Mecanismos fisiopatológicos en la génesis y cronificación del acúfeno

Progress in neuroscience research has given birth to new theories for tinnitus generation. From a point of view where cochlear dysfunctions would be considered as the origin and maintenance mechanisms, it has been introduced the important role of compensation systems from the central auditory pathways. They could act as the most relevant factor for chronic persistent tinnitus after a peripheral aggression. Unmasking of silent synapses or sprouting of new ones activate cortical reorganization for frecuencial areas nearby the non-stimulated ones through brain plasticity. Connections to associative cortex and limbic-amigdala area using the non-classical auditory system explain the presence of hyperacusis, anxiety or depression, factors that increase the severity of tinnitus. Implementation of these physiopathological theories reinforces the tinnitus neurophysiological model. The development of an aversive response through the survival reflex and the participation of negative emotional response are the responsible for signal persistence and vegetative reactions from the autonomous nervous system. Implications of this knowledge for tinnitus treatment involve the central auditory system approach through the combination of medical counselling for reduction of the aversive reaction and sound therapy to diminish its perception.

Dysfunction of the auditory efferent system in patients with traumatic brain injuries with tinnitus and hyperacusis

OBJECTIVES

Tinnitus, hyperacusis and difficulty listening in background noise are common symptoms reported by patients with traumatic brain injury (TBI). The aim of this study was to explore the function of the auditory system in TBI patients with and without auditory complaints but having normal pure-tone audiograms.

METHODS

The study consisted of 24 TBI patients with and 10 TBI patients without auditory complaints. In addition, 15 normal controls were included in the study. The function of the auditory system was tested by recording transient otoacoustic emissions (TEOAE) during the presentation of increasing levels of white noise in the contralateral ear.

RESULTS

Most of the TBI patients with auditory complaints (87%) showed absent or significantly reduced effect of the auditory efferent system as compared with the TBI patients without auditory complaints and to normal controls. However, the global amplitude of the TEOAE was significantly higher in TBI patients with auditory complaints compared to those without.

CONCLUSIONS

Due to its role in peripheral and central auditory activity, dysfunction of the efferent system may be at least partially responsible for these auditory complaints. This study underscores the importance of testing and evaluating the functional integrity of the medial efferent system by an objective and non-invasive method in patients with TBI.

Unique responses of auditory cortex networks in vitro to low concentrations of quinine

The anti-malarial drug quinine has several side effects including tinnitus. The aim of the study was to determine if cultured auditory networks growing on microelectrode arrays exhibited unique dynamic states when exposed to quinine. Eight auditory cortex networks (ACN), eight frontal cortex networks (FCN), and five inferior colliculus networks (ICN) were used in this study. Response of ACNs to quinine was biphasic, with an excitatory phase followed by inhibition. FCNs and ICNs revealed only inhibitory responses. The concentrations at which the spike rate was inhibited by 50% (IC50 mean +/- SE) were 42.5 +/- 3.9, 28.7 +/- 4.8 and 23.9 +/- 2.1 microM for ACNs, FCNs, and ICNs, respectively. Quinine increased the regularity and coordination of bursting in all three tissues. The increased burst pattern regularity of ICNs coupled with the excitatory responses seen only in ACNs between 1 and 10 microM show a unique susceptibility of auditory tissues to quinine that may be related to the underlying mechanism that triggers tinnitus-like activity.

Lidocaine for the Relief of Incapacitating Tinnitus

Tinnitus is tolerated by most patients, but in others it is enough of a problem that they seek medical attention. Results of treatment have been mixed. On occasion, a patient is so distressed by tinnitus that he or she is incapacitated and seeks help in an emergency department. We describe what we believe is the first reported case of recurrent incapacitating tinnitus secondary to inner ear tertiary syphilis in which a patient successfully responded to emergency treatment with intravenous lidocaine.

Enhancement of steady-state auditory evoked magnetic fields in tinnitus

The steady-state auditory evoked magnetic field and the Pbm, the magnetic counterpart of the second frontocentrally positive middle latency component of the transitory auditory evoked potential, were measured in ten tinnitus patients using a 122-channel gradiometer system. The patients had varying degrees of hearing loss. In all patients, the tinnitus frequency was located above the frequency of the audiometric edge, i.e. the location on the frequency axis above which hearing loss increases more rapidly. Stimuli were amplitude-modulated sinusoids with carrier frequencies at the tinnitus frequency, the audiometric edge, two frequencies below the audiometric edge, and two frequencies between the audiometric edge and the tinnitus frequency. Below the audiometric edge, the root-mean-square field amplitude of the steady-state response computed across the whole head as well as the contralateral and the ipsilateral dipole moment decreased as a function of carrier frequency. With carrier frequency above the audiometric edge, the steady-state response increased again. The amplitudes of the transitory Pbm component were patterned in a qualitatively similar way, but without the differences being significant. For the steady-state response, both whole-head root-mean-square field amplitude and the dipole moment of the sources at the tinnitus frequency showed significant positive correlations with subjective ratings of tinnitus intensity and intrusiveness. These correlations remained significant when the influence of hearing loss was partialled out. The observed steady-state response amplitude pattern likely reflects an enhanced state of excitability of the frequency region in primary auditory cortex above the audiometric edge. The relationship of tinnitus to auditory cortex hyperexcitability and its independence of hearing loss is discussed with reference to loss of surround inhibition in and map reorganization of primary auditory cortex.

