Quantitative analysis of the plain radiographic appearance of unicameral bone cysts

The reliability and frequency specificity of the 80-Hz amplitude-modulation-following response (80-Hz AMFR) during sleep detected by phase coherence as a measure of the hearing threshold was evaluated in 169 affected ears of 125 children with hearing impairment. The 80-Hz AMFR at a carrier frequency of 1000 Hz was monitored in all 169 ears and the auditory brainstem response (ABR) elicited by 1000-Hz tone pips was evaluated in 93 ears. Both responses were examined during sleep, and the thresholds were compared with the behavioral hearing threshold, which was determined by standard pure-tone audiometry or play audiometry. In 24 ears of 22 children with various patterns of audiogram, the 80-Hz AMFR was examined at different carrier frequencies, and the threshold pattern was compared with the pure-tone audiogram to investigate the frequency specificity of 80-Hz AMFR. The mean and standard deviation of the difference between the 80-Hz AMFR at a carrier frequency of 1000 Hz and pure-tone thresholds of 1000 Hz was 3.8 and 12.9 dB, and that between the ABR and pure-tone thresholds was 6.8 and 14.1 dB, respectively. The threshold patterns of 80-Hz AMFR clearly followed the corresponding audiogram patterns in all types of hearing impairment. The measurement of 80-Hz AMFR thus appears to be accurate in hearing assessment and to have good frequency specificity in children during sleep.     

Current excitation threshold in sensory neurons of leech central nervous system

1. The sensory neurons in the leech central nervous system differ in their accommodation to linearly rising currents. Advantage was taken of these differences to study the ionic mechanism of accommodation in single pairs of N (noxious), P (pressure), and T (touch) cells. 2. Nonlinearities in membrane-potential changes and current-voltage relationships with square-wave and ramp currents are more pronounced in P and T cells than in N cells. The accommodation coefficients increase in conditions that reflect this delayed rectification. When rectification is absent, the accommodation coefficients depart from unity only slightly or not at all. 3. Accommodation coefficients remain unchanged when half of the chloride in the bathing medium is replaced by sulfate. Accommodation coefficients become greater when the extracellular potassium concentration is reduced from 4 to 0 mM, and decrease when the concentration is raised to 8 mM. The membrane potential changes by only a few millivolts. 4. As extracellular potassium concentration is increased, the action potential is lengthened and the maximal rate of fall of the action potential is reduced. With concentrations greater than 4 mM these relationships are linear, but depart from linearity at lower concentrations. The amplitude of the undershoot decreases linearly as the extracellular potassium concentration increases from 4 to 16 mM, and increases non-linearly at concentrations below 4 mM. 5. The rapid accommodation of leech neurons is based primarily on an increased potassium conductance. The possibility is considered that concentration changes like those produced experimentally may occur naturally, affecting integrative processes in the central nervous system.