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PubMed2002

Central hyperacusis with phonophobia in multiple sclerosis.

Hearing disorders are a well-described symptom in patients with multiple sclerosis (MS). Unilateral or bilateral hyperacusis or deafness in patients with normal sound audiometry is often attributed to demyelinating lesions in the central auditory pathway. Less known in MS is a central phonophobia, whereby acoustic stimuli provoke unpleasant and painful paresthesia and lead to the corresponding avoidance behaviour. In our comparison collective, patient 1 described acute shooting pain attacks in his right cheek each time set off by the ringing of the telephone. Patient 2 complained of intensified, unbearable noise sensations when hearing nonlanguage acoustic stimuli. Patient 3 noticed hearing unpleasant echoes and disorders of the directional hearing. All patients had a clinical brainstem syndrome. ENT inspection, sound audiometry and stapedius reflex were normal. All three patients had pathologically changed auditory evoked potentials (AEPs) with indications of a brainstem lesion, and in magnetic resonance imaging (MRI) demyelinating lesions in the ipsilateral pons and in the central auditory pathway. The origin we presume in case 1 is an abnormal impulse conduction from the leminiscus lateralis to the central trigeminus pathway and, in the other cases, a disturbance in the central sensory modulation. All patients developed in the further course a clinically definite MS. Having excluded peripheral causes for a hyperacusis, such as, e.g., an idiopathic facial nerve palsy or myasthenia gravis, one should always consider the possibility of MS in a case of central phonophobia. Therapeutic possibilities include the giving of serotonin reuptake inhibitors or acoustic lenses for clearly definable disturbing frequencies.

Adult↗
PubMed1982

Developmental and experimental changes in dendritic symmetry in n. laminaris of the chick.

Early acoustic experience affects the structure of neurons in the brainstem of young chickens. In the binaurally innervated cells of the nucleus laminaris the symmetry of the dorsal and ventral dendritic trees normally increases during the embryonic and early postnatal period. Unilateral ear plugs disrupt that development. This study shows that balanced stimulation plays an important role in the development of symmetrical neuronal structures in the central auditory pathway.

Aging↗
PubMed2001

Pure word deafness in two patients with subcortical lesions.

We report two patients with pure word deafness (PWD) with tumour in the III ventricle region with obstructive hydrocephalus. A diagnosis of PWD was made in these two patients in view of impaired verbal comprehension in the presence of adequate hearing, intact acoustic stapedius reflex and well preserved environmental sound perception. Return of verbal comprehension following the radiation therapy observed is probably due to the reduction of the tumour mass and the release of thalamocortical auditory pathways from its compressive effect. Our findings support the hypothesis of the presence of discrete auditory pathways for mediation of verbal and non-verbal stimuli independently.

Adult↗
PubMed1996

A comparison of contextual and generalized auditory-cue fear conditioning: evidence for similar memory processes.

A number of variables influence contextual, but not auditory-cue, fear conditioning. However, several of these variables (isolation, stimulus preexposure, retention interval, and age) affect generalized auditory-cue fear. More generalized fear was found when (a) rats were isolated in a novel environment than when returned to their home cages, (b) the retention interval was 3 hr rather than 24 hr, and (c) in 18-day-old compared with 25-day-old rats. Moreover, preexposure to the auditory cue eliminated the isolation effect. At a behavioral-psychological level, these variables may exert their effects by influencing the processes that construct a memory representation of the stimulus. At a neural systems level, they may influence processing carried out in the thalamo-corticoamygdaloid auditory pathway.

Age Factors↗
PubMed2004

Lysosomal sulfatide storage in the brain of arylsulfatase A-deficient mice: cellular alterations and topographic distribution.

