Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Neural Conduction”

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 577 records · Page 32Linked to original sources
PubMed2005

Intraglomerular inhibition: signaling mechanisms of an olfactory microcircuit.

Microcircuits composed of principal neuron and interneuron dendrites have an important role in shaping the representation of sensory information in the olfactory bulb. Here we establish the physiological features governing synaptic signaling in dendrodendritic microcircuits of olfactory bulb glomeruli. We show that dendritic gamma-aminobutyric acid (GABA) release from periglomerular neurons mediates inhibition of principal tufted cells, retrograde inhibition of sensory input and lateral signaling onto neighboring periglomerular cells. We find that L-type dendritic Ca(2+) spikes in periglomerular cells underlie dendrodendritic transmission by depolarizing periglomerular dendrites and activating P/Q type channels that trigger GABA release. Ca(2+) spikes in periglomerular cells are evoked by powerful excitatory inputs from a single principal cell, and glutamate release from the dendrites of single principal neurons activates a large ensemble of periglomerular cells.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1989

Brainstem auditory evoked responses in rats with experimental chronic renal failure.

1. Chronic renal failure was induced in rats by five-sixths nephrectomy. Brainstem auditory evoked response (BAER) was recorded after 3 months. 2. In the uraemic rats latency of the first wave was delayed, while the interpeak I-V latency was similar to that of the controls. 3. These results suggest a delayed neural conduction along the acoustic nerve or cochlear changes in uraemic rats.

Animals↗
PubMed2001

Phase-coupled oscillator models can predict hippocampal inhibitory synaptic connections.

What factors are responsible for propagating electrical activity in the hippocampus? Using an intact, isolated hippocampus preparation, it is possible to observe spontaneous delta (< or = 4 Hz) waves of rhythmic field potentials. These rhythmic potentials are inhibitory in nature, mediated by GABAergic inhibitory potentials originating from a population of principal neurons. They start in the ventro-temporal region and move longitudinally towards the dorso-septal region with a phase lag of approximately 10% between the extracellular recordings. We use the mathematical framework of phase-coupled oscillators (PCO) to gain some insight into the underlying network system. A chain of 15 nearest-neighbour bidirectionally coupled PCOs is used where each oscillator refers to a segment of the CA1 region of the hippocampus that can generate these slow field potentials. We find that ventro-dorsal delta waves exist if there is a dominance in coupling strength in one direction. Without a one-way coupling dominance, ventro-dorsal waves can still exist, but then the coupling strengths need to be much larger. The relationship between entrained and intrinsic frequencies and the variation of propagation speeds along the longitudinal axis can be used to determine which case applies. Currently available experimental data supports one of the cases, predicting that there is a stronger ventral to dorsal inhibitory effect.

Action Potentials↗
PubMed2001

Discharge patterns of neurons in the medial pontobulbar reticular formation during fictive mastication in the rabbit.

In this study, we describe functional characteristics of neurons forming networks generating oral ingestive motor behaviours. Neurons in medial reticular nuclei on the right side of the brainstem between the trigeminal and hypoglossal motor nuclei were recorded in anaesthetized and paralysed rabbits during two types of masticatory-like motor patterns induced by electrical stimulation of the left (contralateral) or right (ipsilateral) cortical masticatory areas. Sixty-seven neurons in nucleus reticularis pontis caudalis (nPontc), nucleus reticularis parvocellularis (nParv), and nucleus reticularis gigantocellularis (Rgc) were studied. These were classified as phasic or tonic depending on their firing pattern during the fictive jaw movement cycle. Phasic neurons located in the dorsal part of nPontc were active during the jaw opening phase, whilst those in dorsal nParv tended to fire during the closing phase. In most neurons, burst duration and firing frequency changed between the two motor patterns, but there was little change in phase of firing. Tonic units were mainly recorded in the ventral half of nPontc, and at the junction between Rgc and caudal nParv. Cortical inputs with short latency from the contralateral masticatory area were more frequent in phasic (82%) than tonic (44%) neurons, whilst inputs from the ipsilateral cortex were equal in the two subgroups (57% and 56%). Phasic neurons had significantly shorter mean contralateral than ipsilateral cortical latencies, whilst there was no difference among tonic neurons. Intra- and perioral primary afferent inputs activated both types of neurons at oligo-synaptic latencies. Our results show that subpopulations of neurons in medial reticular nuclei extending from the caudal part of the trigeminal motor nucleus to the rostral third of the hypoglossal motor nucleus are active during the fictive masticatory motor behaviour. Unlike masticatory neurons in the lateral tegmentum, the medial subpopulations are spatially organized according to discharge pattern.

