storage and retrieval of information in rodent CNS. In the present study we tested the effects of two ACTH analogs, which were previously reported to influence the processes of learning and memory, on various olfactory learning tasks. The ACTH(4-9) analog HOE 427 produced an apparent increase in storage of olfactory information as shown by the difficulty experienced by the animals to rapidly reverse their behavioral responses to previously learned odors. Similarly, the ACTH (4-9) analog ORG 2766 appears to enhance the storage of olfactory information when administered either before or after the learning trials. These data are consistent with the notion that ACTH and related analogs facilitate performance in a variety of learning tasks. In addition, our results suggest possible mechanisms by which some neuroactive peptides might modulate learning and memory processes in the CNS.

Adrenocorticotropic Hormone↗
PubMedDate not supplied

Prenatal phenytoin exposure and spatial navigation in offspring: effects on reference and working memory and on discrimination learning.

Previous research has shown that rats exposed to phenytoin (PHT) in utero demonstrate abnormal circling, decreased learning, hyperactivity, and delayed air righting reflex development. The effects of prenatal PHT on offspring learning have been found on multiple-T mazes (Biel and Cincinnati types) and on spatial navigation (Morris maze). However, the specificity of the latter effects is unknown. Herein, we tested the effects of prenatal PHT in a Morris maze using six different procedures: cued versus spatial reference memory-based learning, cued versus spatial working memory-based learning, and cued versus spatial discrimination learning. PHT-exposed offspring showed increased preweaning mortality, growth reduction, and abnormal circling as noted in previous studies. PHT offspring were separated into those exhibiting circling and those not. PHT noncircling offspring demonstrated impaired reference memory-based spatial learning (acquisition and reversal), but no other effects. By contrast, PHT circling offspring demonstrated not only impaired reference memory-based spatial learning, but also impaired cued platform learning, impaired spatial discrimination, and impaired working memory-based learning. These data confirm that prenatal PHT induces a specific reference memory-based spatial learning deficit even in asymptomatic (noncircling) offspring that is distinct from the impairment induced in littermates exhibiting the circling impairment.

Analysis of Variance↗
PubMed1981

Facilitation and retardation of discrimination learning after exposure to the stimuli.

In three experiments, rats was required to learn a simultaneous discrimination in a jumping stand between horizontally and vertically striped objects. Experiment 1 showed that prior prolonged exposure to these stimuli in the rats' home cages helped them to learn the discrimination. Experiment 2 showed that a briefer period of exposure (1 hr per day for 50 days) was equally effective when the stimuli were presented in the home cage but produced a retardation of discrimination when the stimuli were presented in the jumping stand itself. Experiment 3 demonstrated that prior exposure to the jumping stand was not in itself enough to produce a retardation of subsequent discrimination learning. Some implications of these results for current theories of perceptual learning and latent inhibition are discussed.

Animals↗
PubMed1991

Amygdalectomy and ventromedial prefrontal ablation produce similar deficits in food choice and in simple object discrimination learning for an unseen reward.

Cynomolgus monkeys (Macaca fascicularis) with either bilateral amygdalectomy or bilateral ventromedial prefrontal cortical ablations showed abnormal choices between apple, lemon, olive, and meat. Not only did they choose meat or olive more often than normal animals, but also their choices were less consistent from trial to trial than the normal animals' choices were. The same animals were subsequently tested for their ability to learn 2-choice simultaneous visual discriminations between objects which they could suck. The positive object yielded fruit juice, which entered the mouth directly without being seen. Both groups of animals with lesions were severely impaired in this discrimination learning task. The reason why amygdalectomy has little effect on simple object discrimination learning in the Wisconsin General Test Apparatus, we suggest, is that the animal can there associate the visual discriminanda with the visual properties of the food reward, a mechanism which is not available when the reward is unseen. These results add to existing evidence of a close functional relationship between the amygdala and the ventromedial prefrontal cortex, and they support the proposal, derived from previous work, that the amygdala is important for associating visual stimuli with the incentive value of reinforcers.

Amygdala↗
PubMed2004

Sound sequence discrimination learning is dependent on cholinergic inputs to the rat auditory cortex.

In rat auditory cortex (AC) slices, synaptic potentiation following heterosynaptic stimulation is affected by the stimulus sequence used for induction. It was hypothesized that this sequence-dependent plasticity might be partly involved in the cellular mechanisms underlying sound sequence discrimination. Sequence dependence is abolished by muscarinic receptor antagonists. Therefore, dependence of sound sequence discrimination learning on cholinergic inputs to the rat AC was investigated. Rats were trained to discriminate the sequences of two sound components and a licking behavior in response to one of two possible sequences was rewarded with water. Atropine, a muscarinic receptor antagonist, attenuated sound sequence discrimination learning. The acquired sound sequence discrimination was not affected by atropine. Injections of the cholinergic immunotoxin 192IgG-saporin into the AC suppressed sound sequence discrimination learning, while discrimination between the two sound components was not affected. An inhibitor of M-current, linopirdine, restores the sequence dependence of synaptic potentiation in the AC slices suppressed by atropine. In this study, sound sequence discrimination learning attenuated by 192IgG-saporin was also restored by linopirdine. These similarities between sequence dependent plasticity in the AC slices and sound sequence discrimination learning support the hypothesis that the former is involved in the cellular mechanisms underlying the latter.

Acetylcholine↗