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At least 883 records · Page 49Linked to original sources
PubMed1976

Vibrotactile and temperature sensory interaction in the human tongue.

Lingual vibrotactile thresholds were used to demonstrate an interaction between the lingual senses of vibrotaction and temperture. Thresholds were obtained on 10 Ss from the anterior midline of the lingual dorsum at a frequency of 250 Hz. Five temperature conditions were tested ranging in 10 degrees C steps from 17 degrees C to 57 degrees C. Thresholds were obtained before and after the introduction of the temperature stimuli. Comparison of mean pre- and post-experimental thresholds demonstrated that temperature is a determining factor in lingual vibrotactile threshold values. The data indicated that systematic variation from normal body temperature resulted in corresponding decreases in lingual vibrotactile sensitivity. Diagnostic and clinical implications of this interaction were discussed.

Adult↗
PubMed2000

Seizure threshold in ECT: I. Initial seizure threshold.

Seizure threshold determination is of crucial importance in optimizing electrical stimulus dosage during administering electroconvulsive therapy (ECT). We measured initial seizure threshold by means of Srinakharinwirot University titration schedule in 150 psychotic patients. Initial seizure threshold was approximately 104 millicoulombs on average, but varied widely (12-fold) across patients. Motor seizure duration was inversely related to initial seizure threshold. Seizure threshold could be strongly predicted by age. The results may have important clinical implications for stimulus dosing strategy in ECT.

Adult↗
PubMed1997

Corticomotor threshold is reduced in early sporadic amyotrophic lateral sclerosis.

The pathogenesis of idiopathic amyotrophic lateral sclerosis (ALS) remains unknown, but accumulating evidence suggests a neuroexcitotoxic mechanism may have some credence. Glutamate-induced hyperexcitability of cortical or spinal motoneurons may be expected to manifest itself as a reduced threshold for activation of these structures. We have measured corticomotor threshold to the first dorsal interosseous (FDI) muscles of 48 patients with sporadic ALS using magnetic brain stimulation and have correlated the findings with physical signs of upper and/or lower motor neuron degeneration. We find that if FDI in patients with ALS shows no weakness, wasting, or signs of an upper motor neuron lesion, mean corticomotor threshold is significantly lower than in 102 healthy control FDI muscles (P = 0.02). In contrast, FDI muscles showing signs of lower motor neuron degeneration only or mixed upper and lower motor neuron signs are associated with a raised corticomotor threshold (P = 0.008, P < 0.001, respectively). We conclude that early in ALS, at a time when hand muscle function is normal, corticomotor threshold is reduced and suggest that this may be a manifestation of abnormal excitability of cortical or spinal motoneurons to neurotransmitters, whose action will ultimately lead to cell death.

Aged↗
PubMed1996

Duchenne phenotype with in-frame deletion removing major portion of dystrophin rod: threshold effect for deletion size?

In a 9-year-old boy with Duchenne muscular dystrophy we found a large in-frame deletion, spanning exons 10 to 53 of the dystrophin gene. The deletion removed almost all of the central rod domain of dystrophin. Using carboxyterminal dystrophin antibodies the immunohistochemical reaction was normal in all muscle fibers. In immunoblot studies we found dystrophin of abnormal size (160 kDa) and normal amount (about 100%). The immunochemical features and the reading frame deduced from DNA analysis are usually associated with Becker muscular dystrophy, but the clinical characteristics were those of the severe Duchenne phenotype. All the cases of in-frame dystrophin deletions reported so far, which involved more than 36 exons, invariably resulted in a severe phenotype. Therefore, a threshold effect for dystrophin length may be reasonably suspected. Very short dystrophin molecules might induce a severe disarray of the dystrophin network.

Blotting, Western↗
PubMed2006

Diagnostic impact of the spectrum of ischemic cerebral blood flow thresholds in sedated subarachnoid hemorrhage patients.

