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PubMed1996

The effects of static indentation on vibrotactile threshold.

Vibrotactile thresholds were measured on the thenar eminence and the volar forearm at different static depths of skin indentation. Three stimulus frequencies (1, 20, and 200 Hz) were delivered through either a 0.008- or a 2.9-cm2 contractor. The indentation depths ranged from 0 to 1 mm (0.25-mm steps) relative to the point of skin contact with the stimulator. There was a significant effect of indentation in all stimulus combinations of contactor size, location, and frequency. These results resolve an apparent discrepancy in the literature regarding threshold reduction with increasing contactor size observed on the forearm at low frequencies.

Adult↗
PubMed2006

Electrical stimulation of mammalian retinal ganglion cells with multielectrode arrays.

Existing epiretinal implants for the blind are designed to electrically stimulate large groups of surviving retinal neurons using a small number of electrodes with diameters of several hundred micrometers. To increase the spatial resolution of artificial sight, electrodes much smaller than those currently in use are desirable. In this study, we stimulated and recorded ganglion cells in isolated pieces of rat, guinea pig, and monkey retina. We used microfabricated hexagonal arrays of 61 platinum disk electrodes with diameters between 6 and 25 microm, spaced 60 microm apart. Charge-balanced current pulses evoked one or two spikes at latencies as short as 0.2 ms, and typically only one or a few recorded ganglion cells were stimulated. Application of several synaptic blockers did not abolish the evoked responses, implying direct activation of ganglion cells. Threshold charge densities were typically <0.1 mC/cm2 for a pulse duration of 100 micros, corresponding to charge thresholds of <100 pC. Stimulation remained effective after several hours and at high frequencies. To show that closely spaced electrodes can elicit independent ganglion cell responses, we used the multielectrode array to stimulate several nearby ganglion cells simultaneously. From these data, we conclude that electrical stimulation of mammalian retina with small-diameter electrode arrays is achievable and can provide high temporal and spatial precision at low charge densities. We review previous epiretinal stimulation studies and discuss our results in the context of 32 other publications, comparing threshold parameters and safety limits.

Action Potentials↗
PubMed1977

Punctate pressure sensitivity: effects of skin temperature.

The dependence on skin temperature of tactile sensitivity to punctiform (hair) stimulation of the finger tip came under study in five subjects. Their data show that punctate sensitivity is relatively stable over a wide range of thermal environments. On the average, some elevation of touch threshold occurred at a skin temperature of 20 degrees C (i.e., about 10 degree below normal), but severe loss of sensitivity first occurred at 10 degrees C. A small but possibly insignificant loss appeared at skin temperatures of 40 and 43 degrees C. The relatively stable behavior of the punctate threshold between about 20 and 40 degrees C contrasts with that of the vibrotactile threshold, which, at least for high frequencies, depends strongly on the skin temperature.

Adult↗
PubMed1975

Effects of testing age and fostering experience on seizure susceptibility of rats treated prenatally with chlorpromazine.

Offspring of rats treated with 2 mg/kg body weight chlorpromazine (CPZ) on Days 5-8 of gestation had lower seizure thresholds than offspring of saline-treated controls at 30, 60, 90, and 120 days of age. The CPZ-treated offspring were also heavier than controls prior to weaning. Further analysis using cross-fostered litters indicated that at least part of the drug effect on seizure thresholds took place before birth, although a postnatal component was also demonstrated. A striking effect of the fostering experience itself on the seizure threshold prevented conclusions about the relative importance of prenatal and postnatal influences.

Age Factors↗
PubMed2005

[Quantitative evaluation of thermosensitivity in patients with mandibular fractures].

