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PubMed1987

What we have learned from phalloidin.

In contrast to popular opinion phallotoxins do not play a role in poisoning with Amanita phalloides when the fungi are ingested orally. All toxic properties of this mushroom are due to amatoxins which, in contrast to the phallotoxins, are absorbed upon ingestion. Nearly all experiments on intact animals were performed by parenteral injection of phalloidin and therefore, most of these are unsuitable for practical consideration. In the present survey, however, a series of important findings are discussed, which provide insight into various functions of liver cells. When present in the blood, phalloidin and other phallotoxins are selectively taken up by hepatocytes. No other types of cells are sensitive to the toxin. No extrahepatic tissue is primarily impaired by phalloidin. Phalloidin cannot be degraded by peptidases or by proteases occurring in animals. Phalloidin is therefore a useful model substance for studies on the uptake of cyclopeptides by liver cells. The carrier system responsible for the active uptake of phalloidin can also translocate antamanide and several cyclic modifications of somatostatin. Phallotoxins bind with high affinity to microfilamentous structures, in particular to F-actin [Govindan et al., Naturwissenschaften, 59 (1972) 521-522] whereas phallotoxins are not bound to the monomer (G-actin). With respect to the strong organotropism of phallotoxins, intravenously injected phalloidin binds preferentially to microfilamentous F-actin of hepatocytes. Phalloidin is therefore a tool for inactivation of microfilamentous functions specifically in liver cells, and is suitable as a prototype of a cholestatic agent. In perfused livers arrest of bile flow is the earliest effect seen after addition of the toxin. In cells from other tissues phalloidin is only toxic when applied by intracellular microinjection. Phalloidin poisoning has been often used as a model for liver damage in the testing of hepatoprotective drugs. This substance is, however, not useful for such studies since the mechanism of phalloidin poisoning is too specific for interpretation in the sense of general liver protection.

Actin Cytoskeleton↗
PubMed2005

Enhanced contrast sensitivity in auditory cortex as cats learn to discriminate sound frequencies.

To better understand the nature and time course for learning-induced cortical reorganization, we examined frequency-specific changes in auditory cortex as cats gradually improved at a difficult sound frequency discrimination task. Three adult cats were trained to discriminate between a tone pip at a fixed target frequency (S-) and a higher deviant frequency (S+). An adaptive training schedule led to an efficient estimate of the frequency discrimination threshold (FDT), which was used to track daily performance. Each cat was also implanted with an array of microwires in auditory cortex. Tone pips with different frequency and amplitude were used to map receptive fields. Onset responses were correlated with training time and the cat's ability to discriminate frequencies. Although lifetime of the neural implants varied among cats, each provided sufficient neural recording to relate at least 3 weeks of learning to response changes in the cortex. An improved FDT was associated with a differential decrease in response strength between the S- frequency and S+ frequencies. Response to the training frequencies gradually located in a local minimum compared to adjacent frequencies (p < 0.001, Cohen's d=0.50). Cortical changes were consistent with a theory of bimodal generalization that enhances stimulus classification by reducing similarity between reinforced and nonreinforced stimuli. Such a strategy may be especially appropriate during an early stage of learning to discriminate similar sounds and differ from later strategies required for fine discrimination.

Animals↗
PubMed2006

Involvement of the CA3-CA1 synapse in the acquisition of associative learning in behaving mice.

One of the brain sites more directly related with learning and memory processes is the hippocampus. We recorded, in conscious mice, the activity-dependent changes taking place at the hippocampal CA3-CA1 synapse during the acquisition, extinction, recall, and reconditioning of an associative task. Mice were classically conditioned to evoke eyelid responses using a trace [conditioned stimuli (CS), tone; unconditioned stimuli (US), shock] paradigm. A single electrical pulse presented to the Schaffer collateral-commissural pathway during the CS-US interval evoked a monosynaptic field EPSP (fEPSP) at ipsilateral CA1 pyramidal cells. The slope of evoked fEPSPs increased across conditioning sessions and decreased during extinction, being linearly related to learning evolution. In contrast, fEPSPs were not modified when evoked in control mice in the absence of a conditioning protocol. Long-term potentiation (LTP) evoked by high-frequency stimulation of Schaffer collaterals prevented acquisition, extinction, recall, or reconditioning, depending on the moment when it was triggered. Learning and memory impairments evoked by LTP induction resulted probably from the functional saturation of the CA3-CA1 synapse, although an additional disturbance of the subsequent information transfer toward postsynaptic circuits cannot be discarded. CGP 39551 [(E)-(+/-)-2-amino-4-methyl-5-phosphono-3-pentenoic acid ethyl ester] (an NMDA antagonist) prevented LTP induction in behaving mice, as well as the acquisition of an eyelid learned response, and the synaptic changes taking place at the CA3-CA1 synapse across conditioning. In conclusion, the responsivity of the CA3-CA1 synapse seems to be modulated during associative learning, and both processes are prevented by experimental LTP or NMDA-receptor inactivation. Our results provide evidence of a relationship between activity-dependent synaptic plasticity and associative learning in behaving mice.

