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PubMed1998

Semicircular canal plane head impulses detect absent function of individual semicircular canals.

We studied the human vestibulo-ocular reflex (VOR) in response to head 'impulses': brief, unpredictable, passive, high-acceleration (up to 4000 degrees/s2), low-amplitude (20-30 degrees) head rotations. We delivered the head impulses approximately in the plane of the semicircular canal (SCC) being tested. To test the anterior and posterior SCCs, the head impulses were delivered in a diagonal plane, midway between the frontal (roll) and sagittal (pitch) planes. We recorded head and eye position in three dimensions with scleral search coils in nine normal subjects, seven patients following unilateral surgical vestibular neurectomy and three patients following unilateral posterior SCC occlusion. In the post-surgical patients we demonstrated a severe, permanent VOR gain deficit (0.2-0.3) for head impulses directed toward any single non-functioning SCC. The sensitivity of the test depends on the physiological properties of primary vestibular afferents, and its specificity depends on the anatomical orientation of the SCCs. The diagonal head impulse is the first test of individual vertical SCC function in humans, and together with the horizontal head impulse, forms a comprehensive battery of SCC-plane tests. These canal-plane impulses could be useful in evaluating patients with vertigo or other vestibular disorders.

Adult↗

PubMed1975

The relationship of impulse control to cognition and adjustment among institutionalized aged women.

Several dimensions of impulse control (i.e., delay of gratification, reflectivity, and motor control) were related to intelligence, mental status, and adjustment among 91 institutionalized aged women. Four different types of impulse control measures were used: Self reports of impulse control, staff ratings, interviewer's ratings, and tests of impulse control. Impulse control measures yielded statistically significant multiple correlations with all outcome measures except life satisfaction. The findings suggest that impulse control in its various forms has a consistent and significant relationship with indices of adaptation. Utilizing stepwise regression analyses, the best predictors of outcome among impulse control measures are presented.

Adaptation, Psychological↗

PubMed1996

Dexfenfluramine and 8-OH-DPAT modulate impulsivity in a delay-of-reward paradigm: implications for a correspondence with alcohol consumption.

Clinical studies identify impulsivity as a defining feature of an alcohol abuse syndrome. We recently reported an animal analogue: impulsivity assessed in a delay-of-reward paradigm strongly predicted magnitude of alcohol consumption. In this study we further explored this relationship. We asked whether serotonergic manipulations previously established to reduce and augment alcohol consumption would have corresponding effects on impulsivity in a delay-of-reward paradigm. This study revealed that two doses (1 and 2mg/kg) of dexfenfluramine, a serotonergic releaser known to reduce alcohol consumption, reduced choice of immediate reward, or impulsivity. We also found that three doses of the 5-HT(1A) agonist, 8-OH-DPAT, caused a biphasic dose effect on impulsivity. There was a clear dose-dependent progression from augmentation (6 and 31µg/kg) to a reduction (62µg/kg) of impulsivity scores. This effect mirrors a biphasic dose effect that has been found for alcohol intake. The findings suggest that impulsivity and alcohol consumption are intimately linked via common serotonergic pathways.

Journal Article↗

PubMed2003

Head-impulse and caloric tests in patients with dizziness.

OBJECTIVE: To test the performance of the head-impulse and caloric tests in terms of sensitivity, specificity, and predictive efficiency. STUDY DESIGN: This was an open and prospective study conducted at a tertiary care center in which 265 patients were subjected to the head-impulse test and caloric test on the same day. The results of the head-impulse test were considered as normal or pathologic. In a similar way, the caloric test was rated as normal when the difference in canal paresis was less than 22 percent and directional preponderance less than 28 percent, and abnormal if canal paresis was more than 22 percent and/or directional preponderance was more than 28 percent. MAIN OUTCOME MEASURES: The results of each test were compared with obtain the specificity, sensitivity, and positive and negative predictive values. A receiver operating characteristics (ROC) curve was obtained from the false-alarm rate and the hit rate value of the head impulse test. RESULTS: The specificity of the head impulse test was 0.91 and the sensitivity was 0.45. The positive predictive value was 0.92, the negative predictive value was 0.41, and the area under the ROC curve was 0.866. A canal paresis value of 42.5 percent was considered to be the limit of the normal response, as seen when the head impulse test was used to predict a normal or abnormal result in a given patient. CONCLUSION: The head impulse test, when used as a bedside test, and the caloric test are by no means redundant methods. The information obtained form both can be used in combination to obtain a better insight into the degree of vestibular dysfunction of patients.

Caloric Tests↗

PubMed1995

Determination of the single-pass impulse response of the body tissues with circulatory models.