OBJECTIVE: Ischemia is the main cause of secondary damage in subarachnoid hemorrhage (SAH). Cerebral blood flow (CBF) measurement is useful to detect critical values. We analyzed the diagnostic impact of CBF ischemic thresholds to predict a new low attenuation area on computed tomography (CT) due to failure of large vessel perfusion. METHODS: We analyzed 48 xenon CT (Xe-CT) studies from 10 patients with SAH. CBF measurements were obtained by means of Xe-CT and cortical regions of interest (ROls). The ROIs which appeared in a hypoattenuation area were recorded. Cortical CBF was tested for specificity and sensitivity as a predictor of hypoattenuation by means of a receiver operating characteristic curve. RESULTS: Mean age was 58 (SD +/- 12.4) years. The median Fisher score and Hunt and Hess scale were 2 and 3, respectively. The area under the receiver operating characteristic curve was 0.912 (CI 0.896 to 0.926). The cut-off value for best accuracy was 6 mL/ 100 g/min, with a likelihood ratio of 37. CONCLUSION: The present study suggests a threshold of 6 mL/100 g/ min as a predictor of a new low attenuation area. However, each clinician should choose the most useful threshold according to pre-test probability and the cost/effectiveness ratio of the applied therapies.

Blood Flow Velocity↗
PubMed1985

A new cause for difficulty in seeing at night.

A syndrome is described in which patients complain of inability to see at night, although their rod and cone thresholds are normal. In such persons the rods, when dark-adapted, elevate cone flicker thresholds by 2 log units or more, and this condition is the basis of their complaint. Patients are often thought to be hysterics or to have congenital stationary night blindness.

Adult↗
PubMed1993

MK-801, a glutamate antagonist, lowers flow threshold for inhibition of protein synthesis after middle cerebral artery occlusion of rat.

The effect of the glutamate antagonist MK-801 on the ischemic threshold of energy metabolism and protein synthesis (CPS) was studied in rats submitted to 3 h occlusion of the left middle cerebral artery (MCA). Local blood flow and CPS were measured by double tracer autoradiography, and local ATP content by bioluminescence imaging. In untreated animals breakdown of energy metabolism occurred at flow values below 15 +/- 1 and CPS inhibition below 51 +/- 15 ml/100 g/min (means +/- S.D.). MK-801 treatment (3 mg/kg immediately after MCA occlusion) did not change the ischemic flow threshold of energy failure (16 +/- 3 ml/100 g/min) but lead to a highly significant decline of the perfusion threshold for the inhibition of CPS to 19 +/- 4 ml/100 g/min (P < 0.01). Our data demonstrate that MK-801 dramatically reduces the threshold for the suppression of protein synthesis which could explain previously reported therapeutical effects on the reduction of brain infarct size.

Adenosine Triphosphate↗
PubMed1975

Variations in pain complaint threshold in psychiatric and neurological patients with pain.

The threshold at which noxious stimulation with a pressure algometer gives rise to a complaint of pain has been studied in neurological and psychiatric patients with pain and in two patients with fluctuating pain of organic origin. A correlation of r = 0.69 (P less than 0.0025) was demonstrated between two observers using the pressure algometer independently. Patients with organic causes for their pain had higher pain complaint thresholds. The threshold was also raised, outside the affected areas, in the two patients with fluctuating pain when the latter was more severe. Some requirements for an improved technique of pressure algometry are discussed.

Adult↗
PubMed2000

Interactions between flicker thresholds and luminance pedestals.

We investigated the interactions between flicker thresholds and luminance pedestals using threshold versus contrast (TvC) and method of constant stimuli paradigms. High amplitude luminance pedestals were found to elevate flicker thresholds, but low amplitude luminance pedestals were unable to reduce flicker thresholds. Luminance pedestals elevated flicker thresholds more at low temporal frequencies. A simple model based on local light adaptation was able to capture the general form of the TvC functions. Our results suggest that flicker thresholds derived in the presence of a luminance pedestal (luminance-pedestal flicker) may vary from those obtained by modulating about a mean luminance (mean-modulated flicker).

Adaptation, Ocular↗
PubMedDate not supplied

Activation of metabotropic glutamate receptors decreases a high-threshold calcium current in spiking neurons of the Xenopus retina.

