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At least 433 records · Page 24Linked to original sources
PubMed2003

Alcohol-induced impairment of behavioral control: effects on the alteration and suppression of prepotent responses.

OBJECTIVE: Alcohol use in humans is associated with aggression and other socially inappropriate behaviors. These adverse effects have been attributed to an acute impairment of behavioral control, and research findings indicate that inhibitory aspects of behavioral control might be particularly vulnerable to the effects of alcohol. The present study tested the degree to which alcohol-induced impairment of behavioral control is due to a specific impairment of inhibitory mechanisms or due to a general information processing deficit. METHOD: Forty subjects (29 men) performed a cued reaction time task before and after receiving 0.65 g/kg alcohol or a placebo. Subjects performed the task under conditions that differed in the type of response needed to maintain behavioral control: response-suppression and response-alteration. RESULTS: Alcohol impairment was observed when behavioral controlwas dependent on response-suppression, but no impairment was observed when control relied on response-alteration. CONCLUSIONS: The findings point to the susceptibility of inhibitory processes by showing that alcohol can be particularly detrimental to behavioral control in situations where prepotent responses must be completely suppressed. Evidence for alcohol-induced impairment of inhibitory functions could provide important clues about basic behavioral mechanisms by which alcohol disrupts such higher order cognitive processes as working memory, learning and decision making.

Adult↗
PubMed1992

Recognition of multiunit neural signals.

An essential step in studying nerve cell interaction during information processing is the extracellular microelectrode recording of the electrical activity of groups of adjacent cells. The recording usually contains the superposition of the spike trains produced by a number of neurons in the vicinity of the electrode. It is therefore necessary to correctly classify the signals generated by these different neurons. This paper considers this problem, and a new classification scheme is developed, which does not require human supervision. A learning stage is first applied on the beginning portion of the recording to estimate the typical spike shapes of the different neurons. As for the classification stage, a method is developed, which specifically considers the case when spikes overlap temporally. The method minimizes the probability of error, taking into account the statistical properties of the discharges of the neurons. The method is tested on a real recording as well as on synthetic data.

Action Potentials↗
PubMed1992

Combining exemplar-based category representations and connectionist learning rules.

Adaptive network and exemplar-similarity models were compared on their ability to predict category learning and transfer data. An exemplar-based network (Kruschke, 1990a, 1990b, 1992) that combines key aspects of both modeling approaches was also tested. The exemplar-based network incorporates an exemplar-based category representation in which exemplars become associated to categories through the same error-driven, interactive learning rules that are assumed in standard adaptive networks. Experiment 1, which partially replicated and extended the probabilistic classification learning paradigm of Gluck and Bower (1988a), demonstrated the importance of an error-driven learning rule. Experiment 2, which extended the classification learning paradigm of Medin and Schaffer (1978) that discriminated between exemplar and prototype models, demonstrated the importance of an exemplar-based category representation. Only the exemplar-based network accounted for all the major qualitative phenomena; it also achieved good quantitative predictions of the learning and transfer data in both experiments.

Concept Formation↗
PubMed2003

Nonintentional task set activation: evidence from implicit task sequence learning.

Studies have shown that task sets could be configured endogenously (i.e., on the basis of memory) according to an explicit sequence or exogenously according to a task cue. In two experiments, we examined whether an implicitly learned sequence could facilitate task set configuration without participants' intention. These experiments led to opposite conclusions regarding this question, but their methodology made it impossible to distinguish between the interpretations. We altered the task-switching paradigm by embedding a hidden task sequence, while randomizing all other aspects, including perceptual (i.e., task cues) and motor elements. We found that a sequence of tasks, proper, was learned implicitly and that the memory of that sequence endogenously facilitated task decision processes without the participants' explicit knowledge.

Functional Laterality↗
PubMed1982

Learning impairment in the radial-arm maze following prolonged cannabis treatment in rats.

Chronic oral administration of cannabis extract to rats (daily delta 9-tetrahydrocannabinol dose 20 mg/kg) was examined in three experiments for its residual effect on radial-arm maze learning following a 1-month drug-free period. Learning a simple eight-arm maze was significantly impaired in rats treated for either 6 months (Experiment I) or 3 months (Experiment II) with the drug. In Experiment III, animals that received the extract for 3 months exhibited significant learning deficits on a much more difficult 12-arm radial maze. The results demonstrate that the deleterious effects of cannabis on radial-arm maze learning are probably due to a tendency toward increased vigilance and perseveration, possibly combined with an impaired utilization of spatial cues.