Inherited deficiency for the lysosomal enzyme arylsulfatase A (ASA) leads to lysosomal storage of sulfatides and to dramatic demyelination in the CNS of humans (metachromatic leukodystrophy, MLD). As an animal model, ASA(-/-) mice have previously been generated by disruption of the ASA gene and are known to develop lysosomal sulfatide storage similar to that in human MLD, and, moreover, to become deaf because of degeneration of the primary neurons of the auditory pathway. The present study deals with the cellular and topographic distribution of sulfatide storage throughout the CNS of ASA(-/-) mice between a few days and 24 months of age. Sulfatide accumulation was detected on the ultrastructural level and by histochemical staining with alcian blue. Sulfatide storage was found in oligodendroglia and neurons in young mice, and in activated microglia (phagocytes) in adult mice. Neuronal sulfatide storage was most prominent in many nuclei of the medulla oblongata and pons, and in several nuclei of midbrain and forebrain. Sulfatide-storing phagocytes were most frequent in the white matter tracts of aged ASA(-/-) mice, whereas no widespread demyelination was obvious. Loss of neurons was found in two nuclei of the auditory pathway of aged ASA(-/-) mice (ventral cochlear nucleus and nucleus of trapezoid body). The distributional pattern of sulfatide storage throughout the CNS of ASA(-/-) mice largely corresponds to data reported for human MLD. An important difference, however, which remains unexplained at present, is the absence of obvious demyelination from the CNS of ASA(-/-) mice up to the age of 2 years.

Age Factors↗
PubMed2001

Projections of the pontine nuclei to the cochlear nucleus in rats.

In the cochlear nucleus, there is a magnocellular core of neurons whose axons form the ascending auditory pathways. Surrounding this core is a thin shell of microneurons called the granule cell domain (GCD). The GCD receives auditory and nonauditory inputs and projects in turn to the dorsal cochlear nucleus, thus appearing to serve as a central locus for integrating polysensory information and descending feedback. Nevertheless, the source of many of these inputs and the nature of the synaptic connections are relatively unknown. We used the retrograde tracer Fast Blue to demonstrate that a major projection arises from the contralateral pontine nuclei (PN) to the GCD. The projecting cells are more densely located in the ventral and rostral parts of the PN. They also are clustered into a lateral and a medial group. Injections of anterograde tracers into the PN labeled mossy fibers in the contralateral GCD. The terminals are confined to those parts of the GCD immediately surrounding the ventral cochlear nucleus. There is no PN projection to the dorsal cochlear nucleus. These endings have the form of bouton and mossy fiber endings as revealed by light and electron microscopy. The PN represent a key station between the cerebral and cerebellar cortices, so the pontocochlear nucleus projection emerges as a significant source of highly processed information that is introduced into the early stages of the auditory pathway. The cerebropontocerebellar pathway may impart coordination and timing cues to the motor system. In an analogous way, perhaps the cerebropontocochlear nucleus projection endows the auditory system with a timing mechanism for extracting temporal information.

Animals↗
PubMed1998

Membrane properties that shape the auditory code in three nuclei of the central nervous system.

OBJECTIVE: We investigated if auditory neurons have an intrinsic ability to radically transform auditory signals. METHOD: We surveyed membrane properties that control coding by neurons, identified with intracellular staining or infrared-DIC videomicroscopy, in three stations of the auditory pathway. We used intracellular and patch-clamp techniques in slices, to study the voltage responses to current pulse injections and distinguished voltage-gated conductances with selective blockers. RESULTS: First order spherical bushy cells in the anteroventral cochlear nucleus responded at a short, stable latency with single spikes, due to a perithreshold interaction of Na+ and Ca2+ conductances. Two K+ conductances suppressed firing after this onset-spike. Second-order principal neurons of the lateral superior olive use unspecified mechanisms to secure stable onset latencies but maintained a very regular tonic firing, resulting in a chopper pattern. Other intrinsic properties induced a marked accommodation in spike rate. When depolarized as during alert states, neurons in the medial geniculate body (MGB) of the thalamus fired with variable latencies in a tonic mode. At negative resting potentials characteristic of sleep states, they responded at the onset of a depolarization and the offset of a hyperpolarization with phasic bursts due to a transient low threshold Ca2+ current. In the phasic, but not tonic mode, MGB neurons produced high-threshold Ca2+ spikes that may couple signal transmission to the neuron's metabolism. The three neuron types exhibit analogue computing abilities that transform the same input into entirely different output patterns. Isoflurane anaesthesia induces a current shunt in MGB neurons, radically changing the properties and preventing normal responses. Thus, thalamocortical auditory codes are compromised under anaesthesia. CONCLUSION: At all investigated stations of the auditory pathway, input signals are transformed by activation of voltage-controlled conductances and other intrinsic membrane properties.

