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PubMed1989

Comparative study of middle-latency responses and auditory brainstem responses in elderly subjects.

Auditory senescence is studied through an electrophysiological investigation of the brainstem, midbrain and thalamocortical tracts of auditory pathways. For this purpose, comparative electrophysiologic studies were carried out by recording middle-latency responses (MLR) and auditory brainstem responses (ABR) in elderly subjects in the 7th-8th and 9th decades of life and in a control group consisting of young subjects in the 3rd decade of life. All these subjects were free of otological, neurological, vascular and metabolic pathologic states. In elderly subjects, the statistical analysis of the results, especially of MLRs, showed a deterioration in the progression of information from the periphery to the center due to changes in morphology, increased latency, reduced amplitude and poorer reproducibility. Furthermore, a different behavior was noticed in females versus males. Indeed, the shorter latency of evoked potentials in the female control group was remarkably reduced in the elderly subjects. MLRs scan a wide tract of auditory pathways and give evident results even by adopting a juxtaliminal stimulation; therefore, they are a more complete and sensitive test than ABRs for the study of involutional processes.

Adult↗
PubMed2001

Acute effect of nicotine on non-smokers: I. OAEs and ABRs.

This paper is the first in a series of three investigating the role of cholinergic mechanisms in the auditory system by assessing the acute effects of nicotine, an acetylcholinomimetic drug, on aggregate responses within the auditory pathway. In a single-blind procedure, auditory responses were obtained from 20 normal-hearing, non-smokers (10 male) under two conditions (nicotine, placebo). After the drug session, plasma tests revealed a subject's nicotine concentration. The effects of nicotine on early, exogenous responses of the auditory system (otoacoustic emissions and auditory brainstem potentials) are described in this first paper. Results indicated that transdermal administration of nicotine to non-smokers does not significantly affect cochlear activity but does acutely affect the neural transmission of acoustic information. Overall, otoacoustic emissions were unaffected by transdermal nicotine while wave I of the auditory brainstem response was significantly increased in latency and decreased in amplitude.

Administration, Cutaneous↗
PubMed2002

The representation of peripheral neural activity in the middle-latency evoked field of primary auditory cortex in humans(1).

Short sweeps with increasing instantaneous frequency (up-chirps) designed to compensate for the propagation delay along the human cochlea enhance the magnitude of wave V of the auditory brainstem responses, while time reversed sweeps (down-chirps) reduce the magnitude of wave V [Dau, T., Wegner, O., Mellert, V., Kollmeier, B., J. Acoust. Soc. Am. 107 (2000) 1530-1540]. This effect is due to synchronisation of frequency channels along the basilar membrane and it indicates that cochlear phase delays are preserved up to the input of the inferior colliculus. The present magnetoencephalography study was designed to investigate the influence of peripheral synchronisation on the activation in primary auditory cortex. Spatio-temporal source analysis of middle-latency auditory evoked fields (MAEFs) elicited by clicks and up- and down-chirps showed that up-chirps elicited significantly larger MAEF responses compared to clicks or down-chirps. Both N19m-P30m magnitude and its latency are influenced by peripheral cross-channel phase effects. Furthermore, deconvolution of the empirical source waveforms with spike probability functions simulated with a cochlear model indicated that the source waves for all stimulus conditions could be explained with the same unit-response function, i.e. a far field recorded cortical response of a very small cell assembly along the medio-lateral axis of Heschl's gyrus that receives input from a small number of excitatory fibres. The conclusion is that (i) phase delays between channels in the auditory pathway are preserved up to primary auditory cortex, and (ii) MAEFs can be described by a convolution of a unit-response function with the summary neural activity pattern of the auditory nerve.

Acoustic Stimulation↗
PubMed2001

Bilirubin and the auditory system.

The auditory system is highly sensitive to bilirubin toxicity. Damage to the auditory nervous system includes auditory neuropathy or auditory dyssynchrony and auditory processing problems which may occur with or without deafness, hearing loss. Auditory dysfunction may occur in children with or without other signs of classical kernicterus. Bilirubin selectively damages the brainstem auditory nuclei, and may also damage the auditory nerve and spiral ganglion containing cell bodies of primary auditory neurons. The inner ear, thalamic and cortical auditory pathways appear to be spared. Noninvasive auditory neurophysiological tests such as the auditory brainstem response (ABR) or brainstem auditory response (BAER) play an important role in the early detection of bilirubin-induced auditory and central nervous system dysfunction in the neonate.