Two types of spiking neuron were identified among acutely dissociated neurons from the Xenopus retina by their responses to a depolarizing current step: single spikers and multiple spikers. In culture, multiple spikers had perikaryal diameters > 15 microns, whereas single spikers had smaller somata, 5-10 microns in diameter. Using a conventional whole-cell patch-clamp technique, both T- and L-type calcium currents were identified in multiply spiking cells whereas only an L-type current was present in singly spiking cells. The metabotropic glutamate receptor (mGluR) agonist trans-(1S-3R)-1-amino-1,3-cyclopentane-dicarboxylic acid (trans-ACPD) significantly decreased the L-type calcium current by 46 +/- 3% (mean +/- S.E.M.) in both types of cell but had only a minor effect on the T-type current in multiply spiking neurons. In the presence of 50 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), 100 microM quisqualate (a potent mGluR1/5 agonist) decreased the L-type calcium current by 47 +/- 9% but had no effect on the T-type current. The selective mGluR4/6/7 agonist (+/-) 2-amino-4-phosphonobutyric acid (L-AP4, 100 microM), and the mGluR2/3 agonist (2S,3S,4S)-alpha-(carboxycyclopropyl)glycine (L-CCG1, 100 microM) decreased the L-type calcium current by 12 +/- 3% and 14 +/- 2%, respectively. The inhibition of calcium current by trans-ACPD was reduced when the patch pipette contained the G-protein inhibitor, GDP beta S. The presence of the G-protein activator GTP gamma S in the patch pipette irreversibly reduced the L-type calcium current, but was without effect on the T-type current. Heparin applied intracellularly significantly reduced the inhibitory effect of quisqualate, indicating an involvement of the inositol triphosphate (IP3) pathway in the mGluR-induced reduction of calcium current. Replacement of internal EGTA with BAPTA significantly reduced the inhibitory effect of quisqualate. In contrast, internal application of cAMP did not prevent an inhibition of calcium current by quisqualate. Thus, the mechanism by which calcium current is inhibited by mGluR seems not to involve an intracellular cAMP cascade. Our findings indicate that activation of mGluR1/5 results in the inhibition of a high-threshold calcium current. This process is mediated by the activation of a G-protein and is consistent with inhibition occurring by an IP3-stimulated release of internal calcium.

Action Potentials↗
PubMed2003

Effects of low volume resistance and cardiovascular training on strength and aerobic capacity in unfit men and women: a demonstration of a threshold model.

A threshold model postulates that prescriptively applying the appropriate cardiorespiratory and strength stimulus at a designated threshold of intensity for a brief time results in the targeted adaptations. A randomized control group design was used with 17 unfit males and females (mean age = 37.1 +/- 6.5 year) assigned to an exercise group (n = 9) who performed a progressive cardiovascular graded exercise protocol and resistance training twice a week for 12 weeks or a nonexercising control group (n = 8). The intervention included a graded exercise protocol involving a 3-min warm-up, exercising 3-4 min at 70-80% of maximum heart rate, and a 3-min cooldown. Progressive resistance exercise consisted of one set of six repetitions on each of six resistance machines. Results showed that the exercise group increased predicted aerobic capacity by 13.4% (p < 0.05), decreased submaximal rate pressure product by 17.2% (p < 0.05), and increased strength by 34% (p < 0.01). The results support a threshold model and show that time for effective exercise can be substantially reduced.

Adaptation, Physiological↗
PubMed1999

Self-sustained rhythmic activity in the thalamic reticular nucleus mediated by depolarizing GABAA receptor potentials.

Intracellular recordings from reticular thalamic (RE) neurons in vivo revealed inhibitory postsynaptic potentials (IPSPs) between RE cells that reversed and became depolarizing at the hyperpolarized membrane potentials that occur during sleep. These excitatory IPSPs can directly trigger low-threshold spikes (LTSs). The oscillatory mechanisms underlying IPSP-triggered LTSs crowned by spike bursts were investigated in models of isolated RE networks. In a one-dimensional network model, external stimulation evoked waves of excitation propagating at a constant velocity of 25-150 cells per second. In a large-scale, two-dimensional model of the reticular nucleus, the network showed transient or self-sustained oscillations controlled by the maximum conductance of the low-threshold calcium current and the membrane potential. This model predicts that the isolated reticular nucleus could initiate sequences of spindle oscillations in thalamocortical networks in vivo.

Action Potentials↗
PubMed1978

On the capacity of directionally selective mechanisms to encode different dimensions of moving stimuli.

