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At least 739 records · Page 41Linked to original sources
PubMed1996

Facilitation of conditioned odor aversion by entorhinal cortex lesions in the rat.

This study examined the role of the entorhinal cortex (EC) in conditioned odor aversion learning (COA). Lateral EC lesions did not impair but rather facilitated COA. In the experiments the delay separating the odor cue presentation from the subsequent toxicosis was varied during acquisition. EC-lesioned rats demonstrated COA for delays up to 2 hr, whereas sham-operated rats displayed COA only if toxicosis immediately followed the odor cue. This facilitation was not dependent on the intensity of the odor and corresponded to a facilitated long-delay learning. EC lesion did not affect conditioned taste aversion, confirming that the facilitation effect does not correspond to a general facilitation of conditioned aversion learning. Taken together, these results indicate that the removal of the EC may allow odor-toxicosis associations across longer delays by extending the duration of the olfactory trace.

Animals↗
PubMed2005

Amygdala central nucleus function is necessary for learning, but not expression, of conditioned auditory orienting.

In Pavlovian appetitive conditioning, rats often acquire 2 classes of conditioned responses: those whose form is determined by the reinforcer, and those whose form is determined by characteristics of the conditioned stimulus (CS). Consistent with the results of previous lesion studies, reversible inactivation of amygdala central nucleus function during pairings of an auditory CS with food prevented the acquisition of conditioned orienting responses specific to auditory CSs, whereas food-related conditioned behaviors were acquired normally. Neither inactivation nor posttraining neurotoxic lesions of the central nucleus affected the expression of previously acquired conditioned orienting. Thus, although the central nucleus is critical to the acquisition of information required for conditioned orienting to auditory cues, it is not needed for maintaining this information for later use.

Amygdala↗
PubMed1993

Context familiarity and delayed conditioned taste aversion in young-adult and old-age rats.

Familiarity with a conditioning context different from the home-cage environment was examined in immediate and delayed (3-hr.) conditioned taste aversion (CTA) learning for young-adult (90-120 days) and old-age (680-750 days) female Wistar albino rats. Context familiarity increased CTA for young adults at the 3-hr. delay. Old-age rats showed no aversion at 3-hr. delays. Results suggest that home-cage cues may be used in mediating long-delay CTA and that the role of these cues may differ with age.

Aging↗
PubMed2003

The multifaceted nature of unsupervised category learning.

A substantial portion of category-learning research has focused on one learning mode--namely, classification learning (a supervised learning mode). Subsequently, theories of category learning have focused on how the abstract structure of categories (i.e., the co-occurrence patterns of feature values) affects acquisition. Recent work in supervised learning has shown that a learner's interactions with the stimulus set also plays an important role in acquisition. The present study extends this work to unsupervised learning situations involving simple one-dimensional stimuli. The results suggest that categorization performance is a function of both learning mode (i.e., study conditions) and learning problem (i.e., category structure). Unsupervised learning, like supervised learning, appears to be multifaceted, with different learning modes best paired with certain learning problems.

Adult↗
PubMed1990

[Effect of conditioned-reflex bilateral avoidance learning on lipid components of the rat brain].

The active avoidance training of rats resulted in a depletion of lipid peroxidation (LPO) products in cerebral cortex. LPO inhibition was also shown in cerebral cortex of "active control" group receiving +non-combined stimuli (the effect of short-term stress). LPO inhibition was more pronounced in rats staining a training criterion compared to rats which received combined stimuli but did not reach the criterion. In the active control group LPO inhibition was accompanied by total phospholipids accumulation and cholesterol depletion in cortical lipid extracts. Irrespective of attaining the criterion in all rats trained for active avoidance the accumulation of cholesterol was seen. Active avoidance training affected also the phospholipid composition of cerebral cortex.

Animals↗
PubMed1998

Classical conditioning, differential conditioning, and second-order conditioning of the Aplysia gill-withdrawal reflex in a simplified mantle organ preparation.

