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PubMed1966

Two types of behavioral contrast in discrimination learning.

Two groups of pigeons received daily discrimination training at two values on a line-tilt continuum. S+ (VI 1) and S- (EXT) intervals alternated, and a 30-sec criterion of no responding to S- was required before S+ returned. Rates of responding to S+ showed two separate contrast effects: at an intermediate stage of training a high peak rate appeared which declined, later in training, to a stable level still in excess of the VI baseline rate. The peak rate was correlated with the total number of responses to S-, while the final rate was not; suggesting that the peak rate and final rate may not be functions of the same variable. These results were compared with performance on a red-green discrimination where the two stages were not so clear. A line-tilt discrimination was repeated with fixed length S- intervals terminated by TO, and showed the same contrast magnitude in the final rate without any peak. The peak rate was interpreted as an effect of the ;punishment' contingency where responding to S- prolongs S- for 30 sec, while the final rate was taken to be analogous to previous demonstrations of contrast.

Animals↗
PubMed1995

Ontogeny of eyeblink conditioning in the rat: auditory frequency and discrimination learning effects.

The present study sought to determine whether acoustic properties of the auditory conditioned stimulus (CS) or the use of a discrimination learning procedure would alter the emergence of eyeblink conditioning between postnatal Days 17 and 24 (Days 17-24) in the rat. In Experiment 1, we employed a 3 x 2 x 2 factorial design, involving pitch of the auditory CS (2.8, 5.0, and 9.0 kHz), training condition (paired vs. unpaired), and age (Days 17 or 24). Associative learning was evident at all tone frequencies on Day 24, but increased across frequencies on Day 17, although large age differences in conditioning remained at all tone frequencies. In Experiment 2, rat pups were trained to discriminate 2.8 versus 9.0-kHz tones on Day 17 or Day 24. Eyeblink conditioning increased with tone frequency on Day 24 but discriminative conditioning failed to appear on Day 17. These findings are discussed in relation to the role of auditory system maturation in the ontogeny of eyeblink conditioning.

Acoustic Stimulation↗
PubMed1984

Effects of chronic manipulations of dietary choline on locomotor activity, discrimination learning and cortical acetylcholine release in aging adult Fisher 344 rats.

Dietary levels of choline have been shown to influence central cholinergic neurotransmission. To further examine the behavioral and neurochemical effects of dietary choline, adult Fisher 344 rats were maintained on choline deficient (n = 6), enriched (n = 6) or usual lab chow (n = 6) diets for 38 weeks. During 14 weeks of free access to these diets, controls gained little weight whereas the deficient group increased and the enriched group decreased. For the remaining 24 weeks the weights of all groups were maintained at 90% of their original level. Locomotor activity did not differ significantly in a 90 min session but during a 20 hr session controls were most active, deficient rats least with the enriched group in between. The groups showed no significant differences in the acquisition or reversal of a discrimination. Spontaneous and evoked cortical release of acetylcholine was enhanced in the enriched group and decreased in the deficient group relative to controls. These data suggest that chronic manipulations of dietary choline may significantly influence locomotor and neurochemical activity but not discrimination learning.

Acetylcholine↗
PubMed1982

The effects of chlorpromazine and lithium on appetitive discrimination learning in the rat.

Rats learned one of two appetitive discrimination tasks varying in terms of cognitive difficulty. Contrary to previous reports showing an impairment in the acquisition of avoidance tasks under the effects of either chlorpromazine (CPZ) or lithium, the results of this experiment indicate that neither drug retards the acquisition of appetitive tasks. Instead, at the highest doses used (2 and 3 mg/kg), CPZ decreased the number of trials required for the difficult task. Rats administered CPZ had longer reaction times than rats administered placebo, and therefore might have achieved criterion earlier because they spent more time in front of and on the discriminanda. The contrary results reported with avoidance tests concerning the effects of CPZ are explained in terms of the anxiety-reducing properties of CPZ, which might reduce drive without impairing cognitive ability.

Animals↗
PubMed1979

Effects of neonatal bulbectomy on later discrimination learning in mice.

The olfactory bulbs of mice were lesioned at 24 h of age and their performance in learning a black-white discrimination task was compared with undernourished mice that grew from birth at the same rate as the bulbectomised animals. The mice were tested at 90 days of age and their behaviour in a Y-maze was compared with that of control operated and unoperated samples. The performance of the bulbectomised mice spent more time at the choicepoint and frequently failed to run the maze. The error rate reduction shown by the bulbectomised mice was similar to that of the controls and is accounted for in terms of a reduced frequency of entry and reversals into the maze arms. The results are discussed in relation to the size of the lesions and factors affecting the neurogenesis of the olfactory brain early in life.

Animals↗
PubMed1995

Spatial discrimination learning and choline acetyltransferase activity in streptozotocin-treated rats: effects of chronic treatment with acetyl-L-carnitine.

Treatment of rats with i.c.v. injected streptozotocin (STREP) may provide a relevant model of neurodegeneration that is induced by a decrease in the central metabolism of glucose. Acetyl-L-carnitine (ALCAR) enhances the utilization of alternative energy sources and by such a mechanism of action ALCAR could antagonize the effects of STREP treatment. In this study the effects of chronic treatment with ALCAR were evaluated on spatial discrimination learning in the Morris task and choline acetyltransferase (ChAT) activity of middle-aged STREP-treated rats. Chronic treatment with ALCAR attenuated both the STREP-induced impairment in spatial bias and the decrease in hippocampal ChAT activity. These findings indicate that ALCAR treatment has a neuroprotective effect, although further studies are needed to characterize the mechanism of action of ALCAR in this model.

