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Biomedical subjects

G M Gerken

Publications and source records attributed to G M Gerken.

At least 19 recordsLinked to original sources
PubMed1991

Temporal integration of electrical stimulation of auditory nuclei in normal-hearing and hearing-impaired cat.

Temporal integration functions were measured, before and after a sound-induced hearing loss, in 5 cats using trains of electrical pulses applied to auditory nuclei in the brainstem. The 8 stimuli ranged from 1 pulse (0.25 ms duration) to 16 pulses (0.25 ms pulses spaced over 240 ms). The stimuli were applied to inferior colliculus or cochlear nucleus via permanently implanted electrodes. One electrode was tested extensively in each animal to obtain 10 sets of behaviorally-measured electrical detection thresholds counterbalanced across stimuli. The animal was then exposed to a 110 dB SPL, 2 kHz tone for 48 h and pre- and post-exposure audiograms were measured. The mean permanent threshold shift for acoustic stimuli was 48.5 dB. Another 10 thresholds for each of the 8 electrical stimuli were then measured. In the normal hearing animals, the mean slope of the temporal integration function for electrical stimulation was -7.6 dB per factor of 10 pulses. Alternatively, the mean time constant was 139 ms. In the hearing impaired animals, the slope was reduced to -1.5 dB per factor of 10 pulses, which corresponded to a mean time constant of 17 ms. In addition, the hearing impaired animals showed a decreased threshold for the electrical stimuli (stimulation hypersensitivity) as well as reduced variability across electrical stimulation thresholds. The results suggest that a major contribution to temporal integration occurs in inferior colliculus or higher. In addition, the results suggest that the reduction in temporal integration that follows hearing impairment is a peripherally-induced, central effect.

Animals↗
PubMed1990

Auditory temporal integration and the power function model.

The auditory temporal integration function was studied with the objective of improving both its quantitative description and the specification of its principle independent variable, stimulus duration. In Sec. I, temporal integration data from 20 studies were subjected to uniform analyses using standardized definitions of duration and two models of temporal integration. Analyses revealed that these data were best described by a power function model used in conjunction with a definition of duration, termed assigned duration, that de-emphasized the rise/fall portions of the stimuli. There was a strong effect of stimulus frequency and, in general, the slope of the temporal integration function was less than 10 dB per decade of duration; i.e., a power function exponent less than 1.0. In Sec. II, an experimental study was performed to further evaluate the models and definitions. Detection thresholds were measured in 11 normal-hearing human subjects using a total of 24 single-burst and multiple-burst acoustic stimuli of 3.125 kHz. The issues addressed are: the quantitative description of the temporal integration function; the definition of stimulus duration; the similarity of the integration processes for single-burst and multiple-burst stimuli; and the contribution of rise/fall time to the integration process. A power function in conjunction with the assigned duration definition was again most effective in describing the data. Single- and multiple-burst stimuli both seemed to be integrated by the same central mechanism, with data for each type of stimulus being described by a power function exponent of approximately 0.6 at 3.125 kHz. It was concluded that the contribution of the rise/fall portions of the stimuli can be factored out from the rest of the temporal integration process. In Sec. III, the conclusions that emerged from the review of published work and the present experimental work suggested that auditory temporal integration is best described by a power function in conjunction with the assigned duration definition. The exponent for the power function is typically less than 1.0, and varies with frequency and hearing level. Second, a means of empirically assaying the contribution of the rise-fall portions of the stimuli is presented and evaluated. Finally, properties of a central auditory integrator are hypothesized.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Auditory temporal integration in the normal-hearing and hearing-impaired cat.

Temporal integration functions obtained from human subjects with sensorineural hearing loss have shallower slopes than the functions obtained from normal-hearing subjects. The present investigation was designed to explore this relation in animals in order to compare normal-hearing cats and humans. Auditory temporal integration functions were measured for five cats before and after they were exposed to a 2-kHz tone at 110 dB SPL for 48 h. To measure the temporal integration functions, ten stimuli were used that had overall durations from 8.32 to 275 ms and that were configured either as single or multiple tone bursts of 6.25 kHz. Twelve thresholds for each stimulus were obtained from each animal before and after the sound exposure. Pre- and postexposure audiograms were also obtained and the mean permanent threshold shift at 6.25 kHz was 32.5 dB. Exponential and power function models were used to describe the data. The exponential model (with grand-mean data) yielded a pre-exposure time constant (tau) of 188 ms [mean absolute residual (MAR) of 1.5 dB] and a postexposure tau of 21 ms (MAR of 1.4 dB). For the power function model with grand-mean data, the pre-exposure slope was 6.6 dB per decade of duration (MAR of 1.4 dB) and a postexposure slope of 3.8 dB per decade of duration (MAR of 0.7 dB). The results indicated that the slope of the temporal integration function was less steep after sensorineural hearing loss of cochlear origin, and that the power function model was more effective in describing temporal integration data for the range of stimulus durations employed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Response enhancement and reduction of the auditory brain-stem response in a forward-masking paradigm.