Animals↗
PubMed1989

Auditory neural activity evoked by pure-tone stimulation as a function of intensity.

The 2-deoxyglucose (2-DG) autoradiographic technique was employed to map activation of the central auditory pathway in the mongolian gerbil during stimulation with a 3.0 kHz tone at several intensities. In most auditory nuclei, the tone produced restricted areas in which 2-DG uptake was markedly higher than that of adjacent tissue, at locations consistent with the known tonotopic organization of the structure. The size of these regions changed relatively little with increasing stimulus intensity from 25 to 65 dB SPL (re 0.0002 dyne/cm2). At higher intensities, evoked uptake spreads into locations which represent frequencies above 3.0 kHz. In the inferior colliculus, relative 2-DG uptake decreased with increasing stimulus intensity in bands on either side of the 3.0 kHz region. These bands of reduced uptake became wider with increasing stimulus intensity from 25 to 85 dB SPL. The optical densities of auditory structures were normalized by the density of non-auditory white matter to derive optical density ratios. In the cochlear nuclei, optical density ratios in the 3.0 kHz region increased monotonically with increasing stimulus intensity, to a plateau at 45 dB SPL. In higher auditory nuclei, relative 2-DG uptake increased to a peak at 45 dB SPL and then declined at higher intensities.

Action Potentials↗
PubMed2003

Boosting GABA improves impaired auditory temporal resolution in the gerbil.

Elderly humans often not only experience peripheral hearing loss but also suffer from more central deficits in temporal auditory processing affecting speech perception. Impaired auditory temporal resolution has also been observed in old rodents. Other studies have demonstrated a reduction of GABAergic function in the auditory pathway of old animals. Here we test the hypothesis that deficits in the GABAergic system affect central auditory processing. Our data suggests that pharmacological augmentation of the GABAergic system ameliorates impaired temporal auditory processing in the gerbil and might be a strategy for the treatment of at least some forms of central hearing loss in humans.

Acoustic Stimulation↗
PubMed1986

Development of auditory-evoked potentials in the cat. II. Wave latencies.

Brain stem and forebrain auditory-evoked potentials were studied parametrically during the first 90 postnatal days in unanesthetized kittens using tonal and click stimuli. This paper describes changes that occur in transmission time through the auditory pathway during development by analyses of the maturational time courses of latencies associated with waves of both auditory brain stem responses (ABR's) and late-occurring auditory-evoked potentials (AER's), recorded subdermally from the vertex. In response to click stimuli, ABR latencies were found to decay rapidly early in postnatal life and more slowly after the third postnatal week. Those trends were modeled as a two-stage sequential process, with a linear stage occurring between 7 and 18 postnatal days followed by an exponential stage during which adult latencies were achieved. AER latencies changes during development were less complicated, and followed a single-stage exponential time course. When threshold influences were taken into account--that is, when data were adjusted so that sensation level (SL) was constant across age--the latency-maturation curves associated with all ABR waves were adequately described by a single exponential, and latencies recorded from young animals were substantially shorter than latencies associated with the same aged animals when analyses were carried out with constant sound-pressure level (SPL) stimuli across age. In addition, the difference function, generated when isoasymptotic SPL and SL latency versus age functions were subtracted from one another, was also represented by an exponential curve, suggesting that at least two processes underlie the latency decay that occurs during postnatal development. Evoked responses to tonal stimuli throughout development were consistent with the basoapical developmental gradient that is observed anatomically.

Aging↗
PubMedDate not supplied

[The effect of neck rotation on auditory evoked brainstem potentials in patients with degenerative cervical spine changes].

