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PubMed1998

Lines and Gabor functions compared as spatial visual stimuli.

Foveal discrimination thresholds were measured for orientation, vernier alignment, bisection, displacement detection and stereoscopic acuity using simple line stimuli and also sinusoidal grating patches with gaussian intensity modulation (Gabor stimuli). Stimulus parameters such as luminance, exposure duration, component separation and, as far as possible, length were identical for both. Orientation discrimination as a function of length is almost identical for the two classes of stimuli, some observers performing slightly better with Gabor patches. Thresholds for displacement detection are also the same. Vernier, stereo and bisection acuities, however, are considerable better with line than with Gabor stimuli.

Differential Threshold↗
PubMed1999

The effects of rehydration on phonation in excised canine larynges.

Experiments using excised canine larynges were conducted to study the restoration of vocal efficiency in dehydrated larynges. Excised larynges were dehydrated with warm, dry air to the point that airflow through the approximated vocal folds would not entrain the folds to produce phonation. The dehydrated vocal folds were then bathed in a saline solution. The rehydrated larynges were then remounted on the bench apparatus that enabled phonation with a constant humidified airflow, and measurements were made of phonation threshold pressure, glottal airflow, and amplitude. Hydration resulted in significantly increased efficiency and decrease in phonation threshold pressure. The findings confirm clinical impressions that hydration is critical in the physiology of normal phonation.

Animals↗
PubMed1986

Effects of antiarrhythmic drugs on the chronic pacing threshold and the endocardial R wave amplitude in the conscious dog.

To determine the effects of antiarrhythmic drugs on the chronic pacing threshold and the endocardial R wave amplitude, we tested seven drugs (representative of Vaughn Williams' antiarrhythmic class-I-IV) on four to six dogs after the implanted ventricular endocardial bipolar leads had reached chronic stable thresholds. The seven antiarrhythmic drugs tested were procainamide (oral [p.o.] and intravenous [IV], class IA), lidocaine (IV, class IB), tocainide (p.o., class IB), flecainide (p.o. and IV, class IC), propranolol (p.o. and IV, class II), amiodarone (p.o. and IV, class III), and verapamil (p.o. and IV, class IC), propranolol (p.o. and IV, class II), amiodarone (p.o. and IV, class III), and verapamil (p.o. and IV, class IV). The drugs were administered in sufficient doses to achieve plasma levels associated with antiarrhythmic efficacy in humans. All oral drugs were given for sufficient time to achieve expected steady state levels. The pacing thresholds, both voltage and current, and the endocardial R wave amplitude were measured in the conscious dog with a Medtronic pacing system analyzer at a pulse width of 0.1, 0.5, 1.0, and 2.0 ms at intervals following IV or p.o. administration of each antiarrhythmic drug. We found that there were no significant effects of the tested seven antiarrhythmic drugs on the chronic pacing threshold and the endocardial R wave amplitude at any of the pulse widths. We conclude that in the healthy dog antiarrhythmic drugs do not alter the pacing threshold and the endocardial R wave amplitude.

Animals↗
PubMed2003

Responses of single motor units in human masseter to transcranial magnetic stimulation of either hemisphere.

The corticobulbar inputs to single masseter motoneurons from the contra- and ipsilateral motor cortex were examined using focal transcranial magnetic stimulation (TMS) with a figure-of-eight stimulating coil. Fine-wire electrodes were inserted into the masseter muscle of six subjects, and the responses of 30 motor units were examined. All were tested with contralateral TMS, and 87 % showed a short-latency excitation in the peristimulus time histogram at 7.0 +/- 0.3 ms. The response was a single peak of 1.5 +/- 0.2 ms duration, consistent with monosynaptic excitation via a single D- or I1-wave volley elicited by the stimulus. Increased TMS intensity produced a higher response probability (n = 13, paired t test, P < 0.05) but did not affect response latency. Of the remaining motor units tested with contralateral TMS, 7 % did not respond at intensities tested, and 7 % had reduced firing probability without any preceding excitation. Sixteen of these motor units were also tested with ipsilateral TMS and four (25 %) showed short-latency excitation at 6.7 +/- 0.6 ms, with a duration of 1.5 +/- 0.3 ms. Latency and duration of excitatory peaks for these four motor units did not differ significantly with ipsilateral vs. contralateral TMS (paired t tests, P > 0.05). Of the motor units tested with ipsilateral TMS, 56 % responded with a reduced firing probability without a preceding excitation, and 19 % did not respond. These data suggest that masseter motoneurons receive monosynaptic input from the motor cortex that is asymmetrical from each hemisphere, with most low threshold motoneurons receiving short-latency excitatory input from the contralateral hemisphere only.

