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PubMed2005

Corollary discharge inhibition and audition in the stridulating cricket.

The romantic notion of crickets singing on a warm summer's evening is quickly dispelled when one comes ear to ear with a stridulating male. Remarkably, stridulating male crickets are able to hear sounds from the environment despite generating a 100 db song (Heiligenberg 1969; Jones and Dambach 1973). This review summarises recent work examining how they achieve this feat of sensory processing. While the responsiveness of the crickets' peripheral auditory system (tympanic membrane, tympanic nerve, state of the acoustic spiracle) is maintained during sound production, central auditory neurons are inhibited by a feedforward corollary discharge signal precisely timed to coincide with the auditory neurons' maximum response to self-generated sound. In this way, the corollary discharge inhibition prevents desensitisation of the crickets' auditory pathway during sound production.

Action Potentials↗
PubMed2003

A unifying basis of auditory thresholds based on temporal summation.

Thresholds of auditory-nerve (AN) fibers and auditory neurons are commonly specified in terms of sound pressure only, implying that they are independent of time. At the perceptual level, however, the sound pressure required for detection decreases with increasing stimulus duration, suggesting that the auditory system integrates sound over time. The quantity commonly believed to be integrated is sound intensity, implying that the auditory system would have an energy threshold. However, leaky integrators of intensity with time constants of hundreds of milliseconds are required to fit the data. Such time constants are unknown in physiology and are also incompatible with the high temporal resolution of the auditory system, creating the resolution-integration paradox. Here we demonstrate that cortical and perceptual responses are based on integration of the pressure envelope of the sound, as we have previously shown for AN fibers, rather than on intensity. The functions relating the pressure envelope integration thresholds and time for AN fibers, cortical neurons, and perception in the same species (cat), as well as for perception in many different vertebrate species, are remarkably similar. They are well described by a power law that resolves the resolution-integration paradox. The data argue for the integrator to be located in the first synapse in the auditory pathway and we discuss its mode of operation.

Animals↗
PubMed2006

Abnormalities in auditory evoked potentials of 75 patients with Arnold-Chiari malformations types I and II.

OBJECTIVE: To evaluate the frequency and degree of severity of abnormalities in the auditory pathways in patients with Chiari malformations type I and II. METHOD: This is a series-of-case descriptive study in which the possible presence of auditory pathways abnormalities in 75 patients (48 children and 27 adults) with Chiari malformation types I and II were analyzed by means of auditory evoked potentials evaluation. The analysis was based on the determination of intervals among potentials peak values, absolute latency and amplitude ratio among potentials V and I. RESULTS: Among the 75 patients studied, 27 (36%) disclosed Arnold-Chiari malformations type I and 48 (64%) showed Arnold-Chiari malformations type II. Fifty-three (71%) of these patients showed some degree of auditory evoked potential abnormalities. Tests were normal in the remaining 22 (29%) patients. CONCLUSION: Auditory evoked potentials testing can be considered a valuable instrument for diagnosis and evaluation of brain stem functional abnormalities in patients with Arnold-Chiari malformations type I and II. The determination of the presence and degree of severity of these abnormalities can be contributory to the prevention of further handicaps in these patients either through physical therapy or by means of precocious corrective surgical intervention.

Adolescent↗
PubMed2001

Acute effect of nicotine on non-smokers: III. LLRs and EEGs.

This paper is the last 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). The effects of nicotine on long-latency responses of the auditory system and on electroencephalograms are described in this paper. Results indicated that transdermal administration of nicotine to non-smokers significantly affects the afferent and efferent transmission of acoustic information, as well as enhancing cortical activation. Long-latency response amplitudes and electroencephalogram activity (dominant power and frequencies) were altered by acute doses of transdermal nicotine.

Acoustic Stimulation↗
PubMedDate not supplied

Models of plasticity in spatial auditory processing.

Both psychophysical and physiological studies have examined plasticity of spatial auditory processing. While there is a great deal known about how the system computes basic cues that influence spatial perception, less is known about how these cues are integrated to form spatial percepts and how the auditory system adapts and calibrates in order to maintain accurate spatial perception. After summarizing evidence for plasticity in the spatial auditory pathway, this paper reviews a statistical, decision-theory model of short-term plasticity and a system-level model of the spatial auditory pathway that may help elucidate how long- and short-term experiences influence the computations underlying spatial hearing.

