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Biomedical subjects

G M Gerken

Publications and source records attributed to G M Gerken.

34 records · Page 2Linked to original sources
PubMed1979

Temporal summation of pulsate brain stimulation in normal and deafened cats.

Behaviorally measured, electrical-stimulation thresholds were obtained from 11 electrodes permanently positioned in the auditory system and other brain loci. Number of pulses and interpulse intervals were varied to determine how detection thresholds were affected by stimulation parameters. Detection thresholds generally decreased with increased number of pulses and with shorter interpulse intervals. A method is presented to describe the parametric threshold data for each electrode in terms of three constants: a single-pulse threshold which characterizes the sensitivity of the placement; a time constant of temporal summation; and a compression factor which describes the range of threshold variation. For three placements in the vicinity of cochlear nucleus, bilateral cochlear destruction permanently altered parametric thresholds. In particular, single-pulse threshold was lowered by 9.2 dB; time constant of temporal summation was reduced by a factor of 100; and the compression factor was increased. Classic strength-duration time constants were determined using behavioral methods and were shown to be equal in magnitude to the greatly reduced time constants for temporal summation in the deafened animals. This implies that capacity for temporal integration may be substantially reduced or lost in at least the lower level of the auditory system following deafness.

Animals↗
PubMed1978

Functional characteristics of cochlear nucleus in behaving cat examined by acoustic masking of electrical stimuli.

1. Cats were trained, using an operant procedure, to detect and respond to electrical stimulation delivered in the vicinity of the cochlear nucleus. The electrical stimuli were presented both in silence and in synchrony with repeated noise bursts to determine whether detection thresholds for the electrical stimuli were elevated by the acoustic masking noise. 2. For stimulation sites centered within auditory structures (cochlear nucleus or acoustic nerve root), the acoustic maskers caused a consistent elevation of the electrical detection thresholds. For stimulation sites that were in or bordered on nonacoustic neural structures (e.g., vestibular), the acoustic maskers caused little or no elevation of electrical detection thresholds. 3. The magnitude of the acoustic masking effect was monotonically related to the intensity of the acoustic masker across the range of intensities tested. 4. The magnitude of the masking effect was strongly dependent on the relative timing of the stimulus pulse and the masker noise burst. Maximum masking occurred when the pulse just followed the onset of the neural activity in cochlear nucleus evoked by the masker burst. Less masking occurred when the electrical pulse occurred at the middle or end of the masker burst, and still less when the pulse occurred just prior to the onset (backward masking) or just after the offset (forward masking) of the masker burst. 5. The magnitude of the masking effect also depended on the frequency of the acoustic masker. For tone bursts, masking was maximal for each electrode at a particular frequency and declined monotonically for masker frequencies above or below the optimal frequency. 6. It is concluded that the masking of an electrical stimulus by an acoustic stimulus depends on a direct interaction between the neural responses evoked by the two stimuli, and that similar central, neural interactions may contribute to acoustic masking of acoustic stimuli. It is also concluded that the technique of masking an electrical stimulus by an acoustical stimulus is a precise and useful tool for the study of sensory-neural organization in intact behaving animals.

Animals↗
PubMed1977

Masking of electrical by acoustic stimuli: behavioral evidence for tonotopic organization.

When pure-tone acoustic masking stimuli of various frequencies were presented simultaneously with electrical stimuli applied to cochlear nucleus, only those maskers within a limited frequency range interfered with the detection of the electrical stimuli. The form of the masking functions obtained suggest that the electrical stimulus directly activated only a small population of neurons which were functioning in a tonotopic fashion.

Acoustic Stimulation↗
PubMed1977

A hearing aid malfunction detection unit.

A system is described, the Hearing Aid Malfunction Detection Unit (HAMDU), that electrically checks for proper operation of several aspects of hearing aid function. HAMDU is a miniature, add-on device which performs a check of hearing aid operation about every half hour, and which indicates malfunction by means of a highly visible, electrically tripped indicator. Functions checked include battery voltage, gain, distortion and noise, and continuity of the receiver cord. In addition, the indicator will be tripped if the hearing aid is turned off. HAMDU is small, low in cost, can be adapted to most body aids, and has no effect on hearing aid performance. The primary features of the system are that the hearing aid is checked periodically throughout its use, and the aid does not have to be removed from the wearer. The unit is designed specifically for body type hearing aids worn by children.

Electromagnetic Phenomena↗
PubMed1975

Human frequency-following responses to monaural and binaural stimuli.

