Biomedical subjects

E Javel

Publications and source records attributed to E Javel.

35 records · Page 2Linked to original sources

PubMed1986

Development of auditory-evoked potentials in the cat. III. Wave amplitudes.

Amplitudes of auditory-evoked brain stem response (ABR) and late-occurring auditory-evoked potential (AER) components were recorded from kittens between birth and 90 postnatal days. All ABR and AER wave amplitudes increased during the first postnatal month. Wave amplitudes exhibited nonmonotonic growth with increasing age, attaining a maximum at 40-60 days of age, after which amplitudes decreased. Amplitudes of waves originating in the auditory nerve matured somewhat faster than waves originating in the brain stem and forebrain, and the order in which waves reached maturity was roughly the reverse order of the latencies of their peaks. Input-output curves for ABR and AER waves displayed nonmonotonic behavior that varied as a function of postnatal age. Wave amplitudes recorded from adult cats increased between threshold and 70 dB SPL, then decreased between 70 and 100 dB SPL, and rapidly increased above 100 dB SPL. The intensity corresponding to the change from increasing to decreasing amplitudes was higher for younger animals and achieved adult values during the first postnatal month.

Aging↗

PubMed1986

Coding of spectral fine structure in the auditory nerve. I. Fourier analysis of period and interspike interval histograms.

The temporal fine structure of discharge patterns of single auditory-nerve fibers in adult cats was analyzed in response to signals consisting of a variable number of equal-intensity, in-phase harmonics of a common low-frequency fundamental. Two analytic methods were employed. The first method considered Fourier spectra of period histograms based on the period of the fundamental, and the second method considered Fourier spectra of interspike interval histograms (ISIH's). Both analyses provide information about fiber tuning properties, but Fourier spectra of ISIH's also allow estimates to be made of the degree of resolution of individual stimulus components. At low intensities (within 20-40 dB of threshold), indices of synchronization to individual components of complex tones were similar to those obtained for pure tones. This was true even when fibers were capable of responding to several signal components simultaneously. Response spectra obtained at low intensities resembled fibers' tuning curves, and fibers with low spontaneous discharge rates tended to provide better resolution of stimulus components than fibers with high spontaneous rates. Strongly nonlinear behavior existed at higher stimulus intensities. In this, information was transmitted about progressively fewer signal components and about frequencies not present in the acoustic stimulus, and the component eliciting the largest response shifted away from the fiber's characteristic frequency and toward the edges of the stimulus spectrum. This high-intensity "edge enhancement" can result from the combined effects of a compressive input-output nonlinearity, suppression, and the fortuitous addition of internally generated combination tones. The data indicate that sufficient information exists for the auditory system to determine the frequencies of narrowly spaced stimulus components from the temporal fine structure of nerve fiber's responses.

Animals↗

PubMed1985

The development of somatostatin immunoreactivity in the interpeduncular nucleus of the cat.

Somatostatin (SS) immunoreactivity was localized in a population of neurons in the interpeduncular nucleus (IPN) of the developing and adult cat. SS-immunoreactive perikarya and fibers were found in several subdivisions of the IPN, but were most heavily concentrated in the central nucleus (IPC). Some immunoreactive fibers appeared to be associated with the ventral surface of the IPN where they may come in contact with the interpeduncular cistern. Bundles of immunoreactive fibers also appeared to leave the rostral pole of the IPN bilaterally. Still other SS-positive perikarya and fibers were associated with the tegmentopeduncular tract and the medial division of the dorsal tegmental nucleus. SS was present in both perikarya and fibers of the IPN at birth. The concentration of immunoreactivity increased dramatically during the first 100 days postnatal, but by 180 days the overall intensity of immunoreactivity had decreased to adult levels. These data indicate that SS may be present in the cat IPN in a specific population of neurons that is most active during early postnatal development. The data are consistent with previous suggestions that SS plays a special role in the development of certain neuronal systems and may be particularly important in the integration of behaviors during the neonatal period.

