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At least 1,045 records · Page 58Linked to original sources
PubMed1986

Learning sets, discrimination reversal, and hippocampal function.

Impairments of discrimination reversal are commonly found following lesions of the hippocampal system. In a recent experiment, however, acquisition of a reversed discrimination was actually facilitated, rather than impaired, by partial lesions of the fimbria-fornix (FFX), an extrinsic fiber connection to the hippocampus. That experiment differed from most previous reversal experiments in that the discriminative stimuli were olfactory rather than spatial or visual, and 3 discriminations were given prior to the reversal of the third discrimination, rather than a single discrimination. The present experiment was designed to determine the generality of the results obtained in the olfactory experiment. Rats with partial lesions of the FFX and operated controls were tested on a series of 3 Go, No-go spatial discriminations, a reversal of the third discrimination, and 4 subsequent discriminations, in that order. Control rats acquired a learning set in the first 3 discriminations, reaching criterion on the third discrimination in fewer trials than they took on the first discrimination. Their choice accuracy was not significantly affected by the reversal and discrimination performance reached an asymptotic level after the reversal. Rats with FFX lesions also acquired a learning set in the first 3 discriminations, but they consistently took longer than control rats to learn each of the 7 discriminations. These rats were especially impaired on the reversal. These results contrast markedly with those obtained when a similar procedure was used with olfactory discriminations. Identification of the variables responsible for these differences should help distinguish those behaviors that require hippocampal function from those that do not.

Acetylcholinesterase↗
PubMed2004

Central blockade of muscarinic cholinergic receptors disrupts affective and attentional set-shifting.

Impairments in multiple aspects of attentional and executive function follow damage to cholinergic neurons in the central nervous system. Affective and attentional set-shifting represent two aspects of executive function controlled by different sectors of the prefrontal cortex. The involvement of cholinergic neural mechanisms in these aspects of executive function has not been specified. To determine whether central muscarinic cholinergic receptors were involved in affective and/or attentional set-shifting, we tested rats on a series of discrimination learning problems, which included affective (reversal learning) and attentional set (extradimensional shift)-shifting components, under the systemic influence of scopolamine, a muscarinic antagonist. Scopolamine impaired both reversal learning and extradimensional shifting, but was without effect on learning new discrimination problems that did not require an affective or attentional shift. Systemic administration of methylscopolamine, which does not cross the blood-brain barrier, did not impair affective or attentional set-shifting, indicating that the scopolamine effects were centrally mediated. These data implicate muscarinic receptors in the central nervous system in the control of executive function. Taken together with other recent data, they may also suggest an important role for cholinergic receptors outside of the neocortex in regulating these aspects of attention and executive function.

Animals↗
PubMed1996

Attention and stimulus processing in the rat.

There is little doubt that rats are an essential species in laboratory testing. Given the substantial amount of anatomical and pharmacological information which is available for this species, rats are the animal of choice for many initial neurobiological investigations of the basic mechanisms of learning and memory as well as for pharmacological screening. Indeed, the study of brain-behaviour interactions is greatly facilitated in the rat given the ease with which brain transmitter systems and structures can be selectively manipulated, in contrast to the technical difficulties involved in undertaking such techniques in non-human primates. However, when considering the processing of information that occurs during cognitive processes such as learning and memory it is important to remember that fundamental to such processes are mechanisms of attention. When considering the concept of attentional functioning, it is important to keep in mind that attention is not a unitary construct but consists of several distinct mechanisms: vigilance, divided attention and selective attention, not all of which have been adequately modelled in the rat. Furthermore, attentional processes are also involved in learning operant discrimination tasks and appear to be quite different from those involved in maintaining high levels of trained performance. Consideration of discrimination learning is important given that firstly, during such learning the animal must select from the environment those stimuli which are relevant and secondly, that this type of learning is obviously inherent in many other tests used to assess cognitive function, such as delayed matching-to-sample procedures. Such issues will therefore form the basis of the following discussion.

Animals↗
PubMed1984

Effects of different stimulus manipulations of the acquisition of word recognition in trainable mentally retarded children.