2-Amino-5-phosphonovalerate↗
PubMed2006

Vancouver, Toronto, Montreal, Austin: enhanced oddball memory through differentiation, not isolation.

What makes a person, event, or object memorable? Enhanced memory for oddball items is long established, but the basis for these effects is not well understood. The present work clarifies the roles of isolation and differentiation in establishing new memories. According to the isolation account, items that are highly dissimilar to other items are better remembered. In contrast, recent category learning studies suggest that oddball items are better remembered because they must be differentiated from similar items. The present work pits the differentiation and isolation accounts against each other. The results suggest that differentiation, not isolation, leads to more accurate memory for deviant items. In contrast, gains for isolated items are attributable to reduced confusion with other items, as opposed to preferential storage.

Affect↗
PubMed2005

Category representation for classification and feature inference.

This research's purpose was to contrast the representations resulting from learning of the same categories by either classifying instances or inferring instance features. Prior inference learning research, particularly T. Yamauchi and A. B. Markman (1998), has suggested that feature inference learning fosters prototype representation, whereas classification learning encourages exemplar representation. Experiment 1 supported this hypothesis. Averaged and individual participant data from transfer after inference training were better fit by a prototype than by an exemplar model. However, Experiment 2, with contrasting inference learning conditions, indicated that the prototype model was mimicking a set of label-based bidirectional rules, as determined by the inference learning task demands in Experiment 1. Only the set of rules model accounted for all the inference learning conditions in these experiments.

Humans↗
PubMed2000

Variation in contrasting forms of 'memorising' and associated observables.

BACKGROUND: There is a posited conceptual distinction in the student learning literature in higher education between contrasting forms of 'memorising': as a process of rehearsal which is usually equated with rote learning, and as a process of committing to memory material that in two separate senses is temporally either 'understood' before or after the event. AIMS: The present study reports on the operationalisation of these contrasting forms of 'memorising' and investigates their empirical association with one another, their gender sensitivity, and their joint association with other modelling sources of explanatory variation in student learning. SAMPLES: Two samples of entering first-year economics students at the Universities of South Australia (N = 896) and Adelaide (N = 448) which are combined in the present study (N = 1344). The combined sample is further distinguishable by gender (females, N = 662, males, N = 682). METHOD: Students were surveyed prior to the commencement of lectures and reported retrospectively on their most recent school-based learning experiences. Resultant data in the form of inventory responses were subjected to exploratory and confirmatory factor analyses, multivariate analysis of variance, and correlation analysis. RESULTS: Empirically the three forms of 'memorising' are independent of one another and they are furthermore sensitive to gender-based response differences in terms of both location and structure. Forms of 'memorising' are respectively associated in a theoretically congruent manner with 'deep'-level processes, learning pathologies, and contrasting conceptions of learning. CONCLUSIONS: The unqualified use of 'memorising' in studies of student learning is contra indicated. Contrasting forms of 'memorising' represent discrete sources of explanatory variation that can be used to construct finer grained models of student learning in process terms.

Adolescent↗
PubMed2001

Finite mixture distribution models of simple discrimination learning.

Through the application of finite mixture distribution models, we investigated the existence of distinct modes of behavior in learning a simple discrimination. The data were obtained in a repeated measures study in which subjects aged 6 to 10 years carried out a simple discrimination learning task. In contrast to distribution models of exclusively rational learners or exclusively incremental learners, a mixture distribution model of rational learners and slow learners was found to fit the data of all measurement occasions and all age groups. Hence, the finite mixture distribution analysis provides strong support for the existence of distinct modes of learning behavior. The results of a second experiment support this conclusion by crossvalidation of the models that fit the data of the first experiment. The effect of verbally labeling the values on the relevant stimulus dimension and the consistency of behavior over measurement occasions are related to the mixture model estimates.

