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Results for “Reversal Learning”

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At least 757 records · Page 42Linked to original sources
PubMed2001

Murine lupus genetics: lessons learned.

Recent reverse genetic studies in murine lupus have taught us the following lessons: (1) Lupus is extremely polygenic; (2) A single locus may be associated with many different phenotypes; (3) What appears to be a single locus may turn out to be a cluster of loci; (4) Different loci facilitate different immunologic steps leading to lupus; (5) Epistatic interactions between loci may engender novel autoimmune phenotypes; (6) Whereas some loci may be pathogenic, others may confer disease resistance; (7) Whereas the expression of some loci is sex-dependent, the expression of others clearly is not; (8) Two or more loci may have an impact on the same phenotype; (9) Lupus susceptibility loci appear to co-cluster with other autoimmunity susceptibility loci; (10) Lupus genes are likely to be polymorphic alleles with subtle impacts, rather than outright mutations with extreme functions. In contrast, forward genetic studies have revealed that molecules that impact apoptosis, the clearance of apoptotic cells, B-cell or T-cell function, and end-organ pathology can all potentially contribute to lupus. Collectively, the loci and genes identified by these two different approaches factorize into a few distinct pathways leading to lupus. Delineating the molecular mediators of these distinct checkpoints is the challenge that lies ahead.

Animals↗
PubMed1997

A rat model of spontaneously arrested hydrocephalus. A behavioural study.

HTX rats with congenital hydrocephalus that survived for more than 2 months are termed spontaneously arrested hydrocephalic rats. These rats showed impairment in learning, a reverse light-dark discrimination task in a Y-maze. A clear relationship between learning impairment and ventricular dilatation was observed in spontaneously arrested hydrocephalic animals. The usefulness and limitations of HTX-rats as an animal model of spontaneously arrested hydrocephalus are discussed.

Animals↗
PubMedDate not supplied

Impairments in acquisition and reversals of two-choice discriminations by aged rhesus monkeys.

The ability to learn and perform reversals of two object, two patterns, and one spatial discrimination was examined in eight aged (28-34 years), and four adult (8-13 years) behaviorally naive monkeys. As a group, the aged monkeys demonstrated significant difficulties in learning and reversing some of the visual discrimination problems, but had no difficulty learning or reversing the spatial discrimination. Additional analyses revealed that an impairment in learning an object discrimination by the aged monkeys was characterized by a prolonged period of chance performance, and the impairments in performing visual discrimination reversals was related to difficulties in two distinct stages of reversal learning. Despite age-related differences, there was considerable variability in performance among the aged monkeys. These experiments provide the first evidence of significant impairments in learning and reversing visual discriminations by aged monkeys that have not had prior exposure to complex behavioral tasks.

Aging↗
PubMed2003

Use of position and feature cues in discrimination learning by the whiptail lizard (Cnemidophorus inornatus).

Animals use a variety of cue types to locate and discriminate objects. The ease with which particular cue types are learned varies across species and context. An enormous literature contains comparisons of spatial cue use to use of other cue types, but few experiments examine the ease with which various nonspatial cues are learned. In addition, few studies have examined cue use in reptiles. Thus, the authors compared whiptail lizards' (Cnemidophorus inornatus) ability to learn and reverse a discrimination using either position (left or right) or visual feature cues. Lizards learned and reversed the task using position cues faster and with greater accuracy than using feature cues.

Animals↗
PubMed1991

Effect of dihydroergotoxine, a cerebral vasodilator, on cognitive deficits induced by prenatal undernutrition and environmental impoverishment in young rats.