Animals↗
PubMedDate not supplied

[Influence of the probability of the random performance of an acquired reaction on the rate of the formation of an instrumental reflex].

Instrumental reflex formation in rats takes place more rapidly at high probability of random performance of instrumental reaction to light; however, it does not depend on the frequency of correct responses positive reinforcements (from 50 to 100%). In case of low probability, the learning process sharply slows down at 50% reinforcement of correct responses in comparison with 100% one.

Animals↗
PubMed1986

Learned helplessness as conditioned inattention to the target stimulus.

Learned helplessness theory explains the impaired performance that follows exposure to uncontrollable outcomes by assuming learned expectation of response-outcome independence that is transferred between tasks. Recent evidence has shown that introducing a second neutral stimulus, contingent on the offset of the uncontrollable stimulus, removes the subsequent interference. This finding has been claimed to support the view that the interference is a result of conditioned inattention rather than of the expectation of response-outcome independence. These conflicting explanations were examined in a series of four experiments that varied induction procedures (passive exposure or inescapability) and stimulus quality (aversive or nonaversive). All four experiments found the predicted interference, but only one, in which passive exposure was combined with an aversive stimulus, obtained results supporting the conditioned inattention hypothesis. We conclude that learned helplessness probably involves more than a single mechanism and that the passive exposure procedure may not be appropriate for demonstrating genuine helplessness deficits.

Adult↗
PubMed2004

Voxel-based morphometry of comorbid schizophrenia and learning disability: analyses in normalized and native spaces using parametric and nonparametric statistical methods.

We employed voxel-based morphometry (VBM) to compare the distributions of grey matter found in structural magnetic resonance imaging (MRI) brain scans of patients with comorbid learning disability with schizophrenia, schizophrenia alone, learning disability alone, and normal controls. Our primary aim was to replicate a previous region of interest (ROI) finding that comorbids and schizophrenics belong to the same population. Nonparametric analysis in normalized space showed no significant differences in grey matter distribution between the comorbid and schizophrenia groups. Furthermore, this analysis showed significant grey matter reductions in the comorbid and schizophrenia groups when compared to the learning-disabled or the normal controls. Parametric analysis localized the significant grey matter reductions between the normal controls and the comorbid and schizophrenia groups to the prefrontal and temporal lobes. It also identified an area of increased grey matter, on the inferior aspect of the postcentral gyrus, in the learning-disabled alone compared to the other groups. Native space parametric and nonparametric analyses, based on modulation of the normalized scans, confirmed the similarity in grey matter distribution of the comorbid and schizophrenia groups. Results confirm the ROI finding that in native space the learning-disabled group possesses the least and normal controls the most grey matter for the cohort. An increase in the basal ganglia of patients with schizophrenia vs. the learning-disabled, probably attributable to antipsychotic medication, was identified in the native space analysis. The native space results did not however register statistically significant temporal lobe reductions found under normalized analysis between schizophrenics and normal controls. This may be attributable to minor physical anomalies (MPA) in the schizophrenic cranium. Overall, these VBM results replicate previous ROI findings and are compatible with the view that comorbid learning disability with schizophrenia is a severe form of schizophrenia, rather than a consequence of learning disability. VBM has the facility to compare grey matter distributions in this structurally diverse cohort.

Adult↗
PubMed1997

Age differences in implicit learning of higher order dependencies in serial patterns.

3 experiments examined serial pattern learning in younger and older adults. Unlike the usual repeating pattern, the sequences alternated between events from a repeating pattern and those determined randomly. The results indicated that no one was able to describe the regularity, but with practice every individual in all 3 age groups (including old old) became faster, more accurate, or both, on pattern trials than on random trials. Although this indicates that adults of all ages are able to learn second-order statistical dependencies in a sequence, age-related deficits were obtained in the magnitude of pattern learning. There were also age differences in what was learned, with only younger people revealing sensitivity to higher order statistical dependencies in the sequence. In addition, whereas younger people revealed evidence of their pattern learning in a subsequent conceptually driven production test, young-old and old-old people did not.

Adult↗
PubMed2004

Impaired probabilistic category learning in hypoxic subjects with hippocampal damage.

