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At least 433 records · Page 24Linked to original sources
PubMed1996

Temporal-spatial pattern of c-Fos expression in the rat brain in response to indispensable amino acid deficiency. II. The learned taste aversion.

Rats rapidly become anorectic when eating an amino acid-imbalanced diet that induces a deficiency of an indispensable amino acid. Recognition of amino acid deficiency is thought to be a function of the anterior piriform cortex. However, the neuronal circuitry underlying the secondary learned aversion to such diets may involve the amygdala. In this study, Fos immunohistochemistry was employed to identify regions of the brain activated during the learned aversion phase of the response to an amino acid-imbalanced diet. c-Fos expression was examined in the brains of rats at intervals from 1 to 6 h after introduction of a diet imbalanced in threonine, a corrected (amino acid-balanced) diet or a basal (low protein) diet. The study has revealed that, within the time frame associated with the learned aversive response, Fos-immunoreactive (Fos-IR) neurons increased selectively in the central nucleus of the amygdala in animals fed a threonine-imbalanced diet. These results suggest a temporal relationship between changes in neuronal activity in the central nucleus of the amygdala and the learned aversion associated with acute amino acid deficiency.

Amygdala↗
PubMed1994

Reducing retroactive interference: an interference analysis.

In 4 experiments on retroactive interference (RI), we varied paired-associate learning lists that produced either appreciable or negligible forgetting. When the category of the stimulus word predicted its response word category, and the response was relatively unique within its category, learning was extremely rapid, and negative transfer and RI were negligible. The more the competing primed items in the predicted response category, the slower the learning and the greater the RI. If cues and responses were unrelated, learning was very slow, and RI was appreciable. Thus, predictive relations that help stimuli retrieve unique responses greatly alter forgetting in RI paradigms.

Adolescent↗
PubMed2000

Acute effects of corticosterone on LiCl-induced rapid gustatory conditioning in rats: a taste reactivity analysis.

Previous research has shown that acute corticosterone treatment can have rapid effects on learning and memory. Using the taste reactivity test (TRT), the present study examined the effect of acute administration of corticosterone on sucrose palatability and the development of LiCl-induced rapid gustatory conditioning. On each of two conditioning days rats were injected with either a low dose of lithium chloride (LiCl; 0.75 mEq, i.p.) or saline (NaCl; 0.9%, i.p.) and 10 min later, received a second injection of either corticosterone (5 mg/kg, i.p.) or cyclodextrin vehicle. Rats were then placed in the TRT chamber, where 1 min intraoral infusions of sucrose (0.3 M) were delivered every 10 min. Taste reactivity responses were videotaped and later analyzed for frequency of occurrence. Rats treated with both LiCl and corticosterone showed enhanced aversive responding and reduced ingestive responding relative to control rats treated with LiCl and vehicle. The implication that corticosterone may have a rapid enhancing effect on gustatory conditioning is discussed.

Animals↗
PubMed1995

RNA folding.

The number of known motifs for RNA folding and RNA tertiary organization is expanding rapidly as we learn more about the diverse biological functions of RNA. Problems in protein and RNA folding have melded in recent investigations of ribonucleoprotein folding. Theoretical and experimental models are rapidly being developed for the pathways and stabilizing forces involved in RNA folding.

Animals↗
PubMed2003

Different mechanisms involved in adaptation to stable and unstable dynamics.

Recently, we demonstrated that humans can learn to make accurate movements in an unstable environment by controlling magnitude, shape, and orientation of the endpoint impedance. Although previous studies of human motor learning suggest that the brain acquires an inverse dynamics model of the novel environment, it is not known whether this control mechanism is operative in unstable environments. We compared learning of multijoint arm movements in a "velocity-dependent force field" (VF), which interacted with the arm in a stable manner, and learning in a "divergent force field" (DF), where the interaction was unstable. The characteristics of error evolution were markedly different in the 2 fields. The direction of trajectory error in the DF alternated to the left and right during the early stage of learning; that is, signed error was inconsistent from movement to movement and could not have guided learning of an inverse dynamics model. This contrasted sharply with trajectory error in the VF, which was initially biased and decayed in a manner that was consistent with rapid feedback error learning. EMG recorded before and after learning in the DF and VF are also consistent with different learning and control mechanisms for adapting to stable and unstable dynamics, that is, inverse dynamics model formation and impedance control. We also investigated adaptation to a rotated DF to examine the interplay between inverse dynamics model formation and impedance control. Our results suggest that an inverse dynamics model can function in parallel with an impedance controller to compensate for consistent perturbing force in unstable environments.

