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PubMed1995

[Auditory comprehension in transcortical motor aphasia due to a medial lesions of the left frontal lobe].

We assessed the anatomical findings and auditory comprehension of six patients with transcortical motor aphasia due to medical lesions of the left frontal lobe. All patients were right-handed and were initially mute for several hours after the onset, and they exhibited mild paresis of the right lower extremity. Their spontaneous speech was sparse and not fluent, and sometimes accompanied by echolalia, but their articulation was normal and repetition was excellent. They had difficulty in recalling words. A diagnosis of transcortical motor aphasia was made on the basis of their clinical symptoms. All patients were found to have an infarct in the left medial frontal region by MRI and/or CT. We administered the Western Aphasia Battery and 50 line drawing pointing task in order to evaluate auditory comprehension. Based on the results we concluded that there is no impairment of auditory comprehension of single words when lesions are limited to the superior frontal gyrus, but that lesions extending to the middle frontal gyrus interfere with auditory comprehension of single words. Our observations indicate that the middle frontal gyrus plays an important role in auditory comprehension of single words. All of the patients displayed impaired auditory comprehension of sentences even when their lesions were strictly limited to the medial frontal lobe. This suggests that the medial frontal lobe plays some role in the auditory comprehension of sentences.

Aged↗
PubMed1995

NMDA-receptor antagonists disrupt the formation of the auditory space map in the mammalian superior colliculus.

In the ferret (Mustela putorius) the map of auditory space in the deeper layers of the superior colliculus (SC) matures over a period of several postnatal weeks, a process known to be guided by both visual and auditory experience. The auditory responses are initially very broadly tuned, and gradually become more selective for specific sound locations that coincide with the visual receptive fields recorded in the same region of the SC. To investigate the possible involvement of NMDA-type glutamate receptors in the postnatal development of this auditory representation, we have reared ferrets in which 400 microns thick sheets of the slow-release polymer Elvax, containing the NMDA receptor antagonists MK801 or APV, were placed on the dorsal surface of the SC. The Elvax was implanted on postnatal day (P) 25-27, just before the onset of hearing, and removed 5-6 weeks later, just prior to recording from the SC on around P61-70. In vitro measurements with Elvax containing 3H-MK801 revealed that the amount of drug released declined sharply over the first 10 d and then stabilized at a fairly constant rate for the following 5 weeks. These in vitro data were found to parallel the in vivo release of MK801 from implanted Elvax slices. Diffusion of MK801 from the implant was measured and significant levels were found within 800 microns of the SC surface, suggesting that the action of MK801 was restricted to the superficial and intermediate layers of the nucleus. Extracellular recordings were made from visual and auditory units in the SC in response to free-field stimulation. The visual responses of units recorded in the superficial layers appeared to be unaffected by either of the drug treatments, and formed a normal, adult-like map of visual azimuth along the rostrocaudal axis of the SC in all animals. Most of the auditory single-unit responses recorded at this age in normal, unoperated controls were spatially tuned and topographically organized, although the map of sound azimuth was less precise than that in adult ferrets. Data from age-matched control animals that had been reared with drug-free Elvax implants were not statistically different from the unoperated juvenile ferrets. However, in animals reared with APV or MK801 Elvax implants, there was an increase in the relative numbers of auditory units that were ambiguously tuned to two or more locations.(ABSTRACT TRUNCATED AT 400 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1994

Auditory evoked potentials in Rett syndrome.

This study was designed to assess auditory function in subjects with Rett syndrome, a rare neurologic disorder that is characterized by progressive symptoms of dementia, ataxia, respiratory disorder, and communication disorder. Auditory evoked potentials, including the auditory brainstem response (ABR), middle latency response (MLR), and late vertex response (LVR), were recorded in 36 subjects with Rett syndrome. Results showed a systematic decline in auditory function from the peripheral to the central auditory system, with normal ABR in all subjects, normal MLR in 50 percent of subjects, and normal LVR in 36 percent of subjects. Results suggest that hearing sensitivity and the functional integrity of eighth nerve and auditory brainstem pathways are not affected in subjects with Rett syndrome. However, abnormality of both the MLR and LVR suggest the presence of central auditory disorder.

Acoustic Stimulation↗
PubMed1996

The effects of superior temporal cortex lesions on the processing and retention of auditory information in monkeys (Cebus apella).

