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Results for “Differential Threshold”

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At least 559 records · Page 31Linked to original sources
PubMed1979

Comparison of contrast thresholds of large bars and checks measured by VECPs and psychophysically as a function of defocusing.

The effects of defocusing the image on the contrast threshold were studied both for checkerboard and bar patterns at various low spatial frequencies, and comparison was made between psychophysical results and visually evoked cortical potentials (VECPs) results. VECP threshold was defined as the contrast necessary for obtaining a criterion amplitude of 5 muV. When increasing the degree of defocusing, the lowest contrast threshold shifted towards larger checks or bars, the contrast threshold increased more abruptly for smaller sizes, and the VECP contrast thresholds increased more than the psychophysical ones, especially for smaller sizes. No significant difference was found in the contrast thresholds between the results with bar patterns and checkerboard patterns, except that for bars, the VECP threshold as defined was approx. 0.2 log units higher than those for checkerboard.

Differential Threshold↗
PubMed2006

Predicting spike timing of neocortical pyramidal neurons by simple threshold models.

Neurons generate spikes reliably with millisecond precision if driven by a fluctuating current--is it then possible to predict the spike timing knowing the input? We determined parameters of an adapting threshold model using data recorded in vitro from 24 layer 5 pyramidal neurons from rat somatosensory cortex, stimulated intracellularly by a fluctuating current simulating synaptic bombardment in vivo. The model generates output spikes whenever the membrane voltage (a filtered version of the input current) reaches a dynamic threshold. We find that for input currents with large fluctuation amplitude, up to 75% of the spike times can be predicted with a precision of +/-2 ms. Some of the intrinsic neuronal unreliability can be accounted for by a noisy threshold mechanism. Our results suggest that, under random current injection into the soma, (i) neuronal behavior in the subthreshold regime can be well approximated by a simple linear filter; and (ii) most of the nonlinearities are captured by a simple threshold process.

Action Potentials↗
PubMed1984

Hyperalgesic activity of parathyroid hormone and its fragments in male rats.

Results presented in this paper indicate that intracerebroventricular injection of parathyroid hormone reduces pain threshold in male rats. This effect is induced by whole molecule (84 amino acids) or by fragments 1-34 and 44-68 of PTH. The fragment 65-84 of PTH does not induce any change in pain threshold.

Animals↗
PubMed1984

Effects of vincristine sulfate on touch dome function in the rat.

The responses of touch domes in hairy skin of the rat to mechanical stimulation were examined after single doses of vincristine sulfate. Within 24 h of drug administration, the mean thresholds of domes to brief mechanical pulses had increased threefold, from 5.2 +/- 2.0 to 14.2 +/- 8.8 microns. This elevated threshold was maintained for 2 weeks but by the 3rd week the domes had recovered normal excitability. Measurements of response latency suggested that the increase in receptor thresholds occurred without impulse propagation being impaired in the axons.

Animals↗
PubMed1983

Palatal receptor contribution to and effects of palatal alteration on taste acuity thresholds.

To determine the contribution of the soft palate to the overall taste mechanism and the effects of palatal compromise (surgery, cleft palate, and trauma), four taste solutions representing sweet, salty, sour, and bitter were applied to the apex and base of the tongue and to the soft palate of 12 subjects in each of the control and palatally compromised groups. Each group was tested on two different occasions with the sessions 2 weeks apart and one in the morning and the other in the afternoon. Results indicate that the soft palate contributes to bitter and salty sensations to a greater degree than the other two sensations. Of these two, bitter is the more acutely experienced. Patients with compromised palates revealed higher taste acuity thresholds than the normal control group, particularly with bitter solutions. Taste acuity thresholds increased with age.

Adolescent↗