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Stimulus Parameters (stimulus + parameter)

Distribution by Scientific Domains

Medical Sciences	64%
Life Sciences	21%

Selected Abstracts

Investigation of the Relationship Between Stimulus Parameters and a Human Muscle Contraction Force During Stimulation of the Gastrocnemius Muscle

ARTIFICIAL ORGANS, Issue 2 2010
Piotr Kaczmarek
Abstract The article presents the results of investigations on the influence of biphasic stimulus parameters such as duration and stimulus interphase interval (IPI) on a gastrocnemius muscle contraction force. Seven healthy volunteers participated in this experiment, and 24 different stimuli patterns were tested. Special attention was paid to the comfort level of a sensory perception while the electrostimulation was applied. During the test, an optimal stimulus pattern evoking contraction at the level over 15% maximum voluntary contraction force and preserving a good comfort perception reported by all of the participants was investigated. It was found that bursts of pulses with width 175 µs and the IPI from 50 to 1000 µs satisfied these criteria. Moreover, it was observed that the increase of the IPI duration generated a significantly stronger contraction force in comparison with the stimulation with the standard biphasic pulses (IPI = 0 µs) having the same amplitude, frequency, and pulse duration. This shows that the modulation of the IPI might be a potentially useful support for the standard force-control methods and may find an application in neuromuscular electrical stimulation systems. [source]

Electric Parameters Optimization in Spinal Cord Stimulation.

NEUROMODULATION, Issue 4 2010
Study in Conventional Nonrechargeable Systems
Background:, Spinal cord stimulation devices provide a means of creating an electric field. The parameters used to produce this electric field are: pulse amplitude, pulse width (Pw), and pulse frequency (F). Aims:, The purpose is to document the effects that the various stimulus parameters have on patient perception of paresthesia and the relationship that this perception has on pain relief. Methods:, Stimulus parameters were varied independently keeping the electrode polarity constant while recording stimulation thresholds. The Pw was varied from 195 to 300 µsec while maintaining the frequency at 50 Hz. The F was varied from 10 to 100 Hz while maintaining the Pw at 300 µsec. We also measured the paresthesia coverage percentage and the subjective perception of quality reported by the patients with each one of the parameter changes. Results:, There was a statistically significant correlation between Pw and all the stimulation thresholds. As for the therapeutic range, the differences observed also were statistically significant. Pw variation did not produce significant differences in coverage and subjective quality of the paresthesia. The perception threshold did not vary significantly with F changes. However, F significantly affected both coverage of the painful area and paresthesia perception quality. Conclusions:, In the usual Pw ranges, it seems that its usefulness is limited to obtaining finer adjustments in the stimulation amplitude. Frequency management may be significantly useful to get a wider coverage of the stimulated area. [source]

Novelty detector neurons in the mammalian auditory midbrain

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2005
David Pérez-González
Abstract Novel stimuli in all sensory modalities are highly effective in attracting and focusing attention. Stimulus-specific adaptation (SSA) and brain activity evoked by novel stimuli have been studied using population measures such as imaging and event-related potentials, but there have been few studies at the single-neuron level. In this study we compare SSA across different populations of neurons in the inferior colliculus (IC) of the rat and show that a subclass of neurons with rapid and pronounced SSA respond selectively to novel sounds. These neurons, located in the dorsal and external cortex of the IC, fail to respond to multiple repetitions of a sound but briefly recover their excitability when some stimulus parameter is changed. The finding of neurons that respond selectively to novel stimuli in the mammalian auditory midbrain suggests that they may contribute to a rapid subcortical pathway for directing attention and/or orienting responses to novel sounds. [source]

Behavioral discrimination of sexually dimorphic calls by male zebra finches requires an intact vocal motor pathway