Functional Anatomy of the Human Cochlear Nerve and Its Role in Microvascular Decompressions for Tinnitus

OBJECTIVE

The functional anatomy (i.e., tonotopy) of the human cochlear nerve is unknown. A better understanding of the tonotopy of the central nervous system segment of the cochlear nerve and of the pathophysiology of tinnitus might help to ameliorate the disappointing results obtained with microvascular decompressions in patients with tinnitus.

METHODS

We assume that vascular compression of the cochlear nerve can induce a frequency-specific form of hearing loss and that when the nerve is successfully decompressed, this hearing loss can recuperate. Thirty-one patients underwent a microvascular decompression of the vestibulocochlear nerve for vertigo or tinnitus. Preoperative audiograms were subtracted from postoperative audiograms, regardless of the surgical result with regard to the tinnitus and vertigo, because the hearing improvement could be the only sign of the vascular compression. The frequency of maximal improvement was then correlated to the site of vascular compression. A tonotopy of the cochlear nerve was thus obtained.

RESULTS

A total of 18 correlations can be made between the site of compression and postoperative maximal hearing improvement frequency when 5-dB hearing improvement is used as threshold, 13 when 10-dB improvement is used as threshold. A clear distribution can be seen, with clustering of low frequencies at the posterior and inferior side of the cochlear nerve, close to the brainstem, and close to the root exit zone of the facial nerve. High frequencies are distributed closer to the internal acoustic meatus and more superiorly along the posterior aspect of the cochlear nerve.

CONCLUSION

The tonotopic organization of the cisternal segment of the cochlear nerve has an oblique rotatory structure as a result of the rotatory course of the cochlear nerve in the posterior fossa. Knowledge of this tonotopic organization of the auditory nerve in its cisternal course might benefit surgeons who perform microvascular decompression operations for the vestibulocochlear compression syndrome, especially in the treatment of unilateral severe tinnitus.

Changes in spontaneous neural activity immediately after an acoustic trauma: implications for neural correlates of tinnitus

Changes in spontaneous activity, recorded over 15-min periods before, immediately after and within hours after an acute acoustic trauma, were studied in primary auditory cortex of ketamine-anesthetized cats. We focused on the spontaneous firing rate (SFR), the peak cross-correlation coefficient (rho) and burst-firing activity. Multi-units (MUs) were grouped according to characteristic frequency (CF): MUs with a CF below the trauma-tone frequency (TF) were labeled as Be, those with a CF within 1 octave above the TF were labeled as Ab1 and those with a CF more than 1 octave above the TF were labeled as Ab2. Immediately after the trauma, the SFR was not significantly changed. The percentage of time that neurons were bursting, the mean burst duration, the number of spikes per burst and the mean inter-spike interval in a burst were enhanced. rho was locally increased in the Ab1-Ab2 and Ab2-Ab2 groups. A few hours post trauma, the SFR was increased in the Be and Ab2 groups, whereas burst-firing returned to pre-exposure levels. Moreover, rho was elevated in the Be-Ab2, Ab1-Ab2 and Ab2-Ab2 groups; this increase was significantly correlated to the changes in SFR. The results are discussed in the context of a neural correlate of tinnitus.

Pathophysiology of tinnitus

Tinnitus is not a single entity but a rather diverse group of disorders. Despite symptoms that indicate the ear is the site of the pathology, there is strong evidence that most forms of severe tinnitus are caused by functional changes in the central nervous system. The changes are induced through expression of neural plasticity, some of which may have been caused initially by abnormalities in the ear or the auditory nerve. The involvement of the nonclassical ascending auditory pathway with its subcortical connections to limbic structures (the amygdala) may explain some of the symptoms of some forms of tinnitus including hyperacusis and affective disorders, such as phonophobia and depression, which often accompany severe tinnitus.

Animal models of tinnitus

Tinnitus is a complex phenomenon that is poorly understood. A significant tool for studying the pathophysiology of tinnitus and exploring potential treatments is an animal model. This article discusses the general techniques for evaluating psychophysical phenomenon in nonhuman subjects. An overview of a model of chronic tinnitus in rats and chinchillas is presented.

Hearing impairment and tinnitus pitch in patients with unilateral tinnitus: comparison of sudden hearing loss and chronic tinnitus

OBJECTIVES

The objectives were to analyze the results of pitch-matching and loudness-balance testing in patients with unilateral tinnitus and to evaluate the relationship between audiological findings based on the tinnitus-affected and tinnitus-unaffected threshold differences and tinnitus pitch by using linear interpolation methods. In addition, the effects of the duration of the tinnitus on this relationship were investigated. Sudden sensorineural hearing loss with tinnitus was selected for the "acute tinnitus" group, and unilateral tinnitus with unknown disease and a duration of more than 3 months was selected for the "chronic tinnitus" group.

STUDY DESIGN

Retrospective study of the clinical records of patients.

METHODS

One hundred thirty-two patients with unilateral tinnitus (comprising 68 female [51.5%] and 64 male [48.5%] patients) were investigated as subjects. Their mean age was 50.4 years (SD = 15.8 y). All patients underwent otoneurological testing, including the pure-tone audiogram and pitch-matching and loudness-balance tests.

RESULTS

The mean difference in the hearing threshold between the tinnitus-affected ear and the tinnitus-unaffected ear was largest near the tinnitus pitch in both the acute and the chronic tinnitus groups. However, the relationship between hearing impairments and tinnitus pitch was somewhat different in the two groups: It exhibited a single smooth peak in the acute tinnitus group but a bimodal peak in the chronic tinnitus group.

CONCLUSION

The results suggest that tinnitus is related to hearing impairment in the same frequency region in patients with sudden sensorineural hearing loss with tinnitus or in patients with chronic tinnitus, whereas some instances of chronic tinnitus are caused by reorganization in cortical cells.

