An active process in cochlear mechanics

A model for cochlear mechanics is proposed to take account of its two systems, one passive and one active. The classical passive system stimulates the inner hair cells directly at levels above about 40 dB SL. At intensities below about 60 dB an active process, the 'cochlear amplifier' (CA), somehow provides additional energy that enhances the vibration of a narrow segment of the basilar membrane near the apical foot of the familiar, traveling wave envelope. The outer hair cells are essential for CA. The active system acts like a high-Q acoustic resonator, and it accounts for the great sensitivity and sharp tuning expressed by the 'tips' of neural tuning curves. The tips are selectively vulnerable to anoxia, noise exposure and other trauma. The CA model explains the detection of small differences in time as well as in frequency, the dual character of the electrocochleogram, recruitment of loudness in cochlear hearing impairment, the long latency of normal neural responses near threshold, acoustic emissions (both stimulated and spontaneous) and the locus of TTS in the frequency range above the exposure tone. Both the classical high-intensity system and the active low-level CA system are highly nonlinear and they combine to compress the great dynamic range of hearing into a much narrower range of mechanical movement of the cilia of the inner hair cells. The mechanism of CA is unknown, and the problem remains of how its action can be triggered by submolecular movements near threshold.     

Linear combinations of stereoscopic depth effects in dichoptic perception of gratings

Three stereoscopic phenomena with gratings as patterns are compared: the aniseikonic depth effect with an equal number of bars in both monocular patterns; the aniseikonic depth effect with an unequal number of bars in both monocular patterns which have the same total width (or height); and the grating equivalent of Wilde's dot-row effect. The results of four experiments are reported. In the first and second experiment horizontal gratings with vertical disparities were used. It was found that the perceived rotation in vertical aniseikonia with an equal number of bars and in the vertical Wilde condition was equal. The perceived rotations were not dependent on spatial frequency in both conditions. In the condition in which only the bars of one of the monocular patterns were magnified relative to the other, but the total height of the patterns was the same, rotation was not perceived. In the third experiment with vertical gratings and horizontal disparity it was shown that the aniseikonic depth effect in the condition in which the bars and the total width of one of the monocular patterns are magnified relative to the other pattern is a linear combination of the Wilde effect and a weighted effect due to aniseikonia of the bars, but not of the total width. The fourth experiment tested the hypothesis of the linear combination in a new stereoscopic phenomenon.     

Basic and clinical evaluation of the measurement of bone resonant frequency

Summary A new computerized apparatus was constructed to measure the resonant frequency of human ulnain vivo with high sensitivity and reproducibility. Experimental studies using aluminum bar and dried human bone revealed the importance of the ulna being positioned parallel to the radius, approximately 90 degree flexion of the elbow joint, and minimal muscle activity in order to demonstrate maximum resonant frequency of ulna. Measurement of bone resonance in monkeysin vivo and after removal of the bonein vitro showed good agreement. Product of F (maximum resonant frequency in Hz) and L (ulnar length in cm), FL, indicating the speed of propagation of sound wave through the ulna, showed a significant positive correlation with bone mineral content/bone width (BM/BW) measured by Norland-Cameron apparatus and age-bound decline in both sexes. Patients with osteomalacia and primary hyperparathyroid bone disease tended to have higher FL values than expected from BM/BW. Two-dimensional display of FL and BM/BW thus appears to be useful in distinguishing osteoporosis from osteomalacia better than the use of BM/BW alone.     

EEG frequency analysis in the course of acute ischemic stroke

Summary In 18 patients with acute cerebrovascular disease (17 ischemic, 1 hemorrhagic stroke) neurological symptoms were scored repeatedly using a rating scale for disturbance of consciousness, motor dysfunctions, disturbance of higher cortical functions, abnormalities of cranial nerves, and impairment of sensations, and related to EEG-abnormalities quantified by frequency analysis. A correspondence between location of neurologic lesion and EEG focus was found in 87%, but correlation between neurologic score and the degree of EEG-abnormality was low. Changes of clinical defects were not significantly related to various quantified EEG parameters. These results suggest that computerized EEG analysis has to be used with caution for quantifying the clinical course of stroke patients.Dedicated to Professor K. J. Zülch on the occasion of his 70th birthday.     