DEVELOPMENTAL NEUROBIOLOGY, Issue 2 2001
David S. Vicario
Abstract Vocal communication between zebra finches includes the exchange of long calls (LCs) as well as song. By using this natural call behavior and quantifying the LCs emitted in response to playbacks of LCs of other birds, we have previously shown that adult male zebra finches have a categorical preference for the LCs of females over those of males. Female LCs are acoustically simpler than male LCs, which include complex acoustic features that are learned during development. Production of these male-typical features requires an intact nucleus RA, the sexually dimorphic source of the main telencephalic projection to brainstem vocal effectors. We have now made bilateral lesions of RA in 17 adult males and tested their discrimination behavior in the call response situation. Lesioned birds continue to call, but lose the male-typical preference for female LCs. The degree of loss is correlated with the extent of RA damage. Further, the simplified LCs of males with RA lesions have a variable duration that is correlated with stimulus features. In effect, the call response behavior of lesioned males becomes like that of females. Apparently, in the absence of RA, the remaining intact structures receive different call information than RA normally does, and/or process it differently. This suggests that the vocal motor nucleus RA could play a role in the transformation of a signal encoding the salience of stimulus parameters into a control signal that modulates the probability and strength of responding. © 2001 John Wiley & Sons, Inc. J Neurobiol 47: 109,120, 2001 [source]

Simulation of nerve bundle activation by simultaneous multipoint extracellular stimulation with surface electrodes

ELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 6 2009
Hirokazu Takahashi
Abstract Neural prostheses for restoring lost functions can benefit from selective activation of nerves. We previously proposed a multipoint gating stimulation, which can selectively activate a desired portion of a nerve bundle, regardless of the density of the electrode. In this paper, we discuss the design of an electrode array and effective strategies to determine the stimulus parameters. Large electrodes were less affected by the relative location of the electrodes and the nodes of Ranvier, suggesting that a rectangular electrode, whose long side along a nerve bundle is longer than the internodal distance (i.e., on the order of 1 mm), would be more effective than a disk electrode. We were able to estimate an appropriate current at each electrode on the basis of a blocking threshold, above which no spike propagation was permitted. For lateral gating stimulation, the gate current should be set above the threshold, while for depthwise gating stimulation, the gate current should be set below the threshold. The spatial resolutions of lateral and depthwise gating stimulation were theoretically estimated to be at least 50 ,m when the grid spacing of the array was 1.2 mm. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(6): 31,40, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10064 [source]

Characterizing the Patterned Images That Precipitate Seizures and Optimizing Guidelines To Prevent Them

EPILEPSIA, Issue 8 2005
Arnold Wilkins
Summary:, The use of guidelines to prevent the broadcast of epileptogenic television program content has reduced the incidence of seizures in Britain and Japan. Epileptogenic content includes both flicker and patterns. The guidelines for flicker were developed on the basis of a model that related stimulus parameters to the proportion of patients affected. We here extend the model to pattern stimuli. A set of rules is advocated that keeps the level of risk to a consistent minimum and simplifies compliance. We propose that striped patterns that last >0.5 s, occupy more than one fourth the area of the screen, and have bright stripes >50 cd/m2 in luminance be restricted as regards the number of cycles admissible. The guidelines are estimated to protect at least two thirds of susceptible patients. [source]

Interactions Between Extracellular Stimuli and Excitation Waves in an Atrial Reentrant Loop

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 10 2003
CHAD R. JOHNSON B.S.E.
Introduction: The interactions between extracellular stimuli and excitation waves propagating in a reentrant loop are a complex function of stimulus parameters, structural properties, membrane state, and timing. Here the goal was a comprehensive understanding of the mechanisms and frequencies of the major interactions between the advancing excitation wave and a single extracellular stimulus, separated from issues of anatomic or geometric complexity. Methods and Results: A modernized computer model of a thin ring of uniform tissue that included a pair of extracellular stimulus electrodes (anode/cathode) was used to model one-dimensional cardiac reentry. Questions and results included the following: (1) What are the major interactions between a stimulus and the reentrant propagation wave, and are they induced near the cathode or near the anode; and, for each interaction, what are the initiating amplitude range and timing interval? At the cathode, the well-known mechanism of retrograde excitation terminated reentry; changes in timing or amplitude produced double-wave reentry or phase reset. At the anode, termination occurred at different cells depending on stimulus amplitude. (2) Relatively how often did termination occur at the anode? For most stimulus amplitudes, termination occurred more often at the anode than at the cathode, although not always at the same cell. (3) With random timing, what is the probability of terminating reentry? Stimulation for 5 msec terminated reentry with a probability from 0% to approximately 10%, as a function of increasing stimulus amplitude. Conclusion: A single extracellular stimulus can initiate major changes in reentrant excitation via multiple mechanisms, even in a simple geometry. Termination of reentry, phase shifts, or double-wave reentry each occurs over well-defined ranges of stimulus amplitude and timing. (J Cardiovasc Electrophysiol, Vol. 14, pp. ***-***, October 2003) [source]

