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PubMed1987

Optimal rates of movement for kinetic perimetry.

Duration, reliability, and sensitivity of kinetic thresholds were evaluated for the I/4e, I/2e, and I/1e Goldmann-equivalent targets as a function of stimulus velocity (1 degrees to 8 degrees/s) using the SQUID automated perimeter. For all targets, the average duration of kinetic meridional scans decreased significantly as stimulus velocity increased from 1 degrees to 4 degrees/s. Minimal reductions in kinetic scan times were present for stimulus velocities above 4 degrees/s. All targets appeared to have reductions in sensitivity at velocities above 4 degrees/s (target detection occurring at more central visual field locations) that were presumably related to the observers' reaction times. There were no consistent differences in the variability of kinetic thresholds for different stimulus velocities. When all factors were considered, a stimulus velocity of 4 degrees/s seemed to be optimal for kinetic scans of all targets in the central and peripheral visual field.

Adult↗
PubMed1992

Peripheral magnesium sulfate enters the brain and increases the threshold for hippocampal seizures in rats.

OBJECTIVES: Our objectives were to determine whether magnesium sulfate crosses the blood-brain barrier and whether it has central anticonvulsant action. STUDY DESIGN: In experiment 1 34 female Long-Evans rats were divided into six groups: control (n = 7); single magnesium sulfate injection and evaluation after 20 minutes in 3 conditions: normal rats (n = 7), sham-operated animals (n = 5), and after electrical stimulation by hippocampal electrode (n = 5); single injection and evaluation after 2 hours (n = 5); and prolonged (2 hours) serum magnesium elevation (n = 5). Serum, cerebrospinal fluid, and specific brain areas were analyzed for magnesium concentrations. In experiment 2 threshold for electrical seizure was measured in eight rats before and after intraperitoneal injections of magnesium sulfate versus saline solution. RESULTS: In experiment 1 there was a significant correlation between blood and cerebrospinal fluid magnesium concentrations (r = 0.80, p < 0.0001). Magnesium concentrations were increased in the cortex and hippocampus, with the largest changes occurring after two hours of sustained serum magnesium concentrations (p < 0.01). Induction of hippocampal seizure activity resulted in further elevations in cerebrospinal fluid magnesium concentrations but did not change brain concentrations. In experiment 2 magnesium sulfate increased the electrical threshold required to induce seizures by 34% (p = 0.01). CONCLUSIONS: Magnesium sulfate enters the cerebrospinal fluid and brain and has a central anticonvulsant effect.

Animals↗
PubMed1987

Leukotriene and prostaglandin sensitization of cutaneous high-threshold C- and A-delta mechanonociceptors in the hairy skin of rat hindlimbs.

Single C- and A-delta fibers were isolated from dissected filaments of the saphenous nerve in pentobarbital anesthetized rats and the corresponding cutaneous receptive fields mapped with calibrated von Frey hairs. Nociceptors were characterized by their responses to noxious mechanical, thermal and chemical stimuli, including intradermal injections of leukotriene B4, prostaglandin E2, bradykinin and capsaicin. Leukotriene B4 decreased the mean mechanical threshold by a maximum of 80% within 10 min and for more than 3 h after intradermal injection of 75 ng of leukotriene B4. The degrees of sensitization of a fiber by leukotriene B4 and prostaglandin E2 were highly correlated. A potentiation effect also was observed, in that injection of prostaglandin E2 or leukotriene B4 1 h after the other eicosanoid further lowered the mechanical threshold of a sensitized fiber, whereas fibers that were not sensitized by leukotriene B4 were unaffected by prostaglandin E2. The sensitizing action of leukotriene B4 and prostaglandin E2 was directed to multiple classes of cutaneous nociceptors including 73% of C-polymodal, 60% of C-mechano-heat, 42% of C-mechano-cold nociceptors and 70% of A-delta high-threshold mechanonociceptors. The pain-evoking substances bradykinin and capsaicin activated 81% and 88%, respectively, of the sensitized C-polymodal nociceptors, 17% and 84% of the sensitized-C-mechano-heat nociceptors, 12% and 37% of the sensitized C-mechano-cold nociceptors, and 17% and none of the sensitized A-delta high-threshold mechanociceptors. The responses of C-fibers to bradykinin and capsaicin were highly correlated.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1988

Intensity coding and the dynamic range problem.