Acetylcarnitine↗
PubMed1988

Changes in discrimination learning and brain activity (ERP's) due to combined exposure to NO and CO in rats.

Carbon monoxide (CO) and nitric oxide (NO) are air pollutants frequently appearing in combination. Information available on the mechanisms of NO intoxication suggests that in mixtures with CO additive effects should be assumed. In this study CO and NO-induced changes and their interaction were investigated at different levels of integration: carboxyhemoglobin (COHb) and methemoglobin (met-Hb) formation as well as centrally mediated effects were analyzed using evoked potential techniques and behavioral data from a complex discrimination learning experiment. Slight enhancements of COHb and met-Hb concentrations were seen for the combined CO + NO exposure conditions at low and high exposure levels when compared to isolated exposure conditions. The performance decrease was clearly higher under NO exposure than under CO exposure. Decrements were overadditive when simultaneous CO + NO exposure was used in higher concentration. Both gases affected early evoked potential components (P10, N30) in the same way: latencies were prolonged and amplitudes increased. Later potential components were differently influenced by CO and NO. Mainly the N150 amplitude was decreased in NO exposure and increased in CO conditions. N150 amplitude was also decreased after combined CO + NO exposure. At high levels this effect was overadditive indicating a dominant role of NO in the CO + NO combinations used in this experiment.

Animals↗
PubMed1983

The effects of lesions to ascending noradrenergic neurons on discrimination learning and performance in the rat.

Three experiments examined the effect of central noradrenergic depletion on the acquisition and performance of a temporal discrimination in auditory or visual modalities. In Experiment 1, 6-hydroxydopamine-induced lesions of the dorsal noradrenergic bundle significantly retarded acquisition compared to a similarly lesioned ventral noradrenergic bundle-group, two sham-operated and one unoperated control group. In Experiment 2, the acquisition impairment produced in the dorsal noradrenergic bundle group was replicated, for both auditory and visual modalities, by lesions depleting hippocampal and neocortical noradrenaline by over 80%. In rats subsequently switched to discriminations involving the unfamiliar modality, the dorsal-bundle lesion also impaired acquisition several weeks after surgery. Experiment 3 showed significantly impaired performance in rats with dorsal bundle lesions when training prior to surgery had not resulted in better than chance performance. In rats previously trained to criterion, the dorsal bundle lesion transiently, but non-significantly, impaired performance. In rats performing better than chance, but not having reached criterion, there were no significant effects of the dorsal bundle lesion. Subsequent manipulations of deprivation and difficulty of discrimination in general failed to distinguish between the dorsal bundle lesion and sham-groups, suggesting that the acquisition impairment did not result from simple sensory or motivational effects. Reducing the interstimulus interval did impair the dorsal bundle group more than controls. However, there was no evidence of altered "distractibility" in the lesioned group when the alternative modality was introduced as a distractor. The results are discussed in terms of other acquisition deficits shown by rats with central noradrenaline depletion and their significance for determining the functions of the projections from the locus caeruleus via the dorsal noradrenergic bundle to the neocortex and hippocampus.

Afferent Pathways↗
PubMed1999

Hormones of the hypothalamo-pituitary-gonadal axis in drug discrimination learning.

More than 30 years ago, T-maze studies with progesterone indicated that sex hormones have the potential to act as a discriminative stimulus in rats. Despite these early positive findings, the interest in discriminative stimulus properties of sex hormones remained low; few studies were dedicated to the investigation of discriminative stimulus properties of hypothalamo-pituitary-gonadal axis hormones (i.e., LHRH, LH/FSH, sex steroids). Nevertheless, the few studies that were published showed some interesting, and often sex-dependent results. Applying various methodologies (T-, or Y-maze, two-lever drug discrimination, taste aversion procedures), it was found that not only progesterone but also the two other principal sex steroids estradiol and testosterone can serve as discriminative stimuli in rodents. In addition to these gonadal hormones, the hypothalamic peptide LHRH (having a key role in the neuroendocrine regulation of steroid release from the gonads) appears to generate discriminative stimulus properties. Interestingly, recent (but preliminary) studies in postmenopausal women suggest that estradiol (and possibly progesterone) may also function as a discriminative stimulus in human subjects.

Animals↗
PubMed1992

[Discrimination learning of rotated faces: a Markov analysis of coding and association processes].

30 subjects participated in a discrimination experiment learning face-letter associations under four rotation conditions (45 degrees, 90 degrees, 135 degrees, 180 degrees). Under each condition two thirds of the faces were presented twice, upright and rotated away from the vertical; the remaining faces were presented once, upright or rotated. Learning is described by a joint Markov model: For faces that are presented twice it assumes a separate association and encoding process (two-stage-model), for faces that are presented once it assumes an association process (all-or-none-model). The Markov model fits the data for all four rotation conditions. The angle of rotation does not affect learning for faces that are presented once. For faces that are presented twice it influences both the association and the encoding process. For the angles employed, the effect of rotation can be approximated linearly. The results suggest that the encoding of a rotated face differs increasingly from an upright face as a function of these angles of rotation. This confirms analogous conclusions from mental rotation experiments.

Adult↗