Three monkeys with extensive preoperative training on visual and auditory memory tasks (delayed matching-to-sample), an auditory pattern-discrimination task, and a visual serial-order task, received bilateral lesions of the superior temporal (ST) cortex in two stages, with testing after each lesion. Unilateral ST cortex lesions resulted in only moderate auditory memory impairments, whereas bilateral ST cortex lesions resulted in severe auditory memory impairments. The bilateral ST cortex lesions also resulted in severe impairments in the ability to relearn the auditory pattern-discrimination task. In contrast to the auditory impairments, neither unilateral nor bilateral ST cortex lesions had any effect whatsoever on either visual memory or visual serial-order behavior. These findings indicate that the ST cortex plays a role in auditory processing and retention similar to that played by the inferior temporal cortex for visual processing and retention.

Acoustic Stimulation↗
PubMed1997

Synergestic effects of noise and aminoglycoside antibiotic (gentamicin) on auditory function in the gerbil.

Exposure to excessive noise can cause auditory impairment in people as well as in animals, which can be aggravated by many different ototoxic substances, such as aminoglycosides. In the present study, the gerbil was selected as the experimental animal because the gerbil has low-frequency auditory sensitivity that is similar to human beings. Auditory function in gerbils upon exposure to noise and/or gentamicin was evaluated from non-invasive records of brainstem auditory evoked potentials (BAEPs). Fifty mature male Mongolian gerbils were divided randomly into four groups. The control group was exposed neither to noise nor to gentamicin. The noise group was exposed to 100dBA noise ten hours a day for four weeks. The gentamicin group was treated with one dose of gentamicin, 75 mg/Kg i.m., daily for four weeks. The noise + gentamicin group was exposed concurrently to both noise and gentamicin treatment. BAEPs were recorded from all gerbils 24 hours before any experimental treatment, then every week for eight consecutive weeks. Long-term exposure to noise and/or gentamicin treatment was found to reduce gerbil's body weight. The increase in auditory threshold upon concurrent exposure to both noise and gentamicin treatment (evaluated from BAEPs) exceeded the sum of effects caused by exposure to noise alone and to gentamicin alone. Although differences of peak or interpeak latencies among the four groups were not statistically significant, large standard deviations were noted in the noise+gentamicin group. Thus the apparent threshold shifts in gerbils indicated a major noise and/or gentamicin induced auditory impairment to the cochlea, and the slight latency variations probably suggested a minor injury to the auditory pathways. We emphasize that noise and aminoglycoside antibiotic gentamicin can cause damage to the hearing ability at the frequency range vital to human speech recognition, and their effects are synergetic.

Animals↗
PubMed1979

Spatial firing patterns of auditory neuron network modelling by computer simulation.

This communication examines, in digital computer simulated network, input signals and response patterns established at excitatory neurons' level i.e. the membrane potential of neuron soma. It is restricted to spatial patterns of the auditory neuron networks and time factor for nervous conduction and transmission is neglected compared with long maintained membrane potentials of neuron somas. The model analyzes the change in the spatial patterns of the membrane potential in the two dimensional networks of the auditory system. In order to evaluate the contribution of the various parameters, it is started that the simplest model has only one parameter, lateral inhibition. The other parameters are then added, one at a time, to successive models. The lateral inhibition is a necessary condition in the auditory nervous system if any sharpening of the response areas in the single neurons is to occur. A necessary condition for the validity of the model is that is should be applicable to the other senses such as vision and chemical patterns, taste. The threshold feature of auditory neurons aids in producing a sharpening in the neuron of the auditory relay nuclei. It does this clipping the spatial response patterns in one dimensional arrays of excitatory neurons. Recurrent inhibition seems a necessary condition in the sensory nervous system that any kinds of input signals are to be preserved over a wide range of stimulus intensity. In other words, this network has a wide dynamic range against any kinds of input signals. A simple self-recurrent negative feedback does not contribute to the sharpening, but more complex socalled averaged type does. A neuron network is capable of responding stably to stimuli with a wide range of intensity and with any kind of spatial patterns if there is a simple negative feedback mechanism. When there is no negative feedback, input signals soon disappear or saturate in the neuron network. Therefore, recurrent inhibition is the most important mechanism. Spontaneous activity appears to aid in the sharpening by providing a kind of contrast, that is by reducting the amount of activity in neurons adjacent to the excitatory area. Moreover, the effect of spontaneous activity in the model seems to make repples around the excitatory area and suggests that an introduction of activity at any stage of the networks, from whatever source for example reticulum formation and thalamus, might appreciably alter the response patterns at subsequent neuron network. This suggests that the mechanism of the consciousness that might be controlled by the thalamus and or reticular formation. These two dimensional neuron networks may be expanded to three dimensional neuron networks. The former might simulate the auditory nervous system while the latter might simulate the visual system.

