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PubMed2002

A laboratory evaluation of an auditory display designed to enhance intraoperative monitoring.

UNLABELLED: Encouraged by the popularity of the pulse oximeter pulse-tone, we developed and tested an auditory display of six physiologic variables. The display consisted of a cardiovascular sound triggered by every heartbeat (conveying heart rate) and a respiratory sound triggered by every breath (conveying respiratory rate). Attributes of the cardiovascular sound were modulated to convey hemoglobin saturation and blood pressure, and those of the respiratory sound were modulated to denote end-tidal CO(2) and tidal volume. Three display formats (auditory, visual, and combined) were compared. Fourteen anesthesia residents monitored dynamic displays of 6 variables to detect and identify 6 predefined events during 21 trials. An event occurred during each trial and the subject's task was to detect when it started and then identify the type of event. Subjects detected every event. They detected events more rapidly with the combined display (10.4 s) than with the visual (12.8 s) or auditory (13.0 s) displays. Subjects correctly identified events least often with the auditory display (60% versus visual 88% and combined 80%). They correctly identified events more quickly with the combined display than with the visual display. We conclude that, with little training, clinicians can successfully detect and identify simulated clinical events using an auditory display of six variables. IMPLICATIONS: We developed and tested an auditory display of multivariable clinical data. With little training, clinicians successfully used the display to detect and diagnose simulated critical events. This suggests that a multivariable auditory display could enhance intraoperative monitoring.

Adult↗
PubMed1993

The effects of auditory feedback from the nucleus cochlear implant on the vowel formant frequencies produced by children and adults.

Cochlear implants provide an auditory signal with which profoundly deaf users may monitor their own speech production. The vowel production of two adults and three children who used the Nucleus multiple-electrode cochlear implant was examined to assess the effect of altered auditory feedback. Productions of words were recorded under conditions where the talkers received auditory feedback (speech processor turned on) and where no auditory feedback was provided (speech processor turned off). Data were collected over 3 days at weekly intervals. First and second formant frequencies were measured and the data were analysed to assess significant differences between auditory feedback conditions, vowel context, and data collection points. Overall, the results varied across talkers, across the data collection days, and depended on the consonant environment of the vowel. However, two effects of auditory feedback were noted. First, there was a generalized shift in first formant frequencies between the processor on and processor off conditions across three of the five subjects, but the shift differed in direction for each subject. Second, for three of the five talkers, the two front vowels /epsilon/ and /i/ were more neutralised in the absence of auditory feedback. However, this effect was less pronounced than that noted by previous studies.

Aged↗
PubMed1996

Physiological plasticity in the auditory system and its possible relevance to hearing aid use, deprivation effects, and acclimatization.

Alterations in the physiological and/or the anatomical properties of the central auditory system (neural plasticity) can be induced by unilateral or bilateral sensorineural hearing loss, auditory stimulation, and conditioning in which sounds are used as conditioned stimuli. These types of neural plasticity have implications for hearing aid use, acclimatization, and deprivation effects. The occurrence of hearing-loss-induced plasticity suggests that the organization of the central auditory system may be altered by the time a hearing aid is fitted. The success of hearing aids may depend, therefore, on how the auditory system responds to the reintroduction of certain sounds by amplification. For example, enhanced auditory stimulation provided by hearing aids may induce "secondary" plasticity in the auditory system, which might contribute to acclimatization and/or deprivation effects. Such functional changes might be further modulated by reinforcing responses to reintroduced sounds using conditioning techniques. This article reviews relevant literature on auditory system plasticity--drawn largely from animal research--with the goal of providing insight into possible mechanisms of acclimatization and deprivation effects.

Brain↗
PubMed2002

The results in patients implanted with the nucleus double array cochlear implant: pitch discrimination and auditory performance.