Animals↗

PubMed1985

Extraction and enhancement of spectral structure by the cochlea.

The intensity dependence of signal processing in the cat cochlea was studied in responses of single auditory-nerve fibers for harmonic complexes having various amplitude and phase spectra. Analyses were based on information present in temporal discharge cadences, and they consisted of assessing Fourier spectra of period histograms synchronized to the period of the waveform fundamental. At low intensities, response spectra resembled filtered versions of the stimulus spectrum, with the amounts of filtering being determined by fibers' tuning curves. At high intensities, response spectra exhibited nonlinear behavior and could differ dramatically from spectra obtained at low intensities. The high-intensity response typically emphasized one or more aspects of the stimulus spectrum. When the stimulus possessed equal component amplitudes and phases, the features that were emphasized at high intensities were the high- and low-frequency edges of the spectrum, and when the component at fiber CF was changed in phase or amplitude relative to the others, fibers primarily signaled the presence of the phase- or amplitude-shifted component. Many of the intensity-dependent changes in response spectra are accounted for by considering the effects of the compressive input-output nonlinearity operating at or peripheral to the hair-cell level on the temporal waveform.

Acoustic Stimulation↗

PubMed1984

The effects of stimulus duration on ABR and behavioral thresholds.

ABR and behavioral thresholds were estimated as a function of stimulus duration for three normal and two hearing-impaired subjects. Stimuli were 2000-Hz tone bursts with 0.5-ms rise/fall times and durations ranging from 1 to 256 or 512 ms. For both groups of subjects, ABR thresholds were independent of stimulus duration. Normal subjects showed greater improvement in behavioral thresholds as a function of duration than did subjects with hearing losses. Thus, it appeared that ABR and behavioral thresholds were affected differently by changes in stimulus duration and that the magnitude of these differences could depend upon the presence of hearing loss. These data indicate that temporal integration may be one factor which makes comparisons between ABR and behavioral thresholds complicated. In the present study, the magnitude of hearing loss, measured by the ABR, would have been underestimated if normal behavioral thresholds for short-duration stimuli were used as the reference.

Auditory Pathways↗

PubMed1983

Single-unit responses to cholinergic agents in the rat inferior colliculus.

Single units were recorded from the inferior colliculi of adult male rats anesthetized with urethane. Units were driven with tonal stimuli, and changes in unit responses to the tones were monitored during iontophoretic application of cholinergic drugs. The cholinergic agonists acetylcholine and carbamylcholine potentiated responses in about 50% and suppressed responses in about 35% of units tested. Cholinergic antagonists typically produced effects when delivered alone. Both d-tubocurarine and atropine methyl nitrate excited over 80% of units tested, while mecamylamine and scopolamine inhibited the majority of tested units. Dihydro-beta-erythroidine was generally ineffective. Alpha-bungarotoxin was generally ineffective when delivered alone, but blocked agonist effects. Post-stimulus time histogram (PSTH) patterns, response-intensity functions and response areas were examined for changes during drug delivery. Cholinergic agents did not differentially affect either time periods within the PSTH or frequency bands of response areas, but were especially effective for those intensities producing larger response rates. Taken together with evidence from biochemical studies, our results suggest the presence of a functional cholinergic input into the inferior colliculus which acts to modulate acoustic processing.

Animals↗

PubMed1983

ABR measurements in the cat using a forward-masking paradigm.

Probe-elicited wave V amplitudes of the auditory brainstem response (ABR) were measured using a forward-masking paradigm. Subjects were anesthetized cats. For individual experiments, probe frequency and intensity were fixed and masker frequencies and intensities were varied. For each masker frequency, the extent to which the probe-elicited wave V amplitude was reduced by the preceding masker was plotted as a function of masker intensity. The rising segments of the masking functions were fitted with straight lines, using a least-squares procedure, to obtain estimates of their slopes. Masking grew most rapidly for masker frequencies below probe frequency, becoming progressively less steep as masker frequency increased. ABR tuning curves were constructed by using the linear fits to define the masker intensity that caused a 50% reduction in probe-elicited wave V amplitude. The shapes of these tuning curves were comparable to whole-nerve action potential (AP) tuning curves obtained under similar stimulus conditions. These results indicate that ABR amplitude measurements in a forward-masking paradigm can be used to estimate the growth of response to masking stimuli and frequency selectivity in a manner similar to AP amplitude measurements.