AIM: The temperature and pain thresholds of 30 patients with mandibular fractures were evaluated with a specially developed measuring device in a prospective study to examine neurosensory disturbances of the inferior alveolar nerve (IAN). PATIENTS AND METHODS: Measurements in 30 patients with 45 mandibular fractures were done before, immediately after, and over the course of half a year after operation. Outcomes of the thermosensitivity measurement (TSM) were compared to the results of the two point discrimination (2-PD) test, sharp/blunt test (SBT), and questioning the patients about their subjective feelings (SF). RESULTS: Post-traumatically, neurosensory testing revealed up to 2.8 degrees C (mean) increased thresholds as compared with the intact side. By contrast, post operative diagnostics clearly revealed up to 8.1 degrees C (mean) increased thresholds. Compared with the clinical sensory tests, the post-therapeutic (3-6 months postoperative) measurements with the TSM device proved a resensitization and threshold decrease by up to 3 degrees C. We found more exact and reproducible results of the TSM in comparison to those of the 2-PD and SBT for the evaluation of sensory disturbances of the IAN. Close agreements between the results of the TSM and the SF could be detected. CONCLUSION: Because of its sensitivity and accuracy in the quantitative detection of temperature and pain thresholds, the TSM is particularly suitable for evaluating neurosensory deficits and monitoring their progression.

Adolescent↗
PubMed2004

Effects of gonadal steroids on the input-output relationship of the corticospinal pathway in humans.

Most of our knowledge about gonadal steroid effects on the nervous system come from studies of limbic structures, while virtually nothing is known about the action of these hormones on the motor system. We carried out experiments on six healthy volunteer males to determine the threshold and gain of the input-output relationship (i.e. stimulus intensity vs. response size) of the corticospinal motoneurones in relation to the transient increase of gonadal steroids induced by a single intramuscular injection of human chorionic gonadotropin (hCG). The motor cortex was excited by focal transcranial magnetic stimuli and the evoked responses from the first dorsal interosseous (FDI) were recorded with surface electromyographic electrodes. In some experiments, the threshold and recruitment curve of the soleus H reflex were determined to assess the gonadal steroid effects on spinal motoneurones. All the subjects showed a significant decrease of cortical motor threshold concomitant with a significant increase of testosterone and oestradiol plasma concentrations. By contrast, there was no significant change of the slope of the curve expressing the relationship between the intensity of magnetic stimulation and the size of the muscle response. Both the threshold and slope of the H reflex were unaffected by the gonadal steroid levels. Latencies of the maximal FDI response to cortical and cervical magnetic stimulation were also unmodified. We conclude that gonadal steroids are involved in regulating the threshold of corticospinal motoneurones in humans. Our observations confirm that the threshold and gain of corticospinal motoneurones are determined by different neural mechanisms.

Adult↗
PubMed2005

Quantitative evaluation of threshold fiber strain that induces reorganization of cytoskeletal actin fiber structure in osteoblastic cells.

The cytoskeletal stress fiber structure plays essential roles in various kinds of cellular functions such as shape maintenance, active motility and mechanosensing, and its structure is dynamically reorganized under each functional process. In known reorganization mechanisms of the stress fibers, a change in its mechanical condition has been suggested as one of the key mediators that affect the reorganization process. Some experimental studies have clarified that tension release in the stress fibers induces fiber depolymerization that is considered to be the initial phase of the reorganization process. However, quantitative mechanical values such as strain or stress that induce depolymerization have still not been evaluated. This study is aimed at the quantitative evaluation of the mechanical value that induces stress fiber depolymerization, to gain a basic understanding of the reorganization phenomenon from a mechanical viewpoint. Osteoblastic cells (MC3T3-E1) were cultured on prestretched silicone rubber substrate. Compressive deformation was applied to the cells by uniaxially releasing the prestretched substrate strain and change in the stress fiber structure was observed. The results indicated that the compressive strain magnitude, not in the whole cell body but in the stress fiber itself, is important to induce disassembly of the stress fiber structure. The existence of a threshold strain magnitude for initiating fiber disassembly was also suggested; the threshold strain magnitude was evaluated as approximately -0.20.

Actin Cytoskeleton↗
PubMed1995

Lower temperature limits for activity of several Ixodid ticks (Acari: Ixodidae): effects of body size and rate of temperature change.

Uncoordinated activity threshold temperature, the temperature below which ticks can no longer seek a host in a coordinated manner, and the activity threshold temperature, when all activity ceases, were examined for three species of ticks found in coastal sections of New York. The mean uncoordinated activity threshold and activity threshold temperatures were determined for nymphal, female and male Ixodes scapularis Say, nymphal, female, and male Amblyomma americanum (L.), and for female and male Dermacentor variabilis (Say). Only the uncoordinated activity threshold and activity threshold temperatures for adult I. scapularis were significantly correlated to the rate of temperature decrease. The mean uncoordinated activity threshold and activity threshold temperatures were significantly correlated to the mean size of each tick species.

