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 451 records · Page 25Linked to original sources
PubMed1985

Modulatory and inhibitory processes in the visual cortex.

The functional role of three putative neurotransmitter systems in the visual cortex is compared; the GABAergic inhibitory interneurons, the interneurones containing somatostatin and the cholinergic input originating from the nucleus basalis of Meynert (nbM). Evidence is presented to support the role of GABAergic processes in the generation of the functional structure of the visual cortex and the view that the cholinergic input exerts a neuromodulatory influence enhancing stimulus selective responses. Although the neuropeptide somatostatin produces facilitatory and inhibitory effects on visual cortical cells there is no clear functional pattern to its action. The possible significance of this data and the interaction of SSt with GABA is discussed in the light of evidence that they may coexist in some cells.

Acetylcholine↗
PubMed1996

Location vs feature: reaction time reveals dissociation between two visual functions.

Reaction time in a detection or a location discrimination task was longer when a target appeared at the same location as in the previous trial (inhibition of return; IOR). However, it became shorter when the task was color or orientation discrimination (facilitation of return: FOR). This dichotomy was observed in the single target as well as in the popout displays. In additional experiments, vernier, size, and luminance discriminations all led to FOR, whereas eye-movement and arm-reaching tasks led to IOR. Moreover, identical stimuli could lead to the opposite patterns of result depending on the nature of the task: inhibition in global location tasks, and facilitation in feature analysis tasks. These may correspond to "where" vs "what" or "action" vs "recognition" pathways neurophysiologically.

Analysis of Variance↗
PubMed1996

Neurophysiological evidence for contrast dependent long-range facilitation and suppression in the human visual cortex.

Long-range spatial interactions in human visual cortex were explored using a lateral masking paradigm. Visual evoked potentials (VEPs) elicited by a Gabor signal presented in isolation or in the presence of two flanking high-contrast Gabor signals (masks) were measured. Response amplitude and phase were recorded for a vertically oriented test, for horizontal and vertical masks and for combinations of vertical tests and vertical or horizontal masks. The amplitudes and phases of the test alone and mask alone responses were added coherently to predict the amplitude for collinear and orthogonal lateral masking conditions. Additivity failures were taken as evidence for neural interactions. At a target-to-mask distance of 2 deg, VEP amplitude exceeded the linear prediction for test contrasts in the range of 8-16% for the collinear, co-axial target/mask combination. Measured response phase also led predicted response phase over the same range of contrast. The VEP amplitudes were less than the linear prediction in the orthogonal target/mask combination and measured response phase lagged the predicted phase. Significant facilitation occurred with collinear test/mask combinations up to at least 3 deg of separation (nine wavelengths). Co-oriented, but non-collinear test/mask combinations (oblique test and mask, horizontal test and mask) did not produce facilitation. Contrast gain thus appears to be set over considerable distances in a configuration-specific fashion.

Contrast Sensitivity↗
PubMed1986

Constraints imposed on taste physiology by human taste reaction time data.

The speed with which an organism responds to stimulus events is reaction time (RT): the minimum time interval between stimulus arrival at a receptor organ, and an overt response by the organism. This time interval specifies maximum duration of all processes necessary for the RT sequence. Responses to any change in taste have RT less than 1 sec for suprathreshold concentrations. Therefore, constituent events at taste receptors, in the central nervous system (CNS), and at the response organ, must have sufficient durations less than 1 sec (Constraint 1). Taste stimulus durations of 50 msec, and therefore taste receptor events of approximately 50 msec, are sufficient for these responses (Constraint 2), as well as for taste quality identification responses (Constraint 3). Taste receptor latencies, neural conduction times, and RT response organ events are even briefer. Thus, 60% to 90% of human taste RT is CNS events. Taste receptor events remain crucial, but CNS processing is important, and apparently time limiting, in all human taste judgments.

Afferent Pathways↗
PubMed1982

Interactions between femoral venous afferents and lumbar spinal reflex pathways.

This study reports findings of spinal reflex connections of afferent fibers electrically excited in the wall of the femoral vein. Condition-test experiments, and EMG recordings revealed that the femoral venous afferents have facilitatory connections to flexor and extensor motoneurons of both the proximal and the distal hindlimb muscles. Femoral venous afferent stimulation which produced facilitation, also produced inhibition of the test reflexes following the facilitation. Because the inhibition was enhanced by diazepam injection and because the inhibitory time-course correlated closely to the time-courses of both dorsal root potentials and individual tests of primary afferent depolarization, the inhibition was suggested to be produced by presynaptic inhibition. The potentially significant role of the venous afferent connections in a reflex-elicited skeletal muscle pump or in an increase in intramuscular venous counterpressure is discussed.