The psychophysical data on intensity discrimination indicate that certain schemes are unlikely as general intensity codes at the level of the auditory nerve and indirectly suggest that the most likely code is one based upon the firing rates of frequency-localized groups of fibers. A detection-theory analysis of a rate-based intensity code indicates that information from very few fibers can, if the information is appropriately combined, account for psychophysical discrimination even at high intensities. This suggests that fibers with similar CFs can code intensity over a wide range and that complex spectra can be represented at the level of the auditory nerve by a rate-CF code over the dynamic range of hearing. The analysis also indicates, however, a substantial discrepancy between the psychophysical data on the dependence of discrimination thresholds on level and the predicted discrimination behavior of a representative population of auditory nerve fibers. Thus, if intensity coding is based on localized firing rate, this fundamental psychophysical behavior does not result solely from peripheral processes.

Differential Threshold↗
PubMed2002

Sex- and age-related elevation of cochlear nerve envelope response (CNER) and auditory brainstem response (ABR) thresholds in C57BL/6 mice.

The C57BL/6 mouse has long been considered, in scores of published studies, as a model of early adult-onset, progressive sensorineural hearing loss (presbycusis). The auditory brainstem response (ABR) has most often been used in these studies as a measure of functional loss. Whereas the ABR measures the response to a rapid acoustic onset, the cochlear nerve envelope response (CNER) measures the ability of cochlear nerve axons to respond to the low frequency modulations of the entire acoustic waveform, acoustic changes that are utilized in vocalizations and music. The present study compared the ability of these two measures to assess presbycusis in male and female C57BL/6 mice, at ages ranging from 50 to 400 days. Thresholds to the CNER were almost invariably more sensitive than the ABR, in response to stimulus frequencies ranging from 8 to 56 kHz. By 100 days of age, mice showed elevation of thresholds in response to high frequency stimuli, and this loss was greater in females than in males. These trends persisted for both measures over the next 300 days, involving successively lower frequencies.

Aging↗
PubMed1995

Laser Doppler flowmetry in the assessment of tooth vitality after Le Fort I osteotomy.

The aim of the present study was to evaluate pulp vitality in 15 patients, 11 to 29 months after a Le Fort I osteotomy. Assessment of pulpal blood flow was obtained by means of laser Doppler flowmetry, and it was measured bilaterally from the first maxillary premolar to the central incisor. The results were compared with those obtained by electric pulp testing in the same teeth. In addition, periodontal ligament perception was evaluated by applying axial loads to the central incisors. Radiographs were also studied. Fourteen subjects served as a control group. There was no significant difference between the level of pulpal blood flow in the teeth of the operated group compared with the control group. Twenty-one per cent of the teeth in the group operated on were insensitive to electric pulp testing, and in the remaining 79% the mean threshold was significantly higher than in the corresponding teeth in the control subjects. Similarly, the axial load threshold for the incisors for the control subjects was below 5 g, but in the group operated on 66% had a threshold above 5 g. These experiments clearly demonstrate that teeth without normal innervation can have an intact blood supply and be vital.

Adult↗
PubMed1981

The effect of low frequency and direct current stimulation on the kindling phenomenon in rats.

An experiment was conducted to evaluate the effect of 1-Hz or direct current brain stimulation on kindling behavior induced by 60-Hz sine wave stimulation. The effective threshold intensity to elicit a convulsion was determined on four separate occasions with 5 days of daily trials between determinations. On each day one group of experimental rats was stimulated with 1-Hz sine wave current before and after stimulation with 60-Hz sine wave current (1-60-1 group). Another group received direct current stimulation and 60-Hz current (D-60-D group). A third group received only 60-Hz stimulation. Suppression of kindling behaviour usually induced by the 60-Hz stimulation occurred with 1-Hz stimulation; the mean threshold value increased on each successive determination. Suppression was most pronounced for the direct current group; it appeared after a single trial and persisted for 32 days after the last threshold determination. In contrast, most of the rats in the 1-60-1 group had recovered from the suppression after the 32 day period of nonstimulation. A second phase of the experiment indicated that the increase in threshold values for the D-60-D group occurred after a single DC stimulation. These results are consistent with the hypothesis generated by previous research that suppression following 1-Hz stimulation is not due to tissue damage.