Effects of nimodipine on quinine ototoxicity

The compound action potential (CAP) in response to a click train stimulus was recorded at the round window of guinea pigs. Administration of quinine hydrochloride (200 mg/kg) significantly elevated the CAP thresholds by 5 to 25 dB (p < .05), and the CAP waveform elicited by the click train stimulus was abnormal. The amplitude of the CAP elicited by the second click was bigger than that elicited by the first click. These changes may be caused by an abnormally broadened N1 response to the first click in the click train. In contrast, CAP waveforms elicited by the second and subsequent clicks appeared normal. After administration of nimodipine (2 mg/kg), the CAP thresholds and waveforms elicited by the click train stimulus were unchanged. Simultaneous administration of both quinine (200 mg/kg) and nimodipine (2 mg/kg) resulted in the same electrophysiological changes as those induced by quinine alone. These results suggest that nimodipine prevents neither the deterioration in the CAP nor the abnormal properties in the response to a click train stimulus.

Expanding the biological basis of tinnitus: crossmodal origins and the role of neuroplasticity

Tinnitus is most often initiated by modality specific otopathologic disturbances affecting peripheral and central auditory pathways. However, there is growing evidence indicating that the anatomical location generating tinnitus occurs at sites different from the initial pathology. Support for this notion is found in individuals where tinnitus can be triggered or modulated by inputs from other sensory modalities or sensorimotor systems (somatosensory, somatomotor, visual-motor). The use of functional imaging methods combined with psychophysics, detailed physical examinations and questionnaire-based assessments has reinforced and validated these observations. Available data suggest that tinnitus-related crossmodal interactions are more common than previously anticipated. This communication reviews these advancements and suggests that a relatively broad multimodal network of neurons is involved in generating and sustaining the tinnitus perception in some forms of the disorder. Also implicated as part of the tinnitus experience are interactions within large-scale neural networks subserving attention, cognition, and emotion. Incorporating this knowledge into contemporary psychophysiological models will help facilitate the conceptualization of this phantom perception in a more comprehensive manner.

Effects of nimodipine on salicylate ototoxicity

The purpose of this study was to examine the effects of nimodipine on salicylate ototoxicity in guinea pigs. The compound action potential (CAP) was recorded at the round window, and the cochlear blood flow (CBF) was measured simultaneously from the lateral wall of the basal turn of the cochlea by laser Doppler flowmetry. After administration of salicylate (100 mg/kg), the CAP thresholds were significantly elevated, by 5 to 20 dB (p < .05), and the CBF was significantly decreased (p < .05). After administration of nimodipine (2 mg/kg), the CAP thresholds were unchanged, but the CBF had increased significantly (p < .05), while systemic blood pressure had decreased significantly (p < .05). Simultaneous administration of both salicylate (100 mg/kg) and nimodipine (2 mg/kg) resulted in significant elevation of the CAP thresholds (p < .05), while the CBF did not decrease. These results suggest that nimodipine prevents the decrease in CBF induced by salicylate, but that nimodipine does not prevent the deterioration in the CAP.

The role of zinc in management of tinnitus

OBJECTIVE

Several therapeutic modalities have been tried in patients with tinnitus. These trials have given rise to unsatisfactory results in most of the patients since the etiology and pathophysiology of tinnitus is unclear. Significant correlation between tinnitus and decreased zinc level and also reduction in severity of tinnitus after zinc therapy has been reported in some clinical studies. The aim of this study is to find out the prevalence of hypozincemia in patients suffering from tinnitus of various origins (presbyacusis, acoustic trauma and ototoxicity) at young and elderly population and to investigate the effect of zinc therapy upon the severity of tinnitus.

METHODS

Forty consecutive patients with severe tinnitus were included in this study between April 1998 and May 2000. There were 32 men (80%) and eight women (20%) with an age ranging between 19 and 67 (mean 40.6 years). Eleven patients were over the age of 50. The zinc level was measured in non-diluted serum by flame atomic absorption spectrophotometry (normal values; 50-120 microg/dl) from fasting blood samples. All the patients were given zinc pills 220 mg each, once a day and 2 h before lunch for 2 months. The patients were required to fulfill a tinnitus scoring scale and a handicap questionnaire before and after treatment. The Wilcoxon rank sum test and McNemar test were used for the statistical analysis.

RESULTS

Six patients were hypozincemic and seven patients had decreased serum zinc levels. No significant change has been observed in frequency and severity of tinnitus measured by audiologic tests after zinc therapy. Twenty-three (57.5%) of these patients reported some relief of tinnitus in the tinnitus scoring scale but the rate of improvement was minor (P>0.05). Decrease in severity of tinnitus after zinc therapy in elder group was better than the younger ones.

CONCLUSION

Our study could not confirm the high incidence of hypozincemia in patients with tinnitus as reported previously. Zinc therapy for 8 weeks presented no promising effect on tinnitus in three groups of patients and the difference between the rate of improvement in severity of tinnitus after zinc intake in patients with normal and low serum zinc level was not significant. Zinc supplement provided relief of tinnitus in some of the elder people who apparently had dietary zinc deficiency.

