AP Tuning Research Articles

A comparison of AP and ABR tuning curves in the guinea pig

AP and ABR tuning curves were measured using a forward masking paradigm in guinea pigs with chronically implanted electrodes. Measurements were made before exposure to wide-band noise and at several intervals after exposure. The noise exposure was sufficient to produce temporary threshold shifts up to 60 dB lasting several days. Results showed similar reductions in Q 10, tip-to-tail ratio and slope of simultaneously recorded AP and ABR tuning curves as a function of threshold shift following noise exposure. Tuning curves based on changes in response latency are presented as well as tuning curves based on changes in response amplitude. AP and ABR latency tuning curves showed similar form and changes with hearing loss as amplitude tuning curves. The similarities between AP and ABR tuning characteristics provide evidence that the ABR is sensitive enough to peripheral changes to be useful as a tool to study auditory frequency selectivity. The similarities between amplitude and latency tuning characteristics suggest that information regarding frequency selectivity of the auditory system can be obtained using response latency as well as response amplitude.

A comparison of AP and ABR tuning characteristics in the guinea pig

AP and ABR tuning curves were measured using a forward‐masking paradigm in guinea pigs with chronically implanted electrodes. Measurements were made before exposure to wide‐band noise and at several intervals after exposure. The noise exposure was sufficient to produce temporary threshold shifts up to 60 dB lasting several days and resulted in a systematic widening of both AP and ABR tuning curves and a reduction in tip‐to‐tail ratios. No significant differences were found between simultaneously recorded AP and ABR tuning curves as measured by Q10, tip‐to‐tail ratio, or the slope of the tuning curves. Tuning curves obtained by measuring AP and ABR response latency as a function of masker level, showed similar form and changes with hearing loss to those based on amplitude of response. The similarities between AP and ABR tuning characteristics provide evidence that the ABR is sensitive enough to peripheral changes to be a useful tool in the study of auditory frequency selectivity.

Brainstem, whole-nerve AP and single-fiber suppression in the gerbil: normative data.

Suppression of gerbil brainstem responses (BSRs) and whole-nerve AP responses was studied by means of a forward masking procedure in which a tone-burst probe was preceded by a narrow-band masker. The effectiveness of the masker in reducing the brainstem response to the probe can be diminished by presenting a tone burst simultaneously with the masker. By varying the frequency and intensity of the third stimulus, BSR suppression areas can be determined. These flank the tails and high-frequency sides of BSR tuning curves in a manner similar to the suppression areas of AP tuning curves. The shapes and sizes of the BSR and AP suppression areas vary greatly across probe frequencies and animals. However, the lower boundaries of suppression areas associated with the tails of the tuning curves occur at similar absolute levels regardless of probe frequency or tuning curve shape. The BSR and AP suppression areas are in some respects similar to areas of two-tone rate suppression in single auditory nerve fibers of the gerbil.

Some otological differences between pigmented and albino-type guinea pigs.

Cochlear action potential thresholds across frequency (AP audiograms) and AP tuning curves were compared in albino (Dunkin-Hartley) guinea pigs and normal pigmented animals. AP audiograms were very similar; on average the albinos had AP thresholds 2-3 dB lower at 2 kHz and below compared with the pigmented guinea pig. AP tuning curves at 16 kHz were, on average, significantly less sharply tuned in the albino, but similar at 8, 4, and 2 kHz. Although we find only small differences in these measures of normal cochlear function, other evidence in the literature suggests that in auditory research the use of "albino" guinea pigs is best avoided.

AP unmasking and AP tuning in guinea pig.