OBJECTIVE: In patients with total or surgically inaccessible cochlear obliteration, only a reduced number of active electrodes can be inserted with standard cochlear implants, resulting in below average auditory performance. Therefore, a special implant with two electrode arrays was developed on the basis of the Nucleus 22 cochlear implant, the socalled Double Array. One electrode array with 11 active electrodes is inserted into the basal turn of the cochlea, while the second array with 10 active electrodes is inserted into the second turn. The Double Array is now available on the basis of the more advanced Nucleus 24 with 11 active electrodes on each array and two reference electrodes, one at the case and the second one an additional ball electrode, which is placed under the temporalis muscle. For device description and surgical technique see Lenarz et al. (2001). This paper presents psychophysical data on pitch discrimination and auditory performance of patients implanted with a Double Array on the basis of the Nucleus 22. STUDY DESIGN: A prospective intra-individual study using a Latin square paradigm was performed in six adult patients with obliterated cochlea who received the Nucleus 22 Double Array. After appropriate fitting and loudness balancing, patients were tested either with the basal, the apical or both electrode arrays. Apart from auditory performance tests including numbers and monosyllable word tests, pitch discrimination was determined with a defined procedure. RESULTS: When activating each array alone, auditory performance was better with the basal array than with the apical array. Both arrays together showed marked improvement compared with the basal array, indicating an additional effect of the second array. Pitch discrimination was significantly better for the electrodes in the basal turn than in the second turn, indicating differences in electrical excitation of the auditory nerve fibers. Pitch discrimination was positively correlated with auditory performance data. CONCLUSION: The additional apical array leads to significant improvement in auditory performance in patients with obliterated cochleae by increasing the number of intracochlear electrodes. Despite reduced pitch discrimination, the apical array provides important information for speech recognition. For this reason the Double Array provides a profound advantage for patients with obliterated or surgically inaccessible cochleae.

Acoustic Stimulation↗
PubMed2002

Results from a European clinical investigation of the Nucleus multichannel auditory brainstem implant.

OBJECTIVE: This study was designed to investigate the perceptual benefits and potential risks of implanting the Nucleus(R) multichannel auditory brainstem implant. DESIGN: Between September 1992 and October 1997 a total of 27 subjects received a Nucleus 20- or 21-channel Auditory Brainstem Implant (ABI). All subjects involved in the trial had bilateral acoustic tumour as a result of neurofibromatosis type 2 (NF2) resulting in complete dysfunction of the VIIIth nerve. The study used each subject as their own control without a preoperative baseline because residual hearing, if existing, was destroyed at surgery by tumour removal. A battery of speech tests was conducted to evaluate each patient's performance and communication abilities. Tests were conducted, where possible, in the auditory-only, visual-only, and auditory-visual conditions at 3 days postoperatively (baseline), at 3-mo intervals for the first year and every 12 mo thereafter. A subjective performance questionnaire was administered together with an extensive neurological examination at each test interval. RESULTS: 27 subjects involved in this trial were successfully implanted with a Nucleus ABI. One subject died 2 days postoperatively due to a lung embolism unrelated to the device. Twenty-six subjects underwent device activation and all but one patient received auditory sensation at initial stimulation (96.2%). On average 8.6 (+/-4.2) of the available 21 electrodes were used in the patients' MAPs. Performance evaluation measures showed that the majority of users had access to auditory information such as environmental sound awareness together with stress and rhythm cues in speech that assist with lipreading. Although most subjects did not achieve any functional auditory-alone, open-set speech understanding, two subjects from this series (7.4%) did receive sufficient benefit to be able to use the ABI in conversation without lipreading. CONCLUSIONS: Although the medical risks and surgical complexity associated with ABI device implantation are far greater than those for a cochlear implant, the clinical results from this trial show that the Nucleus multichannel ABI is capable of providing a significant patient benefit over risk ratio for subjects suffering loss of hearing due to bilateral retrocochlear lesions.

Acoustic Stimulation↗
PubMed1997

Is loudness simply proportional to the auditory nerve spike count?