Previous research has suggested that a probabilistic category learning task (e.g. weather prediction task) can be used to elucidate brain substrates of learning. We tested amnesic subjects with bilateral hippocampal damage due to hypoxia and matched controls on the weather prediction task and a variant, the "ice cream" task, which maintains a similar category structure. The hypoxic subjects were impaired relative to controls on both tasks; in the ice cream task, this difference was evident even early in training (first 50 trials). This finding is similar to functional neuroimaging (fMRI) studies in healthy subjects, which show medial temporal involvement even in early learning on this task. Additionally, strategy analysis of response patterns during learning suggest that the hypoxic group relied more heavily on simple, degraded learning strategies than did the control group. These results may suggest a qualification of the generally held conclusion that amnesic patients are not impaired at probabilistic category learning: at least under some circumstances, amnesic patients show an early and lasting deficit.

Adult↗
PubMed2002

Defining the neural mechanisms of probabilistic reversal learning using event-related functional magnetic resonance imaging.

Event-related functional magnetic resonance imaging was used to measure blood oxygenation level-dependent responses in 13 young healthy human volunteers during performance of a probabilistic reversal-learning task. The task allowed the separate investigation of the relearning of stimulus-reward associations and the reception of negative feedback. Significant signal change in the right ventrolateral prefrontal cortex was demonstrated on trials when subjects stopped responding to the previously relevant stimulus and shifted responding to the newly relevant stimulus. Significant signal change in the region of the ventral striatum was also observed on such reversal errors, from a region of interest analysis. The ventrolateral prefrontal cortex and ventral striatum were not significantly activated by the other, preceding reversal errors, or when subjects received negative feedback for correct responses. Moreover, the response on the final reversal error, before shifting, was not modulated by the number of preceding reversal errors, indicating that error-related activity does not simply accumulate in this network. The signal change in this ventral frontostriatal circuit is therefore associated with reversal learning and is uncontaminated by negative feedback. Overall, these data concur with findings in rodents and nonhuman primates of reversal-learning deficits after damage to ventral frontostriatal circuitry, and also support recent clinical findings using this task.

Adult↗
PubMed2004

A general role for early onset cues and intra-event learning; comment on McDonald and Siegel (2004).

Research on classical conditioning with drug unconditional stimuli has had a profound effect on the understanding of general conditioning processes. The experiment reported by R. V. McDonald and S. Siegel (see record 2004-10475-001) demonstrates that cues coincident with the onset of an event can become associated with the rest of the event. This sort of learning is probably ubiquitous and has been proposed as a mechanism behind the development of panic disorder, in which interoceptive cues coincident with the start of a panic attack can be associated with the rest of the attack and can eventually come to elicit full-blown panic on their own. Evidence that extinction exposure to early onset cues can reduce their power is especially important. Drug conditioning research continues to provide a powerful testing ground for important general principles of learning.

Conditioning, Classical↗
PubMed2000

Memory effects of the Ca2+ and 5-HT antagonists dotarizine and flunarizine.

In experiments on Wistar and Long Evans rats, using behavioral methods for passive (step-down and step-through) and active (shuttle-box two-way avoidance with punishment reinforcement) the newly synthesized diphenyl-methyl-piperazine derivative with Ca2+ and 5-HT antagonistic action dotarizine (DOT) administered repeatedly at oral doses of 50 and 10 mg/kg in some cases improve memory process. Under the same experimental conditions the chemically related to dotarizine Ca2+ antagonist flunarizine significantly facilitated retention. In old (Long Evans and Wistar) rats DOT in large dose decreases values of learning criterion. Probably this is a manifestation of the inherent to drugs with nootropic action "therapeutic window". Earlier investigations of the same and other authors suggest the participation of serotonergic neurotransmission in the mechanism of the memory effects of the drug DOT.

Animals↗
PubMed1988

A unified framework for connectionist systems.

Pattern classification using connectionist (i.e., neural network) models is viewed within a statistical framework. A connectionist network's subjective beliefs about its statistical environment are derived. This belief structure is the network's "subjective" probability distribution. Stimulus classification is interpreted as computing the "most probable" response for a given stimulus with respect to the subjective probability distribution. Given the subjective probability distribution, learning algorithms can be analyzed and designed using maximum likelihood estimation techniques, and statistical tests can be developed to evaluate and compare network architectures. The framework is applicable to many connectionist networks including those of Hopfield (1982, 1984), Cohen and Grossberg (1983), Anderson et al. (1977), and Rumelhart et al. (1986b).

