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At least 1,279 records · Page 71Linked to original sources
PubMed1989

Anterior and medial thalamic lesions, discriminative avoidance learning, and cingulate cortical neuronal activity in rabbits.

Four groups of male albino rabbits were trained to perform a conditioned response (CR, stepping in an activity wheel) to an acoustic (pure tone) conditional stimulus (CS+). A 1.5-2.0 mA shock unconditional stimulus (US) delivered through the grid floor of the wheel was administered 5 s after CS+ onset, but stepping during the CS-US interval prevented the US. The rabbits were also trained to ignore a second tone (a negative conditional stimulus or CS-) of different auditory frequency than the CS+, that was presented in an irregular order on half of the conditioning trials but never followed by the US. One group had bilateral electrolytic lesions in the medial dorsal (MD) thalamic nucleus, a second group had combined bilateral lesions in the MD and the anterior thalamic nuclei, and a third group had no lesions. The fourth group was composed of rabbits with combined lesions that resulted in only partial damage in the anterior and MD nuclei. In all rabbits, multi-unit activity and field potentials were recorded from the cingulate cortical projection targets of the MD and anterior nuclei. The average rate of acquisition in rabbits with MD and partial lesions was not significantly different from that in controls, but the asymptotic performance in rabbits with lesions was significantly impaired, relative to that in controls. None of the rabbits that had the combined MD and anterior thalamic lesions reached the acquisition criterion. The average proportion of trials in which these rabbits performed avoidance responses during their final training sessions was 0.3, compared to 0.8 in controls. The unconditioned response was not significantly affected by the lesions, nor was there any indication that the lesions impaired the sensory processing of the CSs. These results and the massive training-induced neuronal discharges shown in past studies to occur in the limbic thalamic neurons indicate that these neurons are importantly involved in the circuitry that mediates discriminative avoidance conditioning in rabbits. The training-induced neuronal activity in cingulate cortex was dramatically attenuated in rabbits with lesions. Differences in the degree of this attenuation between lesion conditions and with respect to training stages were discussed in relation to a theoretical working model of limbic thalamic and cingulate cortical associative functions.

Acoustic Stimulation↗
PubMed2001

What is learned in patterning discriminations? Further tests of configural accounts of associative learning in human electrodermal conditioning.

Two Pavlovian SCR conditioning experiments investigated positive and negative patterning discriminations in humans by means of transfer tests. In Experiment 1, positive patterning (A-,B-,AB+) was trained interleaved with non-reinforced presentations of an additional stimulus (C-). Then responding to new compounds consisting of either already trained elements (AC,BC) or new elements (DE) was examined. In Experiment 2, negative patterning (A+,B+,AB-) was trained interleaved with reinforced presentations of an additional stimulus (C+). Again, we examined responding to new compounds consisting of either already trained elements (AC,BC) or new elements (DE). In both experiments the initial patterning discrimination was solved successfully. The response patterns to the test compounds in both experiments were in contradiction to configural accounts of associative learning. In positive patterning human participants seemed to utilize 'number' or some other abstract feature in preference to available concrete stimuli. In negative patterning the abstract dimension of 'separate-versus-together' or 'opposite' was used.

Adult↗
PubMed1989

Effects of lithium on appetitive discrimination in the rat.

1. The present study attempted to test the hypothesis that lithium (as chloride, 0.15 mEq/kg) promotes an attentional focus onto stimulation of high salience (Cappeliez and Moore 1988). 2. The effect of lithium treatment was studied within the context of discrimination learning in a Y-maze. 3. When the brightness cue (illuminated/dark goal arm) signalled reinforcement (food) and the spatial cue (right/left location of goal arm) acted as a distractor, lithium-treated rats showed evidence of increased readiness to focus onto the brightness cue. 4. When these experimental conditions were reversed in a second experiment, with the brightness cue now acting as a distractor, the performance of the lithium-treated rats was adversely affected. 5. These results are interpreted as supporting the hypothesis that, under the influence of this dose of lithium, rats are more likely to maintain their attention on stimulation of high salience, with accompanying reduction in the processing of peripheral stimulation. The implications of this theory for the understanding of lithium's action and manic-depressive conditions are discussed.

Animals↗
PubMed2005

Maternal immune activation leads to behavioral and pharmacological changes in the adult offspring.

Maternal exposure to viral infection has been associated with an increased risk of schizophrenia in the offspring, and it has been suggested that the maternal immune response may interfere with normal fetal brain development. Although studies in rodents have shown that perinatal viral infections can lead to neuropathological and behavioral abnormalities considered relevant to schizophrenia, it is not clear whether these consequences are due to the infection itself or to the maternal immune response to infection. We show that an induction of maternal immune stimulation without exposure to a virus by injecting pregnant dams with the synthetic cytokine releaser polyriboinosinic-polyribocytidilic acid (poly I:C) leads to abnormal behavioral and pharmacological responses in the adult offspring. As in schizophrenia, these offspring displayed excessive behavioral switching, manifested in the loss of latent inhibition and in rapid reversal learning. Consistent with the clinical pharmacology of schizophrenia, both deficits were alleviated by antipsychotic treatment. In addition, these offspring displayed increased sensitivity to the locomotor-stimulating effects of MK-801, pointing to developmental alterations of the dopaminergic and/or glutamatergic systems. Prenatal poly I:C administration did not produce learning deficits in classical fear conditioning, active avoidance, discrimination learning and water maze. These results show that the maternal immune response is sufficient to cause behavioral and pharmacological alterations relevant to schizophrenia in the adult offspring.

Animals↗
PubMed1964

ATTITUDE STATEMENTS AS POSITIVE AND NEGATIVE REINFORCEMENTS.

