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PubMed1999

Selective discrimination learning impairments in mice expressing the human Huntington's disease mutation.

Cognitive decline is apparent in the early stages of Huntington's disease and progressively worsens throughout the course of the disease. Expression of the human Huntington's disease mutation in mice (R6/2 line) causes a progressive neurological phenotype with motor symptoms resembling those seen in Huntington's disease. Here we describe the cognitive performance of R6/2 mice using four different tests (Morris water maze, visual cliff avoidance, two-choice swim tank, and T-maze). Behavioral testing was performed on R6/2 transgenic mice and their wild-type littermates between 3 and 14.5 weeks of age, using separate groups of mice for each test. R6/2 mice did not show an overt motor phenotype until approximately 8 weeks of age. However, between 3.5 and 8 weeks of age, R6/2 mice displayed progressive deterioration in specific aspects of learning in the Morris water maze, visual cliff, two-choice swim tank, and T-maze tasks. The age of onset and progression of the deficits in the individual tasks differed depending on the particular task demands. Thus, as seen in humans with Huntington's disease, R6/2 mice develop progressive learning impairments on cognitive tasks sensitive to frontostriatal and hippocampal function. We suggest that R6/2 mice provide not only a model for studying cognitive and motor changes in trinucleotide repeat disorders, but also a framework within which the functional efficacy of therapeutic strategies aimed at treating such diseases can be tested.

Animals↗
PubMed1990

The role of information about the response-outcome relation in instrumental discrimination learning.

In 4 instrumental learning experiments, the hierarchical organization among responses (R), outcomes (O), and stimuli (S) was examined. Each experiment explored the possibility that S becomes associated with the R-O relation by providing information about that relation. In each case, an analogy was developed to a paradigm that has been important for concluding that informational relations affect Pavlovian conditioning. Experiments 1 and 2 found an effect of the information that S provides about the R-O relation, using paradigms analogous to blocking and contingency experiments. Experiments 3 and 4 demonstrated a similar result, using a paradigm like that of relative validity. In each case, the experiments pointed to the importance of the information that S gives about the R-O relation, rather than about the individual R and O elements.

Animals↗
PubMed1975

Effects of within-stimulus and extra-stimulus prompting on discrimination learning in autistic children.

Two different prompting procedures to teach visual and auditory discriminations to autistic children were compared. The first involved presenting an added cue as an extra-stimulus prompt. This required the child to respond to both prompt and training stimulus. The second involved the use of a within-stimulus prompt. This consisted of an exaggeration of the relevant component of the training stimulus and thus did not require that the child respond to multiple cues. The results indicated that (1) children usually failed to learn the discriminations without a prompt, (2) children always failed to learn when the extra-stimulus prompt was employed but usually did learn with the within-stimulus prompt, and (3) these findings were independent of which modality (auditory or visual) was required for the discrimination.

Achievement↗
PubMed1988

Stimulus equalization: temporary reduction of stimulus complexity to facilitate discrimination learning.

Learners with limited behavioral repertoires often have difficulty discriminating complex, multidimensional stimuli. Procedures that use gradual stimulus change have been developed to facilitate such discrimination, but these procedures are often difficult to implement and costly in terms of teacher time and expertise. This study investigated the effectiveness of stimulus equalization, an error reduction procedure involving an abrupt but temporary reduction of dimensional complexity. A microcomputer was used for stimulus presentation, data collection, and response analyses. Preschool children's responding to groups of four stimuli differing along several dimensions was analyzed on four discrimination tasks under several conditions. On each task, one element from a different dimension was programmed as correct. When trial-and-error training failed to establish the discrimination, equalization training began in which differences in the irrelevant dimensions were eliminated. When correct responding developed, the differences were reinstated, and correct performance was maintained in all but one instance. In a repeated acquisition design, stimulus equalization was found to be generally effective and superior to the trial-and-error method. Implications for computer-assisted instruction are discussed.

Attention↗
PubMed1984

Familiar contextual odors promote discrimination learning in preweanling but not in older rats.

For rats 16- or 28-days-old postnatal, we tested the source of the facilitation in instrumental learning provided by odors from home nest materials. Three experiments confirmed that acquisition of a spatial discrimination (to escape footshock) was facilitated not only by the presence of typical nest odors in the training context, but also by the presence of a non-rat odor (banana) to which the animals had been familiarized for 4 hr/day for 7 days. There was a borderline tendency for a similar facilitation after familiarization to the latter odor for only 10 min. These effects occurred for rats 16 days postnatal but not for those 28 days old. The experiments also confirmed that the prior exposure to non-rat odors did not in itself, in the absence of that odor during learning, affect discriminated escape learning, and that enhanced affinity for a contextual odor is not a sufficient condition for enhancement of learning in its presence. There was some indication that the 16-day-old rat was more likely to select a discriminative odor to guide their choice of spatial locations if a familiar contextual odor was present.

Aging↗
PubMed1996

Lateral asymmetries due to preferences in eye use during visual discrimination learning in chicks.