Animals↗
PubMed2000

A simplified index of the plasma sodium threshold for arginine vasopressin secretion-morning fasting, euhydrated sodium levels.

OBJECTIVE: Human pregnancy results in a reduction in plasma osmolality and thus a reduction in the osmotic threshold for arginine vasopressin secretion. Although the functional characteristics of the osmoregulatory system controlling arginine vasopressin secretion have been carefully defined, determination of the osmotic threshold requires a complex, labor-intensive protocol of an intravenous hypertonic saline infusion. To aid in studies of osmotic threshold resetting in pregnancy, we sought to develop a simplified method for determination of this value. STUDY DESIGN: Ten healthy nonpregnant women between the ages of 18 and 40 years were studied over 2 days. All patients were hospitalized, and morning euhydration was ensured by oral water hydration (5-10 mL/kg) the evening before the study. On the first study day, patients were fed a standard no-salt-added diet; plasma osmolality and sodium values were checked just before and 1 and 2 hours after meals. On the second study day, after fasting blood samples were obtained, patients received an intravenous infusion (0.06 mL. kg(-1). min(-1) for 120 minutes) of hypertonic (5%) saline to gradually increase the plasma sodium level. Blood samples were obtained every 15 minutes for measurement of plasma electrolytes and arginine vasopressin. Plasma arginine vasopressin concentrations were regressed against plasma osmolality and sodium concentration to calculate the osmotic threshold for arginine vasopressin secretion. RESULTS: Hypertonic saline injection significantly increased plasma sodium (from 139 +/- 1 to 149 +/- 1 mEq/L) and osmolality (from 284 +/- 2 to 304 +/- 2 mOsm/kg H(2)O). Plasma arginine vasopressin significantly increased (from 5 +/- 1 to 30 +/- 10 pg/mL). The mean sodium and osmolality thresholds for arginine vasopressin secretion were calculated as 137 +/- 2 mEq/L and 285 +/- 15 mOsm/kg H(2)O. The mean morning fasting sodium level was nearly identical to the calculated sodium threshold, whereas the morning fasting osmolality value was significantly different. CONCLUSIONS: The morning fasting, euhydrated sodium level can be used as a simplified index for the plasma osmotic threshold for arginine vasopressin secretion. This index may provide a useful predictive measure for pregnant women in whom the plasma volume does not expand.

Adolescent↗
PubMed2000

Should sensory function after median nerve injury and repair be quantified using two-point discrimination as the critical measure?

Two-point discrimination (2PD) is widely used for evaluating outcome from peripheral nerve injury and repair. It is the only quantifiable measure used in the British Medical Research Council (MRC) classification that was developed by Highet in 1954. This paper reports the results of a study of 41 patients with complete median nerve lacerations to the wrist or forearm. Two-point discrimination thresholds were assessed together with locognosia (locognosia is the ability to localise a sensory stimulus on the body's surface), tactile gnosis, and touch threshold. Using the MRC classification 29 (71%) patients had a result of S2 or below, 11 (27%) were S3, and only one scored S3+. Patients scored much better on the other tests and showed progressive recovery. It remains too difficult for patients to obtain a measurable threshold value on 2PD and the test therefore lacks responsiveness. The rating of outcome from peripheral nerve repair should not be based solely on 2PD testing and must include other tests of tactile sensibility.

Adolescent↗
PubMed1995

The effect of nasal or oral gastric tubes on transesophageal atrial pacing thresholds.

