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PubMed2001

Embryonic development of the central projection of auditory afferents (Schistocerca gregaria, Orthoptera, Insecta).

The auditory system of Schistocerca gregaria is a well investigated sensory network in the adult grasshopper. Here we present a first study on the embryonic development of this neuronal network. Focussing on the auditory receptor cells we show that they differentiate axonal processes at around 45% of embryonic development. These axons fasciculate with the intersegmental nerve and enter the central nervous system by 45-50% of development. First collaterals sprout into the major arborization area, the frontal auditory projection area of the metathoracic ganglion by 60%. This projection increases in density until an adult-like morphology is established by 90% of development. Furthermore, by the end of embryogenesis all three types of receptor fiber projections can be distinguished. This development is independent of a hearing ability, which develops much later during postembryonic life. The auditory projection co-develops with the fusion of neuromeres to the metathoracic ganglion, the formation of the target neuropile areas and the expression of the synapse associated molecule synapsin. Fasciclin I and Lachesin, both potential axon-guidance molecules, are expressed strongly on both, peripheral and central auditory pathways and, although much weaker, within the synaptic target area.

Animals↗

PubMed1991

Left-ear extinction in patients with MRI periventricular lesions.

A dichotic listening test was administered to 22 elderly vascular patients with periventricular white matter changes on magnetic resonance imaging. We found four patients with a moderate-to-severe extent of these changes who showed a pattern of left-ear extinction. These findings suggest that periventricular lesions in patients with vascular risk factors may be associated with a functional disconnection of the interhemispheric auditory pathways.

Aged↗

PubMed1985

Spectral complexity and infant attention.

In two experiments, infants selectively attended to auditory stimuli that presented an increasingly complex spectral structure. Using 2- and 4-month-olds as subjects, the first study demonstrated this selectivity in comparison to the rate of acoustic change. The second study demonstrated the increased attention of 4-month-olds in response to an increasingly complex structure. Results are discussed with respect to the neural activity produced by these stimuli along the auditory pathway, and an analogy to the literature on visual attention is drawn.

Acoustic Stimulation↗

PubMed2004

Responses of dorsal cochlear nucleus neurons to signals in the presence of modulated maskers.

The detection of a signal in noise is enhanced when the masking noise is coherently modulated over a wide range of frequencies. This phenomenon, known as comodulation masking release (CMR), has been attributed to across-channel processing; however, the relative contribution of different stages in the auditory system to such across-channel processing is unknown. It has been hypothesized that wideband or lateral inhibition may underlie a physiological correlate of CMR. To further test this hypothesis, we have measured the responses of single units from the dorsal cochlear nucleus in which wideband inhibition is particularly pronounced. Using a sinusoidally amplitude-modulated tone at the best frequency of each unit as a masker, a pure-tone signal was added in the dips of the masker modulation. Flanking bands (FBs, also amplitude-modulated pure tones) were positioned to fall within the inhibitory sidebands of the receptive field of the unit. The FBs were either in phase (comodulated) or out of phase (codeviant) with the on-frequency masker. For the majority of units, the addition of the comodulated FBs produced a strong reduction in the response to the masker modulation, making the signal more salient in the post stimulus time histograms. The change in spike rate in response to the signal between the masker and signal-plus-masker conditions was greatest for the comodulated condition for 29 of 45 units. These results are consistent with the hypothesis that wideband inhibition may play a role in across-channel processing at an early stage in the auditory pathway.

Acoustic Stimulation↗

PubMed2003

Effects of songs and calls on ZENK expression in the auditory telencephalon of field- and isolate-reared black capped chickadees.

We examined the effects of hearing two different conspecific vocalizations on expression of the immediate-early gene ZENK in the caudomedial neostriatum (NCM) and the caudomedial portion of the ventral hyperstriatum (cmHV) in male and female black-capped chickadees (Poecile atricapilla). Both the fee-bee song and the chick-a-dee call induced Zenk protein expression in NCM and in cmHV, however, patterns of expression to songs and calls varied across brain region. In the dorsal region of NCM, fee-bee songs induced more Zenk expression than chick-a-dee calls. In ventral NCM and cmHV, Zenk expression did not differ between songs and calls. We found that sex of the listener also affected Zenk expression: there was more robust ZENK response in males than in females. Finally, we compared field- and isolate-reared chickadees and found similar Zenk expression to fee-bee song in each group. These findings indicated that the type of conspecific vocalization, as well as the sex of the listener, appear to modulate IEG expression in the songbird ascending auditory pathway.