It is often asserted that the physiological correlate of loudness is the simple sum of the spike activity produced by all neurons in the auditory nerve (the auditory nerve spike count). We will refer to this hypothesis as the spike count hypothesis. The spike count hypothesis has been tested in the past using models of the auditory periphery and in almost all cases, the hypothesis has been supported. Our new technique for recording a compound potential from the chinchilla auditory nerve, the perstimulus compound action potential (PCAP), makes possible the measurement of the growth of the auditory nerve spike count, thus providing data that can be used to test the spike count hypothesis empirically. It was observed that the growth of the auditory nerve spike count in response to a 1-kHz pure tone (in dB/dB) is 33% shallower than the growth of loudness for a 1-kHz tone, and this discrepancy increases to 66% for an 8-kHz tone. In addition, "equal-count" contours were constructed in a manner analogous to equal-loudness contours. It was found that as reference intensity increases, equal-count contours become sharply curved upward at high frequencies whereas equal-loudness contours become increasingly flat. These differences are unlikely to be the result of the cross-species comparison, since the discrepancies are mostly attributable to the skewed pattern of spread of excitation along the basilar membrane, a property shared by humans and chinchillas. Therefore, we conclude that the simple sum of the spike activity in the auditory nerve cannot be the physiological correlate of loudness.

Animals↗
PubMed1987

Univariate and multivariate analyses of risk factors predisposing to auditory toxicity in patients receiving aminoglycosides.

Risk factors predisposing to auditory toxicity of aminoglycosides were analyzed from records of 187 patients enrolled in three prospective randomized trials comparing the toxicity of netilmicin, tobramycin, and amikacin. Patients were eligible if they received three or more days of therapy and at least two serial audiograms were available. The overall auditory toxicity rate was 9.6% (18 of 187). Auditory toxicity was detected in 4.4, 10.8, and 23.5% of patients given netilmicin, tobramycin, and amikacin, respectively (P = 0.05). In the univariate analysis, patients who developed auditory toxicity were significantly older (P = 0.01) and had a significantly higher (P = 0.04) percentage of trough levels of netilmicin or tobramycin above 2 mg/liter or amikacin above 5 mg/liter. In the final logistic regression model, only age was retained as independently influencing the development of auditory toxicity (P less than 0.00001). Conversely, factors that did not add significantly to the prediction of auditory toxicity were aminoglycoside serum levels, total aminoglycoside dose, duration of therapy, sex, peak temperature, presence of bacteremia, shock, liver cirrhosis, dehydration, previous otic pathology or renal failure, and development of renal toxicity. At least in certain populations, age is the most important predisposing factor for the development of auditory toxicity in patients receiving aminoglycosides.

Amikacin↗
PubMed2005

Late-night presentation of an auditory stimulus phase delays human circadian rhythms.

Although light is considered the primary entrainer of circadian rhythms in humans, nonphotic stimuli, including exercise and melatonin also phase shift the biological clock. Furthermore, in birds and nonhuman mammals, auditory stimuli are effective zeitgebers. This study investigated whether a nonphotic auditory stimulus phase shifts human circadian rhythms. Ten subjects (5 men and 5 women, ages 18-72, mean age +/- SD, 44.7 +/- 21.4 yr) completed two 4-day laboratory sessions in constant dim light (<20 lux). They received two consecutive presentations of either a 2-h auditory or control stimulus from 0100 to 0300 on the second and third nights (presentation order of the stimulus and control was counterbalanced). Core body temperature (CBT) was collected and stored in 2-min bins throughout the study and salivary melatonin was obtained every 30 min from 1900 to 2330 on the baseline and poststimulus/postcontrol nights. Circadian phase of dim light melatonin onset (DLMO) and of CBT minimum, before and after auditory or control presentation was assessed. The auditory stimulus produced significantly larger phase delays of the circadian melatonin (mean +/- SD, -0.89 +/- 0.40 h vs. -0.27 +/- 0.16 h) and CBT (-1.16 +/- 0.69 h vs. -0.44 +/- 0.27 h) rhythms than the control. Phase changes for the two circadian rhythms also positively correlated, indicating direct effects on the biological clock. In addition, the auditory stimulus significantly decreased fatigue compared with the control. This study is the first demonstration of an auditory stimulus phase-shifting circadian rhythms in humans, with shifts similar in size and direction to those of other nonphotic stimuli presented during the early subjective night. This novel stimulus may be a useful countermeasure to facilitate circadian adaptation after transmeridian travel or shift work.

