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G M Gerken

Publications and source records attributed to G M Gerken.

At least 19 recordsLinked to original sources
PubMed1997

Summating potential and action potential gradients on and in the vicinity of the round window in guinea pig.

The purpose of this study was to determine the spatial gradients of summating potential (SP) amplitudes, action potential (AP) amplitudes, and SP/AP ratios for recording loci on the round window (RW) membrane and in its vicinity. Sixteen guinea pigs were tested by means of free-field click and tone burst (2.0 kHz) stimuli. Seven recording regions were specified: five equal-area regions on the RW membrane and two basal promontory regions. Statistically significant differences were found between the promontory regions and the RW membrane regions for the SP, AP, and SP/AP obtained with click stimuli, and for the SP and AP obtained with tone burst stimuli. The SP/AP ratio for tone burst stimuli did not differ significantly across the seven regions. The RW membrane was found to be isoelectric, but there were marked spatial gradients on the basal promontory. These results are of consequence for the interpretation of transtympanic electrocochleography recordings.

Animals↗
PubMed1997

Electrocochleographic evaluation of the guinea pig model of endolymphatic hydrops.

Electrocochleography (ECochG) was used to evaluate cochlear function in guinea pigs with experimentally induced endolymphatic hydrops (ELH) before and after osmotic dehydration with either glycerol or urea. We surgically induced ELH in the right ears of 9 guinea pigs, while the right ears of 6 guinea pigs received a sham operation. The left ears of the 15 animals constituted the normal group. Eight weeks after surgery, summating potential (SP) and action potential (AP) amplitudes were measured prior to and following the administration of glycerol or urea. The SPs and SP/AP ratios were reduced in all groups, with no significant differences among groups or between dehydrating agents. Some of the hydropic ears, however, did show an increased AP threshold and a recruitment effect. In measurements from 6 additional animals, serum osmolarity increased more with urea than with glycerol. The guinea pig model remains valuable for investigation of ELH, even though it differs in significant respects from ELH in humans.

Action Potentials↗
PubMed1996

Central tinnitus and lateral inhibition: an auditory brainstem model.

Central tinnitus is used herein either to designate a tinnitus that originates in the central auditory system, or to refer to a component of a peripherally generated tinnitus that is exaggerated by auditory brain mechanisms. Findings from several research areas contribute to this analysis of central tinnitus. The inferior colliculus, in particular, is significant because of the distribution of lateral inhibition in this nucleus and because of the possible change in inhibition that follows bearing loss. There is also a convergence of auditory and non-auditory functions at inferior colliculus. One non-auditory function, the initiation of aversive behavioral responses, may be demonstrated with electrical or chemical stimulation of auditory nuclei in the vicinity of the midbrain. With reduction of central inhibition through hearing loss or aging, tinnitus activity may gain easier access to those subsystems that produce aversive responses. A neural model, conceptually based in inferior colliculus, assumes a pattern of lateral inhibition that is influenced by the distribution of cochlear pathology. Of special importance are the abrupt changes across the tonotopically organized outputs from the cochlea that are reflected in behavioral measures as an 'audiometric edge'. The neural response properties that derive from this assumption are related to properties of central tinnitus.

Acoustic Stimulation↗
PubMed1994

Loss of perilymph affects electrocochleographic potentials in the guinea pig.

Alterations of electrocochleographic (ECoG) potentials recorded from guinea pig cochleae have been reported to occur following round window (RW) membrane perforation (perilymphatic fistula). To further evaluate the pathophysiology of perilymphatic fistula, a study was conducted of the short-term effects of acute RW membrane perforation on the amplitude of the summating potential (SP) and the action potential (AP), and the SP:AP ratio. Acute RW membrane perforation was produced in 15 Hartley guinea pigs. The animals were placed in a head dependent position, so that some perilymph would drain from the inner ear following RW perforation. For both click and low frequency tone burst stimuli (2 kHz), the mean AP amplitudes showed variable but progressive deterioration with time following RW membrane perforation. Action potential latencies showed a significant increase with time for both click and tone burst stimuli. Summating potential amplitudes for click and tone burst were typically stable or slightly decreased. Interanimal variability of all measures was typically high. However, AP and SP amplitudes in the same animal were consistently and differentially affected by perforation of the RW membrane. There also were differential effects on the positive and the negative components of the SP, suggesting the interplay of several generator mechanisms. The authors conclude that AP amplitude and, consequently, the SP:AP ratio are sensitive to the creation of a perilymphatic fistula. These results provide support for the use of ECoG tests in the diagnosis of perilymphatic fistula.

Animals↗
PubMed1993

Alteration of central auditory processing of brief stimuli: a review and a neural model.

