An abnormal brain activity pattern could be a common link between
Parkinson's disease, neuropathic pain, tinnitus, and depression, an international research team suggests.
The brainwave abnormality is similar in all these disorders but occurs in different regions of the brain. This discovery could lead to therapies that target all four conditions, the investigators said.
Findings were published in the study, "Thalamocortical dysrhythmia detected by machine learning," in the journal Nature Communications.
Whether a person is awake or asleep, moving or thinking, the brain produces specific brainwave patterns that represent, to some extent, how the brain works.
Researchers proposed, back in 1996, that specific oscillations in these brainwaves could be common to several neurological diseases, including Parkinson's. This theory — called thalamocortical dysrhythmia, or TCD — suggests that patients with these conditions have a drop in brainwave frequency in neurons of the thalamus, and alpha waves are replaced by theta waves.
Alpha waves inhibit other neurons in the thalamus from firing, having a sort of muting effect in the brain. The loss of these waves allows neighboring cells to be more active, and the thalamus becomes hyperactive.
To confirm the TCD hypothesis, Sven Vanneste, PhD, an associate professor in the School of Behavioral and Brain Sciences at the University of Texas at Dallas, and his colleagues used a computer-based approach to map the major brainwave patterns of people with Parkinson's, neuropathic pain, tinnitus — the perception of ringing or buzzing in the ears — and depression.
The study included 541 individuals, including 264 healthy volunteers, 153 patients with tinnitus, 78 with chronic pain, 31 with Parkinson's, and 15 with major depression.
Using electroencephalography (EEG) data, the computer model revealed that all patients had equivalent changes in brainwave activity. However, depending on the disease, these alterations appeared in different regions of the brain.
For patients with tinnitus, brainwave abnormalities were identified in the auditory cortex, whereas chronic pain patients had these disruptions in the somatosensory cortex. Parkinson's disease affected the motor cortex, and depression patients had brainwave abnormalities in deeper brain layers.
"We fed all the data into the computer model, which picked up the brain signals that TCD says would predict if someone has a particular disorder," Vanneste said in a university news article. "Not only did the program provide the results TCD predicted, we also added a spatial feature to it. Depending on the disease, different areas of the brain become involved."
While more studies are needed to validate these results, the findings seem to validate "TCD as oscillatory mechanism underlying diverse neurological disorders," the investigators wrote in the study.
"Over the past 20 years, there have been pain researchers observing a pattern for pain, or tinnitus researchers doing the same for tinnitus," Vanneste said. "But no one combined the different disorders to say, 'What's the difference between these diseases in terms of brainwaves, and what do they have in common?' The strength of our paper is that we have a large enough data sample to show that TCD could be an explanation for several neurological diseases."
The team is now planning to investigate brainwave abnormalities in other psychiatric diseases and to explore the therapeutic potential of vagus nerve stimulation as a means to reset these brainwave patterns. The approach is being developed by Vanneste and colleagues at the Texas Biomedical Device Center, UT Dallas.
"More and more people agree that something like thalamocortical dysrhythmia exists," Vanneste said. "From here, we hope to stimulate specific brain areas involved in these diseases … to normalize the brainwaves again. We have a rationale that we believe will make this type of therapy work."
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