Frequency-following responses, with latencies circa 6 msec, were recorded from five normal-hearing human subjects to brief 500 c/sec tone bursts presented monaurally. The frequency-following responses appear as peaks occurring at 2 msec intervals superimposed on a slow wave (pedestal-like) component. Comparisons were made between the frequency-following responses evoked by binaural and monaural stimuli. The results show that the binaural responses may be interpreted as the sum of two monaural responses. It is concluded, therefore, that there are two independent populations of neurons, each capable of generating a frequency-following response is not a microphonic-like response but rather that the individual waves in the frequency-following response are evoked by the collective activity of phase-locked single units. Finally, on the basis of the distinctness of the individual waves in the frequency-following response, it is concluded that the neural generators of the response must be spatially compact.

Acoustic Stimulation↗
PubMedDate not supplied

Evoked potentials recorded from brain-stem nuclei in awake cat: interaction of tone bursts and continuous tone.

Previous work indicated that components of the auditory thalamocortical potential evoked by a brief binaural tone burst could be enhanced by certain stimulus combinations, e.g., a brief tone burst in the presence of a continuous tone. The principal questions of the present study were whether enhanced components could be obtained caudal to thalamocortex and whether monaural stimuli would be effective in producing enhancement. Eight cats received permanent electrodes in cochlear nucleus and the nucleus of the inferior colliculus. Custom earmolds were made for each ear of each animal. The median attenuation produced by the earmolds was 35 dB and the use of a single earmold approximated monaural stimulation. Auditory evoked potentials were recorded from the electrodes while the animals were unanesthetized but comfortably restrained. Brief 6.25 kHz tone bursts were presented against a background of silence or of a 4.96 kHz continuous tone. In the presence of the continuous tone, enhanced components were obtained from a majority of the electrodes in inferior colliculus but from none of the electrodes in cochlear nucleus. The late negative component in the colliculus potential was increased in amplitude while other components were reduced in amplitude by the continuous tone. The latencies of all components from all electrodes were increased by the presence of the continuous tone. It was concluded that enhancement effects could be obtained at the level of inferior colliculus, and that binaural stimulation does not appear to be necessary to produce enhanced components.

Acoustic Stimulation↗
PubMedDate not supplied

Summating-potential/action-potential ratio in normal ears: effects of dehydration.

INTRODUCTION: Studies using electrocochleography (ECoG) in patients with Meniere's disease and in patients with perilymph fistula have demonstrated abnormally large summating-potential (SP) components compared with the amplitude of the action-potential (AP). The possible influence of normal physiological variation, methodological differences, and test-retest variations are often difficult to interpret. The purpose of this study is to specify what constitutes a clinically important change in the SP/AP ratio in normal hearing subjects under the condition of dehydration induced by urea. MATERIALS AND METHODS: Baseline ECoG was performed on 20 normal hearing volunteer subjects after an 8 hour fast. Urea, 20 g, was administered orally, following which recordings were made at 60 and 90 minutes. The majority of subjects were found to have maximal SP/AP changes at 60 minutes post dehydration; therefore, only these results were included in the final analysis. Subsets of data were statistically evaluated. RESULTS: In all ears but one, the preingestion SP/AP ratio was less than or equal to 0.37. Male and female data were shown to comprise separate populations both before and following dehydration. The 95% upper limit for baseline SP/AP ratio was 0.39 for males and was 0.25 for females. The gender-related difference remained after dehydration. The mean male SP/AP ratio showed a statistically significant but slight decrease whereas the female SP/AP ratio was unaltered. CONCLUSION: These data demonstrate a statistically significant gender-related difference in SP/AP ratio in normals. The upper limit of normal is 0.39 for males and 0.25 for females. A basis for the gender difference is puzzling and requires further investigation. Dehydration produces a statistically significant reduction in SP/AP ratio in men. This change was not observed in women.

Action Potentials↗
PubMedDate not supplied

Effects of middle ear ventilation on cholesteatoma development in experimental animals.

This study was designed to evaluate the effect of middle ear ventilation on cholesteatoma formation following propylene glycol application in experimental animals. Fifteen chinchillas had stainless steel ventilation tubes chronically implanted in their bullae and 60% propylene glycol was subsequently instilled into the middle ear cavities. The animals were kept alive for 4 weeks, during which time the middle ear pressure was monitored tympanometrically and the tubes were frequently inspected to verify patency. Of the 30 ears in the study, 20 (66.6%) developed middle ear cholesteatoma--a rate of occurrence comparable to that found in earlier studies in which middle ear ventilation was not provided. These results indicate that negative middle ear pressure is not a necessary factor for cholesteatoma development following application of chemical irritants in experimental animals.

Animals↗