Classical in vivo kinetics are based on the analysis of the blood disappearance curve of a substance. This curve is determined by the interplay of the substance transport in the circulatory system and the kinetics of the body tissues. The characteristic response of the body tissues, that is, their single-pass impulse response, is obscured in the disappearance curve by multiple recirculations in the heart-systemic loop. The single-pass impulse response can be appropriately determined with circulatory models. This paper investigates the theoretical aspects of the determination of the impulse response and proposes suitable algorithms for the analysis of experimental data with circulatory models. The problem of what information the most typical experimental configurations yield on the single-pass impulse response, and what assumptions are necessary for determining the impulse response in a given configuration is studied first. It is shown that assumptions are usually necessary, unless a proper experiment design is adopted. Two algorithms are then developed for the determination of the impulse response from experimental data, in the general case. The first calculates the response from an exponential description of the disappearance curve, while the second is based on a state space representation of circulatory models. The first method has the important limitation that it does not always ensure physiologically plausible results; the state space approach overcomes this limitation, and is the method of choice. With the state space approach, the determination of the single-pass impulse response is a standard parameter estimation problem with finite dimensional linear systems. The analysis of real data from a study on glucose kinetics illustrates the practical relevance of the results.

Algorithms↗

PubMed1986

Impulse noise: critical review.

A review of the last 10 years of research on impulse noise reveals certain insights and perspectives on the biological and audiological effects of exposures to impulse noise. First, impulse noise may damage the cochlea by direct mechanical processes. Second, after exposure to impulse noise, hearing may recover in an erratic, nonmonotonic pattern. Third, even though the existing damage-risk criteria evaluate impulse noise in terms of level, duration, and number, often parameters such as temporal pattern, waveform, and rise time are also important in the production of a hearing loss. Fourth, the effects of impulse noise are often inconsistent with the principle of the equal energy hypothesis. Fifth, impulse noise can interact with background continuous noise to produce greater hearing loss than would have been predicted by the simple sum of the individual noises.

Animals↗

PubMed1985

Site of impulse initiation in tendon organs of cat soleus muscle.

A continuing controversy surrounds the question of whether Golgi tendon organs are examples of receptors in which impulses may be generated at more than one site. This paper reports a systematic examination of a number of models incorporating single or multiple impulse generators and of the compatibility of their predictions with experimental observations. Two phenomena, in particular, that must be accounted for are nonlinear summation and cross-adaptation. When two motor units each with a direct effect on the tendon organ are stimulated together, the rate of discharge is greater than either individual rate but is less than their sum. In cross-adaptation a conditioning response elicited by one motor unit contraction produces adaptation of the discharge associated with stimulation of a second motor unit. A model with a central impulse generator can be modified to account for nonlinear summation by postulating a nonlinear transformation in the generator current-to-impulse rate conversion. Experiments measuring summation of responses to stimulation of three inputs produced results that did not support this model. Another variation of the model, which had a nonlinearity in the tension-to-current step and cross-connections (mechanical or neural) between tendon strands stressed by contracting muscle fibers, was able to account for the observations. A second model that provided the right predictions was a multiple impulse generator with cross-connections. Which of the two models best fits the experimental observations can be decided by comparing the calculated summation coefficients and cross-adaptation coefficients. A central impulse generator predicts a negative correlation, the multiple impulse generator a positive correlation. All of the observations were made using tendon organs of cat soleus muscle. Responses were recorded to stimulation of filaments of ventral root. In a comparison between 20 pairs of responses from six tendon organs the correlation between summation and cross-adaptation coefficients was found to be significantly positive. We conclude that the tendon organ model that accurately predicts all of the experimental observations incorporates multiple generators.

Adaptation, Physiological↗

PubMed2001

Effects of impulse noise stimulation on electrocorticogram and heart rate.

It is now recognized that high-level impulse noises penetrate the uterus of pregnant sheep, elevate thresholds of fetal auditory-evoked potential and produce damage to fetal inner ear hair cells. However, little is known about functional effects of airborne impulse noise on the late-term fetus. In the present study, the effects of a series of 20 impulses on the behavioral state of 6 fetal sheep were tested. Noise impulses produced 169.3 peak sound pressure level (pSPL) in air. Peak levels recorded near the fetal head averaged 161.1 dB. Impulses delivered to the fetus during periods of NREM sleep resulted in a decrease in average fetal heart rate (FHR) from 185 +/- 22 beats/min (bpm) before stimulation to 174 +/- 23 bpm 2-5 s after stimulation (p < 0.05). During REM sleep, an FHR acceleration occurred (before stimulation: 177 +/- 24 bpm, after stimulation: 189 +/- 31 bpm; p < 0.05). Impulse exposure during NREM sleep resulted in reductions in delta-, theta- and alpha-band powers. As a consequence, total power decreased from 100 to 72 +/- 16% (p < 0.05). During REM sleep, stimulation provoked a short decrease in total band power from 100 to 73 +/- 20% and a similar decrease in the theta- and beta-band powers. The results indicated that impulse noise evoked short-term alterations in FHR and cortical activity. These changes were mediated by auditory brain stem activation that led to cortical desynchronization during both NREM and REM sleep in late-term fetal sheep.