Bayes Theorem↗
PubMed1990

Learning abilities of rats in multiple T-mazes of two degrees of complexity under the influence of d-amphetamine.

The effect of d-amphetamine on the learning capacity of male Wistar rats was investigated in multiple T-mazes in two experiments of increasing or decreasing degree of difficulty. Running speed, distance covered and the number of errors were scored to indicate proficiency and success of learning. These parameters, as well as the distribution of errors (goal-directed orientation), correction of errors (situational orientation) and latency at the decision points (discrimination time) were considered to represent cognitive components. The results demonstrated an experiment effect in that the rats showed more difficulty in learning, as exhibited by a slower running speed and more errors, in the maze with successively increasing demands than in the one with decreasing demands. Oral self-administered d-amphetamine in a dosage of 3-4 mg/kg/day or 7-8 mg/kg/day significantly increased the running speed in a dose-dependent manner. By contrast, success of learning and goal-directed orientation decreased. Situational orientation was, however, dose-dependently improved, at least in the experiment with the increasing demand.

Animals↗
PubMed2003

Visual resolution of gratings by the compound eye of the bee Apis mellifera.

Early measurements of the resolution of horizontal versus vertical gratings were confirmed, with a limit near a period of 2.5 degrees, and the resolution is similar when vertical or horizontal gratings are tested separately against grey. Bees were next trained to discriminate from a distance between gratings at 45 degrees versus 135 degrees, with no green contrast, on targets presented in a vertical plane at a fixed distance. As expected, they fail to learn; however, with green contrast but no modulation difference the resolution limit is near 3.5 degrees. With vertical and horizontal gratings with no green contrast they discriminate but do not learn an orientation cue. In order to eliminate the orientation cue altogether, new bees were then trained with alternating vertical and horizontal gratings versus grey, or with a black and white checkerboard versus grey. Tests of these trained bees with horizontal or with vertical gratings separately against grey again show a resolution down to a period near 2.5 degrees. These results, taken together, show that when edge orientation alone is the cue, the limit of resolution is near 3.5 degrees, but when receptor modulation is the cue, the limit is near 2.5 degrees.

Animals↗
PubMed2003

Comparison of the effect of NT-0409 and antidementia drugs on learning and memory in rats with chronic cerebral cholinergic deficiency.

Systemic oral administration of NT-0409, a new synthetic agonist of AMPA subtype glutamate receptor, to rats with chronic partial AF64A-induced deprivation of cholinergic functions improved their learning in a Morris water maze. NT-0409 is close to memantine by the effect on learning and, in contrast to cholinomimetic arisept, ensures longer retention of the developed habit.

Alzheimer Disease↗
PubMed1994

Declarative memory following anterior temporal lobectomy in humans.

This study hypothesized that verbal memory decline following anterior temporal lobectomy (ATL) is associated with a lack of significant neuropathology in resected left, but not right, hippocampus and is limited to measures of episodic memory only. Tests of immediate (digit span), semantic (visual naming), and episodic memory as measured by the California Verbal Learning Test (CVLT) were administered before and 6 months after resection of the anterior left (n = 36) or right (n = 26) temporal lobe. There were no effects of hippocampal pathology on measures of immediate or semantic memory for either ATL group or for episodic memory for the right ATL group. Left ATL patients who demonstrated no/mild hippocampal sclerosis exhibited significantly greater postoperative decline in episodic memory compared with those with moderate/marked hippocampal sclerosis on multiple CVLT indices (recall measures, learning characteristics, and contrast measures).

Adult↗
PubMed1989

Depression and learning disabilities in children: a test of an hypothesis.

Performance-Verbal IQ discrepancy scores are compared for 27 depressed and 15 nondepressed children all of whom experienced learning difficulties. Brumbach (1985) reported a significant association between depression and Performance IQ deficits for children with learning difficulties. In contrast to Brumbach's finding, no difference was observed in Performance IQ deficit between depressed and nondepressed children in the current study. Moreover, only 10% of depressed children showed such a deficit. This result differed significantly from Brumbach's findings (34%). Implications of these results are discussed within the context of nascent interest in the relationship between depression and learning disabilities.

Child↗
PubMedDate not supplied

[Capacity for learning and extrapolation of mice selected for having different brain weights].