Action Potentials↗

PubMed1983

Suppression of auditory nerve responses. II. Suppression threshold and growth, iso-suppression contours.

Two-tone "synchrony suppression" was studied in responses of single auditory nerve fibers recorded from anesthetized cats. Suppression thresholds for suppressor tones set to a fiber's characteristic frequency (CF) were approximately equal to discharge rate thresholds for CF tones. Suppression thresholds above and below CF were usually lower than the corresponding discharge rate thresholds. However, at all frequencies studied (including CF), suppression thresholds were higher than the corresponding thresholds for discharge synchronization. Across fibers, rates of suppression growth for suppressors at CF were greatest in low-CF fibers and least in high-CF fibers, and there was a systematic decrease in suppression growth rate at CF as CF increased. Within fibers, rates of suppression growth above CF were typically less than at CF, and slopes were monotonically decreasing functions of frequency. Within-fiber rates of suppression growth below CF were variable, but they usually were greater than rates of growth at CF. Iso-suppression contours (frequencies and intensities producing criterion amounts of suppression) indicated that tones near CF are the most potent suppressors at near-threshold intensities, and that the frequency producing the most suppression usually shifts downward as the amount of suppression increases. These data support the notion that synchrony suppression arises primarily as a passive consequence of hair cell activation.

Acoustic Stimulation↗

PubMed1982

Auditory brainstem responses during systemic infusion of lidocaine.

Auditory brainstem-evoked responses (ABR) to clicks were recorded in unanesthetized restrained cats before, during, and after systemic intravenous infusion of lidocaine hydrochloride. The drug was infused continuously at varying rates. Lidocaine's major effect on ABR was to lengthen latent periods to all wave-form peaks in proportion with the infusion rate. The effect on latent periods was cumulative throughout the auditory brainstem, ie, all interpeak time intervals increased. Increases in ABR latencies were not due to reductions in effective stimulus intensity because lidocaine did not reduce ABR component amplitudes or increase thresholds. The effects of the drug were reversible. The data are consistent with the notion that lidocaine, directly or indirectly, works throughout the auditory brainstem to increase axonal and synaptic conduction times.

Animals↗

PubMed1981

Postnatal development of frequency and intensity sensitivity of neurons in the anteroventral cochlear nucleus of kittens.

Tuning curves and spike count-vs.-intensity functions were derived form tone-burst responses of single neurons of the anteroventral cochlear nucleus of kittens 4-45 days of age. During the first postnatal week tuning curves are relatively shallow and thresholds are high. With advancing age there is a progressive reduction in threshold and sharpness of tuning. Sharpening of tuning during the first several weeks postpartum seems to be due to a differential reduction in threshold between CF and frequencies below CF. Spike count-vs.-intensity functions are steep in young kittens as compared to adults. During the first few postnatal weeks the dynamic range and shapes of the functions take on the characteristics of adult AVCN neurons.

Action Potentials↗

PubMed1981

Suppression of auditory nerve responses I: temporal analysis, intensity effects and suppression contours.

Two-tone suppression was studied in response patterns of single auditory nerve fibers in anesthetized cats. Utilizing suppression of discharge synchronization in response to low- and moderate-frequency tones as an index, it was found that (a) suppression behaves in the same manner when the suppressor tone presented alone is strongly excitatory as when it is ineffective in altering discharge rate; (b) suppression exists throughout an auditory nerve fiber's response area; (c) for fixed-intensity suppressors, suppression is maximal at a fiber's characteristic frequency; and (d) suppression magnitude over a wide intensity range depends only upon the parameters of the suppressor tone and not of the tone being suppressed. The data are in general agreement with previously published reports of suppression behavior, and they support the concept that suppression is generated primarily as a result of interactions occurring within hair cells or in the subtectorial space.