Acoustic Stimulation↗
PubMed1987

Effect of electrical stimulation of the crossed olivocochlear bundle on auditory nerve response to tones in noise.

The discharge rates of single auditory-nerve fibers responding to best-frequency (BF) tones of varying level presented simultaneously with fixed level broadband noise were recorded with and without electrical stimulation of the crossed olivocochlear bundle (COCB). In the absence of COCB stimulation, monotonic increases in noise level produce monotonic increases in the low-level noise-driven response rate of auditory nerve fibers. As a result of adaptation, these increases in noise-driven response rate produce monotonic decreases in saturation discharge rate. At high noise levels, these compressive effects may eliminate the differential rate response of auditory nerve fibers to BF tones. COCB stimulation can restore this differential rate response by producing large decreases in noise-driven response rate and large increases in saturation discharge rate. In backgrounds of quiet, COCB stimulation is known to shift the dynamic range of single auditory nerve fiber BF tone responses to higher stimulus levels. In the presence of background noise, COCB stimulation produces upward shift of dynamic range, which decreases with increasing noise level. At high noise levels, COCB-induced decompression of rate-level functions may occur with little or no dynamic range shift. This enables auditory nerve fibers to signal changes in tone level with changes in discharge rate at lower signal-to-noise ratios than would be possible otherwise. Broadband noise also produces upward shift of the dynamic range of single auditory nerve fiber BF tone response. Noise-induced dynamic range shift of BF tone response was measured as a function of noise level with and without COCB stimulation. COCB stimulation elevates the threshold of noise-induced dynamic range shift. This shift is thought to result from two-tone rate suppression. Increases in the threshold of noise-induced shift due to COCB stimulation therefore suggests an interaction between the mechanism of two-tone rate suppression and the mechanism by which COCB stimulation produces dynamic range shift. These interactions were further investigated by recording auditory nerve fiber rate responses to fixed-level BF excitor tones presented simultaneously with fixed-frequency variable level suppressor tones. Rate responses were recorded with and without COCB stimulation. Experimental results were quantified using a phenomenological model of two-tone rate suppression presented by Sachs and Abbas.

Acoustic Stimulation↗
PubMed1989

Auditory dysfunction in children with school problems.

One hundred thirty-three children with school problems referred to a hospital-based multi-disciplinary clinic were screened audiologically to determine the frequency of auditory problems, and to determine whether one could predict auditory problems from clinical data. Ninety-three (69.9%) failed one or more parts of the screening procedure. Twenty-two children (7.9% of the total group) had abnormal hearing acuity, 33 (30.6%) abnormal speech discrimination in noise, and 73 (62.4%) abnormal short term auditory memory. These figures are significantly higher than those found in a representative sample of school children. Not one of 16 items from parent and teacher questionnaires and neurodevelopmental findings predicted auditory acuity or speech in noise problems; there were correlations between short term auditory memory items and parental and teacher rating of a language problem, teacher rating of reading and sequencing problem, and neurodevelopmental finding of auditory sequencing problem. In view of this inability to clinically predict auditory processing deficits, the authors suggest that a full audiological assessment, including short term memory and speech in noise testing, is warranted as part of the evaluation of children with learning difficulties.

Adolescent↗
PubMed1988

Development of functional innervation in the second and third order auditory nuclei of the chick.