Quinine affects the response properties of compound action potentials elicited by periodic click trains

The effects of systemically applied quinine on the compound action potential (CAP) were investigated in 5 guinea pigs. A dose of 200 mg/kg body weight of quinine hydrochloride was administered intramuscularly, and CAPs were recorded at the round window before and after administration. The CAP thresholds of the animals were elevated by 5 to 25 dB approximately 30 minutes after administration, and thresholds recovered in some animals during the experimental session. The CAP waveform elicited by the click train stimulus was abnormal after administration of quinine. The amplitude of the CAPs elicited by the second click was larger than that of those elicited by the first click. These changes may be induced by an abnormally broadened N1 response to the first click in the click train following quinine administration. In contrast, the CAP waveforms elicited by the second click and by the following clicks in the click train appeared normal.

Mechanisms of tinnitus

The generation of tinnitus is a topic of much scientific enquiry. This chapter reviews possible mechanisms of tinnitus, whilst noting that the heterogeneity observed within the human population with distressing tinnitus means that there may be many different mechanisms by which tinnitus can occur. Indeed, multiple mechanisms may be at work within one individual. The role of the cochlea in tinnitus is considered, and in particular the concept of discordant damage between inner and outer hair cells is described. Biochemical models of tinnitus pertaining to the cochlea and the central auditory pathway are considered. Potential mechanisms for tinnitus within the auditory brain are reviewed, including important work on synchronised spontaneous activity in the cochlear nerve. Whilst the number of possible mechanisms of tinnitus within the auditory system is considerable, the identification of the physiological substrates underlying tinnitus is a crucial element in the design of novel and effective therapies.

Objective tinnitus in children

OBJECTIVE

To discuss the various symptoms and causes of objective tinnitus in children.

STUDY DESIGN

Retrospective case review.

PATIENTS

Five children who had audible signals emanating from their ears caused by audible spontaneous otoacoustic emissions, palatal myoclonus, arteriovenous malformation, and acoustic trauma.

MAIN OUTCOME MEASURE

The tinnitus reported by the patients was linked to acoustic signals that could be measured objectively or heard by the examiner.

RESULTS

Four of the five children had essentially normal hearing. The one child who demonstrated a hearing loss audiometrically was thought to have normal hearing sensitivity, but his intense roaring objective tinnitus appeared to mask his low-frequency thresholds. All five patients had measurable acoustic signals in the ear canal that matched the patients' descriptions of their tinnitus.

CONCLUSION

The cases illustrate how the objective tinnitus was diagnosed and measured, how a treatment algorithm was applied, and the expected results of treatment. In addition, the cases provide support for the use of psychologic counseling throughout the examination and treatment of objective tinnitus in children.

Spontaneous firing activity of cortical neurons in adult cats with reorganized tonotopic map following pure-tone trauma

We hypothesized that moderate sensorineural hearing loss resulting from acoustic trauma would cause (i) a change in the cortical tonotopic map, (ii) an increase in spontaneous activity in the reorganized region and (iii) increased inter-neuronal synchrony within the reorganized part of the cortex. Five kittens were exposed to a 126 dB sound pressure limit tone of 6 kHz for 1 h at both 5 and 6 weeks of age. Recordings were performed 7-16 weeks after the exposure. Auditory brainstem response thresholds for frequencies above 12 kHz were increased by 30 dB on average relative to those in normal cats. Tonotopic maps in the primary auditory cortex were reorganized in such a way that the area normally tuned to frequencies of 10-40 kHz was now entirely tuned to 10 kHz. Spontaneous firing rates were significantly higher in reorganized areas than in normal areas. In order to test for changes in inter-neuronal synchrony, cross-correlation analysis was done on 225 single-unit pairs recorded in the traumatized cats. For the single- and dual-electrode pairs there was no significant difference in peak cross-correlation coefficients for the firings of simultaneously recorded cells between normal and reorganized areas. However, the percentage of correlations that differed significantly from zero was higher in the reorganized area than in the normal area. This suggests a potential correlation between cortical reorganization, increased spontaneous firing rate and inter-neuronal synchrony that might be related to tinnitus found in high-frequency hearing loss induced by acoustic trauma.

Positron emission tomography of cortical centers of tinnitus

Tinnitus is associated with a wide variety of disorders in the auditory system. Whether generated peripherally or centrally, tinnitus is believed to be associated with activity in specific cortical regions. The present study tested the hypothesis that these cortical centers subserve the generation, perception and processing of the tinnitus stimulus and that these processes are suppressed by lidocaine and masking. Positron emission tomography was used to map the tinnitus-specific central activity. By subtracting positron emission tomography images of regional cerebral blood flow distribution obtained during suppression of the tinnitus from positron emission tomography images obtained during the habitual tinnitus sensation, we were able to identify brain areas concerned with the cerebral representation of tinnitus. Increased neuronal activity caused by tinnitus occurred predominantly in the right hemisphere with significant foci in the middle frontal and middle temporal gyri, in addition to lateral and mesial posterior sites. The results are consistent with the hypothesis that the sensation of tinnitus is associated with activity in cortical regions functionally linked to subserve attention, emotion and memory. For the first time, the functional anatomy of conditions with and without the habitual tinnitus sensation was obtained and compared in the same subjects.

Long-term effect of hyperbaric oxygenation treatment on chronic distressing tinnitus

Tinnitus is still a phenomenon with an unknown pathophysiology with few therapeutic measures. During the last two decades, hyperbaric oxygenation therapy (HBO) has been used in the treatment of sudden deafness and chronic distressing tinnitus. In this study, we prescribed HBO to 20 patients who had had severe tinnitus for more than one year and who had already had other forms of tinnitus therapy with unsatisfactory results. Four patients could not cope with the pressure gradient. The effect of HBO was assessed using subjective evaluation and VAS scores before and after HBO. Follow-up continued until one year after treatment. Six patients had a reduction of tinnitus and accompanying symptoms, eight patients did not notice any change and two patients experienced an adverse effect. Any outcome persisted with minor changes until one year after treatment. HBO may contribute to the treatment of severe tinnitus, but the negative effect on tinnitus should be weighed carefully.