Nonassociative learning was previously examined in a simplified preparation consisting of the isolated mantle organs and abdominal ganglion of Aplysia californica that is advantageous for relating cellular events to behavior (T. E. Cohen, S. W. Kaplan, E. R. Kandel, & R. D. Hawkins, 1997). Results of the current study show that the gill-withdrawal reflex in that preparation also underwent 2 associative forms of learning: classical conditioning and differential conditioning. In addition, the reflex underwent second-order conditioning with either forward or simultaneous pairing of a novel conditioned stimulus (CS2) and a previously conditioned stimulus (CS1). Moreover, extinction of CS1 after simultaneous second-order conditioning was accompanied by a decrease in responding to CS2, suggesting that the conditioning might have involved formation of an association between the CSs. In each of these paradigms, learning in the Aplysia mantle organ preparation resembled learning in vertebrates.

Analysis of Variance↗
PubMed1996

Learning and retention of conditioned aversions by freely feeding chicks.

The present experiments assessed poison-based aversion learning and retention in freely feeding and drinking domestic chicks whose drinking water was colored blue and adulterated with LiCl for a 24-hr period. The amount of LiCl self-administered by 11-day-old chicks and their subsequent avoidance of unadulterated water of the same color was examined. The results of four experiments demonstrated that chicks self-administered large and often lethal doses of the LiCl solution. Chicks subsequently avoided blue water during two-bottle preference tests administered 3 to 7 days but not 14 days after exposure. These data indicate that neophobia alone is insufficient to prevent nondeprived chicks from ingesting large quantities of a toxin during their initial encounter with it. The lack of long-term retention in the present experiments indicates that naturally occurring aversions based on visual and illness cues, while effective in the short term, may not be a major factor in the choices made by freely feeding and drinking chicks over the long term.

Animals↗
PubMed1991

Flavor preferences conditioned by sugars: rats learn to prefer glucose over fructose.

The reinforcing effects of glucose and fructose were compared using flavor preference conditioning paradigms. Female rats given access to flavored glucose and flavored fructose solutions developed preferences for the glucose- over the fructose-paired flavor, as well as for unflavored glucose over unflavored fructose. This effect was obtained with 8% and 32% solutions, and with nondeprived and deprived rats. In most cases, the glucose preference was not immediate but appeared only after the rats had one-bottle experience with the two sugars. Female rats also preferred a glucose-paired flavor over a flavor that was paired with a noncaloric saccharin solution. A similar but somewhat weaker preference was displayed for a fructose-paired flavor over a saccharin-paired flavor. Both male and female rats acquired preferences for flavored chow that was paired with the intake of a 32% glucose solution over flavored chow paired with 32% fructose intake. Together, these results indicate that glucose has more potent postingestive reinforcing effects than does fructose. This may explain why rats consume more glucose than fructose in one-bottle acceptance as well as two-bottle preference tests.

Animals↗
PubMed1999

Severe learning impairment caused by combined immunotoxic lesion of the cholinergic projections to the cortex and hippocampus in monkeys.

Monkeys with immunotoxic lesions of both the basal nucleus of Meynert and the vertical limb of the diagonal band of Broca (NBM+VDB) lost cholinergic innervation throughout the cortex and hippocampus. They were impaired at learning discriminations between objects differing in either few, or many, attributes and at learning visuospatial conditional discriminations. Monkeys with immunotoxic lesions of the NBM lost cholinergic innervation of the neocortex only. Initially, they were unable to learn a simple visual discrimination where the stimuli differed in a limited number of attributes but they were unimpaired at learning discriminations between objects that differed in more attributes. They were mildly impaired at learning a visuospatial conditional task. The impairment exhibited by monkeys with lesions of the NBM alone ameliorated with time but that following NBM+VDB lesions did not. Previous experiments have shown that monkeys with immunotoxic lesions of the VDB alone are impaired at learning visuospatial conditional discriminations but are unimpaired at learning simple visual discriminations. When monkeys with NBM lesions were given excitotoxic lesions of the CA1 field of the hippocampus the learning impairment on discriminations between objects which differed in few attributes was reinstated. Pretreatment with a cholinergic agonist improved learning ability on visual discrimination learning in all monkeys but this improvement was significantly greater in monkeys with lesions of the NBM. On conditional discrimination learning, which is particularly sensitive to hippocampal damage, pilocarpine produced a significant improvement in monkeys with NBM+VDB lesions (where the hippocampal dysfunction was cholinergic) but not in monkeys with NBM+CA1 lesions (where the hippocampal damage was structural).

Acetylcholine↗