The neurones that constitute the auditory nuclei of the brainstem in the chick (nuclei magnocellularis, NM, and laminaris, NL) are generated between days 2 and 4 of incubation. These neurones migrate towards the dorsal surface of the brainstem over the next few days and reach their final destination at about day 9 of incubation. We have examined the development of functional connections between the auditory nerve and neurones in NM and between neurones in NM and NL in embryos from stage 34 (day 8 of incubation) using electrophysiological techniques and electron and light microscopy. The earliest extracellular recordings of electrically evoked field and spike potentials were made in NM with stimulation of the ipsilateral auditory nerve and in NL with stimulation of the ipsilateral NM at stage 35 (day 9). No activity could be recorded in NL with stimulation of the auditory nerve at this stage. By stage 37 (day 11), direct stimulation of the contralateral NM evoked responses in NL and by stage 38 (day 12) stimulation of the auditory nerves evoked stable field potentials in NL. These potentials changed polarity as the electrode penetrated NL in a direction that was perpendicular to the laminar arrangement of neurone somas and parallel to the dendritic axes of these neurones. In 18 of 26 analyses of current-source density in NL of 12 preparations between stages 38 and 40 there was a sink of current associated with synaptic activity at levels both above and below the source of current (cell somas) following stimulation of the ipsilateral auditory nerve. In the remaining analyses, and in all 15 analyses from preparations older than stage 40, stimulation of the ipsilateral input evoked only a single sink of current above the level of the cell somas. In all preparations from embryos at stage 38 and older, stimulation of the contralateral auditory nerve was associated with a single sink of current below the level of the cell somas. The axon projections to the ipsilateral NL from neurones in NM were examined using HRP labelling between stages 38 and 40. The presence of terminal fields of single axons in both the dorsal and ventral dendritic regions of the ipsilateral NL at these ages was confirmed. Furthermore, dense vesicles within synaptic terminals in both the dorsal and ventral dendritic fields could be identified in preparations at stage 36 following injection of HRP into NL and stimulation of the ipsilateral NM.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2006

Perturbation of auditory feedback causes systematic perturbation in vocal structure in adult cotton-top tamarins.

Auditory feedback is critical for the development and maintenance of speech in humans. In contrast, studies of nonhuman primate vocal production generally report that subjects show little reliance on auditory input. We examined the extent to which cotton-top tamarin (Saguinus oedipus) vocal production is sensitive to perturbation of auditory feedback by manipulating the predictability of presentation of a 1 s burst of white noise during the production of the species-specific contact call, the combination long call (CLC). We used three experimental conditions: the Begin condition, in which white noise was presented only during the first half of a recording session, the End condition, in which white noise was presented only in the last half, and the Random condition, in which each call had a 50% probability of receiving white noise playback throughout the recording session, making the auditory feedback unpredictable. In addition we recorded calls before and after the experimental series (Baseline condition) to determine whether any changes induced by modification of auditory feedback persisted. Results showed that playback of white noise during the production of the CLC produced changes in the temporal structure of the CLC: calls were shorter and had fewer pulses, indicating that modification of auditory feedback can interrupt vocal production. In addition, calls that received modified feedback were louder and had longer inter-pulse intervals than those that did not, consistent with an adaptive response to the masking effect of white noise playback. The magnitude of this compensatory effect and the interruption rate were both sensitive to whether the feedback modification occurred at the beginning or end of the experimental session: early feedback produced less interruption and more compensation. Finally, when auditory feedback modification was unpredictable, adaptive changes were observed in both calls that received modified feedback and those that received normal feedback, suggesting that tamarins can generate an expectation of noise playback and increase vocal amplitude in anticipation of masking.

Acoustic Stimulation↗
PubMed1988

Effects of auditory, visual and chemical stimuli on the ingestive behavior of newly weaned piglets.