Acoustic Stimulation↗

PubMed1992

Postnatal shift of tonotopic organization in the chick auditory cortex analogue.

The existence of an ontogenetic shift of tonotopic organization throughout the auditory pathway concomitant with cochlea maturation is a matter of controversy. Using the 2-deoxyglucose method we demonstrate here for the first time the shift phenomenon in an auditory forebrain structure, field L, the auditory cortex analogue of the chick. During the first postnatal month isofrequency contours move to positions where, in younger chicks, lower frequencies (up to half an octave) are represented. This developmentally changing place code of sound frequencies at the forebrain level is similar to the one previously reported for brain stem auditory nuclei. It raises the question of constancy of frequency-related pitch perception during development and may be a complication of early auditory learning and memory.

Acoustic Stimulation↗

PubMed2006

Brainstem auditory evoked response in neonatal neurology.

Over the last three decades, the brainstem auditory evoked response (BAER) has been used to assess functional integrity and development of the auditory system and the brain in conditions that affect the brainstem auditory pathway. As a non-invasive objective test, BAER is particularly suitable in very young or sick infants. It is the major tool to detect hearing impairment in high-risk infants, and a component in universal hearing screening. BAER is also a valuable adjunct to detect neurological impairment in many developmental disorders and functional abnormalities in a range of neurological diseases. The maximum length sequence (MLS) technique has recently been incorporated into neonatal BAER study. Recent results indicate that the MLS has the potential to improve the diagnostic value of BAER in some clinical situations, although the wider utility of this relative new technique remains to be further explored.

Auditory Pathways↗

PubMed1991

Auditory properties of the superior colliculus in the horseshoe bat, Rhinolophus rouxi.

Auditory response properties were studied in the superior colliculus (SC) of the echolocating horseshoe bat Rhinolophus rouxi, a long CF-FM bat, by the use of stationary, dichotic stimuli. The most striking finding in the horseshoe bat was an enormous overrepresentation of neurons with best frequencies in the range of the constant frequency component of the species specific echolocation call (72% of the auditory neurons). These neurons had response thresholds as low as 0 dB SPL and were narrowly tuned with Q10dB--values up to 400, just as in the nuclei of the primary auditory pathway in this species. This overrepresentation may suggest the importance of the superior colliculus in the context of echolocation behavior. While noise stimuli were not particularly effective, other auditory response properties were similar to those described in other mammals. 65% of the SC neurons in the horseshoe bat responded only to monaural stimulation of one ear, primarily the contralateral one. 32% of the neurons received monaural input from both ears. The proportion of neurons responsive to ipsilateral stimulation (41%) was rather high. Mean response latency was 8.9 ms for contralateral stimulation. A tonotopic organization is lacking, but high-frequency neurons are less frequent in rostral SC.

Acoustic Stimulation↗

PubMed1979

Some neurochemical studies on auditory regions of mouse brain.

The mouse brain auditory pathway has been dissected into five regions: geniculate bodies, posterior colliculi, superior olives, cochlear nuclei, and cochleas. The following analyses were made in these regions and in the auditory cortex: protein, glutamate, gamma-aminobutyrate, taurine, choline acetyltransferase, and glutamate decarboxylase. Taurine levels (nmol . mg of protein-) were highest in cortex (93) and geniculate bodies (60) and lowest in the cochlear nuclei (27) and cochleas (29). Concentrations of gamma-aminobutyrate (same units) were highest in the geniculate bodies (28), low in the superior olives and cochlear nuclei (9 to 10), and undetectable in the cochleas. The distribution of glutamate decarboxylase activity reflected that of gamma-aminobutyrate. The activities of choline acetyltransferase (nmol . of acetylcholine synthesized . h . -1 mg of protein-1) were highest in the superior olives (60) and low in the cochleas (3). These results are interpreted as biocyemical support for previous physiological and pharmacological identification of the olivo-cochlear bundle as cholinergic and the cochlear-nucleus neurones as non-cholinergic. The results also provide further evidence for a role of GABA in the posterior colliculi, but not in the cochleas.

Animals↗

PubMed1986

Pure-tone audiometry of patients with auditory brainstem response abnormalities.

