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PubMed1999

Low-status monkeys "play dumb" when learning in mixed social groups.

Many primates, including humans, live in complex hierarchical societies where social context and status affect daily life. Nevertheless, primate learning studies typically test single animals in limited laboratory settings where the important effects of social interactions and relationships cannot be studied. To investigate the impact of sociality on associative learning, we compared the individual performances of group-tested rhesus monkeys (Macaca mulatta) across various social contexts. We used a traditional discrimination paradigm that measures an animal's ability to form associations between cues and the obtaining of food in choice situations; but we adapted the task for group testing. After training a 55-member colony to separate on command into two subgroups, composed of either high- or low-status families, we exposed animals to two color discrimination problems, one with all monkeys present (combined condition), the other in their "dominant" and "subordinate" cohorts (split condition). Next, we manipulated learning history by testing animals on the same problems, but with the social contexts reversed. Monkeys from dominant families excelled in all conditions, but subordinates performed well in the split condition only, regardless of learning history. Subordinate animals had learned the associations, but expressed their knowledge only when segregated from higher-ranking animals. Because aggressive behavior was rare, performance deficits probably reflected voluntary inhibition. This experimental evidence of rank-related, social modulation of performance calls for greater consideration of social factors when assessing learning and may also have relevance for the evaluation of human scholastic achievement.

Animals↗
PubMed1998

Neither extended sequential nor simultaneous feature positive training result in modulation of evaluative flavor-flavor conditioning in humans.

In previous attempts to induce Pavlovian modulation of human evaluative flavor-flavor associations, the recurrent finding was that exposure to a Feature Positive (FP) schedule (XA+/A-), in which flavor A was reinforced by the aversive flavor Tween20 if and only if it was accompanied by a feature stimulus X, did not result in the expected X-modulated dislike for target A, but in simple unconditional A-US associations. The first experiment reported here investigated if more extended training results in a shift from simple A-US learning to the development of X-modulated A-US associations. Participants were exposed to a 32-trial, 4-session sequential FP schedule using flavors both for feature and target stimuli. The modulatory and/or excitatory power of the stimuli was assessed after each training session. After initial training, participants again acquired a simple unmodulated target A-US association. Contrary to expectations, the additional training sessions did not result in participants gradually learning the XA+/A- discrimination, but rather seemed to corroborate the already established A-US association. This was true whether or not participants acquired valid explicit knowledge about the conditional X-->(A-US) relation. The second experiment tested the hypothesis that what can be described as conditional flavor preferences may actually be based on a configural learning process. Participants were exposed to a single-session, eight-trial XA+/A- simultaneous discrimination schedule, the parameters of which were selected so as to enhance the probability of configuring XA, while simultaneously making it likely to observe a pattern of evaluations similar to an X-modulated dislike for A (X was less salient than A). Even though there was good evidence that participants noticed flavor X, they again failed to solve the XA+/A- discrimination and most probably acquired an association between the more salient flavor A and the US. The possibility is discussed that evaluative learning, unlike expectancy learning, might ultimately prove not to be subject to modulation.

Adult↗
PubMed1998

Kernel-Based Equiprobabilistic Topographic Map Formation.

We introduce a new unsupervised competitive learning rule, the kernel-based maximum entropy learning rule (kMER), which performs equiprobabilistic topographic map formation in regular, fixed-topology lattices, for use with nonparametric density estimation as well as nonparametric regression analysis. The receptive fields of the formal neurons are overlapping radially symmetric kernels, compatible with radial basis functions (RBFs); but unlike other learning schemes, the radii of these kernels do not have to be chosen in an ad hoc manner: the radii are adapted to the local input density, together with the weight vectors that define the kernel centers, so as to produce maps of which the neurons have an equal probability to be active (equiprobabilistic maps). Both an "online" and a "batch" version of the learning rule are introduced, which are applied to nonparametric density estimation and regression, respectively. The application envisaged is blind source separation (BSS) from nonlinear, noisy mixtures.

Journal Article↗
PubMed1998

Who learns preventive health care information from where: cross-channel and repertoire comparisons.

We studied from which information channels individuals reported learning the most information about preventive health care, how those channels correlated with one another, and how well they were predicted by demographics and health orientations. A probability sample of 1,963 adults from 8 midwestern communities were interviewed from late 1994 to early 1995. Respondents reported learning different amounts of preventive health information from different channels, and a mix in levels of learning was found across channels. Television news and information rated unexpectedly high across the population studied. An exploratory factor analysis indicated a clear grouping or repertoire consisting of television channels, and for magazines and newspapers, but also a distinct personal media repertoire involving a mix of health professionals, family and friends, books, educational materials, and computers. Demographics did better at predicting learning from traditional print media, but personal health orientations were more effective predictors of personal media; television was less well predicted by either.