Action potentials and underlying voltage-dependent currents studied in cultured spiral ganglion neurons of the postnatal gerbil

The excitability of cultured spiral ganglion (SG) neurons from early postnatal gerbil (P0-P1) was examined with the whole-cell patch-clamp technique. The role of voltage-gated currents in shaping the kinetics of action potentials (APs) was analyzed. Cultured SG neurons displayed spontaneous APs with a low rate (< 0.1 Hz). The kinetics of APs were studied by injecting neurons with current pulses of various frequencies and duration. A single depolarizing pulse of long duration elicited only one AP in most SG neurons. When excited by a train of short current pulses given at rates greater than 50 Hz, the firing pattern displayed an adaptive mechanism with the result that successive APs fired with lower amplitude, broader duration and delayed peak time. Pulse trains of higher frequencies had higher failure rates in initiating APs. Current pulses given at 20 Hz or lower elicited APs that had very similar amplitudes. However, the width of the APs gradually broadened. Duration of APs was also found to be affected by the membrane potential of neurons. Between -75 mV and -55 mV, AP duration was broadened at a rate of about 33% per 10 mV depolarization. Voltage-gated currents that underlie the generation of APs were examined under voltage-clamp conditions. Tetrodotoxin-sensitive sodium currents and dihydropyridine-sensitive L-type calcium currents were found. More importantly, inactivation properties of the potassium current provided a direct explanation for the cumulative broadening of APs. This work demonstrated that SG neurons were able to fire APs long before hearing commences in gerbil. Possible roles of spontaneous APs in the development of the cochlea and the role of voltage-gated currents in the function of SG neurons under normal and pathological conditions are discussed.

The relationship of tinnitus to craniocervical mandibular disorders

Patients with craniocervical mandibular (TMD) disorders can present with tinnitus as a primary or secondary complaint. The embryology and functional anatomy of the middle ear, temporomandibular joint, muscles of mastication and associated tendons, ligaments, blood vessels, nerves and lymphatics was found to be helpful in establishing etiologic concepts which relate tinnitus to these temporomandibular disorders. In addition to etiologic concepts, treatment modalities are described. The authors relate their experiences as well as those of others with different patient populations.

Effects of quinine on neural activity in cat primary auditory cortex

The effect of systemically applied quinine on single-unit firing activity in primary auditory cortex was investigated in seven cats. A dose of 100 or 200 mg/kg of quinine hydrochloride was administered intramuscularly and recordings from the same units were performed prior to application and continuously up to on average 5.5 h after administration. All animals showed 10-40 dB of threshold shift about 30 min after administration and some animals showed recovery during the course of the investigation. Significant increases were found in spontaneous firing rates for low-firing-rate units (initial firing rate < 1 spike/s). For high-firing-rate units (initial firing rate > 1 spike/s) no significant changes were observed. There were no significant changes in modal and mean interspike interval. The time-to-rebound peak in the autocorrelation function for spontaneous firings was not altered significantly. The rate of burst occurrence showed no significant change. The best modulation frequency in response to stimulation with periodic click trains decreased after administration, but the limiting rate did not change. Peak cross-correlation coefficients for the spontaneous firings of simultaneously recorded cells showed a significant increase and the correlogram's central peak was significantly narrower after quinine application. Dose effects were only present for cross-correlation results and temporal modulation transfer functions. The results for both spontaneous firing rate, peak width in the cross-correlogram and click stimulation were similar to those observed in salicylate-treated cats (Ochi and Eggermont, 1996). The other findings were different from those observed after salicylate. It is obvious that the effects of quinine on the auditory system are not the same as those of salicylate. The increased synchronization of the spontaneous firings across different neurons observed after application of both drugs may be related to tinnitus.

Detailed analysis of auditory brainstem responses in patients with noise-induced tinnitus

The role of the auditory brainstem in tinnitus is questionable. This study aimed comprehensively to assess auditory brainstem responses (ABRs) in patients suffering from noise-induced tinnitus (NIT). ABRs were recorded from 13 chronic NIT patients (21 ears) and 11 (21 ears) age and hearing matched control subjects without tinnitus. ABRs were recorded with scalp electrodes placed ipsilateral and contralateral to the stimulated ear, and in three orthonormal differential configurations. The ABRs were analyzed as a function of time, frequency and voltage space. A significantly enhanced ipsilaterally recorded, time domain wave III amplitude was observed for the tinnitus patients. This finding was not confirmed by any of the other ABR measures, which were indistinguishable between subject groups. Although this may be a spurious result, it nonetheless may point to an alteration in the functioning of the putative wave III auditory brainstem generator, which deserves further study.