Adult↗
PubMed2003

Three-dimensional symmetric shapes are discriminated more efficiently than asymmetric ones.

Objects with bilateral symmetry, such as faces, animal shapes, and many man-made objects, play an important role in everyday vision. Because they occur frequently, it is reasonable to conjecture that the brain may be specialized for symmetric objects. We investigated whether the human visual system processes three-dimensional (3D) symmetric objects more efficiently than asymmetric ones. Human subjects, having learned a symmetric wire object, discriminated which of two distorted copies of the learned object was more similar to the learned one. The distortion was achieved by adding 3D Gaussian positional perturbations at the vertices of the wire object. In the asymmetric condition, the perturbation was independent from one vertex to the next. In the symmetric condition, independent perturbations were added to only half of the object; perturbations on the other half retained the symmetry of the object. We found that subjects' thresholds were higher in the symmetric condition. However, since the perturbation in the symmetric condition was correlated, a stimulus image provided less information in the symmetric condition. Taking this in to consideration, an ideal-observer analysis revealed that subjects were actually more efficient at discriminating symmetric objects. This reversal in interpretation underscores the importance of ideal-observer analysis. A completely opposite, and wrong, conclusion would have been drawn from analyzing only human discrimination thresholds. Given the same amount of information, the visual system is actually better able to discriminate symmetric objects than asymmetric ones.

Differential Threshold↗
PubMed1989

The optimum placement-site of the electrode in electric pulp testing of the 12 anterior teeth.

The present study of 2,387 recordings of 12 anterior teeth in 53 patients indicates that the incisal edge is the optimal placement-site for the electric pulp tester to determine the lowest response threshold. The results show significant individual variations in the lowest threshold responses of the cervical-third, middle-third, incisal one-third, and incisal edge sites on a tooth, with a confidence level of 99%, according to the analysis of variance. The maxillary teeth gave a higher response threshold than the mandibular teeth and different types of teeth (canines and incisors) had statistically significant different response thresholds. The application of the electric pulp tester to the incisal-edge region with exposed dentin produced the most significant decrease in the threshold response.

Adolescent↗
PubMed1994

[Comparative studies on the evaluation of vibratory perception thresholds using three different instruments, vibratron II, TM-31A and SMV-5--reliability, correlation with age and interrelationship].

Vibratory perception thresholds of 40 (13 males and 27 females) subjects without sensory disturbances were evaluated using three different instruments, Vibratron II, TM-31A and SMV-5, successively three times every third or fourth day to compare their reliability, correlation with age and interrelationship. The intraclass correlation coefficients of the threshold, obtained at the palmar distal phalanx of the index finger of the predominant hand by using Vibratron II and SMV-5 were 0.77 and 0.88, respectively, and those at the radial styloid process on the same side by using TM-31A and SMV-5 were 0.62 and 0.84, respectively. There was a similarity of the intraclass correlation coefficients in the measurement at both sites between the subjects of ages < or = 40 and those of ages > 40, when different instruments were used. However, the thresholds were lower among the subjects of ages < or = 40 than among those of ages > 40. A significantly positive correlation was found between the threshold and the age at both sites when using different instruments. A significantly positive correlation was also found between the thresholds obtained by Vibratron II and SMV-5 at the palmar distal phalanx and between those obtained by TM-31A and SMV-5 at the radial styloid process. The above data indicate that each instrument is applicable not only for diagnosing and evaluating the vibratory sensation disturbances, but also for the follow-up study and evaluation of the efficacy of the specific treatment for the patients with sensory disturbances. They are likewise applicable for the screening and diagnosis of peripheral neuropathy in the occupational and environmental medicines. However, the reliability was lowest in the evaluation by TM-31A, and the correlation coefficient was smallest in the relationship between the age and the threshold obtained by TM-31A.