Journal Article↗
PubMedDate not supplied

Demonstration of lever pressing for oral ethanol by rats with no prior training or ethanol experience.

Male rats of the alcohol-preferring AA line were placed in an operant conditioning chamber with one lever delivering 10% alcohol solution and a second giving water. Free food and water were also continually available in the chamber so the animals should not have been motivated to obtain alcohol for reasons of hunger or thirst. The rats had never had alcohol previously. No shaping was used. The rats simply lived for the next 2 weeks in the operant chamber. All of them eventually learned to work for alcohol. Ethanol responding was significantly higher than pressing for water throughout the second week: on the last day, all rats pressed more than 300 times for alcohol and less than 40 times for water, took in a mean of 5.3 +/- 0.2 g/kg of ethanol, and obtained 72% of their total fluid as earned ethanol solution despite the presence of free water. Their acquisition was, however, much slower than that observed in male AA rats that had previously had prolonged access to drinking alcohol in their home cages. Living continually in the operant chamber is thought probably to have been an important factor in enabling the naïve rats to learn to work for alcohol.

Alcohol Drinking↗
PubMed2005

Contributions of the hippocampus and the striatum to simple association and frequency-based learning.

Using fMRI and a learning paradigm, this study examined the independent contributions of the hippocampus and striatum to simple association and frequency-based learning. We scanned 10 right-handed young adult subjects using a spiral in/out sequence on a GE 3.0 T scanner during performance of the learning paradigm. The paradigm consisted of 2 cues that predicted each of 3 targets with varying probabilities. Simultaneously, we varied the frequency with which each target was presented throughout the task, independent of cue associations. Subjects had shorter response latencies to frequently occurring and highly associated target stimuli and longer response latencies to infrequent target stimuli, indicating learning. Imaging results showed increased caudate activity to infrequent relative to frequent targets and increased hippocampal activity to infrequent relative to frequent cue-target associations. This work provides evidence of different neural mechanisms underlying learning based on simple frequencies versus associations within a single paradigm.

Adult↗
PubMed2005

Neural encoding of olfactory recognition memory.

Our work with both sheep and mouse models has revealed many of the neural substrates and signalling pathways involved in olfactory recognition memory in the main olfactory system. A distributed neural system is required for initial memory formation and its short-term retention-the olfactory bulb, piriform and entorhinal cortices and hippocampus. Following memory consolidation, after 8 h or so, only the olfactory bulb and piriform cortex appear to be important for effective recall. Similarly, whereas the glutamate-NMDA/AMPA receptor-nitric oxide (NO)-cyclic GMP signalling pathway is important for memory formation it is not involved in recall post-consolidation. Here, within the olfactory bulb, up-regulation of class 1 metabotropic glutamate receptors appears to maintain the enhanced sensitivity at the mitral to granule cell synapses required for effective memory recall. Recently we have investigated whether fluctuating sex hormone levels during the oestrous cycle modulate olfactory recognition memory and the different neural substrates and signalling pathways involved. These studies have used two robust models of social olfactory memory in the mouse which either involve social or non social odours (habituation-dishabituation and social transmission of food preference tasks). In both cases significant improvement of learning retention occurs when original learning takes place during the proestrus phase of the ovarian cycle. This is probably the result of oestrogen changes at this time since transgenic mice lacking functional expression of oestrogen receptors (ERalpha and ERbeta, the two main oestrogen receptor sub-types) have shown problems in social recognition. Therefore, oestrogen appears to act at the level of the olfactory bulb by modulating both noradrenaline and the glutamate/NO signalling pathway.

Animals↗
PubMed2003

Effect of noopept and afobazole on the development of neurosis of learned helplessness in rats.

We studied the effects of new psychotropic preparations noopept and afobazole on acquisition of the conditioned active avoidance response and development of neurosis of learned helplessness in rats. Noopept in doses of 0.05-0.10 mg/kg accelerated acquisition of conditioned active avoidance response and reduced the incidence of learned helplessness in rats. Afobazole in a dose of 5 mg/kg produced an opposite effect, which is probably related to high selective anxiolytic activity of this preparation.

Animals↗
PubMed2004

Facilitation of probabilistic classification learning by transcranial direct current stimulation of the prefrontal cortex in the human.