Effects of salicylate on neural activity in cat primary auditory cortex

The effect of systemically applied salicylate on single-unit firing activity in primary auditory cortex was investigated in six cats. A dose of 200 mg/kg sodium salicylate was administered intraperitoneally, and recordings from the same units were performed prior to application and continuously up to, on average. 6 h after administration. Local field potentials were used to track the threshold shifts and general input-output (I/O) behavior following salicylate administration. All animals showed 20-30 dB of threshold shift about 2 h after administration and showed no recovery during the following 4 h. I/O curves were invariably of the recruitment type. Significant changes were found in spontaneous firing rates for two groups of unit separately. Low-spontaneous rate units (initial firing rate < 1 spike/s) showed an increase in spontaneous rate and high-spontaneous rate units (initial firing rate > 1 spike/s) showed a decrease in spontaneous firing rate. There were no significant changes in modal and mean values for interspike-interval (ISI) histograms. The duration-to-rebound peak in the autocorrelation function for spontaneous firings was prolonged significantly after salicylate administration. Peak cross-correlation coefficients for the firing patterns of simultaneously recorded cells showed no significant change but the correlogram's central peak was significantly narrower after salicylate application. The percentage of firings occurring in bursts showed no significant change after administration of salicylate. The best modulation frequency in response to stimulation with periodic click trains decreased after administration. Both the changes in the spontaneous autocorrelogram and in the temporal modulation transfer function suggest a prolongation in the duration of the Ca(2+)-activated K+ conductance of the cortical pyramidal cells following salicylate. This suggests that salicylates affect both the auditory periphery and the auditory cortex.

Salicylate-induced abnormal activity in the inferior colliculus of rats

The evaluation of the spontaneous activity of 471 units from the external nucleus of the IC revealed that salicylate induces an increase of the spontaneous activity and the emergence of a bursting type of activity longer than 4 spikes. For sharply tuned units, the affected cells were from the frequency range of 10-16 kHz, which corresponds to the behaviorally measured pitch of salicylate-induced tinnitus in rats. An exogenous calcium supplement, provided under the conditions shown to attenuate the behavioral manifestation of salicylate-induced tinnitus, abolished the modification of the spontaneous activity induced by salicylate. Finally, profound changes of activity were observed for cells not responding to contralateral sound. We propose that the observed long bursts of discharges represent tinnitus-related neuronal activity. The results are consistent with the hypothesis that GABA-mediated disinhibition is involved in the processing of tinnitus-related neuronal activity.

Anomalous cross-modal plasticity following posterior fossa surgery: some speculations on gaze-evoked tinnitus

A unique and intriguing form of subjective tinnitus evoked by eye gaze is reviewed. A new perspective is presented because this condition is sufficiently different from other forms of subjective tinnitus and its manifestation cannot be adequately explained by existing models or conceptual frameworks. Our examination of this topic considers pathophysiologic changes in the central nervous system in the context of deafferentation-induced plasticity. Potential neuroanatomical areas contributing to this effect include a number of distributed and functionally diverse areas in the brainstem and neocortex involved in the auditory control of eye movements. We also consider contemporary psychophysical methods to evaluate the perceptual correlates of this phenomenon and tools for the development of objective tinnitus measurements. Although theoretical and speculative in nature, this article is intended to stimulate interest in, advance knowledge of, and provide a better understanding about this condition.

Neurophysiological model of tinnitus: dependence of the minimal masking level on treatment outcome

Validity of the neurophysiological model of tinnitus (Jastreboff, 1990), outlined in this paper, was tested on data from multicenter trial of tinnitus masking (Hazell et al., 1985). Minimal masking level, intensity match of tinnitus, and the threshold of hearing have been evaluated on a total of 382 patients before and after 6 months of treatment with maskers, hearing aids, or combination devices. The data has been divided into categories depending on treatment outcome and type of approach used. Results of analysis revealed that: i) the psychoacoustical description of tinnitus does not possess a predictive value for the outcome of the treatment; ii) minimal masking level changed significantly depending on the treatment outcome, decreasing on average by 5.3 dB in patients reporting improvement, and increasing by 4.9 dB in those whose tinnitus remained the same or worsened; iii) 73.9% of patients reporting improvement had their minimal masking level decreased as compared with 50.5% for patients not showing improvement, which is at the level of random change; iv) the type of device used has no significant impact on the treatment outcome and minimal masking level change; v) intensity match and threshold of hearing did not exhibit any significant changes which can be related to treatment outcome. These results are fully consistent with the neurophysiological interpretation of mechanisms involved in the phenomenon of tinnitus and its alleviation.

Auditory event related potentials in chronic tinnitus patients with noise induced hearing loss

In order to explore a possible deficit in auditory central neural activity in tinnitus with noise induced hearing loss (NIHL), auditory event related potentials (ERP) and reaction time (RT) were recorded (measures of central processing) from tinnitus patients (N = 12) and hearing and age matched controls (N = 12). Testing procedure included oddball paradigms and 1 KHz repetitive stimulus, as well as click-induced brainstem auditory evoked potentials (BAEP). ERP amplitudes (waves N1, P2 and P3) in tinnitus patients were significantly lower than in controls in all testing paradigms. No differences were found in ERP peak latencies, BAEP, RT, or response scoring. The lower ERP amplitudes may indicate attenuated or 'abnormal' auditory central processing in NIHL tinnitus patients. It is suggested that this dysfunction reflects an adaptive brain process response to the tinnitus and points to auditory central involvement in tinnitus sensation.

Vitamin B12 deficiency in patients with chronic-tinnitus and noise-induced hearing loss

INTRODUCTION

This study examines the incidence of vitamin B12 deficiency in three groups of noise-exposed subjects: patients with chronic tinnitus and noise-induced hearing loss (NIHL), patients with NIHL only, and subjects demonstrating normal hearing.

MATERIALS AND METHODS

A group of 113 army personnel exposed to military noise was studied. The mean age was 39 years. Chronic tinnitus and NIHL existed in 57 subjects. NIHL alone was observed in 29 subjects, and 27 subjects had normal audiograms. All subjects were queried about noise exposure and dietary habits. Vitamin B12 serum levels were measured.

RESULTS

Patients with tinnitus and NIHL exhibited vitamin B12 deficiency in 47% of cases (blood levels < or = 250 pg/mL). This was significantly more (P < .023) compared with NIHL and normal subjects who exhibited vitamin B12 deficiency in 27% and 19%, respectively.