Using the neck rotation test during recording of auditory brainstem evoked potentials the authors examined 60 subjects aged 16-60 years, including 20 healthy ones and 40 with cervical spondylarthrosis. The Neuromatic 2000 C Dantec device was used. Half the patients with cervical spine changes had also receptive hearing damage of low degree. The study demonstrated that neck rotation affected the latency time of the analysed waves I and II. The time was significantly prolonged in the patients with spondylarthrosis. The authors believe that simultaneous prolongation of the mean latency between waves I-III suggests worse compensation of circulation in patients, especially in the initial part of the auditory pathway. The authors think that the neck rotation test could be used in the study of brainstem auditory evoked potentials as a challenge test.

Acoustic Stimulation↗
PubMed1999

Auditory brainstem responses, electrocochleograms, and cochlear microphonics in the myelin deficient mutant hamster 'bt'.

Electrophysiological studies of the auditory pathway were performed on the mutant hamster 'bt' which is known to have myelin deficiencies in the central nervous system. Auditory brainstem responses (ABRs), electrocochleograms (EcochGs), and cochlear microphonics (CMs) were recorded. ABRs in 'bt' demonstrated markedly transformed waveforms with significantly prolonged latencies. EcochG in 'bt' showed significantly prolonged N1 latencies of the compound action potentials (CAPs) while 'bt' showed normal CMs. The myelin deficient mutant hamster 'bt' may have myelin deficiencies not only in the brainstem auditory pathway but also in the cochlear nerve.

Animals↗
PubMed1993

The effect of sound level, temperature and dehydration on the brainstem auditory evoked potential in anuran amphibians.

Brainstem auditory evoked potentials (BAEPs) were used to examine the effects of sound level, temperature, and dehydration on the auditory pathway of three species of anuran amphibians: Rana pipiens, Bufo americanus and B. terrestris. BAEP latency, amplitude and a measure of threshold were determined for all stimulus and test conditions. Threshold values obtained with this technique were similar to other neural measures of threshold in anurans, and were stable for repeated measures within 12 h and over three days. Transient changes in temperature caused non-linear changes in BAEP threshold and latency. Above 20 degrees C small threshold shifts were elicited, while below 20 degrees C we observed rapid deterioration of threshold. Animals acclimated to a cold temperature (14 degrees C) were acoustically less sensitive than warm (21 degrees C) animals, even when both groups were tested at colder temperatures. Because peripheral components of the BAEP were most affected by both transient and acclimation (longer term) cooling and warming, the sensory epithelium appears to be the most temperature-sensitive component of the auditory pathway. Dehydrated frogs showed no auditory dysfunction until a critical level of dehydration was reached. More dehydration-resistant species (B. terrestris and B. americanus) were less susceptible to BAEP degradation near their critical dehydration level.

Acoustic Stimulation↗
PubMed1990

Early development of brainstem auditory evoked potentials in Down's syndrome.

Early development of brainstem auditory pathway was studied in 14 children with Down's syndrome (age range from 1 month to 3 years). The brainstem auditory evoked potentials (BAEP) during infancy was characterized by elevated threshold and poorly differentiated wave I. All children within 2 years had elevated threshold in one or both ears, suggesting a high incidence of peripheral hearing deficits. Follow-up tests showed that as age increased up to 3 years the elevated threshold gradually decreased and the differentiation of wave I improved. The I-V interpeak interval was slightly shorter and the amplitude of wave V was smaller than the normal controls, which existed continuously during follow-up studies. Our findings suggest that the development of peripheral hearing is delayed, although persistent hearing deficits cannot be excluded, and the functioning and development of the brainstem auditory pathway may also be abnormal in Down's syndrome children.

Aging↗
PubMed2004

Long-term effects of carboplatin brainstem infusions on hearing thresholds in monkeys.

