Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Models, Neurological”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22Linked to original sources
PubMed1992

Modelling magnetic coil excitation of human cerebral cortex with a peripheral nerve immersed in a brain-shaped volume conductor: the significance of fiber bending in excitation.

To help elucidate some basic principles of magnetic coil (MC) excitation of cerebral cortex, a model system was devised in which mammalian phrenic nerve, or amphibian sciatic nerve with its branches was suspended in appropriate Ringer's solution in a human brain-shaped volume conductor, an inverted plastic skull. The nerve was recorded monophasically out of the volume conductor. The site of nerve excitation by the MC was identified by finding where along the nerve a bipolar electrical stimulus yielded a similar action potential latency. MC excitation of hand-related corticospinal (CT) neurons was modelled by giving the distal end of nerve attached to the lateral skull an initial radial (perpendicular) trajectory, with subsequent bends towards the base and posterior part of the skull; this nerve was optimally excited by a laterally placed figure 8 or round MC when the induced electric field led to outward membrane current at the initial bend. By contrast, nerve given a trajectory modelling CT neurons related to the foot was optimally excited when the coil windings were across the midline, but again when membrane current flowed outward at the first bend. Corticocortical fibers were modelled by placing the nerve in the anteroposterior axis lateral to the midline; with the round MC vertex-tangentially orientated, optimal excitation occurred at the bend nearest the interaural line, i.e., near the peak electric field. The findings emphasize the importance of orientation and direction of current in the MC and fiber bends in determining nerve excitation. The findings in the peripheral nerve-skull model help explain (1) why lateral and vertex-tangentially orientated MCs preferentially excite arm-related CT neurons directly and indirectly (through corticocortical fibers), respectively, and (2) why the MC orientations for optimally exciting directly arm and leg-related CT neurons differ.

Action Potentials↗
PubMed1992

Biological and psychological development of executive functions.

The purpose of this overview is to provide a background for understanding the relation between the biological maturation of the frontal lobes and the development of the psychological concept of executive functions. In the first section, an interactive hierarchical feedback model is presented as a heuristic way of conceptualizing the relationship of the frontal lobes and executive functions to other brain regions and abilities. The following two sections present a synopsis of research on biological maturation and the psychological development of executive functions.

Child↗
PubMed1992

The role of the frontal lobes in the regulation of cognitive development.

Between the ages of 1.5 and 5 years, and again between the ages of 5 and 10 years, a sequence of changes takes place in children's behavior which indicates a fundamental reorganization of their attentional, executive, and self-reflexive processes. In the present article, these changes are summarized, and evidence is adduced to support the claims (1) that these changes are frontally mediated and (2) that the underlying mechanism that generates them is similar to the one that generates the changes in EEG coherence during the same time period. The psychological model that has been hypothesized to explain the cycles of cognitive development (Case, 1992) is then compared to the physiological model that has been proposed to explain cycles of EEG development (Thatcher, 1992). It is shown that the two models are complementary, both in the underlying developmental sequence that they postulate and in the recursive dynamic they propose for producing movement through this sequence. A number of implications and predictions are derived, which follow from the proposition that the two sets of changes are different manifestations of a common underlying process.

Attention↗
PubMed1990

A possible role of proopiomelanocortin peptides in self-injurious behavior.

1. The hypothesis that opioids may be involved in self-injurious behavior is supported by fifteen years of basic animal research suggesting that opioid peptides of the brain and spinal cord participate in the modulation of antinociception in animals, and research of animal models for self-injurious behavior utilizing exogenously administered opiate agonists. 2. Clinical biochemical and pharmacological research conducted over the past five years has also suggested the possibility that opioid peptides may play an important etiological role in the elaboration of self-injurious behavior in some individuals. 3. An opioid overactivity self-injurious hypothesis is supported by results of one study indicating elevated Fraction II opioids (enkephalins) in the lumbar-thecal cerebrospinal fluid of self-injurious children compared to controls, and by the five out of six published studies demonstrating statistically significant decreases in the frequency of self-injurious behavior with the opiate antagonist, naltrexone. 4. A very recent investigation has suggested that some self-injurious individuals show abnormalities in their plasma proopiomelanocortin peptide response to naltrexone, thereby indicating a possible dysfunction in the responsitivity of the proopiomelanocortin system of the hypothalamic-pituitary-adrenal axis of these individuals. 5. These data and results of other investigations have resulted in the elaboration of the original opioid hypothesis to a more comprehensive biochemical model that focuses on this proopiomelanocortin dysregulation. 6. Because of biochemical and functional interrelationships between proopiomelanocortin peptides and certain other neurochemical systems in the brain, it is proposed that pineal melatonin and serotonin may also be involved in this dysregulation. Further basic and clinical research will be needed to test the proposed biochemical model for self-injurious behavior.