The present study was designed to assess the efficacy of different procedures for establishing transfer of stimulus control from pictorial representations to printed words in trainable mentally retarded school children. The study consisted of two experiments. In experiment 1, four training conditions were used, i.e. two conditions (stimulus shaping and stimulus connected prompt fading) in which the subjects' attention was guided to the training stimuli, and two conditions (stimulus disconnected prompt fading and no fading) in which the subjects were allowed to respond only to the prompts. The results showed that stimulus shaping and stimulus connected prompt fading were far more effective than either one of the other procedures. Subsequent analyses revealed that 1 the stimulus control of the trained words was restricted to one or two letters, and 2 in case it was restricted to one letter, this was frequently a letter other than the one used for training. Furthermore, it was noted that the learned discriminations deteriorated as time or training progressed. Experiment 2 was designed to replicate some of the findings of experiment 1, and to control for one of the variables contributing to the superior efficiency of stimulus shaping over stimulus connected prompt fading. In general, the results of this experiment confirmed those obtained in experiment 1.

Adolescent↗
PubMed1969

Linguistic structure and transposition.

Transfer of a learned discrimination along the size dimension was studied in groups of American and African tribal children. The language spoken by the African children contains an asymmetry in the expression of size comparisons that is not present in English. Contrary to theories of linguistic mediation of choice behavior, transfer choices were not related to the differing linguistic patterns; however, initial choices and post-test descriptions of choices were so related.

Child↗
PubMed1995

Factor structure of the California Verbal Learning Test in moderate and severe closed-head injury.

A factor analysis with principal components extraction and varimax rotation was performed on 19 California Verbal Learning Test age-uncorrected scores from a sample of 75 moderate and severe closed-head-injured patients. A 6-factor solution was obtained that accounted for 80% of the total variance and was similar to those reported previously. The factors were labeled General Verbal Learning, Response Discrimination, Learning Strategy, Proactive Effect, Self-monitoring, and Serial Position. Factor scores were derived and correlated with other neuropsychological measures. The General Verbal Learning factor scores were significantly correlated with those on measures of memory, complex attention, and strategy induction.

Adult↗
PubMed2005

Enhanced contrast sensitivity in auditory cortex as cats learn to discriminate sound frequencies.

To better understand the nature and time course for learning-induced cortical reorganization, we examined frequency-specific changes in auditory cortex as cats gradually improved at a difficult sound frequency discrimination task. Three adult cats were trained to discriminate between a tone pip at a fixed target frequency (S-) and a higher deviant frequency (S+). An adaptive training schedule led to an efficient estimate of the frequency discrimination threshold (FDT), which was used to track daily performance. Each cat was also implanted with an array of microwires in auditory cortex. Tone pips with different frequency and amplitude were used to map receptive fields. Onset responses were correlated with training time and the cat's ability to discriminate frequencies. Although lifetime of the neural implants varied among cats, each provided sufficient neural recording to relate at least 3 weeks of learning to response changes in the cortex. An improved FDT was associated with a differential decrease in response strength between the S- frequency and S+ frequencies. Response to the training frequencies gradually located in a local minimum compared to adjacent frequencies (p < 0.001, Cohen's d=0.50). Cortical changes were consistent with a theory of bimodal generalization that enhances stimulus classification by reducing similarity between reinforced and nonreinforced stimuli. Such a strategy may be especially appropriate during an early stage of learning to discriminate similar sounds and differ from later strategies required for fine discrimination.

Animals↗
PubMed1984

[Discrimination reversal learning in rats under the treatment of chlordiazepoxide: effect of overtraining].

A total of 48 rats were run in a black-white discrimination (original) learning task to the learning criterion of 18/20 correct responses. Correct responses were rewarded by food and a non-correction method was used. One group was intraperitoneally injected with 15 mg/kg of chlordiazepoxide (CDP) and the other with physiological saline (SAL), 30 min prior to the beginning of the daily trials. For half of the rats (NOT) of each group, reversal learning began on the next day after reaching the criterion, and for the other half (OT), 100 additional trials(overtraining) were given before the reversal. The results showed that CDP as well as overtraining significantly retarded the reversal learning. CDP had no effect on the original learning. Further analysis of the data revealed that perseverative errors early in the reversal increased significantly under the conditions of CDP and overtraining, but trials to criterion after the first occurrence of the correct response were not affected by both CDP and overtraining. These results were discussed in terms of CDP's disinhibitory action and overtraining reversal effect in such relatively easy discrimination task as in the present experiment.