Adolescent↗
PubMed1991

The reproducibility and heritability of individual differences in osmoregulatory function in normal human subjects.

The rise in plasma vasopressin produced by infusion of hypertonic saline varies widely among healthy adults. To determine if these interindividual differences are reproducible, we used linear regression to analyze the relationship of plasma vasopressin to plasma osmolality during repeat hypertonic saline infusion in seven normal subjects. The results confirmed that the slope or sensitivity of the relationship differed widely between subjects (0.12 to 1.66 pg/ml/mOsm/kg) and revealed that these differences were highly reproducible. (r = 0.94 on repeat testing). The individual values for osmotic threshold were less variable (280 to 288 mOsm/kg) as well as less clearly reproducible (r = 0.61). To determine whether these differences are genetically influenced, we compared the vasopressin osmolality relationships within seven monozygotic and six dizygotic twin pairs. We found that the threshold and sensitivity values correlated significantly within monozygotes (r = 0.95 and 0.95) but not within dizygotes (r = 0.34 and 0.21). When the osmoregulation of thirst was similarly evaluated, the individual relationships were as variable as for plasma vasopressin, but only the threshold values in monozygotes correlated significantly (r = 0.92). In 80 healthy adults, the frequency distributions of the osmotic threshold and sensitivity of the vasopressin responses were essentially normal. We conclude that the sensitivity for vasopressin secretion as well as the osmotic thresholds for thirst and vasopressin demonstrate significant polygenetic variance among healthy adults.

Adult↗
PubMed1990

[Experimental study on the difference of ischemic threshold between cerebral cortex and thalamus with middle latency auditory evoked potentials].

Middle latency auditory evoked potentials (ML-AEPs) have not yet been established as a device of assessing neurological events because their origins have not been definitely identified. In this study, we assessed the neurological usefulness of MLA-EPs through experimental approach using canine models of acute ischemia localized within the cerebral cortex or thalamus. Two types of localized cerebral ischemia were produced in mongrel dogs by clipping of major cerebral arteries and inducing of hypotension; they were, unilateral cortical ischemia involving the right primary auditory area (group A) and unilateral thalamic ischemia involving the right medial geniculate body (group B). Using these two ischemia models, auditory evoked potentials (AEPs) were intracranially and extracranially recorded in addition to the measurement of local cerebral blood flow (1-CBF). Prior to the induction of ischemia, it was confirmed that positive waves with a latency of 20 ms (P20) were evoked in the bilateral primary auditory areas by sound stimulation (90 dB 5 Hz click) given to the ear contralateral to the planned ischemic side in both groups. The right P20 disappeared when the 1-CBF in the right primary auditory area decreased below the ischemic flow threshold of synaptic transmission failure, approximately 18 ml/100 g/min, in group A, and when the 1-CBF in the right medial geniculate body decreased below the threshold, 10 ml/100 g/min, in group B.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

The vibrotactile threshold (VT) at the fingertips of chain saw operators.

The vibration sensitivity of the skin at the ten fingertips was tested with 72 chain saw operators examined due to VWF-disease and compared with controls. The vibrotactile perception threshold (frequency f = 125 Hz, load p = 1.3 N) proved to be 3 to 5 times as high for the exposed group compared to controls. There was no correlation between vibration sensitivity and peripheral circulation found in cold provocation test. Two different testing instruments (pallaesthesiometer = vibrotactometer) showed significant differences in results probably due to different technical details of the methods. It may be concluded that a standardization of the instrumentation and method is necessary for testing the vibrotactile perception threshold as a part of the nervous function in a comparable manner.

Adult↗
PubMed2005

Pathways mediating abnormal intracortical inhibition in Parkinson's disease.