Aggression↗
PubMed1988

Problems and paradigms in ERP research.

The ERP technique may provide noninvasive measures that are associated with the processing of psychological information during the performance of a task. Some investigators even regard ERPs as direct manifestations of the psychological processes induced by the demands of the task. Before such a strong claim can be made several methodological problems must be resolved. The present paper discusses the definition and identification of the endogenous components in the ERP, the separation of endogenous components from exogenous components, and the different ways in which inferences can be made about psychological processes on the basis of ERP measures.

Cognition↗
PubMed1988

Decomposing event-related potentials: a new topographic components model.

"Component" notions inherently used with measurement approaches, raw peak determination, PCA and generator approaches are discussed. By combining aspects of them all, a new model of ERP decomposition is established; quite profitable and surprising mathematical properties are illustrated and discussed.

Brain Mapping↗
PubMed1988

Latencies of event related potentials as a tool for studying motor processing organization.

The aim of this experiment was to better define the relative organization of motor processing using both behavioral measures and ERPs. Using the additive factors method, three motor variables; (1) stimulus-response (S-R) compatibility, (2) movement extent, and (3) time uncertainty, were all manipulated in a visuo-bimanual, four-choice, pointing task. As expected, all three variables significantly lengthened RT without interaction. All three motor variables also affected ERP latencies. Both P300 and N200 latencies were lengthened by greater movement extent. Moreover, N200 and P300 latencies were differentially affected by S-R compatibility and time uncertainty. Finally, both RT-minus-N200 and RT-minus-P300 were significantly lengthened by S-R incompatibility and greater time uncertainty whereas movement extent had no effect. In sum, ERP results did not support the assumptions of the classical serial model but rather of a contingent-parallel model. Furthermore, the ERP data can be used to infer the relative order of the different stages in this model.

Adult↗
PubMed1987

Spontaneous formation of regions with different properties in neural nets.

This paper is intended to demonstrate the presence, in a nervous network, of "separate spatial areas", each with its own functional properties, when a "regular external stimulus" occurs. In this preliminary study we deal only with a linear situation, treating a network as a one-dimensional line described by co-ordinate x. We use a continuous approximation with a neuron of the network in each x position.

Models, Neurological↗
PubMed1989

Towards an artificial brain.

Three components of a brain model operating on neuromolecular computing principles are described. The first component comprises neurons whose input-output behavior is controlled by significant internal dynamics. Models of discrete enzymatic neurons, reaction-diffusion neurons operating on the basis of the cyclic nucleotide cascade, and neurons controlled by cytoskeletal dynamics are described. The second component of the model is an evolutionary learning algorithm which is used to mold the behavior of enzyme-driven neurons or small networks of these neurons for specific function, usually pattern recognition or target seeking tasks. The evolutionary learning algorithm may be interpreted either as representing the mechanism of variation and natural selection acting on a phylogenetic time scale, or as a conceivable ontogenetic adaptation mechanism. The third component of the model is a memory manipulation scheme, called the reference neuron scheme. In principle it is capable of orchestrating a repertoire of enzyme-driven neurons for coherent function. The existing implementations, however, utilize simple neurons without internal dynamics. Spatial navigation and simple game playing (using tic-tac-toe) provide the task environments that have been used to study the properties of the reference neuron model. A memory-based evolutionary learning algorithm has been developed that can assign credit to the individual neurons in a network. It has been run on standard benchmark tasks, and appears to be quite effective both for conventional neural nets and for networks of discrete enzymatic neurons. The models have the character of artificial worlds in that they map the hierarchy of processes in the brain (at the molecular, neuronal, and network levels), provide a task environment, and use this relatively self-contained setup to develop and evaluate learning and adaptation algorithms.

Artificial Intelligence↗
PubMed1991

Memory, learning and neuromediators.

We consider a model of a neural network where the individual cells interact only by releasing and absorbing the molecules of a neuromediator. We show that such a system can realize the function of associative memory. A learning mechanism based on the chemotaxis is proposed and numerically investigated.

Association Learning↗
PubMed1984

The 'presynaptic' blocking potency of sulpiride and haloperidol in the rat is age-dependent.

A low dose of pergolide (0.01 mg/kg) caused a marked inhibition of locomotor activity in male rats. Sulpiride significantly blocked the locomotor inhibition in young (6 weeks of age) rats already in low (2.5 mumol/kg) doses, while in adult (15 weeks of age) rats a blockade was achieved first with high 'postsynaptic' doses (50 mumol/kg). Haloperidol slightly blocked the effect of pergolide in both young and adult rats. However, the blocking action of haloperidol was only found in a narrow pharmacological 'window' (0.05 mumol/kg). This study illustrates the importance of considering age-related variations when using behavioural models of 'presynaptic' dopaminergic agonistic activity. It is suggested that 'presynaptic' dopaminergic events are modulated by hormonal changes during growth.