Alterations in the probe evoked auditory brain-stem response (ABR) were evaluated in 15 normal-hearing subjects using several stimulus configurations in a tone-on-tone forward-masking paradigm. The stimulus parameters manipulated in the study included: masker frequency; relative intensity of the masker; overall intensity of the masker-probe pair; and masker rise-fall time. Latency increases for waves III and V and an amplitude reduction for wave III were observed under some stimulus conditions. These changes were interpreted in terms of partial forward-masking effects. The masking effects were shown: to be maximal for masker frequencies in close proximity to the probe; to increase with increasing level of masker; to be independent of the overall level of the masker-probe pair; and, to decrease with increasing rise-fall time of the masker. Collectively, the forward-masking effects were interpreted as peripheral in origin, although, an additional brain-stem locus was not ruled out. In contrast, the same stimuli which increased wave III and V latencies and reduced wave III amplitude produced a robust amplitude increment in wave V which was termed enhancement. Wave V enhancement was shown: to be maximal for masker frequencies in close proximity to the probe; to decrease with increasing masker level; and, to decrease with faster rise-fall times of the masker. The processes mediating wave V enhancement are not clear, however, it was concluded that wave V enhancement probably reflects the resultant of a complex central neuronal interaction, presumably in the vicinity of the wave V generator(s).

Acoustic Stimulation↗
PubMed1985

Behavioral thresholds for electrical stimulation applied to auditory brainstem nuclei in cat are altered by injurious and noninjurious sound.

Each of three young-adult female cats with normal hearing received a total of eight permanent electrodes which were implanted bilaterally in cochlear nucleus (CN) and inferior colliculus (IC). Three experiments were performed using behaviorally measured thresholds for electrical stimulation of CN and IC. In Expt. 1, electrical stimulation thresholds (in dB re 1.0 microA) were obtained in the presence of a continuous tone of moderate intensity and in quiet. In comparison with quiet, electrical stimulation thresholds measured during tone were lower by as much as 15 dB (stimulation hypersensitivity). In Expt. 2, a brief exposure to an intense sound produced a temporary threshold shift (TTS) for acoustic stimuli but only produced small changes in electrical stimulation threshold. The acoustic stimuli used in Expts. 1 and 2 were termed noninjurious since no permanent hearing loss was produced. Expt. 3 employed an exposure to a white noise that resulted in a mean permanent threshold shift (PTS) of 34.1 dB for acoustic stimulation. The PTS was accompanied by a mean stimulation hypersensitivity of 9.6 dB. Comparing Expts. 1 and 3, it was shown that the transient hypersensitivity produced by the noninjurious continuous tone correlated strongly with the permanent hypersensitivity that was produced by the PTS. In regard to the origin of stimulation hypersensitivity, the suggestion is made that it is an indication of a physiological change localizable perhaps in the auditory nuclei of the upper brainstem.

Acoustic Stimulation↗
PubMed1979

Central denervation hypersensitivity in the auditory system of the cat.

Data are reported for seven cats with a total of 29 electrodes permanently placed in or near the cochlear nucleus, the superior olivary complex, the nucleus of the inferior colliculus, and the medial geniculate body. Detection thresholds for pulsate electrical stimuli were measured using an operant behavioral procedure. Electrical stimulation thresholds were measured prior to and following bilateral destruction of the cochleas in all animals. In addition, four of the animals were tested using a site-of-stimulation discrimination prior to and following the cochlear lesion. Finally, hearing loss was evaluated in all cats after the completion of the experiments. Electrical stimulation thresholds showed a mean reduction of 7.9 dB throughout the brain stem auditory system fater cochlear destruction. The ability of the animals to perform the site-of-stimulation discrimination was not permanently impaired by the cochlear lesion. The data indicated the presence of increased sensitivity to electrical stimulation in most regions of the subcortical auditory system, although a lesser effect was found at the thalamic level. It was concluded that stimulation threshold provides an index relevant to the state of auditory neurons proximal to the electrode tip.

Animals↗
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↗