Animals↗
PubMed2003

Reduced influence of the ipsilateral ear on spatial tuning of auditory neurons in the albino superior colliculus: a knock-on effect of anomalies of the acoustic chiasm?

Auditory brainstem abnormalities affecting decussation patterns and nuclei involved in the acoustic chiasm exist in a variety of albino mammals, suggesting that binaural processes underlying spatial hearing may be disrupted in these mutants. To evaluate this we have compared the contribution of the two ears in albino and normally pigmented guinea pigs to the spatial tuning of auditory neurons in the deep layers of the superior colliculus (SC). Broadband noise stimuli at threshold and at suprathreshold intensities were presented from different azimuthal loudspeaker locations under free-field anechoic conditions, and auditory receptive fields were plotted before, during and after occluding the ipsilateral ear. We show that the deep layers of the albino SC contain a map of contralateral auditory azimuth along its anteroposterior axis, which is aligned with the visual map in the superficial layers above, just as in normal animals. We also show that threshold spatial responses are elicited only via the contralateral ear and at similar stimulus intensities (mean approximately 30 dB SPL) in the two pigmentation phenotypes. The mechanisms that maintain spatial tuning at sound intensities of 10-40 dB above threshold, however, differ markedly in these animals. Plugging the ipsilateral ear in normal guinea pigs caused significant expansions of their auditory receptive fields and loss of directional tuning, but in the albinos occlusion had little effect on these spatial properties. The results suggest that while spatial selectivity for relatively loud sounds among SC neurons is normally maintained via the binaural combination of contralateral excitatory drive and ipsilateral inhibition, it is achieved in albinos almost exclusively by monaural input from the contralateral ear. This finding is consistent with an excessive contralateral ear dominance of higher levels of the albino auditory system caused by anomalies of their acoustic chiasm, analogous to the monocular dominance of the visual system that results from excessive axon crossing at the optic chiasm in these animals.

Animals↗
PubMed1998

Corticofugal regulation of auditory sensitivity in the bat inferior colliculus.

Under free-field stimulation conditions, corticofugal regulation of auditory sensitivity of neurons in the central nucleus of the inferior colliculus of the big brown bat, Eptesicus fuscus, was studied by blocking activities of auditory cortical neurons with Lidocaine or by electrical stimulation in auditory cortical neuron recording sites. The corticocollicular pathway regulated the number of impulses, the auditory spatial response areas and the frequency-tuning curves of inferior colliculus neurons through facilitation or inhibition. Corticofugal regulation was most effective at low sound intensity and was dependent upon the time interval between acoustic and electrical stimuli. At optimal inter-stimulus intervals, inferior colliculus neurons had the smallest number of impulses and the longest response latency during corticofugal inhibition. The opposite effects were observed during corticofugal facilitation. Corticofugal inhibitory latency was longer than corticofugal facilitatory latency. Iontophoretic application of gamma-aminobutyric acid and bicuculline to inferior colliculus recording sites produced effects similar to what were observed during corticofugal inhibition and facilitation. We suggest that corticofugal regulation of central auditory sensitivity can provide an animal with a mechanism to regulate acoustic signal processing in the ascending auditory pathway.

Animals↗
PubMed2003

Distortion product otoacoustic emissions and auditory evoked potentials in the hedgehog tenrec, Echinops telfairi.

The hedgehog tenrec, Echinops telfairi, has certain basal mammalian features, like a cloaca and a sparsely differentiated brain with smooth cerebral hemispheres. The peripheral auditory capabilities of this species were investigated by means of distortion product otoacoustic emissions (DPOAE). For comparison, we determined auditory evoked potentials (AEP) in the inferior colliculus and the auditory cortex. Both methods show that the auditory range of E. telfairi extends well into ultrasonic frequencies, with a region of highest sensitivity at around 16 kHz. The total auditory range spans about 4 octaves at 40 dB SPL. The low-frequency limit of auditory processing is found at frequencies of about 2-3 kHz. The DPOAE and the AEP thresholds of E. telfairi do not run fully parallel in the high-frequency range. For a threshold value of 40 dB SPL, cochlear mechanical thresholds as measured with DPOAE extend up to 50 kHz, whereas neuronal thresholds reach the high-frequency limit at about 30 kHz. Frequency tuning, as assessed from DPOAE suppression tuning curves, was low to moderate with Q(10 dB) values ranging from 1.7 to 8. The lack of discontinuity in the group delay (derived from DPOAE measurements) reveals that cochlear frequency representation is tonotopic without any region of specialized mechanical tuning.