Action Potentials↗
PubMed2003

Attention and working memory: a dynamical model of neuronal activity in the prefrontal cortex.

Cognitive behaviour requires complex context-dependent mapping between sensory stimuli and actions. The same stimulus can lead to different behaviours depending on the situation, or the same behaviour may be elicited by different cueing stimuli. Neurons in the primate prefrontal cortex show task-specific firing activity during working memory delay periods. These neurons provide a neural substrate for mapping stimulus and response in a flexible, context- or rule-dependent, fashion. We describe here an integrate-and-fire network model to explain and investigate the different types of working-memory-related neuronal activity observed. The model contains different populations (or pools) of neurons (as found neurophysiologically) in attractor networks which respond in the delay period to the stimulus object, the stimulus position ('sensory pools'), to combinations of the stimulus sensory properties (e.g. the object identity or object location) and the response ('intermediate pools'), and to the response required (left or right) ('premotor pools'). The pools are arranged hierarchically, are linked by associative synaptic connections, and have global inhibition through inhibitory interneurons to implement competition. It is shown that a biasing attentional input to define the current rule applied to the intermediate pools enables the system to select the correct response in what is a biased competition model of attention. The integrate-and-fire model not only produces realistic spiking dynamicals very similar to the neuronal data but also shows how dopamine could weaken and shorten the persistent neuronal activity in the delay period; and allows us to predict more response errors when dopamine is elevated because there is less different activity in the different pools of competing neurons, resulting in more conflict.

Animals↗
PubMed2002

Systemic morphine selectively depresses a thalamic link of widespread nociceptive inputs in the rat.

The lateral part of the ventromedial thalamus (VM l) relays nociceptive inputs from the whole body surface to the dorsolateral frontal cortex. The aim of the present study was to investigate the effects of systemic morphine on nociceptive activity evoked in VM l neurones either by thermal (48 degrees C) or by supramaximal percutaneous electrical stimuli. The noxious thermal evoked responses were depressed by 10.8 +/- 10.1%, 48.3 +/- 23.0% and 67.3 +/- 10.1%, 5 min after i.v. injections of 1.0, 1.73 and 3.0 mg/kg of morphine, respectively. Moreover, strong depressive effects on the Adelta- and C-fibre responses were already present 5 min after the injection. The responses were significantly reduced by 7.2 +/- 5.9%, 32.5 +/ 11.1% and 37.2 +/- 11.8% for Adelta fibres after i.v. injections of 1.0, 1.73 and 3.0 mg/kg of morphine, respectively. The corresponding values for C-fibre evoked responses were 16.3 +/- 16.2%, 57.0 +/- 12.0% and 69.0 +/- 8.2%. The dose of morphine that reduced VM l neuronal nociceptive responses by 50% (1.73 mg/kg) was around 3.5 times lower than that necessary to inhibit the responses of its spinal or medullary relays under similar experimental conditions. These results, added to the data of the literature, suggest that supraspinal effects of morphine are primarily mediated at the thalamic level. It is tempting to speculate that morphine-induced reductions of attentional or psychomotor responses related to pain may be mediated by its action on VM l.

Action Potentials↗
PubMed1988

[Contributions to the Aulhorn flicker test. II: The flicker test and the Pulfrich phenomenon in clinical diagnosis].

Fourteen patients with symptoms of acute unilateral optic neuritis were examined with the Pulfrich test and the Aulhorn flicker test. It was found that the positive Pulfrich response and the depth of the apparent orbit depends on the ocular or neural diseases causing a difference in neural conduction from the two eyes. The Pulfrich test is positive for considerably longer than the flicker test. It may be concluded from this that the Pulfrich test is more sensitive to minor residual dysfunction of the affected optic nerve.

Adult↗
PubMed1984

[Detection of central perceptual decrement in optic neuropathies with computer perimetry (Octopus) and visual evoked potentials].

Contrast sensitivity, as far as tested with pattern-VEPs, and light-difference sensitivity, psychophysically tested with the Octopus in the visual field center, seem to reflect different visual functions, because they are disturbed to a different degree in discrete neuropathies: light-difference sensitivity may be within normal range and a careful numerical analysis is needed in order to find pathologic differences. With VEPs, on the other hand, it is easier to detect a loss of normal neural conduction.

Computers↗
PubMed2001

Thoracic outlet syndrome caused by first rib hemangioma.