Anesthetics, Inhalation↗
PubMed1997

[Activation of proto-oncogene c-fos in the auditory tract of rats stimulation with wide-band noise].

The pattern of expression of the proto-oncogene c-fos was mapped in the auditory pathway of Wistar rats kept in three different experimental conditions: a) a dark, soundproofed room; b) with exposure to usual environmental laboratory noise, and c) with exposure to wide-band noise. Under control conditions (a and b), scattered labeled neurons were found in the ventral periolivary nucleus, lateral lemniscus nuclei, inferior colliculus, medial nucleus of the medial geniculate body, and in three divisions of the temporal auditory cortex. Sound stimulation (c) increased the number of fos-like-immunoreactive (FLI) nuclei in all the auditory pathway structures. FLI nuclei were strong in the dorsal cochlear nucleus, anterior and posterior ventral cochlear nuclei, all the superior olivary complex nuclei, lateral lemniscus nuclei, all areas of the inferior colliculus, medial geniculate body, and the three temporal auditory areas, which showed a barrel pattern. Comparison of these results with the literature indicated that fos activation is not merely a sign of transitory neural activation, but a long-term neural processing pathway that is conditioned by factors such as the frequency, intensity, duration, and direction of the auditory stimulus.

Acoustic Stimulation↗
PubMed1989

Brain evoked responses reflect information processing changes with the menstrual cycle in young female athletes.

In sport activity, information processing plays a role crucial for sport performance. Neuropsychological and psychophysiological evidence based on behavioral and psychophysical tasks has been accumulated showing that the latter changes over the course of the menstrual cycle, but the available data are rather inconsistent. On the other hand, in sport literature, not much attention has been devoted to these topics by researchers who have mainly been asked to investigate changes in mood and well-being. Therefore, a study has been undertaken to investigate the relationships between the menstrual cycle and information processing in young female athletes, some of whom took oral contraceptives. The study was based on Auditory Evoked Responses that, unlike behavioral and psychophysical techniques, were revealed to be an exceptionally reliable tool for the study of neural activity during sensory information processing. The results showed the existence of clear fluctuations over the course of the menstrual cycle in time taken to handle information and in the amount of information processing that, with differences and similarities, could be observed both in spontaneously menstruating and on-pill athletes. In addition, neuroanatomical differences were evident in the response of different neural structures of the auditory pathways. In fact, the effects of the hormonal changes accompanying the menstrual cycle appear to be more effective and influential at higher central levels of the auditory pathway.

Adult↗
PubMed1993

Binaural interaction in auditory evoked potentials: brainstem, middle- and long-latency components.

