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PubMed2003

Colour discrimination learning in black-handed tamarin ( Saguinus midas niger).

Colour is one cue that monkeys use for perceptual segregation of targets and to identify food resources. For fruit-eating primates such as Saguinus, an accurate colour perception would be advantageous to help find ripe fruits at distance. The colour vision abilities of black-handed tamarins ( Saguinus midas niger) were assessed through a discrimination learning paradigm using Munsell colour chips as stimuli. Pairs of chips were chosen from an early experiment with protan and deutan humans. The monkeys (three males and one female) were tested with stimuli of the same hue, but different brightness values, in order to make sure that discriminations were based on colour rather than brightness cues. The results showed that the female, but not the males, presented an above-chance performance for stimuli resembling hue conditions under which tamarins forage (oranges vs greens). Colour vision in S. m. niger is discussed according to the advantages and disadvantages of dichromatism in daily search for food as well as to aspects regarding polymorphism in New World monkeys.

Animals↗
PubMed1994

Magnetic field effects on spatial discrimination learning in mice.

A magnetic sense has been demonstrated in several species, including mice. It has been suggested that the basis of this sense, and its role in navigation, rests on the existence of ferromagnetic materials in the brain. Several researchers have shown changes in navigation during exposure to relatively weak magnetic fields, which presumably interact with magnetite in the brain. In this study, mice were exposed to the powerful magnetic field of an MRI scanner and their left-right discrimination learning was compared with a control group. Results indicate a significant decrement in such learning ability immediately after exposure. Suggestions for future research are presented.

Animals↗
PubMed1997

Exposure to chronic psychosocial stress and corticosterone in the rat: effects on spatial discrimination learning and hippocampal protein kinase Cgamma immunoreactivity.

Previous reports have demonstrated a striking increase of the immunoreactivity of the gamma-isoform of protein kinase C (PKCgamma-ir) in Ammon's horn and dentate gyrus (DG) of rodent hippocampus after training in a spatial orientation task. In the present study, we investigated how 8 days of psychosocial stress affects spatial discrimination learning in a hole board and influences PKCgamma-ir in the hippocampal formation. The acquisition of both reference memory and working memory was significantly delayed in the stressed animals during the entire training period. With respect to cellular plasticity, the training experience in both nonstressed and stressed groups yielded enhanced PKCgamma-ir in the CA1 and CA3 regions of the posterior hippocampus but not in subfields of the anterior hippocampus. Stress enhanced PKCgamma-ir in the DG and CA3 pyramidal cells of the anterior hippocampus. In stressed animals that were subsequently trained, the PKCgamma-ir was increased in the posterior CA1 region to the same level as that found in nonstressed trained animals. Stress apparently abrogated the PKCgamma-ir training response in the CA3 region. In a second experiment, the elevation of plasma corticosterone levels to values that are found during stress did not significantly influence reference memory scores but slightly and temporarily affected working memory. The training-induced enhancement of PKCgamma-ir in the CA1 region was similar in trained and corticosterone-treated trained animals, but the learning-induced PKCgamma-ir response in the posterior CA3 area was absent after corticosterone pretreatment. These results reveal that prolonged psychosocial stress causes spatial learning deficits, whereas artificial elevation of corticosterone levels to the levels that occur during stress only mildly affects spatial memory performance. The spatial learning deficits following stress are reflected only in part in the redistribution of hippocampal PKCgamma-ir following training.

Adrenal Glands↗
PubMed1990

[Right/left discrimination learning in rat pups neonatally treated with 6-hydroxydopamine].

At 2 and 4 days of age, rat pups were treated with 6-hydroxydopamine (6-OHDA; 70 micrograms, ivt) following desmethylimipramine (20 mg/kg, sc) pretreatment. Spontaneous activity test in a novel cage at 16 and 17 days of age revealed a sustained higher level of locomotor activity in 6-OHDA-treated rats, which was characterized by a deficit of habituation. For right/left discrimination learning trained from 18 days of age, "homing" was used as an reinforcer, i.e., pups could enter the goal area adjacent to home cage if they chose a predetermined correct arm of T-maze. Rats were trained 10 trials a day until they attained the learning criterion (at least 17 correct choices in 2 days). Thereafter, they were re-trained for the reversal learning to the criterion (at least 8 correct choices in a day). 6-OHDA-treated rats were required significantly more trials to attain the learning criterion both in the original and the reversal learnings. Biochemical assay confirmed a marked depletion of brain dopamine contents in striatum, cortex and midbrain with thalamus in 6-OHDA-treated rats. Therefore, the neonatal depletion of brain dopamine produced hyperactivity (habituation deficit) and a discrimination deficit during the developmental period.

Animals↗
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↗
PubMed2005

Deficits in experience-dependent cortical plasticity and sensory-discrimination learning in presymptomatic Huntington's disease mice.

Huntington's disease (HD) is one of a group of neurodegenerative diseases caused by an expanded trinucleotide (CAG) repeat coding for an extended polyglutamine tract. The disease is inherited in an autosomal dominant manner, with onset of motor, cognitive, and psychiatric symptoms typically occurring in midlife, followed by unremitting progression and eventual death. We report here that motor presymptomatic R6/1 HD mice show a severe impairment of somatosensory-discrimination learning ability in a behavioral task that depends heavily on the barrel cortex. In parallel, there are deficits in barrel-cortex plasticity after a somatosensory whisker-deprivation paradigm. The present study demonstrates deficits in neocortical plasticity correlated with a specific learning impairment involving the same neocortical area, a finding that provides new insight into the cellular basis of early cognitive deficits in HD.

Age Factors↗
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↗