Trends in Neurosciences
The neuroscience of tinnitus
Section snippets
Is tinnitus in the ear or the brain?
Tinnitus sensations associated with hearing loss are usually localized towards the affected ear(s). Does this mean that tinnitus is generated in the ear? This contentious issue, which has great implications for which types of treatment should be developed, can only be resolved in animal models that are conditioned to signal the presence of tinnitus following application of ototoxic drugs 4, 5 or excessive noise [6]. There is limited support for the assumption that tinnitus is the result of
Cortical reorganization in tinnitus
The animal research reviewed here investigated the response properties of neurons following hearing injuries or application of ototoxic drugs, and points to changes in the balance of excitation and inhibition at multiple levels of the projection pathway [5]. It is reasonable to assume that expression of these effects in the cortex contributes in some way to the perception of tinnitus. One change that has been well documented is alteration of tonotopic maps in AI following cochlear damage
Listening to tinnitus
Changes in cortical organization and in neural dynamics that occur after exposure to noise or tinnitus-inducing drugs should relate to what the tinnitus subject hears. But which changes correlate with the perception of tinnitus?
One possibility is that over-representation in the cortical tonotopic map of edge frequencies (i.e. those frequencies at the low-frequency and/or high-frequency borders of the hearing loss that have near normal thresholds) is itself responsible for the tinnitus sensation
Plasticity gone wrong?
It is unlikely that changes in neural activity (response properties of neurons and cortical organization) that are induced in auditory pathways by noise exposure and other tinnitus-inducing events occur in isolation. In particular, synchronous activity among neurons in the cortex reflects the number of shared axon collaterals (thalamocortical and corticocortical), the strength of their synapses, and their firing rates. Decreases in intracortical inhibition and increases in spontaneous activity
Alleviating tinnitus
At present, evidence for a contribution of neuroplastic processes to tinnitus is indirect, relying on documented properties of neural plasticity, including rapid remodeling of synaptic strengths by temporally coincident inputs, as revealed in physiological studies. Recent evoked potential studies of human subjects confirm that acoustic behavioral training modifies neural dynamics in the auditory cortex [61] with changes occurring in AII and AI [62], although more readily in AII, in agreement
Acknowledgements
We acknowledge the support of the Canadian Institutes of Health Research (CIHR) New Emerging Team grant on ‘Understanding, treating and preventing tinnitus’.
References (69)
Classification and epidemiology of tinnitus
Otolaryngol. Clin. North Am.
(2003)Depression and tinnitus
Otolaryngol. Clin. North Am.
(2003)Effects of chronic salicylate on GABAergic activity in rat inferior colliculus
Hear. Res.
(2000)- et al.
Tinnitus in hamsters following exposure to intense sound
Hear. Res.
(2002) Auditory nerve fibre responses to salicylate revisited
Hear. Res.
(2003)The effects of quinine on cochlear nerve fibre activity in the guinea pig
Hear. Res.
(1999)Detection of glutamate decarboxylase isoforms in rat inferior colliculus following acoustic exposure
Neuroscience
(1999)GAD levels and muscimol binding in rat inferior colliculus following acoustic trauma
Hear. Res.
(2000)Enhanced evoked response amplitudes in the inferior colliculus of the chinchilla following acoustic trauma
Hear. Res.
(1990)Auditory plasticity and hyperactivity following cochlear damage
Hear. Res.
(2000)
Salicylate-induced abnormal activity in the inferior colliculus of rats
Hear. Res.
Salicylate and quinine selectively enhance spontaneous firing rates in secondary auditory cortex
Hear. Res.
Effects of salicylate on neural activity in cat primary auditory cortex
Hear. Res.
Effects of quinine on neural activity in cat primary auditory cortex
Hear. Res.
Changes in spontaneous neural activity in the dorsal cochlear nucleus following exposure to intense sound: relation to threshold shift
Hear. Res.
Moderate noise trauma in juvenile cats results in profound cortical topographic map changes in adulthood
Hear. Res.
Changes in spontaneous firing rate and neural synchrony in cat primary auditory cortex after localized tone-induced hearing loss
Hear. Res.
Changes in spontaneous neural activity immediately after an acoustic trauma: implications for neural correlates of tinnitus
Hear. Res.
Effects of acoustic trauma on dorsal cochlear nucleus neuron activity in slices
Hear. Res.
Plasticity of spontaneous neural activity in the dorsal cochlear nucleus after intense sound exposure
Hear. Res.
Effects of trigeminal ganglion stimulation on unit activity of ventral cochlear nucleus neurons
Neuroscience
Expanding the biological basis of tinnitus: crossmodal origins and the role of neuroplasticity
Hear. Res.
Changes in [14C]-2-deoxyglucose uptake in the auditory pathway of hamsters previously exposed to intense sound
Hear. Res.
Auditory cortical plasticity: a comparison with other sensory systems
Trends Neurosci.
Injury-induced reorganization in adult auditory cortex and its perceptual consequences
Hear. Res.
Cortical reorganization in patients with high frequency cochlear hearing loss
Hear. Res.
Tinnitus: clinical measurement
Otolaryngol. Clin. North Am.
Age-related changes in GABA(A) receptor subunit composition and function in rat auditory system
Neuroscience
Effect of sensory discrimination training on cortical reorganisation and phantom limb pain
Lancet
Tinnitus retraining therapy for patients with tinnitus and decreased sound tolerance
Otolaryngol. Clin. North Am.
Prevalence of hearing disorders in Singapore military conscripts: a role for routine audiometry screening?
Singapore Med. J.
Phantom auditory sensation in rats: an animal model for tinnitus
Behav. Neurosci.
Animal models of tinnitus
Mechanisms of salicylate ototoxicity
Hear. Res.
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