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PubMed1991

Blocking between occasion setters and contextual stimuli.

Two appetitive conditioning experiments with rats used a blocking procedure to compare the mechanisms through which contexts and positive occasion setters control responding to conditioned stimuli (CSs) in discrimination learning. In Experiment 1, a light (L) initially set the occasion for food reinforcement of a tone CS (T). Then a compound of L and a novel context signaled reinforcement of T. Previous learning about L blocked contextual control of responding to T. Blocking was not due to simple excitation conditioned to L during discrimination training; comparable excitation to L in a control group did not result in blocking. Conversely, in Experiment 2, initial learning about the context blocked the acquisition of occasion setting to L. Excitation conditioned to the context could not account for the blocking. In general, the results suggest that contexts and occasion setters may control responding to CSs through similar mechanisms.

Animals↗
PubMed2006

Cortical and subcortical sides of auditory rhythms and pitches.

It is commonly assumed that different perceptual qualities arising from sensory stimuli depend on their physical nature being transformed by specific peripheral receptors, for example, colour, vibration or heat. A notable unexplained exception is the low and high repetition rates of any sound perceived as rhythm or pitch, respectively. Using auditory discrimination learning in bilaterally auditory cortex ablated animals, we demonstrate that the perceptual quality of sounds depends on the way the brain processes stimuli rather than on their physical nature. In this context, cortical and subcortical processing steps have different roles in analysing different aspects of sounds with the complete analysis accomplished not before information converges in the auditory cortex.

Acoustic Stimulation↗
PubMed1989

Personality and conditioning: a test of four models.

Four experiments were conducted to test hypotheses derived from 4 alternative models of individual differences in instrumental conditioning. A standard go--no-go discrimination learning task was used in each of the 4 experiments. The results indicate that individual differences in performance of this discrimination are more consistently and strongly associated with impulsivity and anxiety than with extraversion and neuroticism. In each of the experiments, high anxiety hindered the learning of a go--no-go discrimination more among high impulsive Ss than among low impulsive Ss, and in 2 of the experiments high anxiety actually facilitated learning among low impulsive Ss. These findings are incompatible with Eysenck's and Gray's hypotheses regarding extraversion but are not inconsistent with Newman's. Aspects of these results do support Spence's and Gray's models of anxiety and instrumental conditioning. However, both of these models were contradicted by other trends in the data. A modification of Gray's model of impulsivity and anxiety that emphasizes the role of expectancies was proposed to fit these data.

Anxiety↗
PubMed1980

Functional lateralization of the chicken forebrain revealed by use of intracranial glutamate.

By injecting monosodium L-glutamate into either one of the forebrain hemispheres of the developing chicken brain and examining the behavioural effects which ensue, it has been possible to demonstrate that there is functional lateralization for control of a number of behaviours. Glutamate treatment of the left hemisphere retards visual discrimination learning and auditory habituation, as does glutamate treatment of both hemispheres, but treatment of the right hemisphere is without effect on these behaviours. An imbalance generated by administering glutamate to the left hemisphere causes a marked increase in aggressive and sexual behaviour, which does not occur either after treatment of both hemispheres or treatment of the right hemisphere. A preliminary study on the distribution of radioactive glutamate is also reported.

Aggression↗
PubMed1964

VISUAL FUNCTION OF THE FOREBRAIN COMMISSURES IN THE CHIMPANZEE.

Interocular transfer of learned pattern discrimination tasks in chimpanzees with sectioned optic chiasma is dependent on the forebrain commissures. This function is sustained by the splenium and the anterior commissure, the former pathway being the more capable.

Animals↗
PubMedDate not supplied

Dietary enrichment counteracts age-associated cognitive dysfunction in canines.

Advanced age is accompanied by cognitive decline indicative of central nervous system dysfunction. One possibly critical causal factor is oxidative stress. Accordingly, we studied the effects of dietary antioxidants and age in a canine model of aging that parallels the key features of cognitive decline and neuropathology in humans. Old and young animals were placed on either a standard control food, or a food enriched with a broad spectrum of antioxidants and mitochondrial enzymatic cofactors. After 6 months of treatment, the animals were tested on four increasingly difficult oddity discrimination learning problems. The old animals learned more slowly than the young, making significantly more errors. However, this age-associated decline was reduced in the animals fed the enriched food, particularly on the more difficult tasks. These results indicate that maintenance on foods fortified with complex mixtures of antioxidants can partially counteract the deleterious effects of aging on cognition.