Adaptation, Physiological↗
PubMed1987

Brain stem evoked response in the assessment of learning disabilities.

Evidence has accumulated rapidly to support the hypothesis that neurological anomalies underlie specific forms of learning disability (LD). This article reviews recent studies directed at the electrophysiological assessment of LD children, with emphasis on the brain stem evoked response(BSER) methodology. Child studies appear to indicate that there are significant differences in BSERs between LD and age-matched normal controls. The methodological and statistical differences among these studies, which have clouded the findings and made replication difficult, are reviewed. Improvements in sampling and empirical procedures are suggested, including the use of discriminant analysis to explore BSER asymmetries in LD children. Future inquiry into the measurement and analysis of BSER activity in LD populations is warranted on the basis of these preliminary findings. New information may bring professionals closer to an understanding of the neurological causes of specific subtypes of LD and permit earlier identification of these "at risk" populations.

Adolescent↗
PubMed1990

An asymmetry in transmodal perceptual learning.

Transmodal perceptual learning was examined in a canonical same/different paradigm. Subjects naive to vibrotactile stimulation and unfamiliar with the task were asked to discriminate sequentially presented shapes moving laterally across an aperture. On all trials, the shapes were presented either visually and then vibrotactually or in the opposite modality order, and on all trials the shapes moved in opposite directions. Analyses of the data revealed that although perceptual learning was evident in both groups, the rate of the learning was more rapid in the visual-vibrotactile group. This interaction of modality order and practice was significant and was considered in terms of E.J. Gibson's theory of perceptual learning and in terms of the constructs, suggested by J.J. Gibson, of available and accessible information-in-stimulation and the education of attention.

Adult↗
PubMed1986

Strain difference in learning impairment in rats following lead administration during brain development.

High and stable avoidance with low variability (THA) rats and non-select Wistar rats were administered 2 mg/ml lead acetate solution (0.2-0.27 g/Kg/day as lead) up to seven weeks of age; via placenta from the 13th day of gestation and from maternal milk before weaning, and per os after weaning. Results were as follows. 1) Significant differences were not observed between the lead-exposed rats and the controls regarding the developmental landmarks in both the Wistar rats and THA rats. Body weight of the exposed rats, however, were significantly less than that of the controls of the two rat strains. 2) Low rate of avoidance, slow acquisition of learning and large individual variabilities were exhibited in both the controls and the exposed rats of the Wistar strain throughout the test sessions. No significant difference was indicated between the controls and the exposed rats of the Wistar strain. In the control THA rats, avoidance learning was acquired rapidly, and a high level and very small individual variabilities of avoidance were demonstrated during the latter sessions of the test. Meanwhile, in the exposed THA rats, slow learning acquisition and large individual variabilities were displayed. It is thought that the learning impairment appearing in the THA exposed rats was induced primarily by lead.

Animals↗
PubMed1995

Neuronal recordings in human lateral temporal lobe during verbal paired associate learning.

The temporal lobe has a role in memory and learning. The objective of this study was to assess the activity of neurons in the temporal cortex of humans during learning. Single neuron activity was recorded with extracellular microelectrodes in adults undergoing awake craniotomies for resections for medically intractable epilepsy. Participants were administered control tasks of overt reading, silent reading, nonword visual controls and a recent verbal memory task with distracters followed by a verbal paired associates (PA) paradigm. Forty-nine neurons were identified and characterized by their relationship to language and memory. Neurons related to overt speech (Type A neurons) showed increased activity during learning in patients who were good learners compared to patients who were poor learners. Neurons not related to language or to memory (Type D neurons) showed increased activity with exposure to unlearned word pairs in poor learners compared with those who were good learners. Activity in all groups diminished with practice. Levels of activity in specific types of neurons in human temporal lobe differ in patients who learn word pairs rapidly or poorly.

Craniotomy↗
PubMed2000

Effects of prenatal dexamethasone on spatial learning and response to stress is influenced by maternal factors.