Animals↗
PubMed1998

Spontaneously hypertensive rats: a potential model to identify drugs for treatment of learning disorders.

Spontaneously hypertensive rats (SHR) of 3 to 12 months of age learned and retrieved less information than normotensive Wistar-Kyoto rats (WKY), although no difference was found with animals from 18 and 24 months of age. The combined influence of hypertension and aging had an additive detrimental effect on cognitive functions. Notwithstanding these deficiencies in learning and memory, SHR have seldom been used as a model in the screening of drugs with therapeutic potential for treatment of disorders of cognitive processes. Moreover, the calcium channel blocker nimodipine has beneficial effects on learning in both aged and hypertensive animals and humans. However, no attempt has been made to investigate whether nimodipine can reverse the additive deleterious effects of aging and hypertension in the same subject. We recently reported that deteriorated animals (middle-aged and/or hypertensive) chronically treated with nimodipine (via osmotic minipumps) exhibit higher learning scores. This information indicates that nimodipine can reverse the impairing effects of either aging or hypertension on learning; the presence of the two conditions, however, produces a severe impairment that can be partially reversed by this drug. Therefore, we propose that mature and middle-aged SHR represent a model for the screening of potentially useful drugs in the treatment of learning disorders, probably associated with hypertension and/or aging. Nevertheless, it must be remembered that the SHR is a genetic model and the appearance of neural disturbances could be a parallel genetic phenomenon and not necessarily or exclusively related to hypertension per se.

Aging↗
PubMed2002

The neural basis of human error processing: reinforcement learning, dopamine, and the error-related negativity.

The authors present a unified account of 2 neural systems concerned with the development and expression of adaptive behaviors: a mesencephalic dopamine system for reinforcement learning and a "generic" error-processing system associated with the anterior cingulate cortex. The existence of the error-processing system has been inferred from the error-related negativity (ERN), a component of the event-related brain potential elicited when human participants commit errors in reaction-time tasks. The authors propose that the ERN is generated when a negative reinforcement learning signal is conveyed to the anterior cingulate cortex via the mesencephalic dopamine system and that this signal is used by the anterior cingulate cortex to modify performance on the task at hand. They provide support for this proposal using both computational modeling and psychophysiological experimentation.

Analysis of Variance↗
PubMed1994

Deviation in cerebral excitability: possible clinical implications.

Schizophrenia, a chemical signaling disorder in the brain, is also a deteriorating neurological disorder. The deficit in cerebral excitability, and associated reduced synaptic density, imply a risk of cortical breakdown of circuitry accompanied by an insufficient fill-in mechanism, and persistent silent spots, but no total loss of function, only dysfunction. This is subjectively experienced as deficiencies of cognition, perception and sensorimotor phenomena depending upon localization and connections of the disconnected circuitry. Considering the adversity inherent in this neural network, both the fast Hebbian pre-post form of learning and the slow pre-modulatory coincidence form of learning are probably impaired. The use of Feed Back Loops which usually govern our behaviour might also be impaired. In addition, we have to consider the daily problem of insufficient drive and motivation. Manic depressive psychosis, a chemical signaling disorder in the brain, is a true functional psychosis. The raised excitatory drive and raised synaptic density imply raised risk of uncoupling of circadian rhythms via the direct glutamatergic input to the suprachiasmatic nucleus of hypothalamus (SCN). This episodic brain stem dysfunction illustrates how a deficit in inhibition renders the brain unstable. The requirements of the fast Hebbian form of learning should easily be met, and neither should the slow forms of learning present a problem in networks characterized by excessive density.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral Cortex↗
PubMed2004

New training strategies for constructive neural networks with application to regression problems.

Regression problem is an important application area for neural networks (NNs). Among a large number of existing NN architectures, the feedforward NN (FNN) paradigm is one of the most widely used structures. Although one-hidden-layer feedforward neural networks (OHL-FNNs) have simple structures, they possess interesting representational and learning capabilities. In this paper, we are interested particularly in incremental constructive training of OHL-FNNs. In the proposed incremental constructive training schemes for an OHL-FNN, input-side training and output-side training may be separated in order to reduce the training time. A new technique is proposed to scale the error signal during the constructive learning process to improve the input-side training efficiency and to obtain better generalization performance. Two pruning methods for removing the input-side redundant connections have also been applied. Numerical simulations demonstrate the potential and advantages of the proposed strategies when compared to other existing techniques in the literature.

Algorithms↗