British Tinnitus Association

The British Tinnitus Association - registered charity no: 1011145

Research Update

David Baguley PhD

Many patients with troublesome tinnitus ask about the research situation, keen to be encouraged that there is an ongoing search for treatments that will inhibit the tinnitus signal. In fact there has been an upsurge in tinnitus research in recent years, and in this brief article the present situation is summarised.

Mechanisms

One focus of research has been upon the mechanisms of tinnitus. A useful framework has been introduced that distinguishes between the ignition site for a tinnitus and physiological mechanisms that then promote that signal in the central auditory system.^1,2 Making this distinction allows one to consider these processes, and how they might be influenced to inhibit tinnitus, in individual detail.

Another line of inquiry is looking very carefully at the role of a structure called the dorsal cochlear nucleus (DCN) in tinnitus.^3,4 In cats, the DCN has been implicated in sound localization⁶ and in integrating inputs from the auditory and somatic sensory systems, particularly regarding somatic input from the pinna.⁵ Researchers are considering the idea that the DCN has an inhibiting role in humans with normal hearing, but that when some hearing is lost, this inhibition becomes less effective, thus allowing spontaneous neural activity and noise to progress through the auditory system.³ Interestingly, there are also indications that the DCN is directly influenced by attentional and emotional processes in the human brain.⁴

Models

Another area of enquiry regards models of tinnitus. There are presently two in widespread use : the Jastreboff Neurophysiological Model⁶ and the Habituation Model (often called the Psychological Model)⁷ of tinnitus.

There are significant areas of convergence between the models. They both pay little attention to the ignition of the tinnitus, and more to emotional and behavioural reaction to the tinnitus. In both, the aim of therapy is habituation to the tinnitus. In fact, the main therapy program that derives from the Jastreboff Neurophysiological Model--Tinnitus Retraining Therapy (TRT)--and psychological therapy for tinnitus contain quite similar elements of counselling and sound therapy, though there are differences of style and emphasis.

There are also some significant and important areas of divergence. Specifically, the “directive counselling” used in TRT is one-way and restricted to tinnitus alone, whereas the counselling in a psychological programme is more wide ranging and has, of course, a strong underpinning in psychological practice. Also, the Jastreboff Neurophysiological Model invokes Classical Conditioning theory in explaining the development of persistent troublesome tinnitus.

It has recently been pointed out that there are some potential problems with this, specifically how a sound initially without meaning (i.e., tinnitus) becomes paired with an unconditioned aversive stimulus.⁸The Habituation (or Psychological) Model has shortcomings also, with a surprising lack of underpinning experimental evidence and the potential overemphasis of the role of emotion and anxiety states in tinnitus⁹.

There is a consensus growing that the dichotomy, and controversy, between “Neurophysiological” and “Psychological” models isn’t helpful. Put simply, when is tinnitus, which must involve neural activity in the auditory system, not neurophysiological?² Further, when is troublesome tinnitus, which must involve emotional distress, not psychological? Of course, the answer to both is never.

Therapies

An effective drug treatment continues to elude us. There are, however, some encouraging recent developments.

The first concerns the use of selective serotonin re-uptake inhibitors (SSRI) in tinnitus patients. These modern antidepressants are widely used in the treatment of depression and anxiety, and increase the extracellullar level of serotonin by inhibiting re-uptake. A recent study has demonstrated a positive effect of sertraline over placebo on reported tinnitus severity, though the study design did not control for depression.¹⁰

Disappointingly, a further study that looked at the effect of paroxetine versus a placebo on a group of tinnitus patients who were specifically non-depressed demonstrated no benefit other than in their responses to one question: “How aggravating is your tinnitus?”¹¹ Additional experimental work is needed in this area, as the conceptual argument for serotonin dysfunction being a neurophysiological substrate for tinnitus is strong,¹² involving both the relationship between tinnitus and depression and the role of serotonin as a neurotransmitter in the auditory system.

There are indications that tinnitus services can be delivered effectively in a group context, which may be more suitable for busy clinicians.¹³ There is also some exciting research from Sweden demonstrating the impressive efficacy of psychological therapy for patients with troublesome tinnitus. It is provided via the Internet following an initial face-to-face consultation.¹⁴ While this strategy for delivering services to tinnitus patients is not yet ready for wider use, it does represent an innovative approach that may be of great benefit to patients who live where there is no local tinnitus service.

A number of novel therapies are being developed around the world. These include strategies for using sound, manipulated either by frequency spectrum, or by phase. Presently there is no strong independent evidence to support such techniques.

Summary

Tinnitus research is thriving, and is moving forward on a number of fronts. What is greatly encouraging is the evidence of collaborations between basic scientists and clinicians, and between groups working internationally. In my opinion, cautious optimism about new treatments and understandings of tinnitus is justified.

References

1. Eggermont JJ: Cortical tonotopic map reorganization and its implications for tinnitus. In Dauman R, Bousceau-Faure F, eds. Proceedings of the VIIIth International Tinnitus Seminar. Acta Otolaryngol Supplementum, in press.

2. Baguley DM: What progress have we made on tinnitus? The 2005 Tnndorf Lecture. In Dauman R, Bousceau-Faure F, eds. Proceedings of the VIIIth International Tinnitus Seminar. Acta Otolaryngol Supplementum, in press.

3. Kaltenbach JA, Zhang J, Finlayson P: Tinnitus as a plastic phenomenon and its possible neural underpinnings in the dorsal cochlear nucleus. Hear Res 2005;206(1-2):200-226.

4. Kaltenbach JA: The dorsal cochlear nucleus as a participant in the auditory, attentional and emotional components of tinnitus. Hear Res 2006;Feb 7 (E-pub ahead of print).

5. Kanold PO, Young ED: Proprioceptive information from the pinna provides somatosensory input to cat dorsal cochlear nucleus. J Neurosci 2001;21(19):7848-7858.

6. Jastreboff PJ, Hazell JWP: Tinnitus Retraining Therapy: Implementing the Neurophysiological Model. Cambridge: Cambridge University Press, 2004.

7. Hallam RS, Rachman S, Hinchcliffe R: Psychological aspects of tinnitus. In Rachman S., ed., Contributions to Medical Psychology, Vol. 3. Oxford: Pergamon Press, 1984: 31-53.

8. McKenna L: Models of tinnitus suffering compared and contrasted. Aud Med 2004;2:41-53.

9. Andersson G, Baguley DM, McKenna L, McFerran D: Tinnitus: A Multidisciplinary Approach. London: Whurr, 2005.

10. Zoger S, Svedlund J, Holgers KM: The effects of sertraline on severe tinnitus suffering: A randomized, double-blind, placebo-controlled study. J Clin Psychopharmacol 2006;26(1):32-39.

11. . Robinson SK, Viirre ES, Bailey KA, et al.: Randomized placebo-controlled trial of a selective serotonin reuptake inhibitor in the treatment of nondepressed tinnitus subjects. Psychosom Med 2005;67(6):981-988.

12. Simpson JJ, Davies WE: A review of evidence in support of a role for 5-HT in the perception of tinnitus. Hear Res 2000;145:1-7.

13. Newman CW, Sandridge SA: Incorporating group and individual sessions into a tinnitus management clinic. In Tyler RS, ed., Tinnitus Treatment: Clinical Protocols. New York: Thieme, 2005: 187-197.

14. Andersson G, Kaldo-Sandström V: Internet-based cognitive behavioral therapy for tinnitus. J Clin Psychol 2004;60(2):171-178.

[June 2006]