Aging↗
PubMed1976

Pigeons learn the concept of an "A".

Pigeons learned to discriminate between "A"S and "2"s in eighteen different typefaces. They subsequently showed excellent transfer to twenty-two typefaces that they had not previously seen; one pigeon was tested with handwritten letters and responded correctly to them also. Pigeons' responses to "A's and "2's with parts removed suggested that their performance was controlled by several features, none of which alone could be considered necessary or sufficient. A test in which birds were shown other letters of the alphabet supported this conclusion. It appears that the original discrimination was learned as what Ryle calls a "polymorphous concept".

Animals↗
PubMed2000

Changes in functional connectivity in orbitofrontal cortex and basolateral amygdala during learning and reversal training.

Interconnections between orbitofrontal cortex (OFC) and basolateral amygdala (ABL) are critical for encoding and using associative information about the motivational significance of stimuli. Previously, we reported that neurons in OFC and ABL fired selectively to cues during odor discrimination learning and reversal training. Here we conducted an analysis of correlated firing in the cell pairs recorded in the previous study. Correlated firing during the intertrial intervals was compared across task phases during different phases of acquisition and reversal learning. Changes in correlated activity during initial learning and subsequent accurate performance on the discrimination problems closely resembled the changes in odor selectivity in OFC and ABL reported earlier. Increased correlated firing was most pronounced in OFC during accurate go, no-go performance in the postcriterion phase of performance, whereas correlated firing in ABL increased primarily during an earlier phase of learning. In contrast, findings during subsequent reversal training diverged from our earlier report in which odor selectivity diminished in OFC and reversed in ABL. When the reinforcement contingencies of the odors were reversed after the rat had learned the original associations, correlated firing further increased significantly in OFC but remained stable in ABL. This evidence that associative encoding increments with reversal learning in OFC suggests that the original associations, although not expressed as stimulus driven activity, may be maintained within the network as new associations are acquired.

Amygdala↗
PubMed1976

Free radical theory of aging: effect of dietary fat on central nervous system function.

Free radical reactions have been implicated in aging. A rise in the level of random free radical reactions in a biologic system might have a greater effect on the central nervous system (CNS) than elsewhere, partly because of the presence of glial cells and the unique connections between neurons. To evaluate this possibility, some animal experiments were conducted. The initial experiment involved old male Sprague-Dawley rats fed (since shortly after weaning) with semisynthetic diets characterized by fat differing in amount or degree of unsaturation. The number of errors made in a Hebb-Williams maze was determined and found to be higher as the amount or degree of unsaturation of the fat was increased. Likewise rats aged 6 and 9 months, fed semisynthetic diets containing 20 percent by weight of lard, oleinate, or safflower oil +alpha-tocopherol performed significantly better in a discrimination learning situation (Skinner box) than did rats fed a diet containing 20 percent by weight of safflower oil. The diets employed in these studies did not have a significant effect on the mortality rates. These results are compatible with the possibility that enhancing the level of lipid peroxidation has an adverse effect on the CNS, out of proportion to the effect on the body as a whole, as measured by the mortality rate.

Aging↗
PubMed1986

Role of the supraoptic decussation in the development of asymmetry of brain function in the chicken.

The supraoptic decussation plays an important role in the development of asymmetry of brain function for visual discrimination learning in the chicken. Lesioning the decussation on day 2 has no effect on the asymmetry normally revealed by unilaterally treating either the left or right forebrain hemisphere with cycloheximide on day 4 of life. However, the lesion removes the asymmetry revealed by cycloheximide treatment on day 8 and reverses that revealed by treatment on day 10, albeit to a lesser extent. The asymmetry of learning performance between the left and right eyes present in untreated chickens tested monocularly in the second week of life is also removed by lesioning the supraoptic decussation. Thus, in the first week of life functional asymmetry is present but not dependent on left-to-right side coupling via the supraoptic decussation. The difference between lesioning during the first and second week of life may relate to the relative degree of maturation in the supraoptic decussation.

Age Factors↗
PubMed1986

Comparative neuropsychology of cortical and subcortical dementia.