Auditory, chemical and visual stimuli were used in a factorial trial in an attempt to stimulate feeding in newly weaned piglets. Ninety-six crossbred piglets weaned at 28 d of age were assigned to groups containing four littermates. Each group was placed in a 1.2-m X 1.2-m pen in an isolated room for 48 h. Pens were equipped with nipple waterers and trough-type feeders. The auditory stimulus was piglet and sow nursing vocalizations. A visual stimulus was provided by a lamp that illuminated the feeding area. Auditory and visual stimuli were presented for 5 min once an hour for 48 h. The chemical stimulus consisted of 60 ml of evaporated milk sprayed over the surface of the feed once every 12 h. Water was used in place of milk in control treatments. Piglets were videotaped for 48 h. Frequency and duration of feeding, drinking and lying were recorded for two piglets out of each pen. Auditory stimuli increased (P less than .05) the number of drinking bouts per day from 16.3 to 19.2 and the number of drinking bouts associated with stimulus presentation from 6.2 to 8.0. There also was an auditory X day interaction effect on total time spent feeding. On d 2 postweaning piglets in the auditory treatment group spent more (P less than .05) time feeding than did those without auditory stimulation (127.1 vs 104.2 min, respectively). The relatively simple visual and chemical stimuli tested had no significant effects on ingestive behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed2000

A positron emission tomographic study of auditory localization in the congenitally blind.

We have used positron emission tomography (PET) to measure regional cerebral blood flow (rCBF) in sighted and congenitally blind subjects performing auditory localization tasks. During scanning, the spectral and binaural cues of localized sound were reproduced by a sound system and delivered via headphones. During tasks that required auditory localization both the sighted and blind subjects strongly activated posterior parietal areas. In addition, the blind subjects activated association areas in the right occipital cortex, the foci of which were similar to areas previously identified in visual location and motion detection experiments in sighted subjects. The blind subjects, therefore, demonstrated visual to auditory cross-modal plasticity with auditory localization activating occipital association areas originally intended for dorsal-stream visual processing. To determine the functional connectivity of pre-selected brain regions in primary and non-primary auditory and posterior parietal cortex in the two cohorts, we performed an inter-regional correlation analysis on the rCBF data set. During auditory localization in the blind subjects, rCBF activity in the right posterior parietal cortex was positively correlated with that in the right occipital region, whereas in sighted subjects correlations were generally negative. There were no significant positive occipital correlations in either cohort when reference regions in temporal or left parietal cortex were chosen. This indicates that in congenitally blind subjects the right occipital cortex participates in a functional network for auditory localization and that occipital activity is more likely to arise from connections with posterior parietal cortex.

Adult↗
PubMed2003

[The condition of the auditory tube in patients with chronic purulent otitis media as shown by computed tomography].

Computed tomography (CT) was made in 25 patients with otitis media purulenta chronica (OMPC). Of them 17 patients had meso- or mesoepitympanitis and 8 patients had the history of radical operations on the ear. At first, CT was made of the temporal bone without contrast medium, then with instillation of the contrast medium through the external acoustic meatus and tympanic cavity into the auditory tube. Native computer tomograms of the temporal bones of 43 persons without any middle ear pathology were used as control. Non-contrast computer tomograms showed air in the lumen of the bone part of the auditory tube of all the examinees. It was impossible to obtain the image of the cartilage part of the auditory tube. None of 25 OMPC patients showed the signs of peritubal pneumatisation while it was registered in 14 healthy controls. By CT data, 14 of 17 patients with perforative OMPC had passable auditory tube even in aggravated inflammatory process, 3 of them had unpassable one. All 8 patients after radical operation had unpassable auditory tube. Thus, the method of contrast computer tomography determines passability of the auditory tube in the direction from the tympanic cavity to the nasopharynx and specifies the level of obstruction that is important to know before hearing improving operations of tympanoplasty type. Evaluation of the drainage function of the auditory tube basing on the time of evacuation of the contrast medium from the tympanic cavity to the nasopharynx was declared useless.

Adolescent↗
PubMed2006

The role of S100A1 in external auditory canal cholesteatoma.