Binaural interaction occurs in the auditory evoked potentials when the sum of the monaural auditory evoked potentials are not equivalent to the binaural evoked auditory potentials. Binaural interaction of the early- (0-10 ms), middle- (10-50 ms) and long-latency (50-200 ms) auditory evoked potentials was studied in 17 normal young adults. For the early components, binaural interaction was maximal at 7.35 ms accounting for a reduction of 21% of the amplitude of the binaural evoked potentials. For the middle latency auditory evoked potentials, binaural interaction was maximal at 39.6 ms accounting for a reduction of 48% of the binaural evoked potential. For the long-latency auditory evoked potentials, binaural interaction was maximal at 145 ms accounting for a reduction of 38% of the binaural evoked potential. In all of the auditory evoked potentials binaural interaction was long lasting around the maxima. The binaural interaction component extends for several milliseconds in the brainstem to tens of milliseconds in the middle- and long-latency components. Binaural interaction takes the form of a reduction of amplitude of the binaural evoked potential relative to the sum of the monaural responses, suggests that inhibitory processes are represented in binaural interaction using evoked potentials. Binaural processing in the auditory pathway is maximal in the time domain of the middle-latency components reflecting activity in the thalamo-cortical portions of the auditory pathways.

Acoustic Stimulation↗
PubMed1990

[Clinical and electrophysiological investigations of the influence of phenytoin natrium on tinnitus].

Anticonvulsant drugs like Carbamazepine and Phenytoin natrium (PHT) have been used for suppressing the tinnitus. In this paper, a clinical experience was reported, in that 100 patients with tinnitus were treated with intravenous administration of PHT, and the influence of PHT on auditory systems in the guinea pig investigated in detail electrophysiological examinations was also reported. The results are summarised as follows: 1. Clinical evaluation in the treatment of tinnitus (1) Of the 100 patients, more than 70% were well responded. (2) Pith match, loudness balance test correlated closely with the suppression of tinnitus. (3) Side effects were found in 5%, but there were all mild enough to be well tolerated. 2. Experimental evaluation in the guinea pig (1) In intravenous administration of PHT, latency and amplitude of each waveform peak in ABR were prolonged and decreased. As for the latency, waves III and IV were most prominently affected. The results may indicated that PHT works in the upper brain stem predominantly and effects also to the cochlear nucleus and cochlear nerve. (2) The amplitude of N1 in AP was depressed and its latency was slightly prolonged. These phenomena related closely with change of wave I in ABR. This may indicate that PHT can directly suppress the cochlear nerve. (3) Even at the dose that apparently influenced ABR and N1 in AP, no obvious change was observed on amplitudes in CM and EP, that may indicate PHT cannot affect on hair cells at this dose or it cannot proceed to the cochlea. (4) These changes were considered to be direct effect of PHT on auditory systems, since they were not correlated with change in the circulatory system. (5) In the perilymphatic perfusion of PHT, amplitudes in EP and CM were depressed slightly at the beginning of the perfusion. Changes in EP preceded those in CM. The results may indicate that PHT effects directly on the stria vascularis and secondarily on CM. (6) In this perfusion, no obvious change was found in AP. Nevertheless, the amplitude of N1 in AP increased over the initial level after the perfusion corresponding to the recovery of EP in some animals. The results may indicate that PHT cannot work directly on hair cells nor cochlear nerve and that the suppression of efferent inhibitory neurons can increase AP potentials. (7) PHT works on the large part of auditory pathway without cochlea, as a role of inhibitor. Considering antitinnitic effect of PHT, tinnitus bases on unusual excitement of the auditory pathway.

Adult↗
PubMed2003

Frequency modulated sweep responses in the medial geniculate nucleus.

A basic feature of communication signals is a dynamic change in frequency. One stimulus that lends itself well to investigating the frequency changes contained in these signals is the frequency modulated (FM) sweep. While many studies have investigated FM sweep responses in the auditory midbrain and cortex, relatively few have examined them in the thalamus. To this end, we investigated the responses of single units in the ventral division of the medial geniculate nucleus (MGNv) of the rat to FM sweeps. Both upward- (changing from low to high frequency) and downward-directed (changing from high to low frequency) FM sweeps were presented at four rates of frequency modulation (i.e., speed). Results showed that the majority (76%) of the cells preferred fast or medium FM sweeps. For direction selectivity, just under half of the units (47%) exhibited a preference for the direction of FM sweep. The results suggest that there is a greater degree of direction but not speed selectivity at progressively higher levels in the auditory pathway.

