What Is Tinnitus?
Tinnitus represents temporary, occasional, or permanent perception of sound which does not really exist. Causes of tinnitus are variable, and they include arterial hypertension, neurological diseases, psychiatric conditions, and auditory nerve problems. Still, in most cases, the cause of tinnitus remains unknown (more than 10% of general population) (Henry, Dennis, & Schechter, 2005). Depending on its severity, this can be a very debilitating problem inducing depression, insomnia, or other psychiatric disorders (Frankenburg & Hegarty, 1994). So far, different types of medications were used, along with devices aimed to mask the sound, but the effectiveness of these approaches was not satisfactory.
Possible Cortical Cause of Tinnitus
It has been suggested that physiological changes in auditory cortex (part of the brain cortex responsible for perception of sound) could be responsible for the development of tinnitus (Eggermont & Roberts, 2004). Based on studies conducted both in animals and humans, there are evident metabolic changes in primary and secondary auditory cortex in patients with persistent tinnitus of unknown origin (Muhlnickel, Elbert, Taub, & Flor, 1998). Some of the studies used so called “evoked auditory potentials” to discover electrical changes in brains of these patients. These tests turned out abnormal in high number of subjects, which led to the conclusion that electrical stimulation of the brain may be useful in the treatment of tinnitus (Fregni et al., 2006).
Electrical Brain Stimulation and Tinnitus
Electrical stimulation of the brain has proven useful for relieving the symptoms of many psychiatric and neurological disorders (Tortella et al., 2015). Older methods of brain stimulation, such as electroconvulsive therapy (ECT), often included application of high intensity currents on the brain tissue. Effects of ECT in patients with tinnitus were assessed in several studies (Perez et al., 2015). Besides being invasive, this technique had temporary effects. Transcranial Direct Current Stimulation (tDCS) is one of the novel techniques of neuromodulation. Unlike previously used methods, tDCS uses low-intensity currents, targets specific parts of the brain, and has very minor and temporary side effects (Nitsche et al., 2008). There are two types of tDCS: anodal and cathodal stimulation. While anodal stimulation increases electrical activity of the targeted brain tissue, cathodal stimulation has the opposite effect, making the nerve cells less excitable (Nitsche et al., 2008).
Over the past ten years, there has been an increased interest among scientists in tDCS and its use in the treatment of persistent tinnitus. In one of the studies, anodal tDCS of the left side of auditory cortex induced short-term relief from tinnitus (Fregni et al., 2006). Another study has proven that tDCS can also have long-term effects in patients with tinnitus (Shekhawat, Stinear, & Searchfield, 2013). Namely, 56% of patients had only short term relief, but long-lasting effects were noticed in 44% of patients. More recent studies explained that anodal type of tDCS has preference over cathodal in the treatment of tinnitus (Garin et al., 2011; Joos, De Ridder, Van de Heyning, & Vanneste, 2014).
In conclusion, anodal tDCS has promising effects in the treatment of tinnitus of unknown origin. This could be a potential source of relief for many patients and it would protect them from developing depression and other psychiatric conditions provoked by persistent and debilitating auditory sensations. Although short-term effects of tDCS on tinnitus are slightly more evident, long-lasting effects cannot be ignored. Furthermore, this type of electrical stimulation is perfectly safe and it can be repeated with no fear of severe side effects.
References
Eggermont, J. J., & Roberts, L. E. (2004). The neuroscience of tinnitus. Trends Neurosci, 27(11), 676-682. doi: 10.1016/j.tins.2004.08.010
Frankenburg, F. R., & Hegarty, J. D. (1994). Tinnitus, psychosis, and suicide. Arch Intern Med, 154(20), 2371, 2375.
Fregni, F., Marcondes, R., Boggio, P. S., Marcolin, M. A., Rigonatti, S. P., Sanchez, T. G., . . . Pascual-Leone, A. (2006). Transient tinnitus suppression induced by repetitive transcranial magnetic stimulation and transcranial direct current stimulation. Eur J Neurol, 13(9), 996-1001. doi: 10.1111/j.1468-1331.2006.01414.x
Garin, P., Gilain, C., Van Damme, J. P., de Fays, K., Jamart, J., Ossemann, M., & Vandermeeren, Y. (2011). Short- and long-lasting tinnitus relief induced by transcranial direct current stimulation. J Neurol, 258(11), 1940-1948. doi: 10.1007/s00415-011-6037-6
Henry, J. A., Dennis, K. C., & Schechter, M. A. (2005). General review of tinnitus: prevalence, mechanisms, effects, and management. J Speech Lang Hear Res, 48(5), 1204-1235. doi: 10.1044/1092-4388(2005/084)
Joos, K., De Ridder, D., Van de Heyning, P., & Vanneste, S. (2014). Polarity specific suppression effects of transcranial direct current stimulation for tinnitus. Neural Plast, 2014, 930860. doi: 10.1155/2014/930860
Muhlnickel, W., Elbert, T., Taub, E., & Flor, H. (1998). Reorganization of auditory cortex in tinnitus. Proc Natl Acad Sci U S A, 95(17), 10340-10343.
Nitsche, M. A., Cohen, L. G., Wassermann, E. M., Priori, A., Lang, N., Antal, A., . . . Pascual-Leone, A. (2008). Transcranial direct current stimulation: State of the art 2008. Brain Stimul, 1(3), 206-223. doi: 10.1016/j.brs.2008.06.004
Perez, R., Shaul, C., Vardi, M., Muhanna, N., Kileny, P. R., & Sichel, J. Y. (2015). Multiple electrostimulation treatments to the promontory for tinnitus. Otol Neurotol, 36(2), 366-372. doi: 10.1097/MAO.0000000000000309
Shekhawat, G. S., Stinear, C. M., & Searchfield, G. D. (2013). Transcranial direct current stimulation intensity and duration effects on tinnitus suppression. Neurorehabil Neural Repair, 27(2), 164-172. doi: 10.1177/1545968312459908
Tortella, G., Casati, R., Aparicio, L. V., Mantovani, A., Senco, N., D’Urso, G., . . . Brunoni, A. R. (2015). Transcranial direct current stimulation in psychiatric disorders. World J Psychiatry, 5(1), 88-102. doi: 10.5498/wjp.v5.i1.88