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Biomedical subjects

E F Evans

Publications and source records attributed to E F Evans.

At least 19 recordsLinked to original sources
PubMed1992

Auditory processing of complex sounds: an overview.

The past 30 years has seen a remarkable development in our understanding of how the auditory system--particularly the peripheral system--processes complex sounds. Perhaps the most significant has been our understanding of the mechanisms underlying auditory frequency selectivity and their importance for normal and impaired auditory processing. Physiologically vulnerable cochlear filtering can account for many aspects of our normal and impaired psychophysical frequency selectivity with important consequences for the perception of complex sounds. For normal hearing, remarkable mechanisms in the organ of Corti, involving enhancement of mechanical tuning (in mammals probably by feedback of electro-mechanically generated energy from the hair cells), produce exquisite tuning, reflected in the tuning properties of cochlear nerve fibres. Recent comparisons of physiological (cochlear nerve) and psychophysical frequency selectivity in the same species indicate that the ear's overall frequency selectivity can be accounted for by this cochlear filtering, at least in bandwidth terms. Because this cochlear filtering is physiologically vulnerable, it deteriorates in deleterious conditions of the cochlea--hypoxia, disease, drugs, noise overexposure, mechanical disturbance--and is reflected in impaired psychophysical frequency selectivity. This is a fundamental feature of sensorineural hearing loss of cochlear origin, and is of diagnostic value. This cochlear filtering, particularly as reflected in the temporal patterns of cochlear fibres to complex sounds, is remarkably robust over a wide range of stimulus levels. Furthermore, cochlear filtering properties are a prime determinant of the 'place' and 'time' coding of frequency at the cochlear nerve level, both of which appear to be involved in pitch perception. The problem of how the place and time coding of complex sounds is effected over the ear's remarkably wide dynamic range is briefly addressed. In the auditory brainstem, particularly the dorsal cochlear nucleus, are inhibitory mechanisms responsible for enhancing the spectral and temporal contrasts in complex sounds. These mechanisms are now being dissected neuropharmacologically. At the cortical level, mechanisms are evident that are capable of abstracting biologically relevant features of complex sounds. Fundamental studies of how the auditory system encodes and processes complex sounds are vital to promising recent applications in the diagnosis and rehabilitation of the hearing impaired.

Animals↗
PubMed1992

Behavioural evidence for recovery of auditory function in guinea pigs following kanamycin administration.

Deterioration followed by recovery of behavioural absolute threshold and frequency selectivity has been observed in guinea pigs following kanamycin administration of 200 mg/kg body weight daily for 16 days. Deterioration in function consistently follows a high-to-low frequency pattern and recovery generally occurs at the lowest of the high (8-32 kHz) frequencies affected. The degree of recovery is related to the magnitude of the threshold elevation; where large (40-45 dB) elevations occur initially, the process appears to be partial since threshold recovers only to within 5-12 dB of pre-administration levels. In instances where smaller threshold elevations (5-20 dB) take place initially, recovery can sometimes be complete. However, when threshold elevations of over 50 dB occur, no recovery is apparent. Recovery is relatively slow, taking place over periods of up to 100 days post-kanamycin administration. Hair cell counts have established that the threshold elevation which remains in instances of partial recovery is not related to a reduction in hair cell numbers at the light microscope level.

Acoustic Stimulation↗
PubMed1990

Early detection of hearing damage in young listeners resulting from exposure to amplified music.

Sixty young subjects in the 15-23 age range, selected on the basis of a questionnaire on the degree of exposure to amplified music, underwent 'high resolution' (4 min per octave) sweep-frequency Békésy tracking audiometry, and measurement of auditory frequency resolution at 4 kHz using the psychophysical comb-filtered noise masking technique. The more exposed groups had 10-15% wider bandwidths than the least exposed, and this difference achieved significance when subjects having audiometric notches were excluded, or when a subset of exposed subjects was taken in whom subjective evidence was obtained of Temporary Threshold Shift or post-exposure tinnitus. While the most exposed groups did not show significantly greater averaged thresholds, there was in the older age group, a significantly increased prevalence of notches in the audiograms in the 3.5-6 kHz range. We conclude that exposure to amplified music can be harmful, the earliest sign being decrease in frequency resolution, and that early elevation of thresholds is better detected by high-resolution Békésy tracking (extending over the range 2-8 kHz) than by conventional fixed-frequency audiometry.

Adolescent↗
PubMed1990

Simultaneous dorsal dislocation of interphalangeal joints in a finger.

Simultaneous proximal and distal interphalangeal joint dislocations in a single finger are rare. Even though the joints above and below are routinely evaluated, one of the joint dislocations can be missed. When phalangeal dislocations are suspected, special attention should be given to obtaining sufficient roentgenographic views both before and after reduction. The joints should be thoroughly examined in an attempt to distinguish capsular contraction from soft-tissue interposition. Failure to recognize initial simultaneous dislocations may result in capsular contraction and require surgical intervention.

Adult↗
PubMed1979

Neuroleptanesthesia for the guinea pig. An ideal anesthetic procedure for long-term physiological studies of the cochlea.

The guinea pig is notoriously difficult to anesthetize with conventional agents. Cardiorespiratory depression by general depressant anesthetic agents can render the cochlea abnormal. I report a technique that uses the specific neuroleptic and analgesia properties of the agents droperidol and phenoperidine, respectively, in combination with small doses of pentobarbital sodium, which is required only to produce unconsciousness. These agents can be given intraperitoneally, intramuscularly, or intravenously. The regimen allows performance of substantial surgery (including intracranial) and long-term (minimum, six to ten hours) physiological studies, such as those on the cochlea, with excellent cardiorespiratory stability. The method has been in continuous use in this laboratory since 1974 for single-fiber recordings from the cochlear nerve of normal and kanamycin-treated guinea pigs. This method has proved to be substantially more effective than use of pentobarbital, thiopental sodium, urethan, chloralose, or ketamine alone.

