This is a 3-D image of the left brain hemisphere of a patient with tinnitus (right) and the part of that hemisphere containing primary auditory cortex (left). Different colors indicate different frequencies of brain activity (blue = low, magenta = middle, orange = high) whose strength changed alongside tinnitus. Image courtesy of Will Sedley.
Tapping the highly specialized expertise of a brain research lab at the University of Iowa, researchers have taken advantage of a rare opportunity to record directly from the brain of a person with tinnitus in order to find the brain networks responsible for this often debilitating condition.
About one in five people experience tinnitus, the perception of a sound—often described as ringing—that isn’t really there. The new study, reported in the Cell Press journal Current Biology on April 23, reveals just how different tinnitus is from normal representations of sounds in the brain.
“Perhaps the most remarkable finding was that activity directly linked to tinnitus was very extensive and spanned a large proportion of the part of the brain we measured from,” says study co-leader Will Sedley of Newcastle University in the United Kingdom. “In contrast, the brain responses to a sound we played that mimicked [the subject’s] tinnitus were localized to just a tiny area.”
"This has profound implications for the understanding and treatment of tinnitus, as we now know it is not encoded like normal sound, and may not be treatable by just targeting a localized part of the hearing system," adds study co-leader Phillip Gander, postdoctoral research scholar in the UI Department of Neurosurgery.
The HBRL is a multinational research team that uses direct recordings of neural activity from inside humans’ brains to investigate sensory, perceptual, and cognitive processes related to hearing, speech, language, and emotion.
Only a few groups in the world have the expertise and collaborative infrastructure to conduct these experiments. It is possible because patients who require invasive brain mapping in preparation for epilepsy surgery also volunteer to participate in research studies. In the current study, the patient was a 50-year-old man who also happened to have a typical pattern of tinnitus, including ringing in both ears, in association with hearing loss.
“It is such a rarity that a person requiring invasive electrode monitoring for epilepsy also has tinnitus that we aim to study every such person if they are willing,” Gander says.
Howard and his team conduct their research with about 15 epilepsy surgery patients each year.
“We are putting a recording platform into the patient’s brain for clinical purposes and we can modify it without changing the risk of the surgery. This allows us to understand functions in the brain in a way that is impossible to do with any other approach,” Howard says.
In the new study, the researchers contrasted brain activity during periods when tinnitus was relatively stronger and weaker. They found the expected tinnitus-linked brain activity, but they report that the unusual activity extended far beyond circumscribed auditory cortical regions to encompass almost all of the auditory cortex, along with other parts of the brain.
The discovery adds to the understanding of tinnitus and helps to explain why treatment has proven to be such a challenge, the researchers say.
“The sheer amount of the brain across which the tinnitus network is present suggests that tinnitus may not simply ‘fill in the gap’ left by hearing damage, but also actively infiltrates beyond this into wider brain systems,” Gander adds.
These new insights may help to inform treatments such as neurofeedback, where patients learn to control their “brainwaves,” or electromagnetic brain stimulation, according to the researchers. A better understanding of the brain patterns associated with tinnitus may also help point toward new pharmacological approaches to treatment.
In addition to Gander, Sedley, and Howard, the team included UI researchers Hiroyuki Oya, Christopher Kovach, Kirill Nourski, and Hiroto Kawasaki, as well as Timothy Griffiths at Newcastle University. The research was supported by grants from the National Institutes of Health and the Wellcome Trust and Medical Research Council in the U.K.
Editor's Note: This release is adapted from a release prepared by Cell Press.