Previous studies have used paired-pulse transcranial magnetic stimulation to show that short-interval intracortical inhibition (SICI) is reduced in patients with Parkinson's disease (PD). This study examined whether reduced SICI in PD is caused by an increase in the threshold of inhibitory pathways or a reduction in the threshold of excitatory pathways. Motor-evoked potentials were recorded from a hand muscle in 12 patients with PD (7 patients were tested off and on antiparkinsonian medications) and 12 control subjects. SICI was tested at seven conditioning stimulus intensities (CSIs; 40-100% of resting motor threshold) and at interstimulus intervals (ISIs) of 2, 3, and 4 milliseconds. No differences were found between groups in resting or active motor threshold, SICI threshold, or the extent of SICI at CSIs at or below 80% of resting motor threshold. Significant differences between groups were observed at CSIs of 90% and 100% with an ISI of 3 milliseconds. Antiparkinsonian medication had no effect on SICI. These findings show that the low threshold inhibitory pathways mediating SICI are normal in PD. The suppression of SICI observed at higher CSIs suggests that the threshold of intracortical facilitatory pathways is decreased in PD.

Aged↗
PubMed2004

Elevated threshold for intracortical inhibition in focal hand dystonia.

Differences between control and focal hand dystonia (FHD) subject groups in short interval intracortical inhibition (SICI) as determined by paired transcranial magnetic stimulation (TMS) can be difficult to demonstrate, due to interindividual differences. The purpose of this study was to compare two TMS methods for assessing SICI in 8 control and 7 FHD subjects. Electromyographic (EMG) data were recorded from the first dorsal interosseous (FDI) muscle of the dominant hands of the control subjects and affected hands of the FHD subjects. The first method used a conventional approach of setting conditioning stimulus intensity to 80% of rest threshold (RTh) and test stimulus intensity to 120% RTh. Three interstimulus intervals (ISIs) were used: 2 msec, 3 msec, and the ISI between 2 and 3 msec that produced optimal SICI. The second method was novel in that test stimulus intensity was set to 150% active threshold (ATh), and conditioning stimulus intensity was varied between 50% and 100% ATh. The latter was determined at the threshold for SICI and expressed as a ratio of ATh. There was no difference between the subject groups in the degree of SICI produced using the first method, at the three ISIs studied. However, using the second method, the SICI threshold:ATh ratio was found to be significantly higher for FHD subjects. This finding suggests that determining the SICI threshold:ATh ratio may be a more sensitive measure of intracortical inhibitory function than more conventional methods.

Adult↗
PubMed1998

Heart rate deflection compared to 4 mmol x l(-1) lactate threshold during incremental exercise and to lactate during steady-state exercise on an arm-cranking ergometer in paraplegic athletes.

The deflection point (DP) of the heart rate in relation to the work rate (WR) of 8 male endurance-trained paraplegics and 11 male physically active sports students was investigated during nonsteady-state incremental arm cranking ergometry (IT) and compared to the 4 mmol x l(-1) blood lactate concentration threshold and to blood lactate concentration in steady-state exercise (SST). Heart rate, and lactate concentration from capillary blood, were determined at rest, during IT and SST. The DP was calculated by linear regression analysis of the heart rate during IT. The SST consisted of three consecutive exercise intensities over a period of 8 min at exercise intensities of 10 W below, and at 10 W above the work rate at deflection point (WRDP). No difference was found between the paraplegics and non-handicapped subjects regarding heart rate and blood lactate concentration at rest and during exercise. A DP was established in all the paraplegics and in 72.7% of the non-handicapped subjects, but lactate accumulation was observed in 75% of the paraplegics and in 62.5% of the non-handicapped subjects at the lowest intensity of SST. In summary, endurance-trained paraplegics with an injury level below T5 showed heart rate and blood lactate concentration values comparable to non-handicapped subjects during IT. A linear increase at moderate exercise intensities and a levelling-off at higher to maximal intensities could be identified in all the paraplegics and in 72.7% of non-handicapped subjects. The determination of the anaerobic threshold by DP should be applied with caution, since no causal relationship of DP and the anaerobic threshold was found and the WRDP tended to overestimate threshold values.

Adult↗
PubMed1999

The effect of dynamic exercise on resting cold thermoregulatory responses measured during water immersion.