The finding that attraction is a function of attitude similarity has been interpreted as a special case of the effect of positive and negative reinforcements on attraction. A simple discrimination learning task was employed in which the reinforcements were attitude statements similar and dissimilar to the opinions of the subject. The presentation of similar attitude statements after each correct response and dissimilar attitude statements after each incorrect response significantly changed response probability. The hypothesis that such statements could be used as reinforcers in a learning situation was thus confirmed.

Attitude↗
PubMed1999

Nalorphine's ability to substitute for morphine in a drug discrimination procedure is a function of training dose.

Rats trained to discriminate the mu agonists fentanyl or morphine from their respective vehicles generalize to the partial mu agonist nalorphine incompletely and inconsistently. Any number of factors may influence the generalization patterns obtained, one of which being the specific dose of the full opioid agonist used during training, a factor reported to influence generalization with other partial opioid agonists. To assess if training dose influences stimulus generalization to nalorphine and to support its role in the aforementioned variability across studies, in the present experiments rats were trained to discriminate either a low (5.6 mg/kg) or a high (10 mg/kg) dose of morphine from distilled water within the taste aversion baseline of drug discrimination learning. Subjects were then given a range of doses of morphine, nalorphine, methadone, or naloxone to assess the degree of substitution (if any) of these compounds for the training dose of morphine. For all subjects, morphine fully substituted for itself, and the opioid antagonist naloxone failed to substitute for the morphine cue. Rats generalized the morphine cue to nalorphine in subjects trained at the lower dose but not in subjects trained at the higher dose. Rats generalized the morphine cue to methadone in the latter group (the high dose group), indicating that the failure to generalize to nalorphine in this group was not a general inability of an opioid agonist to substitute for morphine. Naloxone blocked morphine stimulus control in all subjects and nalorphine control in the low-dose group for which nalorphine substituted for morphine, suggesting that morphine control (and the nalorphine substitution) was based on opioid activity. These results indicate that the substitution patterns of nalorphine in morphine-trained subjects are a function in part of the dose of morphine used in training and support the position that nalorphine is a partial opioid agonist with intermediate efficacy.

Animals↗
PubMed1989

Behavioral asymmetries in visual learning of young chickens.

Two-week-old chicks were trained in a simultaneous color discrimination learning task using food reinforcement. They had to discriminate between two discs of a different color whose right-left position was alternated at random. Results showed that chicks made more errors when the nonreinforced color was placed on the left with respect to the animal's body rather than when it was placed on the right. When chicks were trained on a right-left discrimination with two discs of identical color the asymmetry disappeared. Results are discussed in relation to current evidence for functional lateralization in the avian brain.

Animals↗
PubMed2004

Deprivation of parenting disrupts development of homeostatic and reward systems in marmoset monkey offspring.

BACKGROUND: Early environment is a major determinant of long-term mental health, evidenced by the relationship between early-life neglect or abuse and chronically increased vulnerability to developmental psychopathology, including major depressive disorder (MDD). Animal studies can increase understanding of environmentally mediated causal risk processes. We describe how daily deprivation of biological parenting in primate infants disrupts development of homeostatic and reward systems central to MDD. METHODS: Nine breeding pairs of marmoset monkeys provided control twins (CON) and early-deprived twins (ED); the latter were socially isolated for 30-120 min/day on days 2-28. During the first year of life, basal urinary norepinephrine (NE) titers and cardiophysiologic activity were measured. At the end of year 1 (adolescence), automated neuropsychologic tests were conducted to measure responsiveness to changes in stimulus-reward association (simple/reversed visual discrimination learning) and to reward per se (progressive ratio [PR] reinforcement schedule). RESULTS: The ED monkeys exhibited increased basal urinary NE titers and increased systolic blood pressure relative to CON siblings. The ED monkeys required more sessions to reinstate stimulus-oriented behavior following reversal, suggesting increased vulnerability to perceived loss of environmental control; ED monkeys also performed less PR operant responses, indicating that reward was less of an incentive and that they were mildly anhedonic relative to CON. CONCLUSIONS: In marmoset monkeys, neglect-like manipulation of ED leads to chronic changes in homeostatic systems, similar to those in children and adolescents exposed to early-life adversity and in MDD, and to responses to environmental stimuli similar to those that characterize MDD.

Animals↗
PubMedDate not supplied

Brain aging in the canine: a diet enriched in antioxidants reduces cognitive dysfunction.

Animal models that simulate various aspects of human brain aging are an essential step in the development of interventions to manage cognitive dysfunction in the elderly. Over the past several years we have been studying cognition and neuropathology in the aged-canine (dog). Like humans, canines naturally accumulate deposits of beta-amyloid (Abeta) in the brain with age. Further, canines and humans share the same Abeta sequence and also first show deposits of the longer Abeta1-42 species followed by the deposition of Abeta1-40. Aged canines like humans also show increased oxidative damage. As a function of age, canines show impaired learning and memory on tasks similar to those used in aged primates and humans. The extent of Abeta deposition correlates with the severity of cognitive dysfunction in canines. To test the hypothesis that a cascade of mechanisms centered on oxidative damage and Abeta results in cognitive dysfunction we have evaluated the cognitive effects of an antioxidant diet in aged canines. The diet resulted in a significant improvement in the ability of aged but not young animals to acquire progressively more difficult learning tasks (e.g. oddity discrimination learning). The canine represent a higher animal model to study the earliest declines in the cognitive continuum that includes age associated memory impairments (AAMI) and mild cognitive impairment (MCI) observed in human aging. Thus, studies in the canine model suggest that oxidative damage impairs cognitive function and that antioxidant treatment can result in significant improvements, supporting the need for further human studies.

Aging↗