Some effects of disopyramide and its N-dealkylated metabolite on isolated nerve and cardiac muscle

In animals and man the antidysrhythmic agent disopyramide in primarily metabolised by mono-N-dealkylation. The effects of disopyramide and its N-dealkylated metabolite (MIP) have been investigated using isolated cardiac and nervous tissue, and their effects have been compared with the effects of other antidysrhythmic agents. Disopyramide, d,l-propranolol and quinidine all decreased both maximum driving frequency and developed tension in electrically driven guinea pit atria. MIP and procaine amide also decreased maximum driving frequency, but had a positive intropic effect. MIP was only 4 times less active than disopyramide in decreasing maximum driving frequency. There was no evidence that either disopyramide or MIP possessed beta-adrenoceptor antagonist properties. In superfused rat sciatic nerves, it has been shown that neither disopyramide nor MIP possesses significant local anaesthetic properties. Procaine amide and lignocaine were highly active in this test. The possible contribution of MIP to the actions of disopyramide in vivo is discussed.     

Temporal lobe lesions in head injury

Summary In cases of closed head injury temporal lobe lesionse.g. contusion, laceration, pulping, or intracerebral haematoma frequently result in an expanding process. These are frequently associated with an overlying subdural haematoma. Eighty five cases of such lesions from a consecutive series of 1,000 cases of head injury have been analyzed. The lesions are caused by severe injury resulting in loss of concsiousness and skull fracture. Most of them are contre-coup lesions. Clinically they manifest themselves like any other acute or subacute intracranial hematoma. The majority of the patients have contralateral hemiparesis and pupillary abnormalities. Carotid angiography is valuable for diagnosis. These lesions are likely to be missed when exploratory burr holes are made or, are erroneously diagnosed as acute subdural haematoma or brain oedema. Smaller lesions, not showing progressive deterioration, may respond to conservative treatment. However, surgical decompression is essential in most cases. A fronto-temporal osteoplastic craniotomy or a large Scoville trephine hole is essential to deal with these lesions adequately.     

A statistical model of chemoreceptor afferent discharge—the detection of modulation by bin-averaging

Chemoreceptor afferent discharge has been simulated by hardware generation of random pulse trains with their mean frequency modulated by a sine wave. Interpulse intervals were pounched on tape and the pulse tracing subjected to bin-averaging routines and least-squares regression to recover the modulating waveform. The accuracy and variability of the recovered amplitude and phase estimates were assessed for modulation frequencies of 0·25, 0·5 and 1·0 Hz, and modulation amplitudes of 0·75 and 2 impulses/s, varying the number of bins per cycle from 6 to 14, and the number of cycles averaged from 10 to 70. The extent to which spurious waveforms might be obtained from nonmodulated random trains by identical bin-averaging and regression techniques was also estimated.     

Blood flow in human temporal muscle during tooth grinding and clenching as measured by 133Xenon clearance

abstract — Six healthy human subjects performed grinding and clenching of teeth, to assess if pain releasing and strenuous muscular exercise causes a decrease or total stop of the blood flow through the temporal muscles, as measured by ¹³³Xenon clearance. The mean blood flow/volume of muscle tissue was 25.4 ml×min⁻¹×l⁻¹ during rest, whereas the mean flow was 101.8 ml×min⁻¹×l⁻¹ during grinding, and 62.9 ml×min⁻¹×l⁻¹ during clenching. It is suggested that facial pains induced by strenuous exercise of the jaw muscles are not due to ischemia. On the contrary, the blood flow seems to increase about 300% during grinding and about 150% during clenching.     

Genotoxic effects of extremely low frequency (ELF) magnetic fields (MF) evaluated by the Tradescantia-micronucleus assay

Extremely low frequency (ELF) electric fields (EF) and magnetic fields (MF) are generated during the production, transmission, and use of electrical energy. Although epidemiology studies suggest that there is a cancer risk associated with exposure to ELF-MF, short-term genotoxicity assays with bacteria and mammalian cells have produced inconsistent results. In the present study, we investigated the possible genotoxicity of ELF-MF by using the Tradescantia-micronucleus (Trad-MN) assay, a sensitive, reproducible, well-standardized assay for genotoxicity testing. A 50 Hz ELF-MF was generated by a laboratory exposure system consisting of a pair of parallel coils in a Helmholtz configuration. Exposure of Tradescantia (clone # 4430) inflorescences to the ELF-MF, at a flux density (B) corresponding to 1 mT, for 1, 6, and 24 h resulted in a time-dependent increase in MN frequency. The results indicate that a 50 Hz MF of 1 mT field strength is genotoxic in the Trad-MN bioassay and suggest that this assay may be suitable as a biomonitor for detecting the genotoxicity of ELF-MF in the field.