Afferent Pathways↗
PubMed1984

Brain monoaminergic control of male reproductive behavior. II. Dopamine and the post-ejaculatory refractory period.

This study was designed to examine the role of central dopaminergic mechanisms in the control of copulation and the subsequent post-ejaculatory refractory period in the male rat. Disruption of central dopaminergic pathways was achieved in two separate groups of animals by: (1) selective electrolytic lesions of the substantia nigra (the major locus for dopamine cell bodies in the brain); or (2) localized intracerebral injection of 6-hydroxydopamine, a specific neurotoxin for catecholaminergic pathways. A third group of animals was tested for sexual behavior following administration of the dopamine receptor blocker pimozide. Both electrolytic and neurochemical lesions localized in the substantia nigra produced a significant increase in the length of the post-ejaculatory refractory period. Dopamine receptor blockade following administration of pimozide also caused a significant increase in refractory period duration. These results support the hypothesis that central dopaminergic pathways are involved in the motivational or arousal component of copulation and may be integral to the maintenance of a normal post-ejaculatory refractory period.

Amygdala↗
PubMed1984

Brain monoaminergic control of male reproductive behavior. III. Norepinephrine and the post-ejaculatory refractory period.

The present study was performed to examine the role of brain norepinephrine in the control of copulation and the post-ejaculatory refractory period in the male rat. Disruption of central noradrenergic systems was achieved by (1) selective electrolytic lesion of noradrenergic cell bodies in the locus coeruleus or (2) administration of specific inhibitors of norepinephrine synthesis, sodium diethyldithiocarbamate (DDC) or 1-phenyl-3-(2-thiazolyl)-2 thiourea (U-14, 624). Electrolytic lesions of the locus coeruleus produced a significant increase in the duration of the post-ejaculatory refractory period and its concomitant 22-kHz ultrasonic vocalization. Administration of norepinephrine synthesis inhibitors significantly increased both mount and intromission latencies and caused a dramatic increase in the length of the post-ejaculatory refractory period. These findings support the hypothesis that norepinephrine-containing neural pathways are involved in the control of sexual arousal and suggest that a functional noradrenergic system is essential to the integrity of normal masculine copulatory behavior.

Animals↗
PubMed1987

The effect of pulse duration of refractory periods of neurons mediating brain-stimulation reward.

The post-stimulation excitability characteristics of neurons mediating the rewarding effects of electrical stimulation of the medial forebrain bundle were behaviorally assessed at 5 different pulse durations. Recovery from refractoriness was inferred from the results of double-pulse tests in which the interval between conditioning (C) and test (T) pulses of equal amplitude was varied. Pulses of 0.1-0.5 ms had little effect on the time course of recovery which ranged from 0.4 to about 1.5 ms in each animal. In some subjects, however, complete recovery from refractoriness was significantly delayed with 1- and 2-ms pulses, with as much as a tripling in the C-T interval at which recovery approached asymptotic levels. This effect appeared to be placement-specific and was well correlated with the threshold charge, which ranged from 0.5 to 1.3 microC. The highest charge values were obtained in those subjects in which longer pulses displaced the refractory period profile towards a slower recovery; the electrode tips in this group were located in more anterior positions than those subjects in which pulse duration had no effect on recovery from refractoriness. It appears that at some placements slowly recovering elements can contribute to the circuitry underlying brain-stimulation reward when suitable stimulation parameters are employed.

Animals↗
PubMed1985

Two types of rostroventral medulla neurons projecting to the trigeminal spinal nucleus as differentiated by the response to antidromic activation and the histological location.

A population of neurons in the rostroventral medulla, which send their axons to the subnucleus oralis of the trigeminal spinal nucleus of rats, could be differentiated into two types on the basis of their location and the variability of antidromic latency during repetitive stimulation at 10 Hz. Type A neurons were mostly located in the raphe magnus and were activated antidromically with a relatively long latency, which gradually increased during repetitive stimulation. By contrast, type B neurons were located in the medial portion of the gigantocellular reticular nucleus, and responded with a relatively short, stable antidromic latency.

Animals↗
PubMed1986

Synaptic currents at interpositorubral and corticorubral excitatory synapses measured by a new iterative single-electrode voltage-clamp method.