OBJECTIVE: To isolate the central auditory neurotoxicity of carboplatin from its well-established ototoxic effects. DESIGN: The "best-case scenario" of targeted drug delivery to brain cancer was simulated by infusing carboplatin directly into the brainstem of cynomolgus monkeys with chronically implanted catheters. Because this manner of drug administration produced low levels of carboplatin in spinal fluid and blood, it was assumed that resulting deficits were dictated by the central auditory neurotoxicity of platinum compounds and not peripheral ototoxic effects. The magnitude of this hearing loss was estimated by comparing the auditory brainstem response thresholds of treated monkeys with results from normal controls. SUBJECTS: Six adult male cynomolgus monkeys (Macaca fascicularis) weighing 4 to 6 kg (3 received carboplatin treatment and 3 served as normal controls). INTERVENTION: Brainstem infusions of carboplatin. RESULTS: The average threshold of carboplatin-treated monkeys was elevated 8.8 dB (SD = 7.3 dB) relative to normal controls 6 months after the termination of drug delivery and increased to 10.7 dB with less variation between subjects (SD = 5.6 dB) 1 year after drug treatment. Although small in magnitude, the hearing loss was statistically significant (P<.05). CONCLUSIONS: Brainstem infusions of carboplatin induced some degree of hearing impairment in all treated monkeys. These threshold elevations were modest compared with the ototoxic effects that have been reported after systemic doses of carboplatin. Our findings suggest that the neurotoxic sensitivity of cochlear hair cells is not shared by neurons in the central auditory pathways. As a result, methods for reducing the ototoxic effects of chemotherapy remain a viable strategy for preserving auditory function in patients with brain cancer.

Animals↗
PubMed1993

Function-based modeling of binaural processing: level and time cues.

From theoretical considerations, function-based modeling predicts the input-output characteristics of a neural system intended to perform a signal processing task within a sensory system. The sensory task under study here is the time- and level-based localization of a high-frequency, possibly amplitude-modulated, sound source in the horizontal plane. The stimulus is assumed to be represented by each ear's primary-like discharge pattern. An optimal system that extracts azimuthal angle from these discharge patterns, which represent acoustic time and level localization cues, has been derived. This system can be described as the maximization of a sum of three subsystems' outputs. The stimulus cues employed by these systems are interaural level difference for the level-based subsystem, the interaural onset-time difference for the time-based subsystem, and the interaural envelope-phase difference for the phase-based subsystem. The system encompassing all these cues is shown to trade-off the level, time, and envelope-phase cues depending upon the time since stimulus onset, the observation time, and the incident signal's level. How this system might correspond to known structures in the lower auditory pathway is described.

Acoustic Stimulation↗
PubMed1999

Auditory deprivation of the central auditory system resulting from selective inner hair cell loss: animal model of auditory neuropathy.

Auditory neuropathy is often characterized by normal thresholds, present otoacoustic emissions, poor speech discrimination, absent acoustic reflexes, absent or abnormal auditory brainstem response waveform, but normal late cortical potential. This paper describes an animal model that has many characteristics of auditory neuropathy. Chinchillas can be deprived of a significant portion of the neural inputs to the central auditory system by administering carboplatin, an antineoplastic agent that selectively destroys inner hair cells (IHCs) and type I auditory nerve fibers. Selective IHC loss has no effect on distortion product otoacoustic emissions or the cochlear microphonic potential, implying normal outer hair cell function. However, selective IHC loss causes the amplitude of the compound action potential to decrease in proportion to the degree of IHC loss. However, the threshold of the CAP shows little increase with mild to moderate IHC loss. Acoustically responsive auditory nerve fibers in ears with mild to moderate IHC loss have normal thresholds and tuning curves with narrowly tuned tips. Although the central auditory pathway is deprived of much of its sensory inputs, the amplitude of the local field potential in the auditory cortex was normal or enhanced, while those from the inferior colliculus were slightly reduced. The results are related to those of a patient with auditory neuropathy.

Animals↗
PubMed1997

Periodicity coding in the primary auditory cortex of the Mongolian gerbil (Meriones unguiculatus): two different coding strategies for pitch and rhythm?