Direction-specific losses of contrast sensitivity for sinusoidal test gratings as a function of the contrast of a sinusoidal adapting grating were found to be similar to those measured previously with square-wave gratings. Furthermore, both relationships were similar to that between motion aftereffect duration and the contrast of sinusoidal adapting gratings, and all three sets of data can be fit by a single function. The function shows that the magnitude of direction-specific adaptation effects increases linearly with the logarithm of adapting contrast in the low contrast region, but is essentially independent of contrast once the contrast exceeds threshold by more than a factor of five-six. In addition, it was found that direction-specific losses of contrast sensitivity are restricted to limited ranges of spatial frequency.

Adaptation, Ocular↗
PubMed2004

Active renin versus plasma renin activity to define aldosterone-to-renin ratio for primary aldosteronism.

BACKGROUND: In recent years, the assessment of the plasma aldosterone-to-renin ratio (ARR) has become an established screening method for the diagnosis of primary aldosteronism. Plasma renin activity (PRA) is usually measured to define ARR although, increasingly, renin concentration alone is often measured in clinical routine. OBJECTIVE: To determine the threshold of ARR using active renin concentration to screen for primary aldosteronism. DESIGN AND PARTICIPANTS: To determine the ARR threshold based on plasma immunoreactive renin concentration (irR), we measured plasma aldosterone concentration (PAC), irR and PRA in 36 hypertensive patients, nine thereof with adrenal adenoma, and compared ARRs calculated from irR and PRA, respectively. SETTING: Single-centre, hypertension clinic in a tertiary care hospital. RESULTS: PRA ranged from 0.41-14.9 ng/ml per h and irR from 1.1-72 ng/l. There was an excellent correlation between PRA and irR (r = 0.98, P < 0.0001) and between ARRPRA and ARRirR (r = 0.96, P < 0.0001). An ARRPRA > 750 pmol/l per ng/ml per h was previously found to be highly predictive of primary aldosteronism because 90% of the corresponding patients failed to suppress PAC upon saline infusion or fludrocortisone. The corresponding threshold value for ARRirR was 150 pmol/ng in our patients. Using these cut-offs, nine subjects had both increased ARRPRA and ARRirR while, in three patients, either ARRPRA or ARRirR were increased. The nine patients with increased ARRPRA and ARRirR also had PAC > 650 pmol/l. Only these patients had adrenal adenomas. CONCLUSIONS: The ARR threshold to screen for primary aldosteronism may be based on measurement of irR. An ARRirR > 150 pmol/ng may indicate primary aldosteronism.

Adenoma↗
PubMed2005

ECAP, ESR and subjective levels for two different nucleus 24 electrode arrays.

OBJECTIVE: We compared behavioral judgment of maximum comfortable loudness levels (C levels) and behavioral thresholds (Ts) for straight and Contour electrode arrays with two objective thresholds, electrically elicited stapedial reflex thresholds (eSRTs) and electrically elicited compound action potential thresholds (eCAP thresholds), on experienced adult cochlear implant users. Next, we evaluated the predictive value of objective measures for the straight and Contour electrode arrays, respectively. STUDY DESIGN: This is a prospective, two-group comparison study of two objective and subjective levels for two different Nucleus 24 electrode arrays. PATIENTS: Thirty experienced adults with Nucleus 24 cochlear implant were subjects in this study. Half the subjects used the straight electrode array, and the other half used the Contour electrode array. METHODS: Subjective C levels, Ts, and eSRTs were successfully identified for each active electrode. eCAP thresholds were measured on 5 representative basal, medial, and apical electrodes. Correlation and regression analyses between subjective levels and objective thresholds were performed. RESULTS: For our study subjects, there were no significant differences between the straight and Contour electrode array in regard to stimulation requirements between C levels, Ts, and thresholds of eCAP thresholds and eSRTs. CONCLUSION: Both eSRTs and eCAP thresholds may be used equally for estimation of subjective levels for either straight electrode array or Contour electrode array.

Action Potentials↗
PubMed1992

Concentration thresholds for fetal swallowing and vasopressin secretion.