Acoustic Stimulation↗

PubMed2006

Knee angular impulse as a predictor of patellofemoral pain in runners.

BACKGROUND: Identification of mechanical factors associated with patellofemoral pain, the most prevalent running injury, is necessary to help in injury prevention, but unfortunately they remain elusive. HYPOTHESIS: Runners who develop patellofemoral pain have increased knee joint angular impulse in the frontal plane. STUDY DESIGN: Case control study; Level of evidence, 3. METHODS: A retrospective study compared knee abduction impulses of 20 patellofemoral pain patients with those of 20 asymptomatic patients. A second prospective study quantified knee angular impulses during the stance phase of running of 80 runners at the beginning of the summer running season. Epidemiologic data were then collected, recording the type and severity of injury of these runners during a 6-month running period. RESULTS: The patellofemoral pain patients in the retrospective study had significantly higher (P = .026) knee abduction impulses (17.0 +/- 8.5 Nms) than did the asymptomatic patients (12.5 +/- 5.5 Nms). Six patients developed patellofemoral pain during the prospective study. The prospective data showed that patients who developed patellofemoral pain had significantly higher (P = .042) knee abduction impulses (9.2 +/- 3.7 Nms) than did matched patients who remained uninjured (4.7 +/- 3.5 Nms). CONCLUSION: The data indicate that increased knee abduction impulses should be deemed risk factors that play a role in the development of patellofemoral pain in runners. CLINICAL RELEVANCE: Footwear and running style can influence knee angular impulse, and the appropriate manipulation of these variables may play a preventive role for patients who are predisposed to patellofemoral pain.

Adult↗

PubMed2002

A comparison of two analytical techniques for detecting differences in regional vertical impulses due to plantar fasciitis.

The vertical impulse distribution beneath the foot has been shown to be a useful objective method for evaluating gait and the efficacy of treatment programs. However, recent studies employing similar methods, but different analytical techniques, have reached divergent conclusions regarding the effect of plantar fasciitis on hindfoot, midfoot and forefoot impulses. The aim of the current study was to determine whether the impulse distribution beneath the hindfoot, midfoot and forefoot in subjects with, and without, plantar fasciitis was dependent on the analytic technique employed. A pressure platform was used to collect impulse estimates from 16 subjects with plantar fasciitis, and 16 control subjects, while walking at their preferred speed. The findings indicate that an impulse calculation incorporating the position of the center of pressure is more effective in detecting alterations in gait than the conventional method of estimating the impulse distribution beneath the foot. This study also demonstrates that subjects with plantar fasciitis possess modified gait patterns that are primarily manifest by a reduced hindfoot and an increased midfoot impulse, as defined by the pathway of the center of pressure.

Adult↗

PubMed2007

Examining impulsivity as an endophenotype using a behavioral approach: a DRD2 TaqI A and DRD4 48-bp VNTR association study.

BACKGROUND: Research on the genetic basis for impulsivity has revealed an array of ambiguous findings. This may be a result of limitations to self-report assessments of impulsivity. Behavioral measures that assess more narrowly defined aspects of impulsivity may clarify genetic influences. This study examined the relationship between possession of the DRD2 TaqI A and DRD4 48 bp VNTR genetic polymorphisms and performance on a behavioral measure of impulsivity, the delay discounting task (DDT), and three traditional self-report measures. METHODS: 195 individuals (42% male) were recruited from a university campus and were assessed in small group sessions using personal computers. Genotyping was conducted using previously established protocols. For the DRD2 TaqI A locus, individuals were designated as possessing at least one copy of the A1 allele (A1+) or not (A1-), and for the DRD4 48-bp VNTR locus, individuals were designated as having at least one long allele (7 repeats or longer, L+) or not (L-). Principal analyses used multiple univariate factorial 2 (A1+/A1-) x 2 (L+/L-) analyses of variance. RESULTS: A significant main effect of A1+ status on DDT performance was evident (p = .006) as well as a significant interaction effect (p = .006) between both genes. No other significant effects were evident on the self-report measures, with the exception of a trend toward an interaction effect on the Sensation Seeking Scale. Exploratory analyses suggested that the significant effects were not a function of population stratification or gender. DISCUSSION: These data suggest that the DRD2 TaqI A and DRD4 VNTR polymorphisms influence impulsivity as measured with a delay discounting task. Specifically, these findings suggest that an interaction between the functional effects of the two unlinked genotypes results in significant difference in the balance of mesolimbic dopaminergic activation relative to frontal-parietal activation. However, these findings are also the first in this area and must be replicated. CONCLUSION: These findings suggest a meaningful interaction between the DRD2 TaqI A and DRD4 VNTR polymorphisms in the expression of impulsivity and provide initial support for the utility of using behavioral measures for clarifying genetic influences on impulsivity.