Animals↗
PubMed1980

The locus of the posterior subdivision of the inferotemporal visual learning area in the monkey.

In an attempt to define the posterior subdivision of the inferotemporal visual learning area more precisely than before, pattern discrimination retention, serial object discrimination learning and concurrent object discrimination learning were tested in 16 monkeys with lesions in one of four different cytoarchitectural areas; TEO, OA, OB and OC, and in five unoperated monkeys. Marked impairment was found only in pattern discrimination retention and only in the monkeys with lesions of area TEO. It was concluded that the posterior limit of the inferotemporal visual learning area is at the ascending limb of the inferior occipital sulcus, and that the posterior subdivision thus comprises the single anatomical area TEO and does not extend into areas OA and OB.

Animals↗
PubMed1978

Visual recognition in mentally retarded adolescents: cue value and instruction effects.

Recognition scores for positive and negative discriminative stimuli tested after a single trial through a discrimination problem list indicated that the frequency theory shown by Ekstrand, Wallace, and Underwood (1966) to account for the verbal discrimination learning of nonretarded adults may also hold for the visual-discrimination learning of mentally retarded persons (MA 5 to 8 and MA 8 to 11 years). In addition, retarded subjects correctly recognized the stimuli the stimuli more often after a simple inspection trial than after a standard discrimination-learning trial, indicating that they encoded the stimuli differently depending on the instructional set. The encoding difference was mediated by looking patterns. Both MA and serial position of stimuli on presentation and on test affected recognition.

Child↗
PubMed1991

Muscarinic receptor binding increases in anterior thalamus and cingulate cortex during discriminative avoidance learning.

Training-induced neuronal activity develops in the mammalian limbic system during discriminative avoidance conditioning. This study explores behaviorally relevant changes in muscarinic ACh receptor binding in 52 rabbits that were trained to one of five stages of conditioned response acquisition. Sixteen naive and 10 animals yoked to criterion performance served as control cases. Upon reaching a particular stage of training, the brains were removed and autoradiographically assayed for 3H-oxotremorine-M binding with 50 nM pirenzepine (OXO-M/PZ) or for 3H-pirenzepine binding in nine limbic thalamic nuclei and cingulate cortex. Specific OXO-M/PZ binding increased in the parvocellular division of the anterodorsal nucleus early in training when the animals were first exposed to pairing of the conditional and unconditional stimuli. Elevated binding in this nucleus was maintained throughout subsequent training. In the parvocellular division of the anteroventral nucleus (AVp), OXO-M/PZ binding progressively increased throughout training, reached a peak at the criterion stage of performance, and returned to control values during extinction sessions. Peak OXO-M/PZ binding in AVp was significantly elevated over that for cases yoked to criterion performance. In the magnocellular division of the anteroventral nucleus (AVm), OXO-M/PZ binding was elevated only during criterion performance of the task, and it was unaltered in any other limbic thalamic nuclei. Specific OXO-M/PZ binding was also elevated in most layers in rostral area 29c when subjects first performed a significant behavioral discrimination. Training-induced alterations in OXO-M/PZ binding in AVp and layer Ia of area 29c were similar and highly correlated.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Associative visual learning, color discrimination, and chromatic adaptation in the harnessed honeybee Apis mellifera L.

We studied associative visual learning in harnessed honeybees trained with monochromatic lights associated with a reward of sucrose solution delivered to the antennae and proboscis, to elicit the proboscis extension reflex (PER). We demonstrated five properties of visual learning under these conditions. First, antennae deprivation significantly increased visual acquisition, suggesting that sensory input from the antennae interferes with visual learning. Second, covering the compound eyes with silver paste significantly decreased visual acquisition, while covering the ocelli did not. Third, there was no significant difference in the visual acquisition between nurse bees, guard bees, and foragers. Fourth, bees conditioned with a 540-nm light stimulus exhibited light-induced PER with a 618-nm, but not with a 439-nm light stimulus. Finally, bees conditioned with a 540-nm light stimulus exhibited PER immediately after the 439-nm light was turned off, suggesting that the bees reacted to an afterimage induced by prior adaptation to the 439-nm light that might be similar to the 540-nm light.

Acclimatization↗