Chicks were trained to discriminate between two boxes of the same colour (white) on the basis of their positions using the pecking response. Some chicks were trained to peck at the box on their right side, some at the box on their left side. They were then retrained with two boxes of different colours (one red the other green): in one group of chicks the position of the two boxes was randomly alternated in the various trials (thus making colour a conspicuous but irrelevant cue), in the other it was maintained unchanged. A control group was retrained with two white boxes identical to those used during training. In all of the three groups chicks had to discriminate between the two boxes on the basis of their positions. During training, chicks took less trial and errors to learn when the positive box was placed on their right side and the same occurred during retraining with boxes that maintained a fixed position and during retraining in the control condition. During retraining with position alternation, on the contrary, chicks took less trials and errors to learn when the positive box was placed on their left side. Video recording of the chicks' behaviour while approaching the boxes showed that these lateral asymmetries reflect head and body turning associated to preferences in eye use, likely due to the different specializations of contralateral brain structures. It is argued that position cues engage the right hemisphere, with consequent head turning to the right to allow lateral viewing by the left eye; object-specific cues engage the left hemisphere, with consequent head turning to the left to allow lateral viewing by the right eye.

Animals↗
PubMed1994

The effects of lesions to the fornix and dorsomedial thalamus on concurrent discrimination learning by rats.

Rats with lesions in either the fornix or the thalamic nucleus medialis dorsalis were unimpaired on the acquisition of two object discrimination tasks. The same animals were then tested on a concurrent learning task in which various object discriminations were presented at different rates during the same session. This arrangement was primarily designed to minimise any response bias effects. Animals were able to acquire the various concurrent tasks, even when only one trial per day was given for a particular discrimination. It was found that fornix lesions had little or no effect and only produced a mild impairment when the rate of stimulus presentation resembled that used in typical concurrent tasks. Lesions of medialis dorsalis produced a more general, but again mild, deficit. In a final task, the animals were trained to discriminate between two stimuli composed of common elements arranged in different spatial combinations. Fornix lesions impaired acquisition of this spatial configural discrimination, while lesions of medialis dorsalis had a variable effect. The results indicate that fornix lesions can spare concurrent discrimination learning, and that any deficits may be related to interference effects associated with common elements in the stimuli. Lesions in medialis dorsalis appear to affect the initial learning of reward-based performance rules.

Animals↗
PubMed1998

Spatial and discrimination learning in rodents infected with the nematode Strongyloides ratti.

Recent work has shown that mice with subclinical parasitic infections suffer impaired spatial learning and memory, as assayed in an open-field water maze. Although the mechanism underlying this effect is not clear, the phenomenon has been reported following infection with both a protozoan parasite (Eimeria vermiformis) and a gastrointestinal nematode (Heligmosomoides polygyrus). In a variety of experiments, we examined the effects of a different gastrointestinal nematode, Strongyloides ratti, on the ability of rats and mice to learn a spatial or a discrimination task. Animals were tested at various stages post-infection, with different levels of infection, using different lines of S. ratti and with varying experimental protocols. All animals learned the tasks, but we found no evidence of an effect of S. ratti infection on learning or memory. Even rats infected with approximately 5000 S. ratti larvae, a dose which has an impact on rat body size, showed no deficit in learning ability. Various reasons for the conflict between our results and those previously reported for E. vermiformis and H. polygyrus are discussed. Our results show that impaired learning and memory following parasitic infection is not a ubiquitous or at least easily replicated phenomenon.

Analysis of Variance↗
PubMed1984

Chlordiazepoxide impairs the performance of a learned discrimination.

Chlordiazepoxide (CDP) (5 mg/kg) administered on four of eight sessions significantly impaired the performance of a previously learned, reinforcement-cued discrimination in male Sprague-Dawley rats. On four interspersed vehicle-injection sessions, the performance of subjects demonstrated immediate recovery and was indistinguishable from that of controls (0 mg/kg). An analysis of response components indicated that the impairment in discrimination performance was due to a "disinhibitory" effect of the drug on responding during "no-go" phases of the task. The results are discussed in the context of similarities and differences in the effect of CDP on performance and acquisition.

Animals↗
PubMed1976

Functional differentiation within the neostriatum of the rat using electrical (blocking) stimulation during discrimination learning.

Sixteen rats, eight with bipolar electrodes implanted bilaterally in the anterodorsal head of the caudate-putamen and eight with similar electrodes in the posteroventral caudate-putamen, learned a spatial and a form discrimination task and their reversals while receiving "continuous" stimulation. Rats receiving stimulation to the anterodorsal caudate-putamen were imparied on spatial reversal learning compared with the posteroventral group. On form discrimination reversal the posteroventral group were impaired compared with the anterodorsal group. This dissociation is related to the particular cortical neostriatal projection system for the region stimulated and demonstrates a behavioral differentiation in rat neostriatum comparable with that observed in the monkey.

Animals↗