Using a method introduced by Harris [6] AP unmasking was investigated in normal guinea pigs. AP unmasking existed in every guinea pig investigated and proved to be stable over measuring periods as long as 7 h. The average standard deviation of unmasking magnitude was 12%. AP unmasking strength was defined as the average unmasking magnitude across across suppressor levels from 0 to 100 dB SPL at constant masker and test-tone level and constant masker, test-tone and suppressor frequency. The relation between AP unmasking strength and AP thresholds was investigated. AP unmasking strength decreases with increasing AP threshold at the suppressor frequency. No relation with AP thresholds at other frequencies was found. AP unmasking areas were determined along with the corresponding AP tuning curves. High-frequency unmasking was found to be more prominent and more stable than low-frequency unmasking in guinea pig. From a comparison with other studies on AP unmasking and single fibre two-tone suppression it was concluded that a species difference exists with regard to the presence of low-frequency AP unmasking and low-frequency single fibre two-tone suppression.

AP unmasking and AP tuning in normal and pathological human ears.

In a group of seven normal and eight abnormal hearing subjects three-tone AP unmasking experiments and/or AP tuning experiments were performed during electrocochleography. In the unmasking experiments the Shannon forward masking paradigm was applied, i.e. two simultaneous tones (the masker and the suppressor) influence a test tone in a forward masking procedure. Frequency and intensity of the suppressor were varied. It appeared that unmasking effects are clearly present, i.e. the suppressor stimulus can reduce masking of the AP. This effect, however, is very variable, in normal ears as well as in pathological ears. AP tuning quality deteriorated with increasing hearing loss but no correlation was found between AP unmasking parameters and hearing loss. It seems that AP suppression areas shift less upward (or not at all) than the AP tuning curve does upon increasing the test tone level. These results raise some questions about the intercorrelation of the triad: hearing loss, quality of tuning and suppression effects, as single fibre experiments and psychophysical investigations suggest.

ABR measurements in a forward‐masking paradigm

Growth of masking and tuning curves were measured in the cat, using a forward‐masking paradigm in conjunction with farfield recording techniques. Probe tones of 3‐ms duration (20 dB above ABR threshold) were presented subsequent to 99‐ms duration maskers. Masker frequency and level were varied parametrically. Masker and probe were separated by 10 ms and were repeated every 400 ms until 500 responses to the probe had been averaged. The amplitude of the largest component of the ABR (presumably wave V) was measured for each masking condition and then was normalized to the probe response amplitude in quiet. Previous AP data indicated that plots of the decrement in probe response as a function of masker level are similar to single‐unit rate‐level functions [Abbas and Gorga, J. Acoust. Soc. Am. 69, 492–499 (1981)]. The present ABR decrement functions were steepest for frequencies below probe frequency. This effect is similar to the frequency dependence observed for AP masking data. ABR tuning curves (threshold = 50% decrement) were similar in shape to AP tuning curves although they tended to be less sharply tuned. Still, these data indicate that farfield techniques can be used to estimate response growth and frequency resolution. [Supported by NIH Grants NS14880 and NS07147.]

Electrocochleographic measures of frequency selectivity in human deafness.

An important cochlear function is to separate out the frequency components in complex sounds. During transtympanic electrocochleography, objective measures of such frequency selectivity were obtained using two (simultaneous) tone on tone suppression paradigms: (a) iso-suppression curves (AP tuning curves): the frequency/intensity combinations to suppress, by a criterion percentage, the AP.to a near-threshold tone pip; and (b) iso-intensity curves: the reduction of an AP to a near-threshold tone pip, by a constant intensity suppressing tone as a function of frequency. Both methods yield 10-dB bandwidth measures related to cochlear frequency selectivity. The latter test, taking only 5-10 min, can be used routinely in clinical electrocochleography. The relationship between 10-dB bandwidth values and audiometric thresholds can be summarized as follows:In normal ears (threshold elevations of less than 20 dB at the test frequency and ears with no otological problem other than small high-frequency threshold elev...

Forward-masking AP tuning curves in normal and in acoustically traumatized ears.