The aim of our study was to test if the electrical stimulation of the prefrontal cortex (PFC) could modify probabilistic classification learning (PCL). Transcranial direct current stimulation (tDCS) was administered to the left prefrontal and to the primary visual cortex of 22 healthy subjects while they performed a PCL task. In this task subjects learned which of two outcomes would occur on each trial after presentation of a particular combination of cues. Ten minutes of anodal, but not cathodal, stimulation improved implicit learning only when the left PFC was stimulated. Our results show that implicit PLC can be modified by weak anodal tDCS, which probably increases neural excitability, as has been shown in the motor and visual cortices previously. Our results suggest that further studies on the facilitation of learning and memory processes by tDCS are warranted.

Adult↗
PubMed1984

Learning as a function of haptic discriminability among items.

In Experiment 1, braille symbols for the letters A-J were found to be more haptically discriminable from one another than braille symbols for the letters K-T. In Experiment 2, subjects learned the names for the A-J symbols faster than for the K-T symbols. Experiment 3 demonstrated that faster learning of the names for the A-J than for the K-T symbols is attributable to characteristics of the symbol sets themselves (probably to the discriminability of the items from one another) and not to what they are called. The effects of discriminability on learning in these experiments are similar to those from experiments in which other modalities have been used.

Blindness↗
PubMed2002

The illusion of the learning phase for lymphatic mapping.

BACKGROUND: We provide a statistical analysis of the learning phase for sentinel node biopsy. METHODS: Four learning phases were analyzed: 25, 50, 75, and 150 procedures with a corresponding number of 10, 20, 30, and 60 tumor-positive cases. Critical values of nonidentification rate and false-negative rate were defined. The binomial distribution was used to calculate the probabilities of correctly or incorrectly accepting the quality of the performance, given a certain long-term nonidentification or false-negative rate. RESULTS: The chance of incorrectly reaching a favorable false-negative rate of <10% (critical value) in 20 metastasized patients was 18% for a surgeon with a long-term probability of false-negative procedures of 15%. This chance was reduced to 10% with a learning phase of 60 tumor-positive cases. When this chance has to be further reduced to 5%, the critical value has to be lower in smaller groups of patients: 5% false-negative rate in 20 tumor-positive procedures. CONCLUSIONS: A learning phase of at least 150 procedures with 60 tumor-positive cases is needed to draw any reliable conclusion about the quality of sentinel node biopsy. In general, a compromise has to be made between the reliability of the results and the practically achievable number of procedures.

Binomial Distribution↗
PubMed1996

The frontal cortex-basal ganglia system in primates.

The primate basal ganglia receives information from most of the cerebrum, including the frontal cortex, but projects (via the dorsal thalamus) primarily to the frontal lobe, perhaps in its entirety. As such, the frontal cortex and basal ganglia constitute an integrated, distributed neuronal architecture. We review evidence that the frontal lobe and basal ganglia specialize in different, but related, aspects of response learning. Frontal cortex acts when new rules need to be learned and older ones rejected, whereas the basal ganglia potentiate previously learned rules based on environmental context and reinforcement history. Such potentiation increases the probability that the central nervous system will select a particular rule to guide behavior. We outline a possible mechanism for the basal ganglia's proposed role in rule potentiation, one that involves both the direct and indirect striatal output pathways and their dopaminergic input. It has previously been proposed that direct-pathway neurons recognize a pattern of corticostriatal inputs, which promotes activity in recurrent, positive-feedback modules (or loops) of which they are an integral part. We propose that this recurrent activity potentiates a rule associated with those modules. If so, then the dopaminergic system is well situated and organized to modulate rule potentiation in both the short and long term. Dopaminergic neurons of the midbrain increase activity during learning and other periods of relatively unpredictable reinforcement. Dopamine enhances gene expression and other forms of activity in striatal neurons of the direct pathway, while suppressing neurons of the indirect pathway. In the short term, then, dopamine may augment the activity of modules triggered by a recognized context, whereas in the long term it may promote context-dependent activation of the same modules. Together, these modulatory influences could support both rule potentiation and learning the context for potentiating that rule.

Animals↗
PubMed2004

Random presentation enables subjects to adapt to two opposing forces on the hand.

Studies have shown that humans cannot simultaneously learn opposing force fields or opposing visuomotor rotations, even when provided with arbitrary contextual information, probably because of interference in their working memory. In contrast, we found that subjects can adapt to two opposing force fields when provided with contextual cues and can consolidate motor memories if random and frequent switching occurs. Because significant aftereffects were seen, this study suggests that multiple internal models can be acquired simultaneously during learning and predictively switched, depending only on contextual information.

Cues↗
PubMed2002

Neurobehavior effects in four strains of mice offspring exposed prenatally to alprazolam.