Ability for learning a simple food-searching reaction, and for extrapolation of a food stimulus movement has been studied in two lines of laboratory mice selected throughout 15 generations for high (H-line) and low (L-line) brain weight. It has been found that the mice from H-line learn the food-searching reaction more rapidly than those from L-line. In first presentation of the extrapolation task, the percentage of right solvings by mice from H- and L-lines does not differ from the 50%, expected for the random alternative choice. In subsequent presentations, the percentage of right solvings steadily increases in both lines, and taken over all presentations significantly exceeds the 50% random level, while the mean time of performance gradually grows shorter. Thus, no difference is observed between H- and L-lines either in solving the extrapolation task or in learning this practice, in contrast to a noticeable superiority of H-line in learning a simple motor reaction.

Animals↗
PubMed1990

Specificity and variability of practice.

The specificity of learning principle proposes that motor skills are specific and only superficially resemble other similar skills or variations of the same skill. On the other hand, the variability of practice hypothesis derived from schema theory proposes that experiences with task variations are vital to the development of the memories (schemata) responsible for response production and learning. This paper contrasts these two positions in two experiments aimed at determining the influence of providing variable and/or specific acquisition experiences on the retention of a force production task. The results clearly indicated that acquisition practice with variations of the criterion task leads to better retention than practice on the criterion task alone. This finding is contrary to a strict interpretation of the specificity of learning principle and suggests that paradigms investigating schema notions should be expanded to include potential impacts of variability of practice on tasks experienced during acquisition.

Biofeedback, Psychology↗
PubMed1992

Stress-induced facilitation of classical conditioning.

Stress has been shown to impair subsequent learning. To determine whether stress would impair classical conditioning, rats were exposed to inescapable, low-intensity tail shock and subsequently classically conditioned under freely moving conditions with a brief periorbital shock unconditioned stimulus and a white noise conditioned stimulus. Unexpectedly stressed rats exhibited significantly more conditioned eyeblink responses and the magnitude of their individual responses was also enhanced. These results stand in contrast to the learning deficits typically observed and suggest that stress can enhance the acquisition of discrete conditioned responses.

Acoustic Stimulation↗
PubMed1994

Short-term memory and working memory: do both contribute to our understanding of academic achievement in children and adults with learning disabilities?

Seventy-five children and adults with learning disabilities (age range = 5.0 to 42.10 yrs.) and 86 normally achieving children and adults (age range = 5.11 to 58.0 yrs.) were compared on short-term memory (STM) and working memory (WM) tasks to assess the relationship between STM and WM, and to test whether these measures independently relate to achievement. For both ability groups, the factor analyses indicated that STM and WM loaded on different factors, and the regressions and partial correlations showed that these different factors accounted for separate variance in reading comprehension and mathematics. Both STM and WM are important in understanding reading comprehension and mathematics performance in children and adults with learning disabilities; however, WM is more important for children and adults without learning disabilities. In contrast to WM, STM contributed minimal variance to word recognition in both ability groups. Overall, it was concluded that STM and WM do reflect different processes, both of which seem to separate the two ability groups. However, models of memory that view STM and WM as interchangeable, or STM in isolation, do not provide an adequate framework for capturing academic performance in children and adults with learning disabilities.

Achievement↗
PubMed2006

Good sleep, bad sleep! The role of daytime naps in healthy adults.

PURPOSE OF REVIEW: Millions of people all over the world take a nap during the day. People nap out of habit, because they are sleep-deprived as a result of a sleep disorder, or after a long work shift. Individuals of all age groups, from infants to the elderly, indulge in an afternoon nap. This review examines the benefits and drawbacks of daytime naps in healthy adults. RECENT FINDINGS: A nap during the afternoon restores wakefulness and promotes performance and learning. Several investigators have shown that napping for as short as 10 min improves performance. Naps of less than 30 min duration confer several benefits, whereas longer naps are associated with a loss of productivity and sleep inertia. Recent epidemiological studies indicate that frequent and longer naps may lead to adverse long-term health effects. SUMMARY: A nap of less than 30 min duration during the day promotes wakefulness and enhances performance and learning ability. In contrast, the habit of taking frequent and long naps may be associated with higher morbidity and mortality, especially among the elderly. The benefits of napping could be best obtained by training the body and mind to awaken after a short nap.

Circadian Rhythm↗