Compound action potential tuning curves (APTC's) were developed in a series of normal and acoustically traumatized cats. Probe frequency was set to 4 kHz ad probe level was set to 15-20 dB SL re: AP threshold for both normal and impaired ears. In addition, normal ears received the probe tone at a level of 70-75 dB SPL. Probe-elicited AP amplitude was measured in a forward-masking paradigm as a function of both masker level and frequency. Results indicated that the sharpness of the APTC's (defined by Q 10) was unaffected by acoustic trauma. The relative difference between required masker level on the tail and at the tip was reduced for the noise-damaged ears. Thus sharpness around the tip was essentially normal yet low-frequency energy was more effective at masking high-frequency region in these impaired ear. When slope of the decrement in normalized, probe-elicited AP amplitude-versus-masker level functions are calculated for different frequency maskers, normal ears showed a frequency dependence such that low-frequency maskers resulted in the steepest slopes with progressively less steep slopes as masker frequency increased. Some of the noise-damaged ears did not show this same frequency dependence. Specifically, the slopes of these functions were not as different for low-and high-frequency maskers. These slope data may suggest that nonlinearities, present in the normal system, may be reduced as a consequence of this cochlear insult.

The frequency selectivity of the normal and pathological human cochlea.

Human AP tuning curves (tone on tone simultaneous and forward masking curves) were measured during transtympanic electrocochleography. For subjects with near normal thresholds, average Q10 dB values (simultaneous masking) were 2.3 at 2 kHz, 3.6 at 4 kHz, and 4.7 at 8 kHz. Patients with threshold elevations of more than 40 dB, resulting from sensorineural hearing loss of cochlear origin, had tuning curves less sharply tuned by a factor of 2-3, with Q10 dB values of 1-2 at 2 kHz and at 4 kHz, and 1-2.3 at 8 kHz. AP tuning curves and single fibre tuning curves (frequency threshold curves) were measured in normal guinea pigs; cochlear fibre tuning is sharper than AP tuning (simultaneous masking) by a factor of 1.8 (2-20 kHz). Assuming that this factor can be applied to the human cochlea, estimates of normal human cochlear fibre Q10 dB values are 4.2 at 2 kHz, 6.5 at 4 kHz, and 8.5 at 8 kHz.

Effects of hair cell lesions on responses of cochlear nerve fibers. I. Lesions, tuning curves, two-tone inhibition, and responses to trapezoidal-wave patterns.