OBJECTIVE: This study was performed to determine whether prenatal exposure to alprazolam affects offspring behavior in different strains of mice. STUDY DESIGN: Eight to 11 gravid mice of the C3H/He, C57BL/6, A/J, and DBA/2 strains were given either an anxiolytic dose of alprazolam (0.32 mg/kg) or a placebo by gavage on day 18 of an anticipated 19- to 21-day gestation. Neurobehavior tasks were conducted to assess anxiety, learning and memory, and social interaction. Data were analyzed by analysis of variance or a Fisher exact probability test. RESULTS: Anxiety in alprazolam-exposed offspring was reduced in C3H/He (P <.05) and A/J (P <.05) newborn infants by separation vocalization but may be increased in the C3H/He adult strain on the plus maze task. Learning was slower among C57BL/6 mice exposed to alprazolam (P <.01), whereas memory was reduced in exposed A/J and DBA/2 offspring (P <.05). Alprazolam exposure was associated with more aggression among C3H/He and C57BL/6 male offspring (P <.01) and with less group activity by C57BL/6 offspring (P <.05). CONCLUSION: Altered behaviors in several mouse strains after prenatal exposure to alprazolam suggests a vulnerability of GABA-benozdiazepine receptor formation in fetal brain development.

Aggression↗
PubMed1984

Changes of membrane currents during learning.

The integrated response of a population of neurones during conditioning results in long-term (days) changes of specific membrane currents within identified neurones. Prolonged elevation of intracellular calcium during conditioning causes a persistent increase of excitability by reducing K+ currents (IA and probably ICa2+-K+) in the membranes of identified somata. This Ca2+-mediated reduction of K+ currents, which encodes a learned stimulus association is thought to involve changes of Ca2+-calmodulin-dependent phosphorylation of distinct membrane proteins. These changes are contrasted with the short-term regulation of currents by neurohormones during altered behavioural states such as arousal.

Animals↗
PubMed1981

Behavioral effects of early rearing conditions and neonatal lesions of the visual cortex in kittens.

Kittens with neonatal lesions of the marginal and posterolateral gyri, along with unoperated controls, were reared either in an enriched environment or in laboratory cages. Kittens with lesions were inferior to controls at learning mazes and at discriminating forms and gratings, whether they were raised in enriched or impoverished conditions. Enrichment did not facilitate form or grating discrimination by either normal or operated cats, although such experience facilitated maze learning by both groups. It is concluded that early enrichment of sensorimotor experience was probably not the cause of the complete sparing of pattern vision after neonatal damage of the visual cortex reported in earlier studies. Discussion centers on task variables and completeness of the lesions as reasons for sparing of vision.

Animals↗
PubMed2003

The effects of cerebellar damage on maze learning in animals.

The role of the cerebellum in spatial learning has recently been investigated in genetically and non-genetically lesioned animal models, particularly in water mazes, in view of the minimal impact such lesions exert on swimming movements. A dissociation between place and cued learning in the Morris water maze has been observed in several models, including cerebellar mutant mice (Rora(sg), Nna1(pcd-1J), nervous), rats with lesions of either the lateral cerebellar cortex or the dentate nucleus, and rats with selective Purkinje cell loss caused by intracerebroventricular injections of OX-7-saporin, confirming the hypothesis that cerebellar damage may cause a cognitive deficit independently of fine motor control. In addition, the results of hemicerebellectomized rats indicate the probable involvement of the cerebellum in working memory and the procedural aspect of maze learning. The findings of impaired maze learning in cerebellar-lesioned mice and rats are concordant with those of deficient visuospatial functions in patients with cerebellar atrophy. The spatial deficits may be ascribed to altered metabolic activity in cerebellar-related pathways.

Animals↗
PubMed1997

Kindling of the dorsal and the ventral hippocampus: effects on learning performance in rats.

The hippocampus represents a heterogeneous structure which has been associated with different functions. It has been suggested that it plays an important role in both learning and memory and epileptogenesis. Thus, it is not surprising that seizure activity generated in the hippocampal formation interferes with memory storage. Little is known about the functional differentiation between the dorsal (DH) and ventral hippocampus (VH). To study this functional differentiation, we kindled Wistar rats either in the DH or in the VH by electrical stimulation. Afterwards, learning performance of these rats was tested in three different models, i.e., response to change (short-term memory), shuttle box (two-way active avoidance), and Y-chamber (brightness discrimination reaction). It was found that VH-kindled rats reached higher seizure scores than DH-kindled rats, but there was no difference in seizure duration. Kindling induced in the VH significantly impaired shuttle box learning, whereas DH-kindled rats showed a dramatically worsened acquisition in the brightness discrimination task. Different anatomical projections probably account, in part, for these differences.

Animals↗