In adults, plasma osmolality thresholds for hypernatremia-induced arginine vasopressin (AVP) secretion are similar or less than thresholds for stimulation of thirst. In the fetus, the thresholds for swallowing stimulation and AVP secretion have not been defined. Fetal swallowing and AVP secretory responses to hypertonic NaCl and urea were determined in six fetuses (130 +/- 1 1 days) chronically prepared with thyrohyoid, nuchal and thoracic esophagus, and diaphragm electromyograms (EMG), an esophageal flow probe, and vascular catheters. Fetuses received intracarotid injections (0.15 ml/kg) of increasing concentrations of NaCl (0.15, 0.30, 0.45, 0.60, 0.75, and 0.90 M), administered at 2-min intervals. A swallow was defined as a coordinated time-sequence of fetal thyrohyoid, nuchal esophagus, and thoracic esophagus EMG activity. The threshold saline concentration for swallowing was defined as the minimum NaCl dose eliciting swallow responses (within 20 s) after four of five injections at each dose. During a 2-h control period swallowing averaged 25.0 +/- 10.1 ml/h and 39.4 +/- 14.6 swallows/h. The mean NaCl threshold concentration for swallowing stimulation was 0.56 +/- 0.06 M. Fetal plasma AVP (2.6 +/- 0.9 pg/ml) increased significantly at the maximum subthreshold (7.6 +/- 4.0 pg/ml) and the threshold NaCl concentration (8.2 +/- 4.0 pg/ml) that stimulated swallowing. On a subsequent day, equiosmolar urea injections increased plasma AVP (from 2.2 +/- 0.7 to 7.6 +/- 2.6 pg/ml) but had no effect on swallowing activity. Fetal mean arterial blood pressure increased after injections of threshold saline and urea concentrations. Fetal arterial blood osmolality and sodium concentration did not change during any study.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Eliminating transient artifacts in stabilized-image contrast thresholds.

In the measurements of contrast thresholds for stationary, stabilized images, the choice of the psychophysical procedure may profoundly affect the results by constraining the time course of the stimulus presentation. With some procedures, the subject is unable to ignore transients; as a result, he necessarily responds to onset and offset transients rather than to the intended stimulus. Here we report significant effects of (a) the rapidly of onset and (b) the duration of the stimulus on thresholds for stabilized sinusoidal-grating patterns; these effects occur with both forced-choice and standard yes/no procedures. No value of either parameter (a) or (b) can eliminate such presentation effects when these procedures are used. However, we have devised a new, continuous-presentation procedure that yields results that do not depend on these parameters. Contrast thresholds for stabilized and for unstabilized stimuli measured by this procedure differ by 1 log unit or more, in good agreement with the results obtained by careful use of the method of adjustment.

Differential Threshold↗
PubMed2004

[Orofacial touch and pressure sensitivity in children].

This study assessed the thresholds of orofacial touch and pressure sensation in children and compared them with those in adults. Child subjects who were outpatients of TMDU Dental Hospital and who had no particular systemic diseases other than dental problems, were classified into 4 groups: preschool children (4-5 y, n=26), lower-grade elementary school pupils (6-9 y, n=100), higher-grade elementary school pupils (10-12 y, n=36), and junior high school pupils (13-15 y, n=26). Adult subjects were TMDU students (23-31 y, n=37). The thresholds of touch and pressure sensation were measured with a Semmes-Weinstein pressure aesthesiometer which consisted of 20 filaments with different marking values (Fm). Stimulation was applied with the thinner 10 filaments with lower values ranging from 1.65 to 4.31 Fm (0.0045-2.052 gw). The measurements were carried out on the following 10 points in the orofacial area in all the subjects: the upper lip, gingiva of upper anterior teeth, palate, lower lip, gingiva of lower anterior teeth, buccal mucous membrane, tongue tip, skin above eyebrow, cheek skin and mentum skin. The thresholds in the child subjects were not different from those in the adult subjects on most measurement points, but were significantly different on the gingiva and palate. The lower the age, the lower the thresholds on the gingiva. Since these measurement points are located in the chewing mucous membrane, it is considered that the threshold changes occurred due to histological alterations with growth. It is suggested that the threshold values of orofacial touch and pressure sensation obtained from this study could be used as the standard values for an indicator of the development of oral function and structure in children.

Adolescent↗