Acoustics↗

PubMed1980

Coding of AM tones in the chinchilla auditory nerve: implications for the pitch of complex tones.

Responses to sinusoidally amplitude modulated (AM) tones were recorded in single auditory nerve fibers of anesthetized chinchillas. The tones chosen were of a class which, in humans, gives rise to a percept of low subjective pitch. It was found that, for high-frequency stimuli, neurons tuned to high frequencies signaled waveform envolope periodicity when the stimulus was of sufficient intensity. Neurons tuned to low frequencies responded to low-frequency AM tones in an orderly manner which ranged, as overall intensity was raised, from signaling all frequency components to signaling only the component to which the neuron was most sensitive. This result was interpreted to indicate the presence of two-tone suppression. Variation of modulation frequency and modulation depth produced response patterns which were generally predictable based on the relative effectiveness of each of the component frequencies in eliciting discharges. Neurons tuned to low frequencies did not respond at low and moderate intensities to higher-frequency AM tones, even though the subjective pitch of the tones corresponded to frequencies to which the neuron was sensitive. At high intensities, distortion products locked in-phase to the frequency of the subjective pitch were observed. Responses to a single AM tone recorded from different neurons in the same animal displayed considerable diversity in their responses. Response diversity was correlated with neuronal tuning characteristics, stimulus intensiry, and intrinsic factors such as suppression. Neurons retained stimulus finestructure information in the temporal patterns of their discharges as stimulus components were varied from a harmonic relationship to an inharmonic relationship. The data indicate that responses of auditory nerve fibers contain sufficient information for extraction of the subjective pitch of AM tones by a central auditory processor which operates on temporal features of the responses.

Acoustic Stimulation↗

PubMed1978

Two-tone suppression in auditory nerve of the cat: rate-intensity and temporal analyses.

Responses to two-tone stimuli were recorded from auditory-nerve fibers in anesthetized cats. One tone, the suppressor, was set at a frequency above characteristic frequency and was fixed in intensity. A second tone was set at an excitatory frequency and was varied in intensity. The suppressor tone, when set at a sufficient level, always reduced the response to the excitatory tone by an amount equivalent to a fixed number of decibels, regardless of the excitatory tone's intensity. Estimates of suppression magnitude were derived from shifts in rate-intensity function obtained when the suppressor tone was present relative to the functions obtained for the excitatory tone alone. When suppressor-tone intensity was increased, suppression magnitude likewise increased. When the two tones were increasingly separated in frequency, either by varying the excitor or by varying the suppressor, suppression magnitude decreased monotonically. Suppression behaved in the same manner regardless of whether suppresor tone was excitatory or nonexcitatory. When frequency separation was small enough and when both tones were above the neuron's characteristic frequency, responses synchronized to low-order combination tones could be elicited. These responses usually possessed different rate-intensity characteristics and resulted in estimates of suppression magnitude which were spuriously low. When frequency separation is normalized with regard to position of traveling wave maxima within the cochlear duct, the magnitude of two-tone suppression for a given suppressor-tone intensity is seen to be frequency independent.

Acoustic Stimulation↗

PubMed1978

Signs of functional maturation of peripheral auditory system in discharge patterns of neurons in anteroventral cochlear nucleus of kitten.

1. Responses to pure tones were recorded from single neurons in the anteroventral cochlear nucleus (AVCN) in kittens ranging in age from 4 to 45 days. Different response properties mature at different times after birth. 2. The shapes of response areas of AVCN neurons after the 1st postnatal week resemble those recorded in the AVCN and auditory nerve of the adult. During the 1st wk after birth the high-frequency portion of the response area is extended. Phase-locked responses to stimulus frequencies below about 600 Hz occur at this time. Phase vs. frequency measurements and shapes of response areas indicate that by the end of the 1st postnatal week the cochlear partition may be capable of supporting a traveling wave along most of its length. 3. Functional development proceeds through a second phase which lasts until the end of the 2nd or the beginning of the 3rd wk of life. During that time threshold, maximal discharge rate, and average first-spike latency achieve adult values. 4. Phase-locking to low-frequency tones, to the extent displayed by phase-sensitive neurons in the adult AVCN or auditory nerve, is achieved last, after the 3rd or 4th wk postpartum.