Acoustic Stimulation↗
PubMed1993

The influence of stimulus intensity, contralateral masking and handedness on the temporal N1 and the T complex components of the auditory N1 wave.

Components of the auditory N1 wave were recorded to confirm previous findings of contralateral dominance of the negative component (Tb) of the T complex and to examine the differential sensitivity of N1 components to stimulus intensity, contralateral masking and handedness. EEG was recorded from Cz, T3, T4, T5, T6, and at points midway between C3 and T3 and C4 and T4 using a non-cephalic (S-V) reference. Stimuli of 70 and 90 dB SL were presented monaurally with and without contralateral white noise masking. The N100 component generally occurred at all sites and at temporal sites tended to be larger ipsilateral to stimulation and occurred earlier at ipsilateral compared to contralateral sites. Tb was seen at temporal sites and proved to be larger and earlier contralaterally. The positive component (Ta) of the T complex tended to be larger ipsilaterally although its latencies, like Tb, were earlier contralaterally. Although ERP differences associated with handedness were observed they were unrelated to ipsilateral/contralateral auditory pathway patterns. Results are discussed in terms of the functional independence of negativities recorded at temporal sites and the differential utility of these negativities in the examination of auditory pathway function.

Acoustic Stimulation↗
PubMed1981

Development of surface-recorded cochlear and early neural potentials in the cat.

The development of the surface-recorded cochlear and early neural potentials has been studied in the cat from birth to the 8th post-natal week. CM, SP, and each of the neural waves has a characteristic temporal developmental pattern and mature threshold. Wave IV is the most resistant to reduction in stimulus intensity levels, while the thresholds of both cochlear potentials are high. Animals with hereditary unilateral deafness constitute a most convenient model for the study of functional maturation in the auditory pathways, particularly with regard to precise latency estimations.

Aging↗
PubMed1992

Rapid changes in protein synthesis and cell size in the cochlear nucleus following eighth nerve activity blockade or cochlea ablation.

Destruction of the cochlea causes secondary changes in the central auditory pathway through transynaptic regulation. These changes appear to be mediated by an activity-dependent process and can be detected in the avian auditory system as early as 30 minutes after deafferentation. We compared the early changes in cochlear nucleus neurons following deafferentation by cochlea ablation with those seen following activity deprivation by perilymphatic tetrodotoxin (TTX) exposure. Protein synthesis and size of large spherical cells in the anteroventral cochlear nucleus (AVCN) of 14-day-old gerbils were measured during the first 48 hours after the manipulations. Both cochlea ablation and TTX produced a reliable decrease in protein synthesis by AVCN neurons (30-40%) by 1 hour. The magnitude of change in tritiated leucine incorporation was similar at all survival times, in both experimental groups. In contrast to the rapid changes in protein synthesis, the decrease in cell size was first evident 18 hours after TTX exposure and 48 hours after cochlea ablation. There was no significant change in protein synthesis or cell size in control groups at any of the survival times. These findings are consistent with changes in the avian auditory system in response to deafferentation and TTX exposure. Cochlea ablation and TTX exposure induced similar transneuronal changes, supporting the hypotheses that activity of auditory afferents in young mammals plays a regulatory role in the metabolism and morphology of their target neurons in the central auditory pathway, and that early changes following destruction of the peripheral receptor are due to reduction of activity-dependent interactions of presynaptic and postsynaptic cells.

Analysis of Variance↗
PubMed1991

Efferent gating of human auditory attentional processes.

Brainstem evoked potentials were measured while subjects reduced either frontalis or lips/throat activity in response to visual information regarding EMG activity while attending to dichotically presented click stimuli. An inhibition of left ear activity occurred at the level of the cochlear nucleus (Wave 1) during articulatory muscle activity, suggesting that the right ear advantage is related to active inhibition of ipsilateral auditory pathways. Contralateral central inhibition of disattended information at the level of the brainstem (Wave 5) was also implicated. A neurophysiological model accounting for both attenuation of irrelevant stimuli and vigilance for high priority information is proposed.