The terms "cortical" and "subcortical" dementia are controversial; however, the clinical distinction between them is real. For example, although Alzheimer's and Parkinson's disease (prototypical of cortical and subcortical dementia, respectively) share clinical features, they differ in the presence of aphasia, apraxia, and agnosia in Alzheimer's disease but not in Parkinson's dementia. We review our studies aimed at clarifying the mechanisms underlying the differences between these neurological disorders. Experimental paradigms adopted from animal models were used to study the functional anatomy and neuropsychological characteristics of Alzheimer's and Parkinson's disease. The tasks administered include delayed alternation (DA) and delayed response (DR), which are sensitive to frontal system damage, and tactile discrimination learning (TOL) and reversal (TRL) paradigms sensitive to parietal system damage. Alzheimer's patients were significantly impaired on all tasks whereas Parkinsonians with dementia were impaired only on DR and TRL. Consideration of neuroanatomical and neuropsychological mechanisms involved in DA, DR, TOL, and TRL appears to have sharpened the distinction between Alzheimer's and Parkinson's dementia. Dementia in Alzheimer's disease may involve dorsolateral frontal, orbitofrontal and parietal systems. In contrast, dementia in Parkinson's disease may involve prominent dorsolateral frontal system damage.

Dementia↗
PubMed1999

Ethanol-associated olfactory stimuli reinstate ethanol-seeking behavior after extinction and modify extracellular dopamine levels in the nucleus accumbens.

BACKGROUND: Alcohol craving or automatic behavioral responses provoked by alcohol-related cues are thought to contribute to relapse risk in abstinent individuals. However, there is to date only limited direct experimental evidence that supports this hypothesis. The present study employed an operant response-reinstatement model to examine the effects of ethanol-associated environmental stimuli on alcohol-seeking behavior and extracellular dopamine (DA) levels in the nucleus accumbens (NAcc). METHODS: Male Wistar rats were prepared with intracerebral guide cannulae for microdialysis and trained to operantly self-administer ethanol in the presence of discrete olfactory discriminative stimuli (Sdelta's) signaling the availability of ethanol (10% w/v) versus a nonrewarding stimulus (a 50 microM quinine HCl solution). After the discrimination learning phase, responding for ethanol (and quinine) was extinguished by withholding the drinking solutions as well as the corresponding Sdelta's. After reaching and maintaining an extinction criterion of < or = 5 responses/session, the rats were exposed noncontingently to the ethanol and nonreward Sdelta's but without the availability of ethanol or quinine. RESULTS: The ethanol Sdelta's, but not nonreward Sdelta's, elicited significant recovery of responding. Exposure to the operant chamber during a 20 min "waiting period" before presentation of the Ss's was associated with a small but significant increase in dialysate DA levels. Subsequent exposure to the ethanol Sdelta and onset of the reinstatement session was accompanied by a small but significant decrease in DA efflux. Exposure to the nonreward Sdelta did not alter DA levels. CONCLUSIONS: The behavioral data confirm that ethanol-predictive discriminative stimuli reliably elicit ethanol-seeking behavior after extinction. The increase in DA efflux during the waiting period confirms earlier findings and suggests that anticipation of access to ethanol activates mesolimbic DA neurons. The decrease in DA efflux after onset of the reinstatement session in animals that were presented with the ethanol Sdelta's may reflect neurochemical events associated with the mismatch between the predicted (i.e., ethanol availability) and actual (i.e., absence of ethanol) stimulus events. This possibility is supported by the lack of changes in DA efflux in rats that were presented with the nonreward Sdelta's, a test condition that did not involve such a mismatch. Overall, the findings provide further evidence for a role of conditioning processes in the control of alcohol-seeking behavior and, by extension, support the hypothesis that conditioned responses to drug-related stimuli may be an important factor in chronic alcohol abuse and relapse.

Animals↗
PubMed2003

Cyclic estrogen replacement improves cognitive function in aged ovariectomized rhesus monkeys.