Acoustic Stimulation↗
PubMed1980

Evoked auditory activity within the telencephalon of the bullfrog (Rana catesbeiana).

Two auditory responsive regions in the telencephalon of the bullfrog were localized by combining systematic evoked potential depth recordings with subsequent histological studies. Large negative potentials (n1) from the ventral striatum and large positive potentials (p1) from the medial pallium were recorded in response to complex sounds with parameters similar to those found in the species-specific vocalizations. Simple acoustic stimuli, such as clicks and single tones, failed to excite these regions. Although the source of the auditory afferents to the medial pallium is presently uncertain, based on our electrophysiological recordings and previous anatomical studies it seems likely that the ventral striatum is the next ascending area above the auditory thalamus in the anuran auditory pathway.

Acoustic Stimulation↗
PubMed2001

Tympanic membrane oscillations and auditory receptor activity in the stridulating cricket Gryllus bimaculatus.

The ears of stridulating crickets are exposed to loud self-generated sounds that might desensitise the auditory system and reduce its responsiveness to environmental sounds. We examined whether crickets prevent self-induced auditory desensitisation, and measured the responsiveness of the peripheral auditory system of the cricket (acoustic spiracle, tympanic membrane and tympanic nerve) during pharmacologically induced sonorous (two-winged) and silent (one-winged) stridulation. The acoustic spiracles remained open during stridulation, so the self-generated auditory signal had full access to both the external side and the internal side of the tympanic membrane. When the spiracles shut in resting crickets, the responsiveness of the tympanic membrane to acoustic stimuli varied according to the phase of ventilation and was minimal during expiration. The tympanic membrane oscillated in phase with the self-generated sounds during sonorous chirps and did not oscillate during silent chirps. In both sonorously and silently singing crickets, the responses of the tympanic membrane to acoustic stimuli were identical during the chirps and the chirp intervals. Bursts of activity were recorded in the tympanic nerve during sonorous chirps; however, activity was minor during silent chirps. In sonorously and in silently singing crickets, the summed nerve response to acoustic stimuli in the chirp intervals was the same as in resting crickets. The response to stimuli presented during the syllable intervals of sonorous chirps was slightly reduced compared with the response in the chirp intervals as a consequence of receptor habituation. In silently singing crickets, acoustic stimuli elicited the same summed nerve response during chirps and chirp intervals. These data indicate that in the cricket no specific mechanism acts to reduce the responsiveness of the peripheral auditory pathway during stridulation.

Acoustic Stimulation↗
PubMed2004

Does the environment constrain avian sound localization?

A bird needs to keep track not only of social interactions of conspecifics but also of their changing locations in space by determining their directions and distances. Current knowledge of accuracy in the computation of sound source location by birds is still insufficient, partly because physiological mechanisms of few species are studied in well defined laboratory settings, while field studies are performed in a variety of species and complex environments. Velocity gradients and reverberating surfaces may conceivably induce inaccuracy in sound source location (mainly elevation) by distorting the directional cues. However, most birds possess an inherently directional pressure difference receiver, which enhances the directional cues (mainly azimuth), and a computational mechanism in their auditory pathways to suppress echoes of redirected sound.

Animals↗
PubMed1999

Perceptual restoration of missing sounds in a group of hallucinating schizophrenics.

17 subjects diagnosed with schizophrenia and having auditory hallucinations in their case history were compared with 15 control subjects in an experiment on perceptual restoration. A tone pattern was presented, then interrupted by noise, under conditions such that the tone pattern could be heard as going on continuously (restoration). A series of 16 stimuli with a distractor of varying amplitude (noise) were presented. Healthy controls reliably reported restoration in Presentations 9 and 10. Four schizophrenics reported no restoration at all. Three of them reported restoration earlier than controls, and four others reported it later than controls and continued to report the phenomenon after a point at which no healthy controls did. Six other presented an irregular pattern of response to the phenomenon. The results are discussed with respect to the neurophysiological functioning of the auditory pathway and schizophrenic symptoms.