A new iterative single-electrode voltage clamp method was applied to the measurement of synaptic currents in the red nucleus (RN) neuron of the cat. Voltage clamp was attained within 10 repetitions with great stability and the new algorithm was demonstrated to be superior to the original algorithm of iterative voltage clamp. With a conventional microelectrode, it was possible to measure the synaptic current with the time resolution of 50 microseconds. The synaptic currents evoked by stimulation of the contralateral interpositus nucleus (IP) had time-to-peak ranging from 200 to 540 microseconds and fitted well to alpha functions. Corticorubral (CR) synaptic current was also measured by making use of synaptic plasticity. The stimulation of the ipsilateral cerebral peduncle in cats with chronic lesion of the contralateral IP evoked fast rising EPSPs, as reported previously. The CR-EPSPs with times-to-peak less than 1 ms were subjected to voltage clamp. The CR synaptic currents had times-to-peak ranging from 350 to 880 microseconds. Since most of the interpositorubral (IR) synapses and a part of the CR synapses in IP-lesioned cats are situated on the somatic membrane of RN neurons and some of the CR synaptic currents were as rapid as the IR synaptic currents, the observed synaptic currents evoked by stimulation of the IP and those of the fast-rising CR-EPSPs were taken to originate from the synaptic membrane under space-clamp, i.e. soma. The present study provided additional evidence for the sprouting of the CR fibers as well as the time course of the synaptic current at the dendritic synapses remote from the soma, for the first time.

Animals↗
PubMed1994

Dual projections of the ventromedial lamina VI and the medial lamina VII neurones in the second sacral spinal cord segment to the thalamus and the cerebellum in the cat.

Neurons of origin of the crossed spinocerebellar and/or spinothalamic tracts giving off axon collaterals at supraspinal levels were antidromically identified and labeled with horseradish peroxidase in lower sacral spinal cord segments of cats. Their cell bodies were located mainly in the medial part of lamina VII and rarely in the ventromedial aspect of lamina VI. In the S2 segment 77 neurons with axons in the opposite dorsolateral funiculus were recorded; 36 of them were invaded from only the thoracic level, 21 from both the thoracic level and the restiform body, 3 from both the thoracic level and the thalamus, and 17 from both the thoracic level, the restiform body and the thalamus on the contralateral side. These termination areas suggest that the S2 neurons under study transmit peripheral signals of proprioceptive, exteroceptive and nociceptive sensations.

Animals↗
PubMedDate not supplied

Topographic analysis of the effects of isoflurane anesthesia on SEP.

Isoflurane anesthesia induces a striking increase in the P22 potential recorded over the precentral scalp whereas the amplitude of the N20 is reduced. It is not known whether the increased "P22" enhanced by isoflurane arises from the same generator as the small precentral P22 potential recorded in the normal awake subject. Multi-channel recordings of SEP before and during isoflurane anesthesia were performed in 13 normal subjects. Isopotential topographic maps showed that isoflurane did not change the distribution of the precentral "P22" despite its clear amplitude increase. Our data confirm that isoflurane enhances the precentral P22 and that the enhanced "P22" arises from the same generator as the P22 recorded before isoflurane anesthesia.

Adult↗
PubMedDate not supplied

The modulation of somatosensory evoked potentials during the foreperiod of a forewarned reaction time task.

During the foreperiod of a forewarned reaction time (RT) task reflexes in the executing limb increase to a lesser extent than those in the contralateral limb. This is possibly due to input modulation. The present study investigates the possibility of cutaneous sensory modulation during motor preparation by studying the amplitudes of somatosensory evoked potentials (SEPs). Eighteen subjects performed a forewarned RT task with the same fingers as the ones which were electrically stimulated. SEPs evoked during the 4 sec preparatory period were compared to those evoked during movement execution and during the resting period after the motor response respectively. During response execution most SEP components showed smaller amplitudes, i.e., they were gated, which agrees with other studies. In the first part of the foreperiod no SEP modulation was observed. Towards the end of the foreperiod, 500 msec before the response stimulus (RS), the amplitude of the contralateral parietal N70-P100 was significantly decreased, while the P45-N70 showed a similar tendency. However, at the same time the P100-N140 was increased in amplitude. The decrease of the intermediate latency components towards the end of the foreperiod is discussed in terms of gating, while the increase in the long latency component is discussed with respect to a decrease in RT on trials where the fingers were stimulated just before the RS, pointing to the role of attentional mechanisms.

Adult↗