Effects of hair cell lesions on responses of cochlear nerve fibers. I. Lesions, tuning curves, two-tone inhibition, and responses to trapezoidal-wave patterns.R A Schmiedt, J J Zwislocki, and R P HamernikR A Schmiedt, J J Zwislocki, and R P HamernikPublished Online:01 May 1980https://doi.org/10.1152/jn.1980.43.5.1367MoreSectionsPDF (3 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByLessons from Rodent Models for Genetic and Age-Related Hearing Loss29 August 2018Aging Effects on Behavioural Estimates of Suppression with Short Suppressors15 April 2016A Theoretical Analysis of Normal- and Impaired-Hearing Intensity DiscriminationIEEE Transactions on Speech and Audio Processing, Vol. 12, No. 3Response Growth With Sound Level in Auditory-Nerve Fibers After Noise-Induced Hearing LossMichael G. Heinz, and Eric D. Young1 February 2004 | Journal of Neurophysiology, Vol. 91, No. 2An auditory-periphery model of the effects of acoustic trauma on auditory nerve responsesThe Journal of the Acoustical Society of America, Vol. 113, No. 1Cisplatin-Induced Hyperactivity in the Dorsal Cochlear Nucleus and Its Relation to Outer Hair Cell Loss: Relevance to TinnitusJames A. Kaltenbach, John D. Rachel, T. Alecia Mathog, Jinsheng Zhang, Pamela R. Falzarano, and Matthew Lewandowski1 August 2002 | Journal of Neurophysiology, Vol. 88, No. 2Shapes of cat auditory nerve fiber tuning curvesHearing Research, Vol. 81, No. 1-2Cochlear basal and apical differences reflected in the effects of cooling on responses of single auditory nerve fibersHearing Research, Vol. 80, No. 2Responses of peripheral auditory neurons to two-tone stimuli during development: I. Correlation with frequency selectivityHearing Research, Vol. 77, No. 1-2Two-tone suppression and distortion production on the basilar membrane in the hook region of cat and guinea pig cochleaeHearing Research, Vol. 66, No. 1Physiological and histological changes associated with the reduction in threshold shift during interrupted noise exposureHearing Research, Vol. 62, No. 2Electrical stimulation of the auditory nerve in deaf kittens: Effects on cochlear nucleus morphologyHearing Research, Vol. 56, No. 1-2Auditory nerve of the normal and jaundiced rat. II. Frequency selectivity and two-tone rate suppressionHearing Research, Vol. 54, No. 1Enhanced evoked response amplitudes in the inferior colliculus of the chinchilla following acoustic traumaHearing Research, Vol. 50, No. 1-2Tuning and suppression in auditory nerve fibers of aged gerbils raised in quiet or noiseHearing Research, Vol. 45, No. 3Spontaneous rates, thresholds and tuning of auditory-nerve fibers in the gerbil: Comparisons to cat dataHearing Research, Vol. 42, No. 1Eighth nerve fiber firing features in normal-hearing rabbitsHearing Research, Vol. 36, No. 2-3Evoked response ‘forward masking’ patterns in chinchillas with temporary hearing lossHearing Research, Vol. 27, No. 3Ventral cochlear nucleus neural discharge characteristics in the absence of outer hair cellsBrain Research, Vol. 342, No. 2A comparison of brainstem, whole-nerve AP and single-fiber tuning curves in the gerbil: Normative dataHearing Research, Vol. 17, No. 3Single-neuron labeling and chronic cochlear pathology. III. Stereocilia damage and alterations of threshold tuning curvesHearing Research, Vol. 16, No. 1Furosemide selectively reduces one component in rate-level functions from auditory-nerve fibersHearing Research, Vol. 15, No. 1Neurophysiologic Assessment of Endolymphatic Hydrops28 June 2016 | Annals of Otology, Rhinology & Laryngology, Vol. 93, No. 3Correlates of tone-on-tone masked thresholds in the chinchilla auditory nerveHearing Research, Vol. 13, No. 3Some electrical circuit properties of the organ of Corti. I. Analysis without reactive elementsHearing Research, Vol. 12, No. 1Spontaneous and impulsively evoked otoacoustic emission: indicators of cochlear pathology?Hearing Research, Vol. 10, No. 3Response patterns of auditory nerve fibers during temporary threshold shiftHearing Research, Vol. 10, No. 1AP unmasking and AP tuning in normal and pathological human earsHearing Research, Vol. 8, No. 2Boundaries of two-tone rate suppression of cochlear-nerve activityHearing Research, Vol. 7, No. 3Intracellular and extracellular responses in the organ of Corti of the gerbilHearing Research, Vol. 7, No. 2Modulation of responses of spiral ganglion cells in the guinea pig cochlea by low frequency soundHearing Research, Vol. 7, No. 2 More from this issue > Volume 43Issue 5May 1980Pages 1367-89 https://doi.org/10.1152/jn.1980.43.5.1367PubMed7373368History Published online 1 May 1980 Published in print 1 May 1980 Metrics

AP tuning curves and anatomical correlates from acoustically traumatized cats

Compound action potential tuning curves, using a forward‐masking paradigm, were developed on both a control group and a group of acoustically traumatized cats. Differences observed between the two populations included a decrease in the sharpness of the tip, in the sensitivity of the tip, and/or in the sensitivity of the tail region. Phase contrast light microscopy was performed on all exposed ears using a celloidin embedding technique with horizontal sectioning. Whenever an abnormality in an AP tuning curve was seen, histological evidence of damage to the organ of Corti in an appropriate region corresponding to the signal frequency was observed. However, several cases of damage to the cochlea were observed with normal tuning curves. Wherever the tip region of the tuning curve was elevated, evidence of damage to all three rows of OHC and to the IHC was seen. Several other observations relating to the extent of damage to the OHC and IHC independently were found to be similar to results from single‐fiber recordings in acoustically traumatized cats [M. C. Liberman and N. Y. Kiang, Acta Otolaryngol. Suppl (STOCKH) (358). 1–63 (1978)].