The present study investigated the effect of prenatal dexamethasone (Dex) exposure on early perinatal events, hippocampal function, and response to stress. Pregnant rats received Dex in the evening water (2.5 microg/ml) or tap water (Veh) from gestational day 15 until delivery. On the day of parturition, pups were randomized, cross-fostered, and reduced to eight or nine per dam. Four groups resulted: Veh-Veh (offspring exposed to Veh in utero, rearing mother treated with Veh during gestation), Veh-Dex, Dex-Veh, and Dex-Dex. Spatial visual memory was evaluated with the Morris water maze. The corticosterone response to restraint stress was examined, and the expression of hippocampal glucocorticoid and mineralocorticoid receptors mRNA was determined by in situ hybridization. Exposure to Dex caused restlessness in mothers, low birth weights, and poor weight gain in the offspring. The Dex-Dex males had impaired spatial learning, inability to rapidly terminate the adrenocortical response to stress, and decreased hippocampal glucocorticoid receptor (GR) mRNA expression. In contrast, Dex-exposed animals reared by Veh-treated mothers had adequate spatial learning, enhanced glucocorticoid feedback, and increased hippocampal GR mRNA. We conclude that the environment provided by a healthy mother during the postnatal period can prevent the detrimental effects of prenatal Dex administration on cognition, GR mRNA expression of the hippocampus, and the quality of the stress response.

Adrenal Cortex↗
PubMed2005

Generalization of frequency discrimination learning across frequencies and ears: implications for underlying neural mechanisms in humans.

Frequency discrimination thresholds (FDTs) at 750, 1500, 3000, and 6000 Hz were measured in 32 normal-hearing listeners before and after each listener practiced the task for 12 h at one of the above frequencies using a single ear. Marked improvements in thresholds taking place over several hours were observed during the frequency- and ear-specific training period. Comparisons between pre- and posttraining thresholds showed large improvements at the trained frequency, but also at other frequencies. The improvements were initially slightly-but significantly-larger at the trained frequency than at untrained frequencies. However, this trained-frequency advantage disappeared rapidly during the course of the two-hour multifrequency posttraining session, suggesting rapid relearning or learning generalization across frequencies. In contrast, no significant ear specificity was found, not even at early stages of the posttraining session. These findings add to earlier results suggesting that, in humans, frequency discrimination learning is only weakly frequency-specific, and they reveal that a complete generalization across frequencies can occur rapidly with little retraining at the initially untrained frequencies. Implications regarding underlying mechanisms are discussed.

Adult↗
PubMed1998

Transitional portfolios: orchestrating our professional competence.

Reflective professional development results from thoughtful planning of goals and meeting learning objectives. With rapid changes in health care resulting in major reevaluation and even modification of the role and functions of an occupational therapy practitioner, producing a historical record of competencies in order to learn from one's own experience and to plan for change is essential. A new use of the portfolio is presented to show that a portfolio can be more than the typical repository of completed projects. The transitional portfolio is introduced as a tool for one to self-direct professional development through thoughtful engagement with artifacts created during one's career in relationship to professional goals and desired roles. The transitional portfolio process is holistic, flexible, and reflective. It can serve as a way to document accumulated knowledge and skill acquisition as well as facilitate thoughtful, planned reflection on one's career development in occupational therapy. This article describes the use of transitional portfolios to connect professional development learning experiences, accomplishments, and future opportunities for occupational therapy practitioners.

Career Mobility↗
PubMed1988

Factors affecting degree of perceived foreign accent in English sentences.

This study used interval scaling to assess degree of perceived foreign accent in English sentences spoken by native and non-native talkers. Native English listeners gave significantly higher (i.e., more authentic) pronunciation scores to native speakers of English than to Chinese adults who began learning English at an average age of 7.6 years. The results for the "child learners" suggest that a sensitive period for speech learning is reached long before the age of 12 years, as commonly supposed. Adults who had lived in the U.S. for 5 years did not receive higher scores than those who had lived there for only 1 year, suggesting that amount of unaided second-language (L2) experience does not affect adults' L2 pronunciation beyond an initial rapid stage of learning. Native speakers of Chinese who rated the sentences for foreign accent showed the same pattern of between-group differences as the native English listeners. The more experienced of two groups of Chinese listeners differentiated native and non-native talkers to a significantly greater extent than a less experienced group, even though the subjects in both groups spoke English with equally strong foreign accents. This suggests that tacit knowledge of how L2 sentences "ought" to sound increases more rapidly than the ability to produce those sentences.

Adult↗
PubMed2000

Rapid automatized naming in children referred for evaluation of heterogeneous learning problems: how specific are naming speed deficits to reading disability?

Because the Rapid Automatized Naming (RAN) test reliably predicts reading skill, it is typically viewed as a diagnostic indicator of risk for reading disability (RD). Since most of the work on naming speed has been undertaken within the framework of reading research, however, the extent to which poor RAN is specifically associated with RD or with learning impairment (LI) in general is uncertain. We tested the hypothesis that slow naming speed is specific to RD. Participants were 188 children (ages 7 to 11) referred for evaluation of learning problems. Receiver operating characteristic (ROC) analysis was used to evaluate the utility of the RAN task for classifying children in diagnostic groups. RAN was an excellent tool for detecting risk for learning problems in general, but it was much less effective at distinguishing LI children with and without RD from each other.