Adult↗
PubMed2004

MMN to natural Arabic CV syllables: 1-normative data.

Mismatch negativity response parameters; latency, amplitude, and duration to natural Arabic CV syllables differing in durational change (Baa-Waa) and in spectrotemporal change (Gaa-Daa) were obtained from normal hearing young adult Egyptians. The aim was to get normative data for MMN response parameters and to find any differences between both primary and non-primary auditory pathways in encoding and processing speech signals. Statistically significant differences between durational and spectrotemporal contrasts for latency and duration were found. This was attributed to acoustic differences and to physiological differences between primary and non-primary auditory pathways.

Acoustic Stimulation↗
PubMed1991

Auditory projections from the cochlear nucleus to pontine and mesencephalic reticular nuclei in the rat.

We investigated projections from the cochlear nucleus in the rat using the anterograde tracer Phaseolus vulgaris-leucoagglutinin. We focused on nuclei in the brainstem which are not considered to be part of the classical auditory pathway. In addition to labeling in auditory nuclei, we found presumed terminal fibers in 4 pontine and mesencephalic areas: (1) the pontine nucleus (PN), which receives bilateral projections from the antero- and posteroventral cochlear nuclei; (2) the ventrolateral tegmental nucleus (VLTg), which receives a contralateral projection from the rostral portion of the anteroventral cochlear nucleus; (3) the caudal pontine reticular nucleus (PnC), which receives bilateral input originating predominantly in the dorsal cochlear nucleus; and (4) the lateral paragigantocellular nucleus (LPGi), which receives projections from all subdivisions of the cochlear nuclei. In the VLTg and PnC, anterogradely labeled varicose axons were often found in close apposition to the primary dendrites and somata of large reticular neurons. Injections of the retrograde fluorescent tracer Fluoro-Gold into the VLTg demonstrated that the neurons of origin are mainly located contralaterally in the rostral anteroventral cochlear nucleus and in the cochlear root nucleus. The relevance of these auditory projections for short-latency audio-motor behaviors and acoustically elicited autonomic responses is discussed.

Animals↗
PubMed2006

Threshold minima and maxima in the behavioral audiograms of the bats Artibeus jamaicensis and Eptesicus fuscus are not produced by cochlear mechanics.

Behavioral audiograms of Artibeus jamaicensis and Eptesicus fuscus are characterized by two threshold minima separated by a threshold maximum at 40 kHz, for A. jamaicensis, and 45 kHz, for E. fuscus [Koay, G., Heffner, H.E., Heffner R.S., 1997. Audiogram of the big brown bat (Eptesicus fuscus). Hear. Res. 105, 202-210; Heffner, R.S., Koay, G., Heffner H.E., 2003. Hearing in American leaf-nosed bats. III: Artibeus jamaicensis. Hear. Res. 184, 113-122.]. To investigate whether these characteristics are due to cochlear properties, we recorded distortion product otoacoustic emissions (DPOAEs) and calculated DPOAE threshold curves. We found that in both species cochlear sensitivity, assessed by DPOAE recordings, does not show local threshold maxima. The DPOAE threshold curve calculated for A. jamaicensis reveals a broadly tuned minimum for frequencies between 20 and 50 kHz and the threshold curve of E. fuscus shows a broad sensitive area for frequencies between 15 and 60 kHz. In none of the two species any pronounced threshold irregularities were found. The characteristic pattern of a threshold maximum followed by a minimum observed in behavioral studies seems to be shaped by transfer characteristics of the outer ear and/or neuronal processing in the ascending auditory pathway rather than by cochlear mechanics.

Animals↗
PubMed1997

Modification of tonotopic representation in the auditory system during development.