Age Factors↗
PubMed1996

Assessing the dimensions of pain: a multitrait-multimethod evaluation of seven measures.

A multitrait-multimethod design was used to examine the convergent and discriminant validity of seven pain measures from three widely used self-report instruments designed to assess the sensory, affective and intensity dimensions of pain. The instruments were the McGill Pain Questionnaire, the Pain Perception Profile and Numerical Ratings. Three distinct factor models, each corresponding to a different hypothesis about how these pain measures are related, were tested using confirmatory factor analysis in a sample of 419 headache sufferers. A three-factor model, postulating three correlated factors defined by the three assessment instruments best explained the correlations between the pain measures. Measures of sensory, affective and intensity dimensions from the three instruments failed to exhibit convergent or discriminant validity. Rather, instrument variance obscured the pain qualities the three pain instruments were designed to assess. These findings suggest that greater attention needs to be paid to how formal characteristics of pain assessment instruments influence patients' descriptions of their pain.

Adolescent↗
PubMed1991

Of dreaming and wakefulness.

Following a set of studies concerning the intrinsic electrophysiology of mammalian central neurons in relation to global brain function, we reach the following conclusions: (i) the main difference between wakefulness and paradoxical sleep lies in the weight given to sensory afferents in cognitive images; (ii) otherwise, wakefulness and paradoxical sleep are fundamentally equivalent brain states probably subserved by an intrinsic thalamo-cortical loop. From this assumption, we conclude that wakefulness is an intrinsic functional realm, modulated by sensory parameters. In support of this hypothesis, we review morphological studies of the thalamocortical system, which indicate that only a minor part of its connectivity is devoted to the transfer of direct sensory input. Rather, most of the connectivity is geared to the generation of internal functional modes, which may, in principle, operate in the presence or absence of sensory activation. These considerations lead us to challenge the traditional Jamesian view of brain function according to which consciousness is generated as an exclusive by-product of sensory input. Instead, we argue that consciousness is fundamentally a closed-loop property, in which the ability of cells to be intrinsically active plays a central role. We further discuss the importance of spatial and temporal mapping in the elaboration of cognitive and perceptual constructs.

Afferent Pathways↗
PubMed1991

Phasic versus tonic dopamine release and the modulation of dopamine system responsivity: a hypothesis for the etiology of schizophrenia.

A novel mechanism for regulating dopamine activity in subcortical sites and its possible relevance to schizophrenia is proposed. This hypothesis is based on the regulation of dopamine release into subcortical regions occurring via two independent mechanisms: (1) transient or phasic dopamine release caused by dopamine neuron firing, and (2) sustained, "background" tonic dopamine release regulated by prefrontal cortical afferents. Behaviorally relevant stimuli are proposed to cause short-term activation of dopamine cell firing to trigger the phasic component of dopamine release. In contrast, tonic dopamine release is proposed to regulate the intensity of the phasic dopamine response through its effect on extracellular dopamine levels. In this way, tonic dopamine release would set the background level of dopamine receptor stimulation (both autoreceptor and postsynaptic) and, through homeostatic mechanisms, the responsivity of the system to dopamine in these sites. In schizophrenics, a prolonged decrease in prefrontal cortical activity is proposed to reduce tonic dopamine release. Over time, this would elicit homeostatic compensations that would increase overall dopamine responsivity and thereby cause subsequent phasic dopamine release to elicit abnormally large responses.

Afferent Pathways↗
PubMed1992

Loss of the acoustic startle response following neurotoxic lesions of the caudal pontine reticular formation: possible role of giant neurons.

The effect of the excitotoxic N-methyl-D-aspartate agonist quinolinic acid in the caudal pontine reticular formation on the acoustic startle response was investigated in rats. Bilateral injections of 90 nmol of quinolinic acid led to large lesions in the reticular formation characterized by the loss of all neurons and a marked reduction or even abolition of the acoustic startle response; 18 nmol of quinolinic acid led to smaller lesions characterized by a selective loss of giant neurons within the caudal pontine reticular formation and a reduction of the startle amplitude. The partial correlation analysis revealed that the reduction of the amplitude of the acoustic startle response can be correlated with the loss of the giant neurons (r = 0.575; d.f. = 29; P less than 0.001) but not with the reduction of the number of all neurons (r = 0.207; d.f. = 29; P greater than 0.2) in the caudal pontine reticular formation. These findings were reconciled with electrophysiological and anatomical data indicating that the giant neurons in the caudal pontine reticular formation receive acoustic input and project to motoneurons of the spinal cord. It is concluded that the caudal pontine reticular formation is an important element of the startle pathway and that the giant reticulospinal neurons constitute an important part of the sensorimotor interface mediating this response.

Acoustic Stimulation↗