S100 proteins were reported to be involved in different biological activities such as transduction of intracellular calcium signalling. It has been reported that each member of the S100 protein family exhibits a distinct tissue-specific pattern of expression. Furthermore, altered S100 protein expression and function correlate with many diseases. The expression of S100A1 was reported to be increased in different tissue with hyperplasia. The external auditory canal cholesteatoma (EACC) is a benign hyperplasia of the auditory meatal skin. However, without treatment, EACC destroys adjacent tissue. Seventeen EACC specimens were collected and investigated immunohistochemically against S100A1. Normal auditory meatal skin served as control. In the EACC, S100A1 showed a more homogeneous staining pattern, positively expressed throughout the epithelial layers. The keratin debris showed no detectable expression of S100A1. In the auditory meatal skin (control), S100A1 was only expressed in the basal layer of the epithelium. We showed that there are different staining patterns in normal auditory meatal skin, middle ear cholesteatoma and external auditory canal cholesteatomas. The immunoreactivity increased with the stage of the disease. Contrary to that reported previously in the middle ear cholesteatomas, the reactivity was strongest in the upper epithelial layers. In our collective, the epithelial matrix of the EACC showed strong reactivity throughout all the layers. Surprisingly, there is no study regarding the connection between growth factors and S100A1. In previous experiments we showed significant increase of growth factors in EACC. This correlates with our new data concerning S100A1. This is the first study to show the different reactivity pattern of S100A1 in the external auditory canal cholesteatoma.

Adult↗
PubMed1997

Development of adult-type inhibitory glycine receptors in the central auditory system of rats.

Inhibitory synaptic activity is crucial for many aspects of acoustic information processing and mainly mediated by glycine and gamma-aminobutyric acid, the two principal inhibitory neurotransmitters in the auditory system. Glycine exerts its inhibitory action via binding to postsynaptic receptors existing in various isoforms. Here we have investigated the spatiotemporal distribution of adult-type, strychnine-sensitive glycine receptors (GlyRs) in the rat auditory system by using a specific antibody against the ligand-binding alpha1 GlyR subunit. In adults, alpha1 GlyRs were found at all relay stations of the auditory pathway except for the medial geniculate body and the auditory cortex. In most brainstem nuclei, labeling was characterized by dense clusters of heavily immunoreactive puncta outlining the somata and proximal dendrites, indicative of a powerful glycinergic inhibition. No alpha1 immunoreactivity was seen in the auditory system of fetal rats, consistent with results obtained by others in the spinal cord. At birth, labeling was weak and restricted to defined nuclei of the cochlear nuclear complex and the superior olivary complex. By postnatal day 8, labeling was seen in all brainstem nuclei. At the first appearance of immunoreactivity, alpha1 GlyRs were diffusely distributed on the neuronal surface, yet they became clustered with age, finally densely incrusting the somata and proximal dendrites between the 3rd and 4th postnatal week, when the mature pattern of immunoreactivity was established. We never observed an overexpression of alpha1 GlyRs or a transient appearance in areas that are devoid of the receptor in adults. The late formation of glycinergic synapses harboring the adult-type GlyRs in the auditory system, at a time when internuclear connections have already formed, indicates that alpha1 GlyRs do not participate in early synaptogenesis.

Aging↗
PubMed1998

Imaging subcortical auditory activity in humans.

There is a lack of physiological data pertaining to how listening humans process auditory information. Functional magnetic resonance imaging (fMRI) has provided some data for the auditory cortex in awake humans, but there is still a paucity of comparable data for subcortical auditory areas where the early stages of processing take place, as amply demonstrated by single-unit studies in animals. It is unclear why fMRI has been unsuccessful in imaging auditory brain-stem activity, but one problem may be cardiac-related, pulsatile brain-stem motion. To examine this, a method eliminating such motion (using cardiac gating) was applied to map sound-related activity in the auditory cortices and inferior colliculi in the brain stem. Activation in both the colliculi and cortex became more discernible when gating was used. In contrast with the cortex, the improvement in the colliculi resulted from a reduction in signal variability, rather than from an increase in percent signal change. This reduction is consistent with the hypothesis that motion or pulsatile flow is a major factor in brain-stem imaging. The way now seems clear to studying activity throughout the human auditory pathway in listening humans.

Auditory Cortex↗