To determine the pure-tone thresholds of patients with brainstem disorders, pure-tone audiometry was done on 22 patients with partial auditory brainstem response wave disappearance (including wave I response, wave I-III response, and wave I-IV response). This group of patients was selected since partial wave disappearance indicates pathology of the auditory nerve and/or the brainstem auditory pathway. The pure-tone threshold of these patients was essentially normal or very mildly impaired, except for patients with an acoustic tumor or an other cerebellopontine angle tumor.

Audiometry↗

PubMed1985

[Electrophysiologic studies on the course of the adaptation phase following noise stress].

It was the aim of this study to settle the problem whether the post-stimulatory pattern of the extent of excitation (amplitude, latency) registered with the cortical evoked potentials can be verified in the recovery phase via leads from the brain stem region and cochlea. In this context electrophysiological measurements with human and animal material were performed. After a five-minute stimulation with a wide-band noise of various intensity we examined in the post-stimulation phase the specific stimulus pattern of the evoked potentials during an interval of 5 minutes with a resolution of 5 sec. We determined the change in response patterns of evoked potentials. Finally, the relevance of the results with regard to various nuclei of the auditory pathway is compared with corresponding electrophysiological measurements of the cochlear microphonics potentials, the VIII nerve compound action potential, and evoked potentials of different units of the brain stem and brain.

Animals↗

PubMed1996

Brainstem auditory evoked responses in primary hypertension.

Brainstem auditory evoked potential responses (BAEPs) were recorded from CZ-A1 and CZ-A2 scalp regions in 23 hypertensive and 14 normotensive subjects. Hypertension was graded depending upon the extent of raised blood pressure. BAEPs in patients of grade I and II hypertension did not show any change when compared to normotensive subjects. However, grade III hypertensive case showed significant prolongation of absolute peak latencies of wave I, II, V and interpeak latency of wave III-V indicating involvement of brainstem auditory pathways. Multiple regression analysis revealed significant correlation of rise in systolic and diastolic blood pressure with absolute peak latencies of BAEPs in hypertensive patients.

Auditory Pathways↗

PubMed1994

Discrimination of speech-like contrasts in the auditory thalamus and cortex.

The neurophysiologic discrimination of acoustic contrasts was investigated as reflected by the mismatch negativity (MMN) response. Evoked responses were recorded from guinea pig thalamus (medial geniculate nucleus) and epidural surface in response to synthesized speech contrasts /ga/-/da/ and /ba/-/wa/. From the caudomedial portion of the medial geniculate nucleus, /ba/-/wa/ elicited a strong mismatch response, whereas /ga/-/da/ did not. Neither stimulus contrast elicited an MMN from the ventral, or primary, portion of medial geniculate. Both stimulus contrasts elicited an MMN from the midline surface. Neither contrast elicited an MMN from the surface over the temporal lobe. Results indicate a hierarchy of processing of the spectrotemporal changes which characterize formant transitions. Also, results indicate that the nonprimary portions of the auditory pathway contribute substantially to the MMN.

Animals↗

PubMed1994

Auditory brainstem responses in cats with Chediak-Higashi syndrome.

Auditory brainstem responses ABRs were recorded in cats with Chediak-Higashi syndrome using monaural stimulation. The components appearing between 1 and 3 ms after stimulus onset were greatly attenuated in the ABRs recorded using a reference contralateral to the stimulated ear. These data suggest that abnormalities exist in the brainstem auditory pathway in the region of the superior olivary complex in cats with Chediak-Higashi syndrome.

Albinism↗

PubMed1994

Age-related changes in brainstem auditory neurotransmitters: measures of GABA and acetylcholine function.