Animals↗
PubMed1979

Some aspects of temporal coding by single cochlear fibres from regions of cochlear hair cell degeneration in the guinea pig.

Some temporal coding properties of cochlear nerve fibers are investigated in kanamycin-treated guinea pigs (GPs) with various degrees of outer hair cell (OHC) degeneration. In particular, the phase locking ability of fibres from pathological cochleas, and also their adaptation properties are compared with the properties of normal cochlear fibres. No systematic effects of OHC loss on these properties have so far been found. These preliminary results therefore suggest (in so far as these animals can be regarded as models of sensorineural hearing loss of cochlear origin in man) that little deterioration should be expected in functions purely dependent upon faithful temporal coding of the stimulus waveform.

Acoustic Stimulation↗
PubMed1978

Peripheral auditory processing in normal and abnormal ears: physiological considerations for attempts to compensate for auditory deficits by acoustic and electrical prostheses.

The processing of complex acoustic signals, such as speech, by the normal peripheral auditory system is described in terms of the properties of individual cochlear nerve fibres and the effects of lateral inhibition in the cochlear nucleus. The implications of the peripheral filtering of signals is indicated in psychophysical terms. In cochlear pathology, these filtering characteristics deteriorate, and the implications arising from the consequent deterioration in auditory frequency selectivity are outlined for the coding of loudness and for the analysis of speech. These considerations suggest theoretically ideal methods of compensation for recruitment by multichannel instantaneous compression, and for deterioration in format analysis by dichotic frequency partition. Finally, the implications for a minimal design for artificial electrical multi-electrode array stimulation of the cochlea in order to impart speech information to the profoundly deaf, are explored. Single wire stimulation, on the other hand, should be able to impart useful prosodic and minimal speech feature information to aid in lip reading and in the acquisition of speech.

Animals↗
PubMed1977

Evidence that catecholamines are not the afferent transmitter in the cochlea.

Beta-receptor blocking agents (practolol, propranolol) and alpha-receptor blocking agents (phenoxybenzamine, phentolamine), when applied intracochlearly do not eliminate the afferetn discharges or compound action potential of the cochlear nerve. Under the assumption that the drugs used reach the synaptic site, it is therefore concluded that these drugs do not interfere with afferent synaptic transmission. Phentolamine,, however, has a toxic effect upon the cochlea independent from the synaptic process. Local application of catecholamines does not increase spontaneous activity of single fibres of the cochlear nerve. These findings show that catecholamines are not likely to be the afferent transmitter.

Acoustic Stimulation↗
PubMed1975

Cochlear tuning properties: concurrent basilar membrane and single nerve fiber measurements.

Removal of perilymph from the cochlea has been reported to destroy the sharp tuning of cochlear neurons. That these changes are mechanical in origin is refuted by the concurrent recording of sharp neural tuning with broad basilar membrane responses from the same region of the partially drained cat cochlea. A second cochlear filter is therefore necessary.

Action Potentials↗
PubMed1975

Blood flow in muscle groups and drug absorption.

Resting human muscle blood flow (MBF) was determined simultaneously in the usual intramuscular injection sites to resolve whether variance in MBF could account for differences in drug absorption. Three pairs of muscles (gluteus maximus, vastus lateralis, and deltoid) were studied in each of 20 adult subjects. Use of dual, matched linear rate meters allowed two muscles to be studied simultaneously, with the order of injection random within an incomplete block design. MBF was calculated from the 133xenon washout rate using a single exponential that the computer found to best fit the data. Deltoid MBF (11.6 ml/100 gm/min plus or minus 0.5) was significantly (p smaller than 0.05) greater than gluteus MBF (9.6 plus or minus 0.5), with vastus or between right and left sides for each muscle. These data indicate that there are consistent differencies in resting MBF among specific muscle groups of sufficient magnitude (19%) to affect the rate of absorption and peak serum levels following intramuscular administration of drugs.

Absorption↗
PubMed1975

The sharpening of cochlear frequency selectivity in the normal and abnormal cochlea.

In the normal (anaesthetized) animal cochlea, the frequency threshold curves for single primary fibres are up to an order of magnitude sharper than the analogous function derived from various reported measurements of the basilar membrane amplitude of vibration. This enhanced neural frequency selectivity is found in the same species and under conditions similar to those in which the mechanical measurements are taken. The sharpening process (at least near threshold) appears to be linear and is not dependent upon lateral inhibitory mechanisms. The variability of the neural frequency selectivity and its vulnerability to metabolic, chemical and pathological influences suggests the hypothesis that the sharpening is due to some form of "second filter" subsequent to the relatively broadly tuned basilar membrane. All fibres recorded from in the cochlear nerve in the normal cochlea show this enhanced frequency selectivity; in contrast, in pathological cochleas, all fibres, or a substantial proportion, have high-threshold, broadly tuned characteristics, approximating to those of the basilar membrane. The frequency selectivity of normal cochlear fibres is adequate to account for the analogous psychophysical measures of hearing. It is proposed that loss of this normal frequency selectivity occurs in deafness of cochlear origin, accounting for widening of the critical band. A new hypothesis for recruitment is proposed on this basis.

Acoustic Stimulation↗