Age Factors↗

PubMed1977

Organization of auditory cortex in the owl monkey (Aotus trivirgatus).

The region of cerebral cortex in the owl monkey that is responsive to acoustic stimulation is located on the dorsal and lateral surfaces of the rostral half of the superior temporal gyrus. Systematic microelectrode mapping of this area has revealed multiple frequency representations. The boundaries of these fields determined electrophysiologically correlate with the architectural boundaries apparent in Nissl stained material. On the basis of combined cytoarchitectonic and electrophysiological maps we have divided auditory cortex into five fields. Two of them, the primary field (AI) and the field rostral to it (R) are somewhat similar architectonically and constitute the central core of auditory cortex. Each of these two fields has a complete and orderly representation of the audible frequency spectrum within it. Surrounding these fields is a belt of cortex in which units are generally less responsive to acoustic stimulation and the frequency organization is more complex than in AI or R. Electrophysiological and cytoarchitectonic evidence suggest that this belt is composed of at least three and possibly four separate auditory fields.

Acoustic Stimulation↗

PubMedDate not supplied

Prognostic validity of auditory brainstem evoked response screening in newborn infants.

The effectiveness of the auditory brainstem evoked response (ABR) test as a screening test for permanent hearing loss in neonates is examined in 32 published studies including 4,945 infants. Follow-up studies validating initial test failure were available for only 658 infants. Significant differences in methodology exist among these studies, and these differences may have affected their outcomes. Despite this problem, data from these studies were pooled, and they revealed that 16.5 per cent of neonates failed the initial ABR test. Of these, 5.1 per cent were later confirmed to be hearing-impaired or otherwise neurologically impaired. This implies that many of the false-positive results occurred in neonates who had transient disorders, such as conductive hearing loss or neurologic abnormalities, at the time of the screening test, or that the pass/fail criterion was too stringent. Lack of data on false-negative results or the rate of correct identification of normal infants makes it impossible to assess the sensitivity of the test accurately. Firm estimates of the prognostic validity of the neonatal ABR screening in identifying the impaired population can be achieved only when the actual impairment rate can be estimated, and when the distributions of ABR latencies and thresholds for both normal and impaired populations are known. These data could be obtained by following groups of high-risk infants longitudinally and by pooling raw ABR data from the normal and impaired populations that are collected using standardized procedures and similar equipment.

Audiometry↗

PubMedDate not supplied

Neurophysiological correlates of auditory maturation.

At the time of its birth, the auditory system of the cat is not completely developed. Anatomic maturity of the peripheral auditory system, ie, the cochlea, auditory nerve and cochlear nucleus, is attained at about two or three weeks of age. Physiological response properties of neural elements of the peripheral auditory system change radically during the first few weeks of life, with most measures of responsiveness to acoustic stimuli reaching adult status by the end of the third of fourth postnatal week. The physiological maturation of neural responses correlates well with the anatomic maturation of the auditory structures. At least one physiological response property, namely the ability of cochlear nucleus neurons to time their discharges in response to low-frequency tones, is not fully achieved until the sixth postnatal week or later. Although considerably less is known about the development of the central auditory system, it appears that it is in part dependent upon the maturation of more peripheral elements. Auditory evoked responses, for example, follow roughly the same developmental time course as do the majority of response properties of peripheral neurons. This implies that the central system is ready to function at birth, but that it must await the maturation of more peripheral elements before it can function properly. In contrast to that of the cat and other mammals, the auditory system of the human is relatively well advanced at birth. Certain aspects of brain development, such as dendritic aborization and axonal myelination, undergo considerable change postnatally. How these factors influence hearing is not known.

Animals↗