Among the identified risks and benefits of hormone-replacement therapy, the effects of treatment on cognitive function in postmenopausal women have proved difficult to define. Here we conducted a controlled, prospective analysis in a nonhuman primate model to test whether surgical menopause and estrogen replacement influence the cognitive outcome of normal aging. Sixteen aged rhesus monkeys were ovariectomized, and throughout the course of subsequent neuropsychological assessment, half received a regimen of low-dose, cyclic estradiol replacement. Hormone treatment substantially reversed the marked age-related impairment vehicle-injected monkeys exhibited on a delayed response test of spatial working memory. Modest improvement was also observed on a delayed nonmatching-to-sample recognition memory task. In contrast, ovariectomy exacerbated age-related deficits in object discrimination learning; the magnitude of this effect was equivalent among vehicle- and estrogen-treated monkeys. Together, these results demonstrate that ovarian hormone status can broadly influence normal cognitive aging in monkeys, affecting capacities mediated by multiple brain regions, including the prefrontal cortex and the medial temporal lobe memory system. The animal model established here should enable progress toward defining the neurobiological mechanisms that mediate the beneficial effects of estrogen on age-related cognitive decline in primates.

Aging↗
PubMed1997

Shift in the performance of 24-month-old Wistar rats in the Morris water escape task: a comparison across 36 experiments.

Spatial discrimination learning in aged rats serves as an animal model of cognitive aging. We assessed the replicability of spatial discrimination performance in the standard Morris water escape task. To this end the learning curves and the performance in a probe trial of 24-month-old outbred Wistar (HsdWin:Wu) control rats from 36 experiments were compared. These experiments had been performed at our laboratory under strictly controlled conditions over a period of 71 weeks. There was a very high variability in the learning curves between experiments. The initial performance level, i.e. the performance during the first session, did not change systematically across the 36 experiments. In contrast, the final performance level, i.e. the level reached in the fifth training session, decreased over the 71 week period, when the platform escape latency and the distance swam to reach the platform, measured as number of line crossings, were considered. In the last experiments of the series, learning curves were no longer seen: the rats did not improve their performance across the acquisition sessions. By contrast, the swimming speed and, in the probe trial, the bias for the quadrant where the platform had been positioned during training, did not change. This indicates that a decrease across experiments occurred predominantly with respect to spatial orientation performance, whereas the motor performance appeared to be unchanged. Explanations for this observation, such as differences in viability between shipments and the possible occurrence of genetic drift, are discussed.

Aging↗
PubMed1982

A computerized data management system for behavioral teratology studies.

A computerized system was designed for behavioral teratology studies to (1) generate preprinted data recording/submission forms, (2) calculate testing dates, (3) generate a daily activity schedule for testing, and (4) update established data sets for access by data entry personnel. The computer-generated forms are used to record data from the following behavioral/developmental tests for rats: pup weights, pinna detachment, surface righting, cliff avoidance, incisor eruption, eye opening, negative geotaxis, olfactory discrimination, swimming development, open field, swimming maze and operant visual discrimination learning. Three behavioral teratology studies have been conducted in our laboratory using this computerized system. The human error rates in these studies were 0.26, 0.34 and 0.46 percent, respectively. The advantages of this system include: (1) computer-calculated test dates; (2) elimination of manual data transcription; (3) more consistent data recording and scoring conditions; (4) better scheduling control; and (5) faster data entry and statistical analysis.

Animals↗
PubMed1983

Thinking disorder in depression.

This experiment demonstrated abstract reasoning deficits in depressed patients and detailed some of the components of cognition that may determine such deficits. Subjects were given a discrimination learning problem in which possible solutions had to be formulated and tested against new information. Depressed subjects performed more poorly on the task than controls. Two types of errors--inability to narrow down the set of possible solutions (poor "focusing") and perseveration on disconfirmed hypotheses--hampered the performance of depressed but not control subjects. While logic, memory, and attention were intact at an elementary level, the inability to coordinate these functions in a complex task appeared to be an important feature of the depressive impairment.

Adult↗
PubMed2002

Evaluation and development of a connectionist theory of configural learning.

A configural theory of associative learning is described that is based on the assumption that conditioning results in associations between the unconditioned stimulus and a representation of the entire pattern of stimulation that was present prior to its delivery. Configural theory was formulated originally to account for generalization and discrimination in Pavlovian conditioning. The first part of the article demonstrates how this theory can be used to explain results from studies of overshadowing, blocking, summation, and discrimination learning. The second part of the article shows how the theory can be developed to explain a broader range of phenomena, including mediated conditioning, reinforcer devaluation effects, the differential outcomes effect, acquired equivalence, sensory preconditioning, and structural discriminations.

Animals↗