1. Neural Mechanisms of Tinnitus
Alexandra Watts and Dr. Ann Perreau
Department of Communication Sciences and Disorders, Fall 2016
Therefore, the limbic system is strongly related to the presence of tinnitus that accounts for tinnitus-related distress. Other research indicates that these emotional responses are learned, but they neglect to account for certain properties of the brain (Leaver et al., 2011). Structural differences in the limbic systems of the brains of people with tinnitus are indicative of neural correlates for tinnitus distress that do not reflect a learned response. Rather, the involvement of the limbic system, where emotional responses are coded, explains the emotional symptoms associated with tinnitus. This understanding has the capability to enhance our treatment of tinnitus distress to make it more effective for those who suffer from tinnitus-related distress.
Discussion (Continued)
The ear is a transducer of sound composed of three parts that transmits mechanical waves into electrical impulses. These neural impulses coding sound are interpreted in the auditory cortex within the temporal lobe of the brain. When the hearing system is damaged, many auditory disorders can result, including tinnitus.
Tinnitus is the perception of sound in the absence of an external auditory stimulus. Approximately 15% of people in the United States experience some type of tinnitus (Center for Disease Control, 2013). Tinnitus can be perceived as different sensations: a high pitched tonal noise, crickets chirping, buzzing, whooshing, etc. The presence of this inescapable sound can have a profound impact on people who suffer from tinnitus. Some individuals experience anxiety, depression, and social withdrawal as a result of their tinnitus.
Background
Figure 1. Voxel Based Morphology of Tinnitus Patients
Primary auditory cortex regions (circled in green).
Nonprimary auditory cortex regions (circled in blue).
Shows increased connectivity in the right supramarginal gyrus and increased connectivity in the left posterior middle temporal gyrus.
(Davies, Gander, Andrews, & Hall, 2014)
The different structures implicated in tinnitus can be organized into two models of tinnitus etiologies:
a) Peripheral models of tinnitus
Tinnitus as a mechanism of the cochlea or auditory nerve.
b) Central models of tinnitus
Tinnitus as a result of a reorganization of the central auditory pathway
Research shows that peripheral and central models alone cannot explain the neural presentation of tinnitus (Henry, Roberts, Caspary, Theodoroff & Salvi, 2015). However, as there are many causes to tinnitus, these models account for these various clinical symptoms in different ways. Damage to the peripheral system influences the central system in a profound way, and the neural plastic characteristics of the cortex shows how it reorganizes following a peripheral injury. Through peripheral injury and consequential tonotopic reorganization, the existence of hyperexcited neurons causes the perception of tinnitus in the absence of an external stimulus.
Discussion (Continued)
Table 1.Percentage of Patients Reporting Difficulties Associated with Tinnitus
(Tyler & Baker, 1983)
Percentage of Respondents
Difficulties Associated with Tinnitus
36%
Depression
35.5%
Worsened Speech Comprehension
34%
Irritation
33%
Worsened Concentration
16%
Feelings of Insecurity
14%
Embarrassment 6%
Nervous Strain 5%
Loneliness
4.2%
Interference with Work 2%
Loss of Confidence
Fiber tracts connecting limbic system structures
Anterior thalamic nuclei
Cingulate gyrus
The purpose of this project was to address the neural mechanisms of tinnitus by answering the following questions:
1. What neurophysiological changes in the hearing mechanism contribute to tinnitus?
2. How do different neurological models of tinnitus explain the presence of tinnitus?
3. How do these neural mechanisms of tinnitus relate to one’s emotional and physiological reactions to tinnitus?
Purpose
Hypothalamus
Amygdala
Hippocampus
Figure 3. Anatomy of limbic lobe structures.
(Retrieved from
What neurophysiological changes in the hearing mechanism contribute to tinnitus?
Changes in the auditory network and auditory cortices result in tinnitus.
2. How do different neurological models of tinnitus explain the presence of tinnitus?
Central and peripheral models alone cannot explain tinnitus, but by recognizing the influence of each model on each other, we can create a comprehensive model that accounts for neurological changes as a result of tinnitus.
3. How do these neural mechanisms of tinnitus relate to one’s emotional/physiological reactions to tinnitus?
The limbic lobe has been proven to be an integral part of the presentation of tinnitus. This relationship is indicative of neural correlates to tinnitus distress.
Conclusions
There are two general neurophysiological changes that cause the hearing disorder:
Changes in the auditory network
Increased functional connectivity between right supramarginal gyrus and left posterior middle temporal gyrus.
Changes in auditory structures:
Inferior colliculus
Mediodorsal nucleus
Striatum
Orbitofrontal cortex and lateral prefrontal cortex
b) Changes in the auditory cortices (specifically in the auditory cortex and limbic system).
Temporal Lobe (Medial Heschl’s Gyrus)
Limbic Lobe
Discussion
Figure 2. Auditory Nervous Pathway
(Bhatnagar, 2013)
Acknowledgments
References
I would like to thank Dr. Ann Perreau, for her constant support and motivation throughout this process, and my entire experience at Augustana College. She has been an incredible role model, and mentor and the opportunities she has given me have greatly increased my passion and enthusiasm for pursuing a career in hearing science.
1. Bhatnagar, S.C. (2013). Neuroscience for the study of communicative disorders: Fourth edition. Philadelphia, Pennsylvania, Wolters Kluwer.
2. Center for Disease Control. (2013, December). National Health and Nutrition Examination Survey. Retrieved from
3. Davies, J., Gander, P.E., Andrews, M., & Hall, D.A. (2014). Auditory network connectivity in tinnitus patients: A resting-state fMRI study. International Journal of Audiology, 53,
4. Henry, J.A., Roberts, L.E., Caspary, D.M., Theodoroff, S.M., & Salvi, R.J. (2015) Underlying mechanisms of tinnitus: Review and clinical implications. Journal of the American Academy of Audiology, 25, 5-22.
5. Leaver, A.M., Renier, L., Chevillet, M.A., Morgan, S., Kim, H.J., & Rauschecker, J.P. (2011). Dysregulation of limbic and auditory networks in tinnitus. Neuron, 61,
6. The Limbic System and the Reticular Formation (2011, November). Antranik. Retrieved from
7. Tyler, R.S., & Baker, L.J. (1983). Difficulties experienced by tinnitus sufferers. Journal of Speech and Hearing Disorders, 48,