Periodic envelope or amplitude modulations (AM) with periodicities up to several thousand Hertz are characteristic for many natural sounds. Throughout the auditory pathway, signal periodicity is evident in neuronal discharges phase-locked to the envelope. In contrast to lower levels of the auditory pathway, cortical neurons do not phase-lock to periodicities above about 100 Hz. Therefore, we investigated alternative coding strategies for high envelope periodicities at the cortical level. Neuronal responses in the primary auditory cortex (AI) of gerbils to tones and AM were analysed. Two groups of stimuli were tested: (1) AM with a carrier frequency set to the unit's best frequency evoked phase-locked responses which were confined to low modulation frequencies (fms) up to about 100 Hz, and (2) AM with a spectrum completely outside the unit's frequency-response range evoked completely different responses that never showed phase-locking but a rate-tuning to high fms (50 to about 3000 Hz). In contrast to the phase-locked responses, the best fms determined from these latter responses appeared to be topographically distributed, reflecting a periodotopic organization in the AI. Implications of these results for the cortical representation of the perceptual qualities rhythm, roughness and pitch are discussed.

Acoustic Stimulation↗
PubMed2004

Effects of salicylate on spontaneous activity in inferior colliculus brain slices.

Salicylate is a well-known substance to produce reversible tinnitus in humans and animals. It has been shown that systemic application of salicylate changes the neuronal spontaneous activity in several parts of the auditory pathway. Salicylate has also a direct influence on cochlear outer hair cell electromotility. The effects observed in the central auditory structures in vivo could therefore be based upon the change in afferent cochlear input to the auditory system and in addition by a direct action of salicylate on neurons within the auditory pathway. The present study investigated the direct effect of salicylate application on the spontaneous activity of mouse inferior colliculus neurons in brain slices. Out of 92 neurons, 87% responded statistically significantly to the superfusate by changing their firing rates. 70% increased and 17% decreased their firing rates, respectively. Salicylate superfusion induced a general increase of electrophysiological activity within the inferior colliculus brain slice preparation which was similar to those obtained during systemic application of salicylate. The results suggest that the salicylate sensitivity of inferior colliculus neurons can modulate to a great extent the salicylate-induced generation of tinnitus.

Action Potentials↗
PubMedDate not supplied

Electrophysiological studies of the auditory system.

Electrophysiological measures of cochlear function can be obtained using the techniques of transtympanic electrode and surface electrocochleography. These provide measures of the basic parameters of the cochlear microphonic, cochlear nerve and auditory brainstem nuclei action potentials, which enable the functional mechanisms of the cochlea and auditory pathway to be defined for normally hearing subjects and, by comparison, give diagnostic information about the pathologies involved in auditory disorders. Data are presented on the values and variability of the responses obtained from normally hearing subjects. The comparative values of each technique in estimating auditory threshold, cochlear function and in evaluating neurological conditions are discussed using data from clinical patients.

Acoustic Stimulation↗
PubMed2000

Response properties of neurons in the central nucleus and external and dorsal cortices of the inferior colliculus in guinea pig.

The inferior colliculus (IC) represents a mid-brain structure which integrates information from many ascending auditory pathways, descending corticotectal projections and intercollicular pathways. The processing of information is different in each of the three main subdivisions of the IC--the central nucleus (CNIC), the dorsal cortex (DCIC) and the external cortex (ECIC)--which may be distinguished morphologically as well as by different inputs and outputs. To assess the differences in information processing we compared the response properties of single neurons in individual subnuclei of the IC in anesthetized guinea pigs. In comparison with DCIC and ECIC neurons, the CNIC neurons as a group were characterized by a sharper frequency tuning (as expressed by Q10 values), a lower average threshold, a shorter average first-spike latency of response to tones at the characteristic frequency (CF), a higher occurrence of non-monotonic rate/level functions and a higher rate of spontaneous activity. CNIC neurons and DCIC neurons reacted to tones at the CF more frequently by a sustained type of response than did ECIC neurons. The difference between the parameters of DCIC neuronal activity and ECIC neuronal activity was found to be smaller. The frequency tuning (expressed in Q10 values), spontaneous activity and dominance of monotonic rate/level functions were very similar in both structures; ECIC neurons expressed a higher average threshold and a shorter average first-spike latency than did DCIC neurons. Responsiveness expressed as the average maximal firing rate to tones at the CF was significantly higher in the CNIC than in the ECIC. The results give additional support to the idea that the CNIC is a part of a fast, frequency-tuned, low threshold and intensity-sensitive ascending pathway, whereas the other two subdivisions are involved in additional processing of information that involves feedback loops and polysensory pathways.

Acoustic Stimulation↗