Journal Article↗

PubMed1999

Impulse conduction in a sponge.

All-or-none propagated electrical impulses were recorded from the hexactinellid sponge Rhabdocalyptus dawsoni using suction electrodes attached to lumps of aggregated sponge tissue grafted onto the surface of pieces of the same sponge. Impulses were normally evoked by means of externally applied electrical shocks. Recorded externally using an a.c.-coupled amplifier, the electrical event was triphasic and lasted approximately 30 s; integration gave a diphasic waveform. A further integration to give the form of the membrane action potential produced a monophasic signal. Impulses propagated at 0.27+/-0.1 cm s-1 with an absolute refractory period of 29 s and a relative refractory period of approximately 150 s. Concurrent thermistor flow meter recordings confirmed that water flow through the sponge was arrested following the passage of an impulse, presumably as result of the cessation of beating of the flagella in the flagellated chambers. Tactile stimuli also evoked impulses, as did addition of particulate material to the incoming water stream. Impulses continued to propagate through the sponge during arrests, indicating that the conduction and effector systems were independent. Sponges lack nerves, and a variety of evidence indicates that the conducting tissues are the syncytial trabecular reticulum and pinacoderm layers. Na+-deficient solutions had little effect on the action potential, but propagation was blocked by 10 mmol l-1 Co2+, 1 mmol l-1 Mn2+ or 24 micromol l-1 nimodipine. Tetraethylammonium ions at 1-5 mmol l-1 also blocked propagation without prolonging the action potential. Impulse conduction in the sponge is discussed in relation to excitability and conduction in the protozoa and in plants and to non-nervous conduction in more advanced animals.

Journal Article↗

PubMed1986

Impulsiveness of vibration as an additional factor in the hazards associated with hand-arm vibration.

Impulsiveness is defined as the difference between peak and root-mean-square signals. As the difference varies in time, the cumulative distribution function has been used to describe the probability of achieving a certain value of impulsiveness. To make numerical comparison of different vibration signals possible, an impulse index has been selected from the cumulative distribution function. Symptoms of vibration-induced white finger were observed and compared to those expected on the basis of measurements taken according to guidelines of the International Organization for Standardization (ISO). Agreement was found for chain-saw vibration. In the case of pedestal grinding, the ISO draft underestimated the hazardous effects of vibration. Stone workers using pneumatic hammers were exposed to highly impulsive but asymmetrical vibration. The corresponding asymmetry was not, however, observed between the symptoms of the left and right hands, a finding which indicates that coupling between the tool and the hand is important for impulse vibration. The results suggest that the impulse character of vibration increases the risk of vibration-induced pathology. The analysis of high-impulse acceleration peaks obtained by the method presented in this study could provide additional data necessary to improve risk assessment.

Fingers↗

PubMed1998

Inner ear damage in guinea pigs exposed to stable and impulse noise.

OBJECTIVE: To investigate the inner ear damage after exposure to stable noise, impulse noise and stable plus impulse noise in guinea pigs. METHODS: Ninety-six healthy guinea pigs were divided into 3 equal groups. (1) Stable noise group: exposed to 110 dBA stable noise for 3 days, 4 hours per day. (2) Impulse noise group: exposed to 165 dBA simulated cannon fire impulse noise 10 times successively at an interval of 10 seconds. (3) stable plus impulse noise group: exposed to the same stable noise as that in the first group, then after a 2-hour rest, the animals were followed with impulse noise exposures as that in the second group. After those exposure, each of the 3 groups was further divided into 4 subgroups according to the time after the noise exposure, namely, the right after, 7 d, 14 d and 30 d groups. The evoked cortical potential responses to click and tone burst stimulation sound were examined. The surface preparation and celloidine embedded serial section of the cochlea were observed under a light microscope. RESULTS: Both the stable and impulse noise could increase the hearing threshold and damage the inner ear hair cells. The damage in the first group was relatively slight, whereas in group 3 the damage was more severe than that in the other 2 groups. CONCLUSION: For seamen who are working in heavy noise environment, corresponding measures should be taken to protect their ears from noise which induces hearing loss.