This study was performed to evaluate whether the presence of either nasal or oral gastric tubes (GTs) would affect the ability to accomplish transesophageal atrial pacing (TAP). After endotracheal intubation, pacing esophageal stethoscopes were placed and the TAP thresholds were measured in 20 patients. With the PES fixed in position, GTs were inserted and pacing thresholds were remeasured. TAP was accomplished in all patients pre- and postinsertion. The mean +/- SD, range, and median TAP thresholds (mA) were 13.7 +/- 5.8, 7-25, and 12 preinsertion and 13.9 +/- 5.2, 5.5-25, and 13 postinsertion. The preinsertion-postinsertion differences ranged from -6 to 5 mA with a mean of the difference of -0.2 mA (95% confidence interval, -1.61-1.21 mA). No significant difference between the pre- and postinsertion groups was detected by the paired t-test, P = 0.77. In summary, the presence of GTs does not significantly affect TAP thresholds. Attempts to achieve TAP are expected to be successful in patients with either a nasal or oral GT in place.

Adult↗
PubMed1984

Threshold of airway response to inhaled methacholine in healthy men and women.

Threshold of airway response to inhaled methacholine was determined using maximum expiratory partial flow-volume curves in 21 men and 36 women with similar age distribution, all of them healthy nonsmokers. Mean threshold was on average 1.3 doubling dose lower in women than men. There were no sex differences in the increase of maximum expiratory flows after a full inspiration when the airways were constricted by methacholine.

Adolescent↗
PubMed1984

Antagonism by taurine of pressure-induced tremor in the guinea pig.

The tremorogenic effect of high pressure was antagonized in guinea pigs by intravenous treatment with taurine in doses of 250 and 500 mg/kg. Also pretreatment with 250 mg/kg taurine suppressed tremor development as evidenced by increased threshold and decreased amplitude. It is hypothesized that antagonism of pressure-induced tremor by taurine may be related to changes in membrane calcium transport.

Animals↗
PubMed1985

Postadaptation orientation discrimination.

An orientational difference of only 0.3-0.5 deg can be discriminated between two gratings or two lines, although psychophysical channels and cortical cells both have comparatively broad orientation bandwidths of 10-25 deg. One proposed explanation for the fineness of orientation discrimination is that, while detection is determined by the most excited orientation-tuned neural elements, superthreshold orientation discrimination is determined by difference signals between these elements [Westheimer et al., J. Opt. Soc. Am. 66, 332 (1976)]. This implies that, if stimulus orientation is changed slightly, the most important elements for discriminating this change will be those whose relative activity changes most, even though the excitation of these elements may be comparatively weak. In accord with this prediction, we found that adapting to a high-contrast grating degraded discrimination for test gratings inclined at about 10-20 deg to the adapting grating while having little effect on the detection of these inclined gratings. For test gratings parallel to the adapting grating, discrimination was improved, but detection was degraded. Either an opponent-process or a line-element model can account for these effects of adaptation. An opponent model can also explain our findings that subjects do not confound orientation change with contrast change and that suprathreshold orientation discrimination is almost independent of contrast, varying by only +/- 10% from about 3 to about 25 times contrast threshold. A discrimination model must incorporate reliable storage of spatial frequency, because discrimination was not affected by increasing the interval between grating presentations from 1 to 10 sec.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Ocular↗
PubMed1977

Threshold and reaction time to noxious stimulation: their relations with scores on Manifest Anxiety Scale and Maudsley Personality Inventory.

With 20 male Japanese undergraduates relationships between electric shock threshold and reaction time to electric shock with 10 v and personality factors were investigated. Significnat product-moment correlations of --.79 and --.69 between response to noxious stimulation and Manifest Anxiety and Maudsley Neuroticism scores were found.

Differential Threshold↗
PubMed2005

Orientation discrimination across the visual field: size estimates near contrast threshold.