We report a case of first rib hemangioma that caused thoracic outlet syndrome. A 50-year-ole woman who was admitted to our hospital with a clinical diagnosis of thoracic outlet syndrome presented with fullness and easy fatigue of her right arm. Her right arm discomfort was associated with intermittent engorgement of superficial veins over the shoulder girdle. A chest radiograph revealed an enlargement of the anterior aspect of the first rib with fine bony trabeculations. Computed tomography scan showed contrast enhancement over the enlarged rib. Our tentative preoperative diagnosis was a benign first rib hypertrophic change, such as an old fracture with exuberant callus formation. A right-arm venogram revealed a patent subclavian vein with an extrinsic compression, which occluded on arm abduction. The findings of neural conduction studies of both upper extremities were symmetric and normal. The patient agreed to surgery because of the occlusive condition of the subclavian vein on arm abduction and progressive arm weakness in recent months. Segmental transection of the offending portion of the enlarged first rib was complicated by difficulty in isolating the whole length of the compressed but normal-appearing subclavian vein by our initial transaxillary and infraclavicular approaches because the medial aspect of the subclavian vein was obstructed by the enlarged first rib, which extended medially to the junction of the right jugular and subclavian veins. Successful segmental transection of the enlarged first rib was finally accomplished by combined transaxillary, infraclavicular, and supraclavicular approaches. A moderate amount of rib bleeding from resection ends was noted during segmental resection of the enlarged first rib, resulting in local hematoma formation. A 470-mL bloody discharge was collected from the vacuum ball inserted via the transaxillary route during her 12-day hospitalization. Pathologic examination revealed an intraosseous hemangioma. The patient had a prolonged course to partial recovery of her arm numbness, but signs of venous compression were much improved at 6 months' follow-up. Although hemangioma is benign, its hypervascular nature may cause catastrophic intraoperative bleeding.

Bone Neoplasms↗
PubMed1996

Auditory stimulus detection is not suppressed during saccadic eye movements.

Auditory detection and pitch discrimination thresholds were measured during saccades and during periods of fixation. The accuracy of auditory localisation under these two conditions was also measured. These thresholds were unaffected by whether the sound was presented during a saccade or during periods of steady fixation: there is no evidence for saccadic suppression of auditory processing.

Auditory Perception↗
PubMed1975

Observations on impulse conduction along central axons.

This note calls attention to the facts that (i) the conduction velocities of central axons may not be predicted on the basis of diameter alone, (ii) that such structure-function relations as do exist may not be invariant. Data are presented which indicate that conduction velocities of rabbit callosal axons vary with the history of impulse conduction along the fiber. Increases and decreases of conduction velocity occur. Constant latency does not, therefore, constitute a necessary condition for identification of antidromically activated neurons, and variable latency does not constitute a sufficient condition for identification of synaptically activated neurons. The results are further discussed in terms of temporal coding of information in the central nervous system.

Animals↗
PubMed2000

Hemispheric equivalence and age-related differences in judgments of simultaneity to somatosensory stimuli.

Hemispheric asymmetries, interhemispheric transfer time (IHTT), and age-related differences in judgments of simultaneity to tactile stimulation were examined. Two mechanical stimulators were employed to: (1) Determine whether both cerebral hemispheres are equally capable of processing fine tactile temporal information; (2) determine whether there is an age-related differential hemispheric decline in judgments of simultaneity, and (3) determine if simultaneity thresholds for tactile stimuli increase with advanced age. Tactile simultaneity thresholds were measured by using a modified parameter estimation by sequential testing algorithm. Participants judged whether pairs of tactile stimulation to index and middle fingers were delivered simultaneously. Results of both bimanual and unimanual conditions supported a model of hemispheric equivalence in that both hemispheres were equally capable of making judgments of simultaneity to fine tactile stimuli. The results further suggested that the hemispheric equivalence for judgments of simultaneity remains stable across adulthood. However, IHTTs of older adults were more than double that of younger adults, indicating a significant decrease in the speed of neural conduction. As well, relative to younger adults, older adults had significantly higher simultaneity thresholds.

Adult↗
PubMed1985

A pharmacological overview of opioid mechanisms mediating analgesia and hyperalgesia.

We present a review of the opioid mechanism of analgesia and hyperalgesia and attempt to integrate some of the most recent findings in neuro-anatomy, neuro-physiology and neuropharmacology that indicate the presence of two distinct opioid systems; the one analgesic and the other hyperalgesic. The initial finding of a paradoxical effect of naloxone in which it was able to enhance the analgesic effects of nitrous oxide under certain circumstances led us to postulate the existence of such antagonistic opioid systems which appear to be important in the perception. The review details the further experimental evidence that has subsequently emerged to support our original hypothesis. This includes a hypothesis developed by other workers (viz. diffuse noxious inhibitory control system) which has attempted to explain the analgesic effects of naloxone. Recent anatomical evidence locating the hyperalgesic system in the medullary pontine region is given.