Acoustic Stimulation↗
PubMed2000

Consequences of neural asynchrony: a case of auditory neuropathy.

The neural representation of sensory events depends upon neural synchrony. Auditory neuropathy, a disorder of stimulus-timing-related neural synchrony, provides a model for studying the role of synchrony in auditory perception. This article presents electrophysiological and behavioral data from a rare case of auditory neuropathy in a woman with normal hearing thresholds, making it possible to separate audibility from neuropathy. The experimental results, which encompass a wide range of auditory perceptual abilities and neurophysiologic responses to sound, provide new information linking neural synchrony with auditory perception. Findings illustrate that optimal eighth nerve and auditory brainstem synchrony do not appear to be essential for understanding speech in quiet listening situations. However, synchrony is critical for understanding speech in the presence of noise.

Auditory Cortex↗
PubMed1989

Brainstem auditory evoked potentials in receptive developmental language disorder.

It has been hypothesized that receptive developmental language disorder (RDLD) may be explained by an auditory processing deficit. The neuroanatomical locus of this deficit is unknown. Brainstem auditory evoked potentials (BAEPs) reflect the functioning of the auditory nerve and auditory brainstem pathways to high-frequency acoustical stimulation in humans and reflect the first stages of auditory processing. These were studied in 12 subjects with RDLD (four females and eight males, ages 12 to 19) and twelve control subjects (three females and nine males, ages 14 to 24). Click intensity and rate of stimulation were varied. The BAEPs for the RDLD group were comparable to the control group as well as to hospital norms across intensity levels and stimulation rates. The evidence obtained suggests that a disorder in the neurophysiological systems underlying the BAEPs and reflecting initial stages of auditory processing is not essential for RDLD.

Adolescent↗
PubMed1990

Acquired word deafness, and the temporal grain of sound representation in the primary auditory cortex.

This paper explores the nature of the processing disorder which underlies the speech discrimination deficit in the syndrome of acquired word deafness following from pathology to the primary auditory cortex. A critical examination of the evidence on this disorder revealed the following. First, the most profound forms of the condition are expressed not only in an isolation of the cerebral linguistic processor from auditory input, but in a failure of even the perceptual elaboration of the relevant sounds. Second, in agreement with earlier studies, we conclude that the perceptual dimension disturbed in word deafness is a temporal one. We argue, however, that it is not a generalized disorder of auditory temporal processing, but one which is largely restricted to the processing of sounds with temporal content in the milliseconds to tens-of-milliseconds time frame. The perceptual elaboration of sounds with temporal content outside that range, in either direction, may survive the disorder. Third, we present neurophysiological evidence that the primary auditory cortex has a special role in the representation of auditory events in that time frame, but not in the representation of auditory events with temporal grains outside that range.

Animals↗
PubMed1987

Auditory responses in the nucleus basalis of the pigeon.

Single-unit responses and field potentials evoked by sound stimuli were recorded from the nucleus basalis in the frontal lobe of the pigeon brain. Auditory units in this nucleus showed phasic responses to tonal stimuli and sharp frequency tuning. The latency of responses was 5.8 +/- 0.6 ms. The response properties of these units were similar to those of units in the nucleus mesencephalicus lateralis, pars dorsalis (a mesencephalic auditory nucleus), where fibers from the auditory nuclei in the medulla terminate. This suggests that the nucleus basalis receives projections from medullary auditory neurons. Averaged auditory field potentials in the frontal lobe had three prominent components. Regional changes in the polarity of each component suggest that auditory neurons in the medulla project directly to the nucleus basalis, which in turn projects to the frontal neostriatum.

Animals↗
PubMed2004

Evaluation of hearing and auditory nerve function by combining ABR, DPOAE and eABR tests into a single recording session.