There is evidence that the manner in which the central auditory system processes transient signals can be altered by either of two seemingly unrelated experimental factors, namely, hearing loss, or the presence of a continuous tone of moderate intensity. In particular, altered processing of brief signals in the central auditory system is indicated by either: (i) lower (better) behaviorally measured thresholds for pulsate electrical stimulation of brain-stem auditory nuclei, or (ii) an increased amplitude of some components of the brain stem or cortical potentials evoked by brief acoustic stimuli. A simple two-neuron model which evolved from the above findings and related visual system phenomena was used to evaluate the effects produced by hearing loss or continuous tone. In the model, a "hearing loss" condition, which was represented by less spontaneous neural activity (and, hence, reduced inhibition) relative to a "normal hearing" condition, yielded both increased gain for steady-state stimuli and increased responsiveness for transient stimuli. Thus the model provides two possible, and simultaneously operable, explanations of reduced electrical stimulation thresholds and increased evoked potential amplitude: one based on increased steady-state gain and the other based on increased responsiveness to transient stimuli. A third condition, "normal hearing with a longer excitatory time constant," yielded effects that were similar to those produced by reduced inhibition, thereby suggesting a physiological basis for alteration of psychophysically measured time constants.

Acoustic Stimulation↗
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↗
PubMed1984

Hypersensitivity to electrical stimulation of auditory nuclei follows hearing loss in cats.

The purpose of the study was to determine if permanent, sound-induced hearing loss altered behaviorally measured thresholds for the detection of electrical stimulation applied to auditory nuclei. Electrodes were placed in cochlear nucleus and inferior colliculus in four cats. Behaviorally measured thresholds for the detection of brief trains of electrical pulses were determined before and after a 48 h exposure to a 1 kHz tone of approximately 110 dB SPL. The mean decrease in electrical stimulation threshold as a result of the sound exposure was 10.4 dB. The ongoing electrical activity (in microV, rms) recorded from the electrodes showed a mean 2.2 dB decrease after the sound exposure. In some electrodes, there was partial recovery towards pre-exposure levels for stimulation threshold and for ongoing activity, but typically, the changes persisted until the animals were terminated 30 days later. The magnitudes of the decreases in stimulation threshold and background activity proved not to be highly correlated. The permanent auditory threshold shift across all cats and all frequencies was 19 dB. This mild hearing loss produced a marked alteration in certain characteristics of the central auditory mechanisms.

Animals↗
PubMed1983

Post-stimulation effects on the auditory brain stem response partial-masking and enhancement.

The auditory brain stem response (ABR) was recorded in human subjects using the stimulus configuration of a tone-on-tone forward-masking paradigm, but with all stimuli at suprathreshold levels. A masking stimulus preceded, by delta t msec, the probe stimulus which elicited the ABR. The latency vs. delta t functions for waves III and V were essentially parallel to each other and were interpreted in terms of a partial forward-masking effect, possibly originating in the cochlea. Likewise, the amplitude function for wave III showed varying degrees of decrement as a function of delta t that was also compatible with a partial forward-masking interpretation. In contrast, wave V showed an amplitude increment relative to the unmasked wave that was maximal for delta t values of 15 and 45 msec. The amplitude increment in wave V was termed enhancement and was interpreted as a central process governed by the timing of sound sequences.

Brain Stem↗
PubMed1983

Three models of temporal summation evaluated using normal-hearing and hearing-impaired subjects.

Temporal summation effects were measured in normal-hearing and hearing-impaired subjects using stimuli of different durations and temporal patterns. Threshold decreased with increasing stimulus duration for either single- or multiple-burst stimuli, but the hearing-impaired group showed smaller threshold shifts, which differed from those obtained with the normal-hearing group at the .0001 level of significance. Three models of temporal summation were evaluated: One model employed a time constant in an exponential function, one used a power function characterized by an exponent, and the last combined the properties of the exponential and power functions and was also characterized by an exponent. Estimates of the parameters that best described the data were obtained for each model. Data from the hearing-impaired subjects provided the most critical test of the models. The power function model and the combined model were both satisfactory with the range of stimulus durations used, but the exponential model failed to describe the data from the hearing-impaired subjects. It is suggested that there may not be a decrease in the time constant for temporal summation for subjects with sensorineural hearing-loss, but that a factor related to the utilization of sensory input is altered.

Acoustic Stimulation↗
PubMed1983

Frequency information in the auditory brainstem response evoked by tonal transients.

The auditory brainstem response (ABR) is a composite of potentials generated by neural activity stemming from several regions of the cochlea. A derivation technique is described for reducing the contributions to the ABR that arise from frequencies outside of the frequency band of interest. The technique treats averaged waveforms in an algebraic manner and uses a method of successive substitutions to obtain a derived waveform. The recorded and derived ABR waveforms were analyzed with respect to changes of latency and morphology. The behavior of the waveform components of the derived regional responses was in accord with the data of other studies in which narrow-band responses were derived from waveforms produced by high-pass masking of click stimuli. Frequency information was thus extracted from the ABR without the simultaneous presence of other stimuli as in masking-based derivations. The method of successive substitutions used with brief transient stimuli of different frequencies appears to yield derived ABRs that reflect activity from different cochlear regions.

Adult↗
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↗