Adrenergic Fibers↗
PubMed2002

Responses of spinohypothalamic tract neurons in the thoracic spinal cord of rats to somatic stimuli and to graded distention of the bile duct.

Anatomical studies indicate that a relatively large percentage of spinohypothalamic tract (SHT) neurons are located within thoracic spinal segments. The aim of this study was to characterize the responses of SHT neurons in these segments of rats to innocuous and noxious stimulation of the skin and of a visceral structure, the bile duct. In addition, we attempted to determine the trajectories of the axons of the examined neurons within the diencephalon and brainstem. Fifty-three SHT neurons were recorded within segments T8-T13 in urethane anesthetized rats. Each cell was antidromically activated using current pulses < or = 30 microA delivered from the tip of an electrode located within the contralateral hypothalamus. The recording points were located in the superficial dorsal horn (9) and deep dorsal horn (44). All examined SHT neurons had receptive fields on the posterior thorax and anterior and ventral abdomen of the ipsilateral side. Ninety percent of the 41 SHT neurons responded exclusively (13) or preferentially (24) to noxious cutaneous stimuli. Thirteen of 27 (48%) examined units were activated by forceful distention of the bile duct. Response thresholds ranged from 30 to 40 mmHg. Responses incremented as pressures were increased to 50-80 mmHg. The axons of 22 of 28 (79%) examined SHT neurons appeared to cross the midline within the hypothalamus and terminate in the ipsilateral hypothalamus, thalamus or midbrain. The results indicate that SHT neurons in thoracic spinal cord of rats are capable of conveying somatic and visceral nociceptive information from the bile duct directly to targets at various levels of the brain bilaterally.

Animals↗
PubMed2004

Auditory brainstem evoked responses in insulin-dependent (ID) and non-insulin-dependent (NID) diabetic subjects with normal hearing.

Hearing impairment has been reported to be one of the late complications of diabetes mellitus (DM), and the frequency varies. Previous data suggest that auditory brainstem potentials deteriorate long before the hearing impairment appears in patients with DM. Delay in neural conductance along the auditory pathway due to DM was assessed by means of auditory brainstem response (ABR) in 43 patients with normal hearing in a controlled study. Patients were classified according to age, presence of neuropathy. metabolic control, and duration and type of DM. ABR recordings revealed that absolute latencies of waves I, III and V were prolonged significantly in the diabetic group when compared to the control group (p < 0.05). When two diabetic groups (insulin-dependent and non-insulin-dependent) were compared with each other, the difference between the latency of wave I and the inter-peak latencies of I-III, III-V and I-V was not significant (p > 0.05). However, the difference between the latencies of waves III and V in the two diabetic groups was statistically significant. The duration of diabetes, blood glucose level and age were not associated with prolonged ABR latencies (p > 0.05). Prolongation of latency of ABR in patients with DM should alert us to possible damage to the auditory nerve, and close follow-up is needed in these patients.

Adolescent↗
PubMed1972

Dynamics of encoding in a population of neurons.

A simple encoder model, which is a reasonable idealization from known electrophysiological properties, yields a population in which the variation of the firing rate with time is a perfect replica of the shape of the input stimulus. A population of noise-free encoders which depart even slightly from the simple model yield a very much degraded copy of the input stimulus. The presence of noise improves the performance of such a population. The firing rate of a population of neurons is related to the firing rate of a single member in a subtle way.

Models, Neurological↗
PubMed2003

An exact method to quantify the information transmitted by different mechanisms of correlational coding.

We derive a new method to quantify the impact of correlated firing on the information transmitted by neuronal populations. This new method considers, in an exact way, the effects of high order spike train statistics, with no approximation involved, and it generalizes our previous work that was valid for short time windows and small populations. The new technique permits one to quantify the information transmitted if each cell were to convey fully independent information separately from the information available in the presence of synergy-redundancy effects. Synergy-redundancy effects are shown to arise from three possible contributions: a redundant contribution due to similarities in the mean response profiles of different cells; a synergistic stimulus-dependent correlational contribution quantifying the information content of changes of correlations with stimulus, and a stimulus-independent correlational contribution term that reflects interactions between the distribution of rates of individual cells and the average level of cross-correlation. We apply the new method to simultaneously recorded data from somatosensory and visual cortices. We demonstrate that it constitutes a reliable tool to determine the role of cross-correlated activity in stimulus coding even when high firing rate data (such as multi-unit recordings) are considered.

Action Potentials↗