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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↗
PubMed2002

Limbic thalamic lesions, appetitively motivated discrimination learning, and training-induced neuronal activity in rabbits.

A substantial literature implicates the anterior and mediodorsal (limbic) thalamic nuclei and the reciprocally interconnected areas of cingulate cortex in learning, memory, and attentional processes. Previous studies have shown that limbic thalamic lesions severely impair discriminative avoidance learning and that they block development of training-induced neuronal activity in the cingulate cortex. The present study investigated the possibility that the limbic thalamus and cingulate cortex are involved in reward-based discriminative approach learning, wherein head-extension responses yielding oral contact with a drinking spout that was inserted into the conditioning chamber after a positive conditional stimulus (CS+) were reinforced with a water reward but responses to the spout after a negative conditional stimulus (CS-) were not reinforced. In this task, the rabbits learned primarily to omit their prepotent responses to the spout on CS- trials. Acquisition was severely impaired in rabbits given limbic thalamic lesions before training. As during avoidance learning, posterior cingulate cortical neurons of control rabbits developed learning-related neuronal responses to task-relevant stimuli, but this activity was severely attenuated in rabbits with lesions. These results support a general involvement of the cingulothalamic circuitry in instrumental approach and avoidance learning. The fact that learning consisted of response omission indicated that the cingulothalamic role is not limited to acquisition or production of active behavioral responses, such as locomotion. It is proposed that cingulothalamic neurons mediate associative attention, wherein enhanced neuronal responses to stimuli associated with reinforcement facilitate the selection and production of task-relevant responses.

Acoustic Stimulation↗
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↗
PubMed2002

Crossed unilateral lesions of temporal lobe structures and cholinergic cell bodies impair visual conditional and object discrimination learning in monkeys.

Monkeys with excitotoxic lesions of the CA1/subiculum region in the right hemisphere and with immunotoxic lesions of the cholinergic cells of the diagonal band in the left hemisphere were impaired on a visual conditional task. In this task, correct choice of one of two objects depends on which of two background fields both objects are presented against, irrespective of the spatial positions of the objects. They were not impaired on simple object or shape discrimination tasks. The pattern of impairments is the same as that seen after bilateral excitotoxic lesions of CA1/subiculum, implying that the diagonal band lesion disables the ipsilateral CA1/subiculum. It also argues that CA1/subiculum, sustained by its cholinergic input, is necessary for some forms of nonspatial conditional learning. Addition of an inferotemporal (IT) cortical ablation to the left hemisphere did not affect simple visual discrimination learning, although all the monkeys then failed to learn a new visual conditional task. This demonstrates that intact IT cortex in only one hemisphere is sufficient to sustain simple visual discrimination learning but implies that the cholinergic input and the inferotemporal cortical input to the hippocampus both contribute to visual conditional learning. The subsequent addition of an immunotoxic lesion of the basal nucleus of Meynert in the right hemisphere resulted in an additional impairment on a difficult shape discrimination. This argues that it is the cholinergic projection to the inferotemporal cortex, rather than to the rest of the cortex, which contributes to visual discrimination learning and memory.

Animals↗