investigate related, non-auditory brain functions. We have studied attentional, emotion-processing, and resting-state networks in the brain that have been changed (in terms of both function and anatomy) in individuals with tinnitus. The imaging research is complemented by behavioral or psychoacousti- cal studies. We are currently using survey studies to assess tinnitus from the patients’ point of view— ascertaining what patients are currently using to manage their tinnitus and measuring their expecta- tions for different treatment regimens.
Magnetic resonance imaging (MRI): Provides a visual image of an individual brain’s anatomical structure
Functional magnetic resonance imaging (fMRI): Records changes in brain activity by measuring associated changes in blood flow through differ- ent structures of the brain
Resting state networks: The network of regional interactions in the brain, measured when a patient is at conscious rest
BF: Tinnitus seems like an ear condition because it is something we hear. But in actuality, it has more to do with the brain. Can you explain this?
FH: We hear with our brains. The ear is important, as it is the conduit to getting auditory information to the brain, but at the end of the road, we hear with our brains. Our brain is what puts sound together, pro- cesses sound, assigns meaning to sound, and gener- ates reaction to sound.
In the same way, we hear tinnitus with our brain. But with tinnitus there is no external source creating the sound. The source of the tinnitus signal is within the brain itself. I would say that everyone has some low level of noise (one can say neural noise) in the brain, but in the case of tinnitus, for some reason, the neural noise is not suppressed and rises to the level of consciousness. In short, tinnitus is a percep- tion of noise the brain is generating within itself. By the time you hear tinnitus, the ears are no longer involved. (You should of course continue to protect your hearing as further damage to the inner ear can exacerbate your hearing loss and tinnitus.)
In addition to generating and perceiving tinnitus, our brain controls how we react to tinnitus and the extent to which we are affected by it.
BF: Where in the brain is tinnitus? In other words, what parts of the brain are generating the percep- tion of ringing?
FH: This is an important and, in some ways, still an unanswered question. Several structures in the auditory pathway, from the inner ear to the cerebral cortex, show changes in activity that is associated with tinnitus. These structures include the auditory nerve, the cochlear nucleus, the inferior colliculus, the thalamus, and the primary and secondary auditory cortices. (Definitions for these terms are on the following page.) Researchers also have shown extra-auditory networks, including those involved in attention and emotion, to be involved. This leads scientists to believe that tinnitus is not located in one single part of the brain, but rather involves changes in a multitude of brain structures where sounds are processed.
BF: How do we know this?
FH: We know this because of numerous human and animal studies. Animal studies use single or multiple electrodes, implanted in the brain, which record brain activity at the neuronal level. Human studies, which require less invasive tools, record at a more gross level, at the level of millions of neurons. Human studies use brain imaging tools such as electroencepha- lography (EEG), magnetoencephalography (MEG), functional magnetic resonance imaging (fMRI), and positron emission tomography (PET). With all of these tools we can see the neuroplastic changes in the brain that result in the perception of tinnitus.
Electroencephalography (EEG): Measures and records the brain’s spontaneous electrical activity through the use of electrodes placed on the scalp
Magnetoencephalography (MEG): Measures the shifting magnetic fields in the brain, which are generated by the brain’s natural electrical currents
Positron emission tomography (PET): Produces a 3-dimensional model of anatomical processes, by tracking charged ions as they move through the body
BF: What do you mean by neuroplastic changes?
FH: Neuroplastic changes (or neural plasticity) refer to changes in brain structure and function in response to changes in environment, behavior, or injury/trauma. These changes can occur within neurons, within individual brain structures, or at a more global systems level in the brain.
It is fairly accepted that clinically-defined hearing loss is a prominent trigger for tinnitus. One theory regarding tinnitus holds that it is “neuroplasticity gone bad,” as a result of the brain trying to deal with
Spring 2014 | Tinnitus Today 17
SCIENCE & RESEARCH
GLOSSARY
GLOSSARY
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32