Two‐Tone suppression areas in the chinchilla auditory nerve

Frequency Threshold Curves (FTC) and two‐tone supression (2TS) areas have been determined for single, primary fibers. 2TS is defined as a 20% or greater decrease in the firing rate evoked by a tone at the unit's characteristic frequency (CF) 10 dB above CF‐threshold associated with the addition of a second variable tone. The shape and size of 2TS areas vary systematically as a function of fiber CF. The low side 2TS areas (second tone below CF) are located outside the limits of the fiber's FTC for high CF units and within the boundaries of the FTC for units with CF of approximately 3 kHz and below. With our criterion, low side 2TS areas are rarely found for low CF units (less than 2 kHz). Whole‐nerve AP tuning curves collected with a forward masking procedure and AP supression areas collected with an unmasking method are similar to the single unit data for probe frequencies above about 4 kHz. Below 4 kHz, AP supression areas are smaller than their unit counterparts. Forward masking AP tuning curves are consistently broader than single unit FTCs.

Physiological masking functions in normal and acoustically traumatized cats

In cats that have undergone acoustic traumatization, it has been observed that several characteristics in the shape of single auditory nerve fiber tuning curves correspond to histological changes in the hair cells of the cochlea [N. Y. S. Kiang, M. C. Liberman, and R. A. Levine, Ann. Otol. Rhinol. Laryngol. 85, 752–768 (1976)]. Dallos and Cheatham (J. Acoust. Soc. Am. 59, 591–597 (1976)] using the whole‐nerve action potential as a response have demonstrated masking curves in normal animals similar in shape to single‐fiber tuning curves. We have measured whole‐nerve action potential tuning curves (AP tuning curve) in both normal and acoustically traumatized cats to investigate the sensitivity of such a measure in reflecting changes in single‐fiber tuning curves. A tonal masker in a forward‐masking paradigm was used to elicit the measured responses. AP tuning curves were generated at several signal frequencies in order to measure the physiological changes at different places along the cochlea. A preliminary review of the data indicate that the AP tuning curves in acoustically traumatized animals can show a broadening of the tip region relative to normals.

THE RESPONSE OF SINGLE AUDITORY-NERVE FIBERS TO ACOUSTIC STIMULATION

THE AIM OF the experiments described here was to study the response of single auditory-nerve fibers to acoustic stimulation delivered to the intact ear. Similar studies on other single afferent fibers have remarkably extended knowledge of the mode of action of diverse sensory mechanisms, while at the same time emphasizing their fundamental similarities. The present report describes the behavior of single auditory fibers and stresses similarities to other sensory nerves; in a subsequent paper we hope to relate these findings to a specific theory of action of the mammalian cochlea. METHOD Young cats anesthetized with dial (0.75 cc. per kilo) were used in these experiments. The postero-dorsal aspect of the auditory nerve was exposed by removing the lateral portion of the occipital bone where it meets the petrous bone. Bleeding from the sinus petrosus inferior was stopped by judicious cauterization or by Clotting Globulin. * A Ringer-filled glass micropipette with Ag-AgCl wire inserted as close as possible to the tip served as the active lead from the nerve. It was early established that pipettes with openings greater than 5~ do not allow isolation of the action potentials of single auditory fibers. The 3 to 5~ electrodes used have an impedance of about 1 megohm when tested on a resistance-capacity bridge between 0.6 and 2.5 kc. The microelectrode and the indifferent electrode (a silver plate in the neck muscles) led to a capacity-coupled amplifier (Grass) with an input done photographically