The purpose of this study was to evaluate the effect of exercise on the subsequent post-exercise thresholds for vasoconstriction and shivering measured during water immersion. On 2 separate days, seven subjects (six males and one female) were immersed in water (37.5 degrees C) that was subsequently cooled at a constant rate of approximately 6.5 degrees C x h(-1) until the thresholds for vasoconstriction and shivering were clearly established. Water temperature was then increased to 37.5 degrees C. Subjects remained immersed for approximately 20 min, after which they exited the water, were towel-dried and sat in room air (22 degrees C) until both esophageal temperature and mean skin temperature (Tsk) returned to near-baseline values. Subjects then either performed 15 min of cycle ergometry (at 65% maximal oxygen consumption) followed by 30 min of recovery (Exercise), or remained seated with no exercise for 45 min (Control). Subjects were then cooled again. The core temperature thresholds for both vasoconstriction and shivering increased significantly by 0.2 degrees C Post-Exercise (P < 0.05). Because the Tsk at the onset of vasoconstriction and shivering was different during Pre- and Post-Exercise Cooling, we compensated mathematically for changes in skin temperatures using the established linear cutaneous contribution of skin to the control of vasoconstriction and shivering (20%). The calculated core temperature threshold (at a designated skin temperature of 32.0 degrees C) for vasoconstriction increased significantly from 37.1 (0.3) degrees C to 37.5 ( 0.3) degrees C post-exercise (P < 0.05). Likewise, the shivering threshold increased from 36.2 (0.3) degrees C to 36.5 (0.3) degrees C post-exercise (P < 0.05). In contrast to the post-exercise increase in cold thermal response thresholds, sequential measurements demonstrated a time-dependent similarity in the Pre- and Post-Control thresholds for vasoconstriction and shivering. These data indicate that exercise has a prolonged effect on the post-exercise thresholds for both cold thermoregulatory responses.

Adult↗
PubMed1998

Rimcazole, a sigma receptor ligand, and the anticonvulsive action of conventional antiepileptic drugs.

Rimcazole (a selective sigma receptor antagonist) at 5 and 10 mg/kg, 30 min before the test, lowered the electroconvulsive threshold, being ineffective at 2.5 mg/kg. Rimcazole (2.5 and 5 mg/kg) enhanced the protective activity of phenobarbital and valproate, but not that of carbamazepine and diphenylhydantoin against maximal electroshock. The effect of rimcazole upon the electroconvulsive threshold was reversed by haloperidol (0.5 mg/kg), but the rimcazole-induced potentiation of the anticonvulsive action of antiepileptics was not. Moreover, rimcazole (2.5 mg/kg) did not alter the total or free plasma levels of valproate or phenobarbital, so a pharmacokinetic interaction is not probable. The combined treatment of rimcazole with antiepileptic drugs, providing a 50% protection against maximal electroshock, did not affect motor performance in mice, although it resulted in significant long-term memory deficits. Our data indicate that rimcazole, in spite of lowering the seizure threshold, may enhance the protective activity of some antiepileptic drugs.

Animals↗
PubMed1987

Spatial organization of human perioral reflexes.

Reflex responses recorded from the upper and lower divisions of the human orbicularis oris muscle were studied as a function of the site of stimulation. Stimuli were applied to 11 sites, ranging from the glabrous skin of the upper and lower lip vermilion borders to the hairy skin of the cheek. Highly localized, innocuous mechanical stimuli were created by displacing a servo-controlled probe over the surface of the perioral skin. Reflex response amplitude was strongly dependent on the site of stimulation. Stimulation of some sites, for example the ipsilateral corner of the mouth, the chin, and cheek, produced no responses, whereas stimulation of other sites, particularly the ipsilateral vermilion borders, produced large reflex responses. Changes in response amplitude as a function of stimulation site were the same for the upper lip and lower lip muscle recordings, with the largest responses at both recording sites produced by stimulation of the ipsilateral upper lip vermilion border. These results suggest that the upper and lower divisions of orbicularis oris share common synaptic drive, at least from inputs generated via reflex pathways, and that the upper vermilion border may be more densely innervated with mechanoreceptors than the lower. The latter hypothesis was supported by an additional experiment examining two-point discrimination thresholds for the glabrous skin of the upper and lower lips. Two-point thresholds were significantly smaller for the upper compared with the lower lip vermilion border.

Adult↗