The study was conducted on 64 Charles Foster strain albino rats, which were equally distributed into 8 evenly matched groups, following a 2 x 2 x 2 factorial design, by varying three independent factors at two levels: nutrition--normal and undernutrition; environment--enrichment and impoverishment, and drug treatment--vehicle and dihydroergotoxine (3 mg/kg, i.p.). Prenatal undernutrition was induced by restricting the mother's food intake. The environmental enrichment/impoverishment and the vehicle/dihydroergotoxine treatments were given during the postweaning period of the pups. The rats were subjected to original and subsequent reversal brightness discrimination learning tests in a single unit T-maze at 8-9 weeks of age. Thereafter, the animals were tested for passive avoidance learning. The results indicate that undernutrition caused significant original and reversal discrimination learning, deficits whereas environmental deprivation attenuated only the original discrimination learning performance. Dihydroergotoxine treatment facilitated the learning performance of rats in both the original and reversal learning tests. Nutritional, environmental and dihydroergotoxine treatments had no effect on the retention of the passive avoidance learning, both at 24 hr and 1 week intervals. Dihydroergotoxine treatment attenuated the learning deficits induced by prenatal undernutrition. The results indicate that dihydroergotoxine is not likely to be useful in cognitive deficits, induced by malnutrition, though it facilitated learning acquisition, since it had no effect on retention.

Animals↗
PubMed2002

Impaired learning of a color reversal task after NMDA receptor blockade in the pigeon (Columba livia) associative forebrain (neostriatum caudolaterale).

The neostriatum caudolaterale (NCL) in the pigeon (Columba livia) forebrain is a multisensory associative area and a functional equivalent to the mammalian prefrontal cortex (PFC). To investigate the role of N-methyl-D-aspartate (NMDA) receptors in the NCL for learning flexibility, the authors trained pigeons in a color reversal task while locally blocking NMDA receptors with D,L-2-2-amino-5-phosphonovalerate (AP-5). Controls received saline injections. AP-5-treated pigeons made significantly more errors and showed significantly stronger perseveration in a learning strategy applied by both groups but were unimpaired in initial learning. Results indicate that NMDA receptors in the NCL are necessary for efficient performance in this PFC-sensitive task, and that they are involved in extinction of obsolete information rather than in acquiring new information.

Animals↗
PubMed1981

Syndrome produced by lesions of the amygdala in monkeys (Macaca mulatta).

Behavioral effects of subtotal amygdaloid lesions were investigated in an attempt to dissociate some of the abnormalities seen after total amygdalectomy. Twelve monkeys received bilateral stereotaxic lesions centered in the basolateral amygdala, lateral amygdala, dorsal amygdala, or the temporal white matter lying adjacent to the lateral amygdala. These monkeys were compared with others with control operations. The control monkeys then received total amygdaloid lesions (AMX). The AMX monkeys exhibited the typical amygdaloid syndrome of hypoemotionality, meat eating, coprophagia, and excessive exploration. In contrast, the monkeys with subtotal amygdaloid lesions would not eat meat or feces, though they were more willing than control monkeys to investigate inanimate objects. Although minor changes in affect were observed, the extreme emotional changes seen after total amygdalectomy were found only in the monkey with the largest subtotal lesion. Only those animals that were hypoemotional showed a deficit in learning successive reversals of an object discrimination. This close association suggests that both the hypoemotionality and the successive reversal deficit arise from the same underlying dysfunction.

Amygdala↗
PubMed1986

Visual learning and retention examined with reversible cold lesions of the anterior temporal lobe.

Learning and retention of visual discriminations and delayed match-to-sample (DMS) performance were examined in monkeys while cooling the anterior temporal lobe. Four cryodes were bilaterally implanted on the dura overlying the anterior temporal cortex, an anterior pair covered the temporal pole (TP) and a posterior pair covered the anterior inferior temporal cortex (AIT). The visual discriminations were examined under 4 different test combinations of cooling and not cooling the anterior temporal lobe. Learning deficits were produced by cooling either TP or AIT. Once learned, there was no difficulty recalling discriminations under cooling or control conditions for either TP or AIT. There was a deficit during cooling in the recall of discriminations that had been learned prior to cooling TP or AIT. The animals were then trained and tested on a DMS task at a 0-s and 10-s delay. They performed at chance when either TP or AIT was cooled in the 0-s delay. Only TP was cooled at the 10-s delay and it also resulted in chance performance. The cold lesions demonstrated that the anterior temporal cortex, i.e. TP and AIT, has an important role in the processes of learning and, to a lesser extent, retention of visual information. The results also support previous findings regarding the participation of this area in DMS performance. The findings were discussed in relation to the amnesic syndrome.

Animals↗