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PubMed1977

Effects of reserpine on retention of escape reversal in mice: absence of state-dependent learning.

A discriminated escape training paradigm was used to study the effects of reserpine on learning and memory in mice. Intraperitoneal injection of reserpine before reversal training had no effect on acquisition but did produced a time-and dose-dependent impairment of retention test performance 10 days later. These results suggested that reserpine may have interfered with some aspect of memory storage. Retention impairments observed when a 2.0 mg/kg reserpine injection was given 2 hr before reversal training were not attenuated by readministering the drug before testing, a finding that provides no support for a state-dependency interpretation. Furthermore, animals treated with reserpine exhibited inferior retention of previous training, regardless of the pharmacological state present during that learning. This was interpreted as a drug-induced impairment of memory retrieval. In addition, performance during the initial discriminated escape training session suggested that reserpine may also impair acquisition under some conditions. In the last experiment, it was found that when the catecholamine precursor L-dihydroxyphenylalamine (100 mg/kg) and the indole amine precursor D,L-5-hydroxytryptophan (125 mg/kg) were both given after reserpine treatment, subsequent retention performance was not significantly impaired. The results are discussed in terms of the possible roles of biogenic amines in arousal, learning, and memory.

5-Hydroxytryptophan↗
PubMed1999

Effects of mammillary body lesions on spatial reference and working memory tasks.

This work examines the effects of electrolytic mammillary body (MB) lesions on the performance of rats in different spatial memory tasks in the Morris water maze. The first experiment assessed the effect of MB lesion on performance in a spatial reference memory task (place learning with multiple trials). The second experiment examined the effect of a lesion in this nucleus on performance in a spatial working memory task (single-trial place learning). The results show that lesion of the MB impairs the animals performance in spatial working memory tasks but does not impair acquisition in spatial reference memory tasks (place learning, transfer task, reversal task) or in a visual-cued task. However, the deficit in the spatial working memory task does not appear to vary with the delay between acquisition and retention trials (30 s and 5 min). Our results demonstrate a clear role of the mammillary bodies in the processing of spatial information in a working memory task. Lesion of the MB impairs performance in a working memory task but does not affect reference memory processes.

Animals↗
PubMed1988

Parallel modifications of spatial memory performances, exploration patterns, and hippocampal theta rhythms in fornix-damaged rats: reversal by oxotremorine.

Learning scores and degrees of divergence of the exploratory patterns (EP) displayed during the acquisition stage of a radial eight-arm maze task were examined in fornix-damaged and sham-operated rats injected either with oxotremorine (0.1 mg/kg) or saline. Modifications of hippocampal rhythmic slow activity (theta) recorded in each condition were analyzed in CA1 and dentate gyrus. Dorsal fornix sections reduced choice accuracy but also induced the adoption of weakly divergent EP. Oxotremorine in animals with lesions reinstates both learning scores and degree of divergence of EP at the levels respectively observed in saline sham-operated animals. Finally, oxotremorine in sham-operated animals did not significantly improve choice accuracy but strongly modified the EP. Preoperatively, theta rhythms indicated a decrease of frequency after oxotremorine administration. Postoperatively, they showed an increase of frequency in animals with lesions that were reinstated at the preoperative level by oxotremorine.

Animals↗
PubMed1987

Relative effects of scopolamine and electroconvulsive shock upon habit reversal in white rats.

30 adult male white rats were equally divided into control, scopolamine, and electroconvulsive shock groups to learn 20 successive reversal problems in an E-maze for water after 23 1/2 hr. of deprivation. The noncorrection method was used. After 1 mo. of preliminary training, each scopolamine animal received an intraperitoneal injection of 1 mgm of scopolamine hydrobromide per kgm of body weight while each in the shock group was given an ECS of 35 mA for .2 sec. at the end of every 10 daily trials. When a rat obtained 9 correct of 10 trials, the goal was switched to the opposite side of the maze. Controls were much superior to both experimental groups. While scopolamine animals experienced more detrimental effects initially, they caught up with the shock group and finally became superior. This shift is interpreted in terms of building tolerance to scopolamine and increasing anxiety to shock as effects of differential treatments accumulated.

Animals↗
PubMed2006

Impairments in water maze learning of aged rats that received dextromethorphan repeatedly during adolescent period.

RATIONALE: Dextromethorphan (DM), an over-the-counter cough suppressant, has been recently used as a drug of abuse by teenage groups in some countries, such as the United States, Canada, and Korea. We previously showed that repeated administration of DM, a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptors, impairs spatial learning performance in adolescent rats. OBJECTIVES: In the present study, long-term adverse effects of repetitive DM use at adolescence were examined in rats. METHODS: Male and female Sprague-Dawley rat pups received either intraperitoneal DM (40 mg/kg) or saline daily during postnatal days 28-37, and were then subjected to the Morris water maze task at the age of 18 months. Expression levels of NMDAR1, functional subunit of NMDA receptors, in the prefrontal cortex and the hippocampus were examined by Western blot analysis. Changes in plasma corticosterone levels responding to stress were determined by radioimmunoassay. RESULTS: DM-experienced male rats exhibited deficits in the probe trial, and female rats in the initial learning and the reversal training, in water maze performance. Expression levels of NMDAR1 in the brain regions were significantly increased in DM-experienced rats, compared to control rats. Stress-induced increases in plasma corticosterone levels were blunted both in male and female DM rats. CONCLUSIONS: The results suggest that repeated administration of DM at high doses during adolescent period may induce permanent deficits in cognitive function and that increased expression of NMDAR1 in the prefrontal cortex and the hippocampus may take a role in DM-induced memory deficits.