This study was designed to determine if there are age-related alterations in the bio-synthetic enzyme glutamic acid decarboxylase (GAD), the degradative enzyme GABA-transaminase (GABA-T), and the uptake system for GABA in the central nucleus of the inferior colliculus (CIC), the cochlear nucleus (CN), and/or nuclei of the lateral lemniscus (NLL) of Fischer-344 rats. For purposes of comparison, the cholinergic neuronal system was studied in parallel in young adult (3-7 months), mature (15-17 months) and aged (24-26 months) rats. In young adults GAD activity was highest in the CIC (219 nmol/mg protein/h; N = 5), intermediate in NLL (82 nmol/mg protein/h), and lowest in CN (34 nmol/mg protein/h). Choline acetyltransferase (ChAT) activity was highest in NLL and CN, and approximately 35-40% lower in CIC. A more uniform pattern was observed with GABA-T activity. Reductions in GAD activity were seen in the CIC of mature (-31%) and aged (-30%) rats that were not graded with age when compared to young adult, P < 0.05 (N = 5). This effect was regionally selective, since the CN did not show any loss of GAD or ChAT activity. The neurotransmitter selectivity of this deficit in CIC is supported by the non-parallel changes in ChAT activity (-22%, aged vs. mature, P < 0.05) that occurred after the changes in GAD activity. In contrast to the loss of GABAergic biosynthetic capacity in aged CIC, high affinity uptake processes (Kd and Vmax) for 14C-GABA and 3H-D-aspartate were not significantly altered (P > 0.05). Similar to the CIC, the NLL showed remarkable age-related deficits, but these deficits were more substantial for the cholinergic system (ChAT activity: -56% aged vs. young adult, P < 0.05; GAD activity: -35% aged vs. mature). None of the areas examined showed a significant loss of GABA-T activity with aging. These data suggest: 1) Age-related loss of GABA-mediated inhibition in the CIC of Fischer-344 rats is not attributable to changes in uptake or degradation of GABA, but may be related loss of biosynthetic capacity (i.e. activity or quantity) of the GAD present; 2) processing centers of the central auditory pathway (i.e. CIC and NLL), but not necessarily primary (i.e. CN) integrative nuclei, demonstrate selective, age-related neurochemical deficits; and 3) age-related neurochemical changes in central auditory structures may contribute substantially to the abnormal perception of signals in noise and loss of speech discrimination observed in neural presbycusis.

4-Aminobutyrate Transaminase↗

PubMed1991

The effects of long and short term profound deafness on the responses of inferior colliculus to electrical stimulation of the cochlea.

It is widely assumed that adequate sensory stimulation is important for the proper post-natal development of the central nervous system, particularly during certain critical or sensitive periods in development. To examine the functional effects of long-term profound deafness on the development of the auditory system, the response properties of neurons in the inferior colliculus (IC) to electrical stimulation of the cochlea were investigated in chinchillas (i) deaf from birth and (ii) deafened as adults. In animals deafened as adults there was a 50% reduction in the number of neurons activated by electrical stimulation of the cochlea, compared with studies in normal controls. In contrast, very few or no responses could be elicited from IC of animals made deaf from birth. The results imply that lack of neural activity in the ascending auditory pathways from an early stage of development results in an inactivation of IC neurons. It is not clear if such inactivity is temporary or permanent.

Amikacin↗

PubMed1999

Lesion site in sudden deafness: study with electrocochleography and transiently evoked otoacoustic emission.

We examined electrocochleogram (ECochG) and transiently evoked otoacoustic emission (TEOAE) on five cases of sudden sensorineural hearing loss which had no abnormalities detected on diagnostic imagings and showed complete recovery of hearing. At the initial examination, three cases showed a broadened wave 1 with prolonged latency in the auditory brainstem response (ABR) at 90 dB HL. The ECochG AP showed a broad waveform, low amplitude, and high threshold. CM threshold, although increased, was relatively well preserved compared with hearing threshold measured with conventional pure-tone audiometry. The thresholds in TEOAE examination were similar to those for CM and preserved better when compared with pure-tone audiometric thresholds. These findings suggest that the location of the disorder in these three cases involved not only the cochlea but also the retrocochlear auditory pathway. The other two cases showed normal ABR waveforms at 90 dB HL at the initial examinations. ECochG examination showed that a normal AP in one case and a smaller amplitude AP, an elevated threshold, and normal waveform of AP in the other ear. CM thresholds coincided with the conventional audiometry thresholds. These findings suggest that hearing loss in these two cases involved primarily the sensory hair cells.

Acoustic Stimulation↗

PubMedDate not supplied

Electrophysiological (BAEPs) changes in subacute sclerosing panencephalitis.

Over a period of time, the authors have studied a case of subacute sclerosing panencephalitis (SSPE), by means of brainstem auditory evoked potentials (BAEPs). The observed abnormalities of the conduction time along the early auditory pathways appeared to be related to the clinical picture; in fact, during periods of transitory clinical improvement these abnormalities were less evident. In addition, the encountered electrophysiological alterations consisted of a marked pathologic increase in the III-V interpeak latencies. The authors suggest that the BAEPs findings in their case could have been influenced by either unfavourable endogenous conditions (edema, electrolyte changes, etc.) or CNS segmental lesions due to focal viral distribution.

Adolescent↗