Achievement↗
PubMed1997

Training for Norplant implant removal: assessment of learning curves and competency.

OBJECTIVE: To determine the learning curves and rapidity with which clinicians become competent in implant removal using two Norplant removal techniques. METHODS: Twenty-four physicians, none of whom were experienced in the use of Norplant implants, were randomly assigned to learn either the "U" removal technique or the standard technique. The physicians in the two groups received identical training in all other respects. Each physician then performed ten supervised removals. Removal times, procedure problem rates, and the number of procedures performed by the clinicians before they were judged "competent" were assessed for both groups. RESULTS: Data from 240 removals were analyzed. Mean removal times were 38% faster in the "U" group than in the standard group. None of the "U" group procedures took longer than 20 minutes, compared with 11% of removals in the standard group (P < .001). The mean number of cases required before the provider consistently performed all steps adequately was significantly (P < .02) higher in the standard group (5.8 cases) than in the "U" group (3.9 cases). CONCLUSIONS: Using competency-based training methods, the "U" removal technique was learned easily by inexperienced clinicians. It appears to offer significant improvements in speed and achievement of proficiency over the standard technique recommended by the manufacturer. Large-scale programs should consider using competency-based training and the "U" technique as the removal method of choice when providing training in implant removal.

Clinical Competence↗
PubMed2005

Beyond sensory substitution--learning the sixth sense.

Rapid advances in neuroscience have sparked numerous efforts to study the neural correlate of consciousness. Prominent subjects include higher sensory area, distributed assemblies bound by synchronization of neuronal activity and neurons in specific cortical laminae. In contrast, it has been suggested that the quality of sensory awareness is determined by systematic change of afferent signals resulting from behaviour and knowledge thereof. Support for such skill-based theories of perception is provided by experiments on sensory substitution. Here, we pursue this line of thought and create new sensorimotor contingencies and, hence, a new quality of perception. Adult subjects received orientation information, obtained by a magnetic compass, via vibrotactile stimulation around the waist. After six weeks of training we evaluated integration of the new input by a battery of tests. The results indicate that the sensory information provided by the belt (1) is processed and boosts performance, (2) if inconsistent with other sensory signals leads to variable performance, (3) does interact with the vestibular nystagmus and (4) in half of the experimental subjects leads to qualitative changes of sensory experience. These data support the hypothesis that new sensorimotor contingencies can be learned and integrated into behaviour and affect perceptual experience.

Adaptation, Physiological↗
PubMed2006

Amygdala response to facial expressions reflects emotional learning.

The functional role of the human amygdala in the evaluation of emotional facial expressions is unclear. Previous animal and human research shows that the amygdala participates in processing positive and negative reinforcement as well as in learning predictive associations between stimuli and subsequent reinforcement. Thus, amygdala response to facial expressions could reflect the processing of primary reinforcement or emotional learning. Here, using functional magnetic resonance imaging, we tested the hypothesis that amygdala response to facial expressions is driven by emotional association learning. We show that the amygdala is more responsive to learning object-emotion associations from happy and fearful facial expressions than it is to the presentation of happy and fearful facial expressions alone. The results provide evidence that the amygdala uses social signals to rapidly and flexibly learn threatening and rewarding associations that ultimately serve to enhance survival.

Adult↗
PubMed1979

Speech perception in early infancy: perceptual constancy for spectrally dissimilar vowel categories.

While numerous studies on infant perception demonstrate the infant's ability to discriminate individual speech-sound pairs, very few demonstrate the infant's ability to recognize the similarity among phonetic units when they occur in different phonetic contexts, in different positions in a syllable, or when they are spoken by different talkers. In two studies, six-month-old infants demonstrated the ability to distinguish two spectrally dissimilar vowel categories (/a/ and /i/) in which the vowel tokens were generated to simulate tokens produced by a male, a female, and a child talker. In experiment I, the infants were initially trained to discriminate the /a/ and /i/ tokens produced by the computer-simulated male voice. They were then gradually exposed to a number of novel tokens in a progressive transfer-of-learning task. In experiment II, the infants were initially trained to discriminate the same vowell contrast, but were then immediately tested with all of the tokens in both vowel categories. In both experiments the infants demonstrated rapid transfer of learning from the training tokens produced by the male talker to the tokens produced by female and child talkers. Both experiments provide strong evidence that the six-month-old infant recognizes acoustic categories that conform to the vowel categories perceived by adult speakers of English.

Female↗