In this article, we describe an efficient method for testing both auditory receptor and auditory nerve function in a single recording session. Auditory receptor function is tested in response to pure tone, tone burst and click acoustic stimuli (i.e. distortion products of otoacoustic emissions, DPOAE; and auditory-evoked brainstem responses, ABR). The function of the auditory neurons and nerve is measured in response to direct electric current stimulation (i.e. electrically evoked auditory brainstem responses, eABR). All measurements were obtained from anesthetized laboratory rats during single recording sessions using hardware and software stimulation and analysis programs developed by Intelligent Hearing Systems, Miami, FL.

Acoustic Stimulation↗
PubMed2001

What has MMN revealed about the auditory system in schizophrenia?

Evidence that deficits in early auditory processing occur in schizophrenia was first provided by an ERP study demonstrating that mismatch negativity (MMN) to duration increments is reduced in medicated patients. Our subsequent research, which is reviewed in this paper, demonstrates that duration MMN reduction cannot be attributed to neuroleptic medication, and is specific to schizophrenia. It is not dependent upon the nature of the task used to distract attention away from the auditory modality. Most importantly, a reduced duration MMN in schizophrenia is a replicable result, having been observed in multiple independently-selected groups of patients from two separate laboratories. It also occurs in unaffected first-degree relatives of patients, suggesting that it may be a vulnerability marker of the disorder. The most intriguing questions however, relate to what underpins the reduced MMN to duration increments in schizophrenia and therefore, what it reveals about the nature of the auditory system deficit in this disorder. Three hypotheses are considered here: a pervasive problem in auditory sensory memory; a specific impairment in duration processing; or an abnormality within the window of temporal integration, coincident with the early phase of auditory sensory memory. Our data so far offer preliminary support for the third hypothesis only, although the possibility of a more broadly defined deficit in temporal processing restricted to brief or rapidly-presented auditory stimuli is canvassed.

Acoustic Stimulation↗
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↗
PubMed2003

Auditory nerve fibre responses to salicylate revisited.

Ototoxicity of salicylate is accompanied by a temporary hearing loss and tinnitus and has therefore been used to study tinnitus in animal models. Salicylate induced elevated central auditory activity has been interpreted as a correlate of tinnitus. Whether this elevated activity in the central auditory system is due to an increased activity in the auditory nerve is still under discussion. To explore this issue, we recorded the activity of single auditory nerve fibres in anaesthetised gerbils following systemic injection of salicylic acid. Firstly, compound action potential (CAP) thresholds were determined at 5-0 min intervals. Fifteen to 30 min after 200 mg/kg salicylic acid, threshold loss developed in the high frequency range. At 2 h CAP threshold loss reached a plateau amounting to 15-20 dB above 16 kHz, 0-5 dB below 2 kHz. An almost immediate start of threshold loss was observed after 400 mg/kg salicylic acid. A plateau of threshold loss was reached after 1.5 h with values of 25 dB in the high, 5-10 dB in the low frequency range. Secondly, responses of single auditory nerve fibres were studied after administration of 200 mg/kg salicylic acid. Frequency tuning curves and rate intensity (RI) functions at characteristic frequency (CF) were measured. Two hours and more after application, single fibre thresholds were elevated by about 20 dB at all CFs. Sharpness of tuning was reduced. Mean spontaneous rate was significantly reduced at CFs below 5 kHz (mean: 44 vs 28 AP/s). At CFs above 5 kHz mean spontaneous rate remained unchanged. In RI functions no change in maximum discharge rate was observed. The altered response properties can be interpreted by the known effects of salicylate on the prestin mediated active process of the outer hair cells. The elevated activity in the central auditory system after salicylate intoxication thus cannot be caused by cochlear nerve hyperactivity.

Action Potentials↗
PubMed2002

Human cortical representation of virtual auditory space: differences between sound azimuth and elevation.

Sounds convolved with individual head-related transfer functions and presented through headphones can give very natural percepts of the three-dimensional auditory space. We recorded whole-scalp neuromagnetic responses to such stimuli to compare reactivity of the human auditory cortex to sound azimuth and elevation. The results suggest that the human auditory cortex analyses sound azimuth, based on both binaural and monaural localization cues, mainly in the hemisphere contralateral to the sound, whereas elevation in the anterior space and in the lateral auditory space in general, both strongly relying on monaural spectral cues, are analyzed in more detail in the right auditory cortex. The binaural interaural time and interaural intensity difference cues were processed in the auditory cortex around 100-150 ms and the monaural spectral cues later around 200-250 ms.

Acoustic Stimulation↗