Age Factors↗
PubMed2004

Increased rate of visual field loss associated with larger initial visual field threshold values on follow-up of open-angle glaucoma.

PURPOSE: To determine the changes in the visual field over time and the factors that contribute to these changes on follow-up of open-angle glaucoma patients. PATIENTS AND METHODS: From a retrospective review of patients' charts and visual fields, 30 eyes from 30 patients with open-angle glaucoma with a minimum of 3 years of follow-up were chosen. Visual fields were obtained with the Octopus perimeter about every 4 months. Regression analysis was used to obtain the slope for all the threshold values for each eye for the total field and nine different regions over time. Optic disc area was measured from single fundus photographs obtained at the beginning of the period of observation. RESULTS: The open-angle glaucomas were observed for a mean of 6.7 +/- 2.3 years. The number of visual fields per eye was 20.7 +/- 8.0. The mean threshold value of the total field for the first three visual fields was 18.0 +/- 5.2 dB. The visual fields of the 30 eyes with a mean intraocular pressure of 18 +/- 2 mm Hg during follow-up showed a significant decrease in their visual field slope of -0.384 dB/y for the total visual field. On multivariate analysis, the slope or rate of visual field loss was significantly correlated with the average of the first three initial visual field thresholds for the total visual field, temporal, and central regions so that the greater the threshold value the more rapid the rate of the visual field loss. For the total visual field and for the nasal, superior nasal, and temporal regions with lower initial threshold values, the rate of visual field loss was curvilinear with the rate of visual field loss increasing at greater initial mean threshold values. The other regions of the visual field showed a linear increasing rate of visual field loss with larger initial threshold values. Other factors significantly associated with progression of visual field loss were refractive error, race, the slope of the pulse rate, and the mean percent false positives and false negatives for initial to final observations. The mean and the slope of intraocular pressure from initial to final observation were not significant variables. CONCLUSION: In open-angle glaucomas observed for 6.7 +/- 2.3 years, there was a more rapid rate of visual field loss associated with larger initial threshold values and a less rapid rate of visual field loss associated with smaller initial threshold values indicating that the progression of visual field loss is greater in an earlier stage of disease.

Differential Threshold↗
PubMed1993

Pharmacological and immunohistochemical evidence for serotonergic modulation of cholinergic nucleus basalis neurons.

Identified electrophysiologically by low threshold bursts and transient outward rectification, cholinergic nucleus basalis neurons were recorded and labelled intracellularly in guinea-pig basal forebrain slices. By means of a triple labelling immunofluorescent technique, serotonin-immunoreactive fibres were visualized in close proximity to the soma and dendrites of the biocytin-labelled, choline acetyl transferase (ChAT)-immunoreactive cells. By bath application, 5-hydroxytryptamine (5-HT) produced a direct hyperpolarization of the identified cells which was mimicked by 5-HT1A receptor agonists, suggesting that it may inhibit the tonic firing but also modulate the low threshold bursting of the cholinergic nucleus basalis neurons.

Animals↗
PubMed1978

Auditory duration discrimination in the parakeet (Melopsittacus undulatus).

Two parakeets were trained by a method of avoidance conditioning to respond to duration differences in successively occurring tone bursts. Difference limens for duration were obtained at six durations (20-160 ms) of a 2.86-kHz tone presented at a sensation level of 60 dB. Calculations of the Weber fractions at each duration showed threshold values which compare favorably to similar measures for man ranging between 0.10 and 0.20.

Animals↗
PubMed1982

Localized effects of spatial frequency adaptation.

The spatially localized threshold-elevation aftereffect of spatial-frequency adaptation was measured by using localized, aperiodic test patterns that have bandpass Fourier transforms. At a given retinal location, the threshold-elevation curves are consistent with the fatigue of size-turned mechanisms with center-surround sensitivity profile. Only a few different sizes of such mechanisms were required to fit the local results. The local aftereffect was also measured as a function of eccentricity near the fovea. The results indicate that the threshold-elevation aftereffect of spatial-frequency adaptation is not spatially homogeneous.