Methods of gastric electrical stimulation and pacing: a review of their benefits and mechanisms of action in gastroparesis and obesity

NEUROGASTROENTEROLOGY & MOTILITY, Issue 3 2009
W. L. Hasler
Abstract, Development of gastric electrical stimulation techniques for treatment of gastric dysmotility syndromes and obesity has been a long-standing goal of investigators and clinicians. Depending on stimulus parameters and sites of stimulation, such methods have a range of theoretical benefits including entrainment of intrinsic gastric electrical activity, eliciting propagating contractions and reducing symptomatology in patients with gastroparesis and reducing appetite and food intake in individuals with morbid obesity. Additionally, gastric stimulation parameters have extragastrointestinal effects including alteration of systemic hormonal and autonomic neural activity and modulation of afferent nerve pathways projecting to the central nervous system that may represent important mechanisms of action. Numerous case series and smaller numbers of controlled trials suggest clinical benefits in these two conditions, however better controlled trials are mandated to confirm their efficacy. Current research is focusing on novel stimulation methods to better control symptoms in gastroparesis and promote weight reduction in morbid obesity. [source]

Electric Parameters Optimization in Spinal Cord Stimulation.

Analysis of magnetic source localization of P300 using the multiple signal classification algorithm

PSYCHIATRY AND CLINICAL NEUROSCIENCES, Issue 6 2006
TETSUO UOHASHI md
Abstract, The authors studied the localization of P300 magnetic sources using the multiple signal classification (MUSIC) algorithm. Six healthy subjects (aged 24,34 years old) were investigated with 148-channel whole-head type magnetencephalography using an auditory oddball paradigm in passive mode. The authors also compared six stimulus combinations in order to find the optimal stimulus parameters for P300 magnetic field (P300m) in passive mode. Bilateral MUSIC peaks were located on the mesial temporal, superior temporal and parietal lobes. Interestingly, all MUSIC peaks in these regions emerged earlier in the right hemisphere than in the left hemisphere, suggesting that the right hemisphere has predominance over the left in the processing activity associated with P300m. There were no significant differences among the six stimulus combinations in evoking those P300m sources. The results of the present study suggest that the MUSIC algorithm could be a useful tool for analysis of the time-course of P300m. [source]

Target-to-target interval versus probability effects on P300 in one- and two-tone tasks

PSYCHOPHYSIOLOGY, Issue 3 2003
R. J. Croft
Abstract The P3(00) is an electrophysiological index of neural processing that varies with such stimulus parameters as interstimulus interval (ISI) and target probability, with a common view being that it reflects an endogenous form of memory update. Building on previous research, we argue that relations between P3 amplitude and both ISI and probability may be attributable to the target-to-target interval (TTI). Employing between-subject (Experiment 1; N=24) and within-subject (Experiment 2; N=10) designs, the present paper addresses this by testing subjects on a standard two-tone auditory oddball task as well as a one-tone task. In both studies, P3 amplitude increased and latency decreased linearly with TTI, and these relations were relatively unaffected by ISI or probability. This suggests that ISI and probability per se do not independently affect P3 amplitude, and that TTI offers a strong explanation of the reported relations between P3 amplitude and both ISI and probability. [source]