During the early development of the bird and the mammalian peripheral auditory system, a restricted range of low--mid frequencies is recorded in immature animals. These early recordings are correlated to the base or mid-basal region of the cochlea which codes high frequencies in the adult. In order to reconcile the functional observations with anatomical ones, two main hypotheses have been put forward: one called the development of the place principle derived from observations of acoustic trauma in chick cochlea and a second derived from auditory nerve fiber recordings in kittens. Whatever the theories, the tonotopic shift during development is a well-established phenomenon in both birds and mammals that could be explained by a synthetic theory including active and passive cochlear processes. The tonotopic shift observed in the central auditory system mimics quite closely the frequency representation of the peripheral auditory system. The same trend is observed in all auditory nuclei including the cortex, except that the frequency representation is more complex because it shows tonotopic maps that can be twisted in three dimensions. From current observations, there is a simultaneous onset of tonotopic maps across auditory nuclei up to the cortex. A hypothesis is presented related to the frequency changes observed in the cochlea that affect the central auditory pathway, along with possible consequences on auditory behavior.

Animals↗
PubMed1986

Short-latency auditory evoked potentials in the monkey. II. Intracranial generators.

The generators of the short-latency auditory evoked potentials (SLAEPs) in the monkey have been defined by intracranial mapping from cochlea to auditory cortex. SLAEP components other than 1a and the slow negativity (SN) following wave 7 derive from compound action potentials propagated in subcortical auditory pathways. The component generators are complex due to the presence of two bursts of activity in the eighth nerve, to the fact that the ascending auditory fibers both synapse on and bypass specific relay nuclei, and to the differences in orientation of segments of the auditory pathways. Most SLAEP components recorded at the surface reflect the summation of activity from multiple generators. However, much of the activity seen within subcortical structures cannot be traced to the surface of the brain. Component 1a is identified with the cochlear summating potential, while 1b reflects the initial afferent volley in the distal portion of the eighth nerve. Component 2 represents the initial depolarization of the eighth nerve terminals within the ipsilateral cochlear nucleus. Component 3h reflects the second volley of activity in the distal portion of the eighth nerve and the outflow of the cochlear nucleus which decussates in the trapezoid body. Component 3v represents the initial cochlear nucleus outflow volley ascending the lateral lemniscus. Component 4 principally reflects the second volley of activity within the eighth nerve terminals, and outflow from the ipsilateral superior olivary complex ascending in that lateral lemniscus, with a possible contribution from activity in the contralateral CNC. Component 5 represents the outflow of the contralateral superior olivary complex ascending in that lateral lemniscus. Component 6 reflects another volley from the ipsilateral superior olivary complex ascending in that lateral lemniscus, as well as outflow from both inferior colliculi propagating in their brachii. The generators of component 7 are the most complex encountered, representing volleys in both lateral lemnisci, activity of the contralateral inferior colliculus, and activity in both auditory radiations. A component that follows wave 7, seen best in mastoid-to-mastoid recording linkage, represents outflow from both inferior colliculi propagating in their brachia. Components 8 and 9 principally reflect propagated action potentials in the auditory radiations bilaterally, with an additional contribution from activity of both inferior colliculi. The SN mainly represents volume-conducted postsynaptic potentials from both inferior colliculi and cochlear nuclei.

Animals↗
PubMed2002

A corollary discharge maintains auditory sensitivity during sound production.

Speaking and singing present the auditory system of the caller with two fundamental problems: discriminating between self-generated and external auditory signals and preventing desensitization. In humans and many other vertebrates, auditory neurons in the brain are inhibited during vocalization but little is known about the nature of the inhibition. Here we show, using intracellular recordings of auditory neurons in the singing cricket, that presynaptic inhibition of auditory afferents and postsynaptic inhibition of an identified auditory interneuron occur in phase with the song pattern. Presynaptic and postsynaptic inhibition persist in a fictively singing, isolated cricket central nervous system and are therefore the result of a corollary discharge from the singing motor network. Mimicking inhibition in the interneuron by injecting hyperpolarizing current suppresses its spiking response to a 100-dB sound pressure level (SPL) acoustic stimulus and maintains its response to subsequent, quieter stimuli. Inhibition by the corollary discharge reduces the neural response to self-generated sound and protects the cricket's auditory pathway from self-induced desensitization.

Acoustic Stimulation↗
PubMed2003

Chemically defined parallel pathways in the monkey auditory system.