Animals↗
PubMed1986

Deficits in spatial-memory tasks following lesions of septal dopaminergic terminals in the rat.

The behavioral effects of 6-hydroxydopamine, injected bilaterally into the lateral septum, were investigated in two tests of spatial memory (radial 8-arm and T-maze). Three different experiments were conducted in the radial maze. In experiment I, rats were permitted to learn the task with food reinforcement in all arms of the maze. In experiment II, retention of the spatial information (working memory) learned in experiment I was tested by interposing various time intervals between choice 4 and 5 of each trial. In experiment III, reference and working memory were simultaneously assessed by only reinforcing 4 choices in the radial maze. Performances were compared in spaced versus massed trials. In the T-maze, the rats were first tested for learning a spatial discrimination between the two arms of the maze, and subsequently for reversal of the previously learned response. The results showed that the rats with lesions were impaired in all experiments. This impairment was particularly marked in some aspects of the procedures used: (1) in the search for the last 4 pellets in experiment I, (2) in the first presentations of various intervals interposed between choices 4 and 5, (3) in the search for food in the baited arms when the trials were massed in experiment III and (4) in the reversal of previously learned spatial discrimination in the T-maze. These behavioral deficits in the rats with septal dopaminergic lesions were interpreted as an increased susceptibility to interference. The lesions were shown to have selectively depleted dopamine concentrations in the septum without damaging noradrenergic terminals or cholinergic cell bodies. It was concluded that dopaminergic neurons could have a modulatory influence on memory processes.

Animals↗
PubMed1977

Limbic and prefrontal contributions to somesthetic learning in monkeys.

Monkeys with forebrain commissurotomies and either lateral temporal, medial temporal, dorsal prefrontal, or ventral prefrontal removals from the right hemisphere were compared with control animals in learning tactual discriminations and reversal with the left hand. The lateral temporal removal yielded no effect, confirming the modality-specific roles of this sector in audition (superior temporal gyrus) and vision (inferior temporal gyrus). The dorsal prefrontal removed yielded a deficit in discrimination learning, possibly as a result of the contralateral sensory neglect or the spatial disorder produced by this lesion. Each of the two remaining lesions, medial temporal and ventral prefrontal, yielded deficits in both discrimination learning and reversal; and the effects of combined removal of these two limbic sectors appeared to be additive. Taken together with earlier findings in vision and audition, the results indicate that the two limbic sectors contribute to learning in all sensory modalities, and that they do so through cortico-cortical interaction with the sensory systems.

Animals↗
PubMed2003

Perceptual attentional set-shifting is impaired in rats with neurotoxic lesions of posterior parietal cortex.

The posterior parietal cortex (PPC) is believed to be involved in the representation of spatial information, including spatial attentional processing. Because the PPC is extensively interconnected with frontal cortical regions involved in attention and executive function, we sought to determine whether PPC was involved in nonspatial attentional processes such as those of the frontal areas to which it projects. Lesions of the medial frontal cortex (in rats) or lateral prefrontal cortex (in nonhuman primates) impair the ability to shift attention from one perceptual dimension of a stimulus to another (referred to as an extradimensional shift). Rats with neurotoxic lesions of the PPC tested in an attentional set-shifting paradigm demonstrated a pattern of impairment identical to that of rats with medial frontal cortex lesions: they were selectively impaired on the extradimensional shift phase of the task. Performance in other phases of the task was indistinguishable from that of control rats, including the ability to reverse a previously learned discrimination. These findings are consistent with models that assign the PPC a prominent role in cortical attentional processing networks, as well as a role for the PPC in processing information about expectancy and surprise. They also suggest, importantly, that the interaction between the PPC and the frontal cortex is not limited to spatial attentional processing.

Animals↗
PubMed2002

Learning to recognize talkers from natural, sinewave, and reversed speech samples.

In 5 experiments, the authors investigated how listeners learn to recognize unfamiliar talkers and how experience with specific utterances generalizes to novel instances. Listeners were trained over several days to identify 10 talkers from natural, sinewave, or reversed speech sentences. The sinewave signals preserved phonetic and some suprasegmental properties while eliminating natural vocal quality. In contrast, the reversed speech signals preserved vocal quality while distorting temporally based phonetic properties. The training results indicate that listeners learned to identify talkers even from acoustic signals lacking natural vocal quality. Generalization performance varied across the different signals and depended on the salience of phonetic information. The results suggest similarities in the phonetic attributes underlying talker recognition and phonetic perception.