Animals↗

PubMed1999

Head impulses reveal loss of individual semicircular canal function.

We studied individual semicircular canal responses in three dimensions to high-acceleration head rotations ("head impulses") in subjects with known surgical lesions of the semicircular canals, and compared their results to those of normal subjects. We found that vestibular-ocular reflex (VOR) gains at close to peak head velocity in response to yaw, pitch and roll impulses were reliable indicators of semicircular canal function. When compared to normals, lateral canal function showed a 70-80% decrease in VOR gain at peak of yaw head velocity during ipsilesional yaw impulses. After the loss of one vertical canal function there was a 30-50% decrease in vertical and torsional VOR gain in response to ipsilesional pitch and roll impulses respectively. Bilateral deficits in anterior or posterior canal function resulted in a 80-90% decrease in vertical VOR gain during ipsilesional pitch impulses, while the loss of ipsilateral anterior and posterior canal functions will result in a 80-90% decrease in torsional VOR gain in response to ipsilesional roll impulses. Three-dimensional vector analysis and animation of the VOR responses in a unilateral vestibular deafferented subject to yaw, pitch and roll impulses further demonstrated the deficits in magnitude and direction of the VOR responses following the loss of unilateral lateral, anterior and posterior canal functions.

Adult↗

PubMed1975

Impulse activity of a single motor unit upon the rhythm of the summated muscle activity.

The impulses of single motor units (MUs) are recorded using the method of selective leading off with surface bipolar electrodes with small interpolar distance. Parallel recording is made of the summated EMG and of its apparatus-transformed form-the mean voltage curve of the EMG. The correct position of the electrodes with regard to the MU is controlled by means of a vector-electromyographic (VEMG) method. The statistical parameters of the impulse series of the individual MUs and of the groups of impulses in the summated EMG are determined, as well as the time interrelations between the impulses of the selected MUs and the groups of impulses in the mean voltage curve of the EMG. The delay in the appearance of the impulses from the selected MUs with regard to the beginning of the group of impulses, proved a statistically distributed value according to a bimodal type which becomes more pronounced upon rating to the intervals.

Electrodes↗

PubMed1989

Changes in the capillary flow of gingiva due to the influence of some impulses.

75 healthy men and women, aged from 20 to 45 years, were divided into five groups of 15 persons each. Na131I resorption halftime values from the examined area of the gingiva, pulse frequency as well as systolic and diastolic blood pressure were examined. Tests were carried out twice. One group served as a control group. During the second test emotional, light, sound or tactile impulses were applied to the other groups. The control group that was not exposed to any of the impulses investigated during the second examination showed no significant differences in values with any of the observed indices. Under the influence of emotional, sound or light impulses, a significant increase in pulse frequency as well as in systolic and diastolic blood pressure was noted. This suggested that both the one-minute volume and the peripheral resistance of the circulation system increased. Na131I resorption half-time values from the examined area of the gingiva significantly increased under the influence of emotional and sound impulse by 64%, of light impulse by 84% and of tactile impulse by 93%. This meant that the blood flow through the capillary gingival bed had significantly reduced due to the influence of these impulses. It is to assume that their long-term influence could contribute to the development of parodontopathies.

Acoustic Stimulation↗

PubMed1989

[The effect of acetylcholine and cholinergic transmission blockers on the neuronal impulse activity of the cat motor cortex in a conditioned reflex].

Influence of acetylcholine, atropine, d-turbocurarine and hexonium on the background and evoked impulse activity of the motor cortex neurons was investigated in cat under instrumental placing reaction. Only those neurons were analyzed whose responses preceded conditional movement. It was shown that acetylcholine increased the background impulse activity in one group of cortical neurons and decreased it in the other neuronal group. During iontophoretic application of acetylcholine the background activity of some neurons declined in spite of the increase of their evoked conditional response. Atropine inhibited background impulse activity, the conditional impulse response being preserved. The background impulse activity increased and evoked conditional response was inhibited during iontophoretic application. Hexonium inhibited the background activity and conditional evoked impulse activity. It is suggested that cholinergic fibers in the natural state participate in supporting the background activity of cortical neurons by means of m-cholinoreceptors and at the sam time they evoke the impulse activity linked with conditional responses through n-cholinoreceptors.

Acetylcholine↗