CONCLUSION

These observations suggest a relationship between vitamin B12 deficiency and dysfunction of the auditory pathway. Some improvement in tinnitus and associated complaints were observed in 12 patients following vitamin B12 replacement therapy. The authors recommend that routine vitamin B12 serum levels be determined when evaluating patients for chronic tinnitus.

A neurophysiological approach to tinnitus: clinical implications

This paper presents a neurophysiological approach to tinnitus and discusses its clinical implications. A hypothesis of discordant damage of inner and outer hair cells systems in tinnitus generation is outlined. A recent animal model has facilitated the investigation of the mechanisms of tinnitus and has been further refined to allow for the measurement of tinnitus pitch and loudness. The analysis of the processes involved in tinnitus detection postulates the involvement of an abnormal increase of gain within the auditory system. Moreover, it provides a basis for treating patients with hyperacusis, which we are considering to be a pre-tinnitus state. Analysis of the process of tinnitus perception allows for the possibility of facilitating the process of tinnitus habituation for the purpose of its alleviation. The combining of theoretical analysis with clinical findings has resulted in the creation of a multidisciplinary Tinnitus Centre. The foundation of the Centre focuses on two goals: the clinical goal is to remove tinnitus perception from the patient's consciousness, while directing research toward finding a mechanism-based method for the suppression of tinnitus generators and processes responsible for enhancement of tinnitus-related neuronal activity.

Late course of preserved hearing and tinnitus after acoustic neurilemoma surgery

The late course of preserved hearing and tinnitus following retrosigmoid transmeatal surgery for acoustic neurilemoma is reported. Over a period of 5 years, useful hearing was preserved in 15 patients after preservation was attempted in 42 patients. In five patients the hearing was better than the preoperative level; in three it was worse. Three patients developed delayed worsening and fluctuations of hearing in the surgically treated ear during a median follow-up period of 2 1/2 years. While the exact reason for such worsening was not clear in two patients, in one patient it appeared that the muscle graft placed in the internal auditory canal after tumor resection resulted in fibrosis and compromise of the cochlear nerve. The causes of delayed worsening of hearing in the absence of tumor recurrence are analyzed, and possible treatment and methods of prevention of worsening are suggested. In six patients, tinnitus persisted after surgery in the ear with successful preservation of hearing, but hearing was not worsened and the tinnitus was not bothersome to the patient. In one patient with preoperative tinnitus, hearing was not preserved and tinnitus persisted sufficiently to necessitate reexploration and cochlear nerve section.

Geriatric tinnitus: causes, clinical treatment, and prevention

1. Tinnitus is seldom recorded in the clinical database of the elderly, despite the fact that next to hearing loss, tinnitus is the most commonly reported ear problem by the elderly population. 2. Common problems of the elderly that demand special counseling and teaching skills of the nurse are decreased tolerance to tinnitus due to coexistent complex morbidity, social problems, and losses; worry that the tinnitus is a sign of an impending crisis, such as stroke, brain tumor, or insanity; and boredom with excess time with little to do but to listen to one's tinnitus. 3. Tinnitus in aging is a symptom that is usually due to an identifiable disease, and is rarely of subjective type, high-pitched quality, chronic, irreversible, idiopathic, and bilateral. 4. The common causes and aggravating factors about tinnitus in aging can provide the clues to effective nursing-initiated measures, many of which are simple household activities or personal interactions.

Zinc in the management of tinnitus. Placebo-controlled trial

To assess any possible beneficial effect from zinc on tinnitus we performed a placebo-controlled, randomized, double-blind investigation. Forty-eight patients with tinnitus were randomized to either placebo or the administration of zinc sulfate as sustained-release tablets of 22 mg Zn++ (Zinklet). The tablets were administered three times daily for 8 weeks. Every week the patients stated the severity of tinnitus on a number scale from 0 to 10. The levels of zinc and albumin in serum were determined both before and after treatment. Of 48 patients with tinnitus, hypozincemia was found in only one patient. The zinc level increased significantly in the patients treated with zinc. We could not demonstrate any beneficial effect from zinc on tinnitus. One of the essential reasons for this finding could be that the zinc levels in serum were in the normal range previous to treatment.

Tinnitus

Tinnitus, a common complaint, reportedly affects more than 37 million Americans. Most often, it is associated with a sensorineural hearing loss in the high-frequency range. Tinnitus, however, is a symptom and not a disease. Complacency about this symptom complex may cause physicians to overlook a severe underlying pathologic process. Patients with unilateral tinnitus, pulsatile tinnitus, fluctuating tinnitus, or tinnitus associated with vertigo should undergo thorough assessment, including elicitation of a complete history, physical examination, and audiologic analysis. In many instances, treatment is effective. Masking of tinnitus, medical therapy, and biofeedback and counseling are some measures that have been used in the management of tinnitus.

On the pathophysiology of tinnitus; a review and a peripheral model

In this paper I investigate the consequences of the assumption that tinnitus is the result of correlated neural activity in auditory nerve fibers under 'no sound' conditions. Two possible pathological conditions capable of causing this correlation are ephaptic excitation of one nerve fiber by neighboring nerve fibers and synchronization of the various synapses in individual hair cells. The first condition is likely to be found in cases suffering from acoustic neuroma where the myelin sheath of the auditory neurons is damaged. The second condition is attributed to a spontaneous excess influx of K+ or Ca2(+)-ions into the hair cell resulting in transient hair cell depolarizations causing synchronous transmitter release at all hair cell synapses. This condition is postulated in noise trauma and ototoxic drug damage of the inner hair cell membrane. The model produces the excess of short interspike intervals found in auditory nerve fiber recordings in animal models of tinnitus as well as the theoretically required correlation in the activity of neighboring neurons.