Acoustic Stimulation↗
PubMed1986

Binaural response organization within a frequency-band representation of the inferior colliculus: implications for sound localization.

The auditory system of the mustache bat (Pteronotus parnellii) contains a disproportionately large representation of a narrow frequency band, corresponding to the dominant, 60 kHz component of its echolocation signal. In the inferior colliculus (IC), the 60 kHz representation comprises an architectonically distinct region called the dorsoposterior division (DPD), which is accessible for detailed physiological study. We examined the topographic distribution of binaural responses within this one frequency-band representation of the inferior colliculus. We describe two primary results. First, neurons with different binaural response properties are spatially segregated into one of four binaural response-specific regions of the DPD: a large region of monaural (EO) responses; two regions containing neurons excited by sound from both ears (EE); and a region containing neurons excited by one ear and inhibited by the other (EI). Regions dominated by 60 kHz EI responses are also found in the lateral extremity of the IC, probably within the external nucleus. These results demonstrate functionally defined subdivisions in a single frequency-band representation of the IC. Moreover, they suggest that brain stem auditory projections to the DPD and/or intrinsic connections within the DPD are highly organized. Second, within the EI region of the DPD, there is a systematic shift in the sensitivity of EI multiunit responses to interaural intensity disparities (IIDs). Dorsally, EI neurons are suppressed only by relatively loud ipsilateral sounds, and there is a systematic decrease in the relative ipsilateral intensity required for suppression at more ventral recording sites. This result demonstrates that neurons sensitive to a sound localization cue are systematically organized within a frequency-band representation of the inferior colliculus. It has implications for the manner in which the location of a sound source is encoded within the primary auditory pathway.

Animals↗
PubMed1997

Processing of complex sounds in the auditory cortex of cat, monkey, and man.

One of the fundamental features in the organization of sensory cortices which has emerged from 30 years of research in the visual system is the existence of multiple representation of the sensory world in the cerebral cortex. Compared with the visual system much less information exists about the functional specialization of multiple maps in the central auditory system. This is surprising, since an understanding of central auditory representations seems necessary for an understanding of higher auditory processing, including the perception of speech and the perception of auditory space. We have recorded single neuron activity in higher areas of auditory cortex of cats and rhesus monkeys. In cats, activity was recorded in the caudal part of the anterior ectosylvian (AE) cortex (areas AEA and AAF). More than half of the neurons were clearly tuned to the location of a sound source in azimuth and elevation. Frequency-modulated (FM) sounds elicited best responses at fast rates of modulation. By contrast, neurons in the posterior ectosylvian (PE) areas (PAF, VPAF) responded better to slow FM rates. This suggests a possible specialization for the processing of spatial attributes in the AE cortex, and a possible preference for auditory "patterns" in PE. In macaque monkeys, we explored the question of parallel processing in the higher auditory pathways by combining lesion and anatomical tracer techniques with single unit recording. Inactivation of primary auditory cortex (AI) abolished pure-tone responses in the caudomedial area (CM), but not in the rostral area (R). Injections of retrograde fluorescent tracers into R showed strong labeling of the main, ventral nucleus of the medial geniculate (MGv). Both findings suggest the existence of parallel pathways in the auditory cortex, originating at more peripheral sites and possibly specialized for the processing of auditory space vs. auditory patterns. The auditory pattern pathway in Macaque auditory cortex was further explored by using complex stimuli including Macaque-specific communication sounds. Neurons in the lateral belt areas (AL, ML, and CL) respond very selectively to bandpassed noise stimuli, to FM sounds of a certain rate and direction, as well as to certain classes of monkey calls. We are now in the process of exploring higher areas of human auditory cortex by measuring cortical activation with noninvasive functional magnetic resonance imaging (fMRI) while stimulating with complex auditory sounds.

Animals↗