The pathways ascending through the brain stem to the medial geniculate complex of the thalamus can be distinguished by immunostaining for the calcium binding proteins parvalbumin and calbindin and by the properties of the neurons in the subdivisions of the medial geniculate complex in which they terminate. The parvalbumin pathway, ascending from the central nucleus of the inferior colliculus, is the more direct and terminates in the ventral nucleus. The calbindin pathway is more diffuse in its origins and terminates in the dorsal and medial nuclei. Ventral nucleus neurons are sharply tuned, tonotopically organized and consistent in their responses. They project to core areas of the auditory cortex characterized by high parvalbumin immunoreactivity and by similar neuronal properties. Neurons in the dorsal and medial nuclei are not frequency specific or tonotopic and are labile in their responses. They project more diffusely to belt areas of the auditory cortex in which parvalbumin immunoreactivity is reduced and in which neuronal responses are less specific than in the core. The belt areas are the origins of streams of corticocortical connections leading into the temporal, parietal, and frontal lobes. These routes can be differentially engaged in functional imaging studies of monkeys responding to biologically significant sounds.

Animals↗
PubMed1987

Maps of auditory cortex in cats reared after unilateral cochlear ablation in the neonatal period.

The responses of many neurons recorded in the high best-frequency region of primary auditory cortical field, AI, of the normal adult cat depend upon intensity differences of the sounds arriving at the two ears. These binaural interactions are exhibited early in postnatal life, well before structural maturation of the auditory pathways from the ear to the cortex is complete. The aim of the present work was to study certain aspects of the functional development of the auditory cortex in adult cats unilaterally deaf from birth. In adult animals reared with a neonatal cochlear ablation, field AI ipsilateral to the non-operated ear showed a normal tonotopic map, which was derived from single neurons and neuron clusters driven securely by best-frequency tonal stimulation in virtually every electrode penetration. The acoustic thresholds at many recording sites were as low as those obtained in AI contralateral to the non-operated ear. These findings are in marked contrast to those from control experiments on normal adult cats where only about 65% of AI neurons were excited by a sound delivered to the ipsilateral ear and where thresholds to ipsilateral ear stimulation were significantly higher than contralateral thresholds. The spatial distribution of cortical neurons based on acoustic thresholds also appeared to be different in cats unilaterally deaf from birth when compared to control cats. Closely spaced electrode penetrations in AI ipsilateral to the non-operated ear suggested that neurons were separated into low-threshold regions and high-threshold regions. There was no evidence for this type of non-random segregation in control experiments.

Animals↗
PubMed2001

Doxorubicin ototoxicity is induced in mice by combination treatment with cyclosporin A.

Although doxorubicin [adriamycin (ADM)] ototoxicity has not been detected to date, it has been reported that neurotoxicity in the central nervous system was induced by chemotherapy with ADM in patients receiving chronic cyclosporin A (CsA) treatment. ADM ototoxicity may be induced by combination therapy with CsA because extrusion of ADM from the inner ear by p-glycoprotein (p-gp), which acts as an extrusion pump and is expressed on the surface of endothelial cells of capillary blood vessels, might be inhibited by CsA. resulting in significant accumulation of ADM in the inner ear. ADM (10 mg/kg) was administered to FVB mice either with or without CsA (200 mg/kg). Auditory brainstem responses (ABRs) were recorded before and after treatment. ABR changes were not observed in mice treated with either ADM or CsA alone. Threshold elevation, elongation of wave I-V latencies and interpeak latencies of waves I-II, I-III, I-IV and I-V were detected in mice treated with ADM in combination with CsA. These changes reached their peak values 3 weeks after treatment, and then recovered to pre-treatment levels. In normal mice, ADM is extruded by p-gp from the inner ear and auditory pathway, thus preventing hearing disorder. However, ADM ototoxicity was induced by combination therapy with CsA, indicating that CsA has an inhibitory action on p-gp function in the auditory pathway, including the inner ear. After organ transplantation, therefore, clinical administration of ADM in combination with CsA should be performed with caution.

ATP Binding Cassette Transporter, Subfamily B, Mem↗