Performance in detection and discrimination tasks can often be made equal across the visual field through appropriate stimulus scaling. The parameter E2 is used to characterize the rate at which stimulus dimensions (e.g., size or contrast) must increase in order to achieve foveal levels of performance. We calculated both size and contrast E2 values for orientation discrimination using a spatial scaling procedure that involves measuring combination size and contrast thresholds for stimuli with constant size-to-contrast ratios. E2 values for size scaling were 5.77 degrees and 5.92 degrees. These values are three to four times larger than those recovered previously using similar stimuli at contrasts well above detection threshold (Sally & Gurnsey, 2003). E2 values for contrast scaling were 324.2 degrees and 44.3 degrees, indicating that for large stimuli little contrast scaling (.3% to 2.3% increase) was required in order to equate performance in the fovea and the largest eccentricity (10 degrees). A similar pattern of results was found using a spatial scaling method that involves measuring contrast thresholds for target identification as a function of size across eccentricities. We conclude that the size scaling for orientation discrimination at near-threshold stimulus contrasts is much larger than that required at suprathreshold contrasts. This may arise, at least in part, from contrast-dependent changes in mechanisms that subserve task performance.

Differential Threshold↗
PubMedDate not supplied

Personality and the effects of acute alcohol intake. A contingent negative variation study in healthy subjects.

This study investigates the relationship between blood alcohol concentrations (BACs) and contingent negative variation (CNV). Fourteen healthy subjects were divided on the basis of their personality profiles--the Minnesota Multiphasic Personality Inventory (Hs+Hy+D/3)--into a high score (HS) and low score (LS) subgroup. The CNV was recorded using a choice-reaction time (RT) task. CNV recording was performed in two conditions: inter-stimulus intervals (ISIs) of 1500 ms and 2500 ms at three different BACs (0.3, 0.5 and 0.8 g/L) after acute alcohol administration. At the high BAC (0.8 g/L), both subgroups showed a reduced CNV amplitude area and a longer RT (p<.05) in both ISI conditions. No effects either on the CNV or on the RT were observed at the low BAC (0.3 g/L). At the intermediate BAC (0.5 g/L), the HS subgroup displayed an increased CNV amplitude (p<.05), not accompanied by a significantly longer RT (short ISI condition), and a reduced late CNV (p<.05) with a longer RT (p<.05) (long ISI condition). In the LS group, only a longer RT was observed in the long ISI condition. CNV modifications point to an individual, apparently personality-related, threshold of sensitivity to different alcohol levels.

Adult↗
PubMed1987

The effect of syringeal deafferentation on the stimulated vocalization in the domestic chick (Gallus gallus).

The rôle of syringeal feedback on the electrically elicited vocalization in chickens (Gallus gallus) was studied. The vocalization patterns elicited by stimulating the low-threshold "calling areas" in the midbrain, was examined before and after syringeal deafferentation obtained by cutting the X-XII anastomosis on either the left and right side. The results show that section of the X-XII anastomosis on the left side produces consistently a clear-cut lowering of the threshold for vocalization and an increase of the amplitude of the individual calls with no change in the repetition rate of the call sequences. All these effects are enhanced when the contralateral anastomosis is also severed. These results show that the bilateral syringeal deafferentation does not change the overall song pattern performance, that remains stereotyped both in duration and complexity, consistent with the hypothesis that, in adult birds, stable song patterns are not dependent on peripheral sources of feedback, but are ruled by a learned central control program. However the modification of vocalization threshold and amplitude suggests the hypothesis that the syringeal feedback plays an inhibitory rôle on vocalization by modulating the excitability of the central structures involved in the vocalization activity.

Afferent Pathways↗
PubMed1987

Determination of the threshold of simultaneity and temporal order using the "step-ladder" method.

The article considers the sensitivity of the mechanisms for perceiving simultaneity and temporal order. A method similar to the psychophysical "staircase" method is used for determining the thresholds of the perception of simultaneity and temporal order. The simultaneity and temporal order thresholds are measured for two levels of visual adaptation of the subjects. Two clearly distinguishable thresholds are established: simultaneity threshold and temporal order threshold. The threshold values for simultaneity and temporal order are preserved, irrespective of the adaptation level, which suggests that the general illumination does not affect the mechanisms for perceiving simultaneity and temporal order.

Adaptation, Ocular↗