Phantom auditory perception (tinnitus): mechanisms of generation and perception

Phantom auditory perception--tinnitus--is a symptom of many pathologies. Although there are a number of theories postulating certain mechanisms of its generation, none have been proven yet. This paper analyses the phenomenon of tinnitus from the point of view of general neurophysiology. Existing theories and their extrapolation are presented, together with some new potential mechanisms of tinnitus generation, encompassing the involvement of calcium and calcium channels in cochlear function, with implications for malfunction and aging of the auditory and vestibular systems. It is hypothesized that most tinnitus results from the perception of abnormal activity, defined as activity which cannot be induced by any combination of external sounds. Moreover, it is hypothesized that signal recognition and classification circuits, working on holographic or neuronal network-like representation, are involved in the perception of tinnitus and are subject to plastic modification. Furthermore, it is proposed that all levels of the nervous system, to varying degrees, are involved in tinnitus manifestation. These concepts are used to unravel the inexplicable, unique features of tinnitus and its masking. Some clinical implications of these theories are suggested.

Efficacy of self-hypnosis for tinnitus relief

The efficacy of self-hypnosis (SH) on tinnitus relief was compared with two control procedures: 1) presentation of a brief auditory stimulus (BAS) to the ear with tinnitus; 2) waiting list (WL), i.e. patients receiving no formal treatment. The results have shown that 73% of SH subjects reported disappearance of tinnitus during treatment sessions, as compared with only 24% in the BAS group. Moreover, the short-term (1 week) and long-term (2 months) symptom profiles of only SH subjects revealed a significant improvement. Thus, SH may well be a beneficial method for the relief of tinnitus.

The tricyclic trimipramine in the treatment of subjective tinnitus

We examined 26 consecutive patients with subjective tinnitus. All subjects were treated with the tricyclic antidepressant trimipramine in a double-blind study, each subject acting as his own control. All subjects were evaluated with pure tone audiometry, site of lesion testing, and auditory brain stem evoked response. The tinnitus assessment consisted of frequency and intensity matching, the determination of masking levels, and a subjective evaluation of severity. Plasma levels of trimipramine were monitored at regular intervals, and the Zung and Millon inventories were administered at the beginning and end of each study period. Nineteen subjects completed the study. Within the trimipramine group, one reported complete disappearance of his tinnitus, eight reported improvement, three no change, and seven that tinnitus was worse. Within the placebo group, eight reported improvement, seven no change, and four that tinnitus was worse. The natural history of tinnitus is such that what has been observed may reflect the evolution of the disease itself, rather than the effect of treatment. We feel that while tricyclics may not have been shown to be effective, the placebo effect played a significant role in the results obtained.

The state of tinnitus after inner ear surgery

A retrospective study of several procedures--for either treatment of vertigo or resection of acoustic neuromas--was performed to determine their effect on tinnitus. Subjective ratings of the state of tinnitus (resolution, improvement, maintenance, or deterioration) were obtained by questionnaire. Surgical procedures performed for correction of vertigo frequently alter tinnitus. In general, procedures that conserve hearing--namely, retrolabyrinthine vestibular neurectomy (RVN), middle fossa vestibular neurectomy (MFVN), and endolymphatic shunt procedures (ELS)--have a 50% to 65% chance of helping relieve tinnitus and up to a 22% chance of worsening tinnitus. When there is no serviceable hearing, cochleovestibular neurectomy (CVN) offers the best cure rate for tinnitus (76%) and the least chance of worsening tinnitus (3%). When hearing is minimal and the patient complains of tinnitus, a CVN--rather than a labyrinthectomy--should be recommended. However, when useful hearing is present, a CVN is not usually recommended for relief of tinnitus, since the actual cure rates are only 35%. When vertigo is not a complaint, there is currently no surgical procedure known that can be recommended for the treatment of tinnitus.

Ictal tinnitus

Unilateral high pitched tinnitus was the sole epileptic ictal manifestation of a 45-year-old woman. Electrographic seizures originated from the contralateral midtemporal area and consistently correlated with tinnitus. Computed tomography (CT) demonstrated a lesion involving the superior temporal gyrus and inferior portion of the supramarginal gyrus. The case illustrates a cortical origin of tinnitus.

Effects of extracochlear direct current stimulation on the ensemble auditory nerve activity of cats

The influence of direct current applied by round window stimulation on the whole nerve response of the auditory nerve of the cat has been studied. Effects on acoustically driven activity (CAP) and on the ensemble spontaneous activity of the nerve were observed. Stimulation with positive current suppressed driven and spontaneous activity. The strength and spread of suppressive effects was a function of the applied current level. After a period of positive electrical stimulation, driven and spontaneous activity rapidly returned to normal values. A rebound effect was sometimes observed, marked by a brief increase in spontaneous activity above the normal level. Negative current initially produced an increase in the amplitude of driven and spontaneous responses. Prolonged stimulation with negative current (greater than 30 s) resulted in a subsequent, graded reduction of neural activity, until a profound suppression of spontaneous and evoked neural activity was attained. The amplitude/latency relationship of CAPs was altered during passing of negative currents but not during passing of positive currents. Recovery from the suppression generated by negative currents was commonly prolonged for anything from a few seconds to many minutes; prolongation was dependent on stimulus amplitude, duration and duty cycles.