Female↗
PubMed1998

Adaptation of visually guided behavior during reversed vision in schizophrenia: a preliminary study.

This preliminary study evaluated the adaptation of visually guided behavior to reversed vision in schizophrenia. The study included 54 patients who met DSM-III-R criteria for schizophrenia. Visuomotor reaction times (VRTs) during reversed vision were measured in six blocks of 35 consecutive trials. The VRTs of schizophrenics were compared with those of normal subjects. A good fit (R2 = 0.9981) for the adaptation process of VRTs during reversed vision was found with the equation y = 1030 + 1499/x, where x is the order of the block and y is the group mean VRT for each block. The VRTs in schizophrenics were significantly slower than those in normal subjects. However, the adaptation process to reversed vision essentially did not differ from normal. The adaptation of visually guided behavior during reversed vision may involve procedural learning; this task may thus be useful in evaluating such learning. The VRTs during reversed vision may be related to some aspects of symptoms in the patient with schizophrenia and may also be useful in predicting clinical outcome.

Adult↗
PubMed1992

Differential effect of right and left hemispheric lesions on two memory tasks: free recall of items and recall of spatial location.

The effect of lateralized cerebral damage on free recall of items and recall of spatial location, under intentional and incidental learning conditions, was investigated. Eleven right brain-damaged (RBD) patients, 10 left brain-damaged (LBD) patients, 14 young and 11 elderly normal controls, participated in this study. The overall performance of the control groups was better than that of the patient groups. For all groups, free recall was better under intentional than under incidental learning condition. On recall of spatial location the learning condition had a differential effect on the groups. The RBD group performed better than the LBD group under intentional learning condition, while the reverse was found under incidental learning condition. The young-control group showed an advantage over the elderly-control group under intentional but not under incidental learning condition. The results are discussed in regard to different approaches to the distinction between automatic and effortful memory processes and their lateralization in the cerebral hemispheres.

Adult↗
PubMed1992

Facilitation and recovery of shuttle box avoidance behavior after frontal cortex lesions is induced by a contingent electrical stimulation in the ventral tegmental nucleus.

A bilateral ablation of the frontal cortex was performed in rats before and after training in an active avoidance task in a shuttle box. Animals with this lesion showed an impairment in learning and in the reversal of the avoidance task. If the animals with the lesion were implanted with an electrode in the ventral tegmental nucleus and received an electrical stimulation in this area contingent to a correct response (avoidance or escape response) in the behavioral task, they did not show any impairment in the performance of the task. Furthermore, the effect of the stimulation persisted after it was retrieved. The present findings indicate that the motivational and cue properties of the electrical stimulation of the ventral tegmental nucleus may serve to facilitate learning and reversal in an avoidance task and to induce at the long term a recovery process in animals in which the frontal cortex has been ablated. Therefore, this method may be useful to study the adaptative changes which take place in the nervous system after recovery from brain damage occurs.

Animals↗
PubMed2002

Testing learning theories: the NUL hypothesis.

INTRODUCTION: In the spirit of Scrooge and the Grinch, I describe the nasty unpalatable learning (NUL) hypothesis as a new theory of learning. This is an exercise to explore how difficult it would be to develop a new learning theory by reversing the social and altruistic tenets of most existing learning theories. THE NUL HYPOTHESIS: The NUL hypothesis has four propositions. These are: (1) the value of rote learning; (2) the usefulness of authority figures in teaching within a clear hierarchy; (3) the use of fear in teaching, and (4) the value of internal consistency without any necessary connection to the outside world. CONCLUSIONS: The NUL hypothesis may promote reflection not only on the construction of learning theories, but also on the design of critical experiments. It also seems to imply that efficiency may be a better measure of learning success than effectiveness.

Education, Medical↗
PubMed2005

Chronic ethanol consumption impairs learning and memory after cessation of ethanol.

Acute consumption of ethanol results in reversible changes in learning and memory whereas chronic ethanol consumption of six or more months produces permanent deficits and neural damage in rodents. The goal of the current paper was determine whether shorter durations of chronic ethanol ingestion in mice would produce long-term deficits in learning and memory after the cessation of ethanol. We first examined the effects of four and eight weeks of 20% ethanol followed by a three week withdrawal period on learning and memory in mice. We determined that three weeks after eight, but not four, weeks of 20% ethanol consumption resulted in deficits in learning and long-term memory (seven days) in T-maze footshock avoidance and Greek Cross brightness discrimination, step-down passive avoidance and shuttlebox active avoidance. Short-term memory (1 hr) was not affected. The deficit was not related to changes in thiamine status, caloric intake, or nonmnemonic factors, such as, activity or footshock sensitivity. Lastly, we examined if the mice recovered after longer durations of withdrawal. After eight weeks of ethanol, we compared mice after three and 12 weeks of withdrawal. Mice that had been off ethanol for both three and 12 weeks were impaired in T-maze footshock avoidance compared to the controls. The current results indicate that a duration of ethanol consumption as short as eight weeks produces deficits in learning and memory that are present 12 weeks after withdrawal.

Alcohol Drinking↗