Adaptation, Ocular↗
PubMed1987

Some properties of the double-flash illusion.

When a field of light (an inducing field) is extinguished, and a subsequent probe pulse is presented (5-msec duration, interstimulus interval of 80-320 msec), the single probe pulse appears to be a double flash. We measured the frequency of seeing this double-flash illusion when it was induced by high-contrast flickering fields. The illusion is dependent on inducer-field frequency, showing a major peak and, for some interstimulus intervals, subpeaks. There are notable interobserver differences in the frequency location of the peaks. We evaluated whether the results represented the transient response of a mechanism analogous to a single-harmonic oscillator. A second experiment compares the threshold illuminance for detecting the probe pulse with the illuminance above threshold required to see the double-flash illusion. The illuminance required for a double-flash threshold is high, being 7-20 times the illuminance required for pulse detection.

Adult↗
PubMed1976

Changes of the vibratory sensation threshold in workers using vibrating tools.

Vibratory sensation thresholds of ten fingertips of each person were measured by each of the three frequencies in groups using three kinds of vibrating tools and the control groups. The subject groups were using leg-drill (n=37), chipping-hammer (n=25) and chain-saw (n=19). The control groups were engaged in desk work or outdoor work in a bureau of forest management (n=24), a local forest office (n=30) and a gas company (n=22) (Table 1). The tested frequencies were 63 Hz, 125 Hz and 250 Hz. The room temperature was kept at 20 degrees C. 1) The threshold values were found in such order as V greater than IV greater than III greater than I and II-finger in the subject groups, whereas I and V greater than II, III and IV-finger in the control groups. No significant difference between left and right hands was found in any group, both the subject and the control. 2) The threshold values were significantly higher in the chipping-hammer group and the chain-saw group than in the control (p less than 0.05 at 63 Hz, p less than 0.01 at 125 Hz and 250 Hz). They were higher in the leg-drill group than in the control but it was statistically not significant. 3) Regression analysis was performed about age and experience-years of the subject groups which were thought to have an effect upon the threshold change. But the effect of both factors to the threshold values were small in all subject groups. 4) The patterns of threshold values made up by each of the three frequencies were different among the three subject groups. The chipping-hammer group had the higher vibratory sensation threshold shift in the order of 250 Hz, 125 Hz and 63 Hz, the leg-drill group had almost equal threshold shift among the three frequencies, and the chain-saw group had the intermediate tendency between the other two groups. 5) Frequencies of 125 Hz and 250 Hz were more advantageous than that of 63 Hz in order to discriminate between the subject group and the control. Both 125 Hz and 250 Hz vibratory sensation threshold should be measured to find early disorders of vibration disease if possible, because the relation between thresholds of 125 Hz and 250 Hz was not so linear. 6) The observed significant differences of threshold values among the control groups were thought to be caused by different climatic circumstances.

Adult↗
PubMed1984

Implications of stimulus factors governing kindled seizure threshold.

Seizure threshold was measured in kindled rats by delivering trains of specified duration, consisting of bipolar pulses of specified width, at increasing current intensities, at specified intertrain intervals. The effect of decreasing pulse width was to elevate seizure threshold, but considerably less total energy was required to elicit a seizure. Seizure threshold was also found to be an inverse function of train duration, within asymptotic limits. Seizure "threshold" is not a single number but a function of stimulus-duration factors. In the case of train length, a putative threshold-altering agent may alter one or the other asymptotic value so that the curve is shifted upward or to the right.

Animals↗
PubMed1979

Interaction effects of extraversion and neuroticism on detection thresholds.

Detection thresholds for electrocutaneous stimulation were measured in young male subjects by two different methods - a method of limits and a forced-choice method - the latter assumed to be less influenced by decision processes. Relations between the threshold measures and scores in the EPI extraversion (E) and neuroticism (N) scales were studied. High N-low E ("unstable introvert") subjects had the lowest thresholds. The result is in line with the predictions made on the basis of Eysenck's personality theory.

Adult↗