Investigation of the Relationship Between Stimulus Parameters and a Human Muscle Contraction Force During Stimulation of the Gastrocnemius Muscle

Positive inotropic effect of coenzyme Q10, omega-3 fatty acids and propionyl-L-carnitine on papillary muscle force-frequency responses of BIO TO-2 cardiomyopathic Syrian hamsters

BIOFACTORS, Issue 1-4 2008
Romina Vargiu
Abstract The inability of heart muscle to generate ventricular pressure to adequately propel blood through the cardiovascular system is a primary defect associated with congestive heart failure (CHF). Force-frequency relationship (FFR) is one of the main cardiac defects associated with congestive heart failure. Thus FFR is a convenient methodological tool for evaluating the severity of muscle contractile dysfunction and the effectiveness of therapeutic agents. Papillary muscle isolated from BIO TO-2 cardiomyopathic Syrian hamsters (CMSHs), show a depressed FFR and represents an animal model of human idiopathic dilated cardiomyopathy. In the present study we investigated the effect of CoQ10, omega-3 fatty acids, propionyl-L-carnitine (PLC) and a combination of these 3 agents (formulation HS12607) on FFR in 8 month old BIO TO-2 CMSHs. Papillary muscles isolated from the anesthetized animals were placed in an incubation bath and attached to an isometric force transducer. A digital computer with an analog/digital interface allowed control of both muscle developed force and electrical stimulus parameters. Force-frequency response was evaluated, at Lmax, with increasing frequencies: 0.06, 0.12, 0.25, 0.5, 1, 2 and 4 Hz. HS12607-treatment produced a positive inotropic effect resulting in a significant enhancement (p < 0.05) of the peak force at the highest frequencies (1,4 Hz). In the range of frequency of 1,4 Hz also CoQ10 and omega-3 significantly(p < 0.05) attenuated the fractional decline in developed force. The significant improvement (p < 0.05) of the timing parameter peak rate of tension rise (+T') and peak rate of tension fall (,T') indicating a faster rate of muscle contraction and relaxation respectively, found in CoQ10, omega-3 and PLC-treated CMSHs, may be due to the positive effects of these substances on sarcoplasmic reticulum functions. These findings suggest that naturally occurring CoQ10, omega-3 and PLC, particularly when administered together in a coformulation, might be a valid adjuvant to conventional therapy in dilated cardiomyopathy especially when considering that they are natural substances, devoid of side effects. [source]

3251: From elementary concept in animal models to new frontiers in humans: neurovascular coupling in the ocular circulation

ACTA OPHTHALMOLOGICA, Issue 2010
C RIVA
Purpose The retina and optic nerve, both optically accessible components of the central nervous system, are ideally suited for the investigation of the intrinsic physiological process by which blood ,ow, metabolism and neural activity are tightly coupled (Roy and Sherrington. 1890). Methods Using various techniques in the cat and human eye, the changes in blood flow in the retina and optic nerve in response to increased neural activity by flicker stimulation have been determined. The effect of varying the stimulus parameters, such as flicker modulation depth, frequency, luminance and red-green color ratio, on the blood flow response was investigated. Putative mediators of the activity-induced flow changes and the relationship between activity, blood flow and metabolic changes were assessed. Results Visual stimulation with flicker increases rapidly and markedly both retinal and optic nerve blood ,ows (functional hyperemia). Moreover, the data reveal unequivocally the presence, under specific conditions of flicker, of a neurovascular/neurometabolic coupling in these tissues, partly mediated by local potassium ions and nitric oxide production. Furthermore, the activity-induced hyperemia is altered during a number of physiological and pharmacological interventions and in some pathologic conditions. Conclusion Flicker stimulation of the retina offers a new and powerful means to modulate blood flow and investigate the neurovascular coupling in the neural eye tissues. Exploration of this activity-induced hyperemia and the mechanism(s) underlying the neurovascular coupling will lead to an increased understanding of the pathophysiology of various ocular diseases. [source]