Parkinson’s disease is the second most common degenerative neurological disorder. The incidence of Parkinson’s disease, let’s call it PD for short, is increasing rapidly with an aging population. The root cause of PD is the death of nerve cells that produce a chemical called dopamine. The loss of these dopamine-producing cells occurs in a part of the brain commonly known as the basal ganglia and specifically the substantia nigra.
This part of the brain, the basal ganglia, is known to influence movement and diseases or lesions of the basal ganglia produce what are collectively called movement disorders that include Parkinson’s disease. Parkinson’s disease is characterized by slow movements called bradykinesia (brady = slow, kinesis = movements), tremors, and other signs of abnormal muscle function. One of the most bothersome symptoms that can occur in patients with PD is freezing from walking.
The voluntary movement takes place in two fundamental stages. In order to move, we create the intention to move in part of the brain. So part of the brain plans movement and the actual movement commands that activate muscles occur in a different part of the brain. So we plan a movement and this plan is executed by other circuits in the brain which then execute this plan.
In many patients with Parkinson’s disease, planned movements such as walking have delayed or failed execution. It’s called Freezing the gait and it can seriously decrease the quality of life of a patient with Parkinson’s disease. Although we call this gel gait symptom, it can actually occur with any voluntary movement, such as reaching for a drink, brushing your hair, or getting up from a sitting position to stand up. It often leaves the PD patient unable to initiate movement or stuck in the middle of a planned action. It shouldn’t be difficult for you to imagine how freezing could seriously impair a patient’s functional abilities and interfere with their daily activities.
Unsurprisingly, freezing has also been linked to falls and injuries in patients with PD.
Medical treatments for Parkinson’s disease include drugs that replace dopamine lost with black matter degeneration. In general, dopamine replacement therapies are quite effective for patients with PD with two notable exceptions:
- They are generally not particularly effective for freezing-like symptoms and
- They usually lose their effectiveness over time
A number of research groups believe they have identified the specific part of the brain that malfunctions and causes freezing symptoms in patients with Parkinson’s disease. It is known as the pedunculopontin nucleus (let’s call it PPN for short) in the brainstem. This has led to a number of trials of electrical stimulation of PNP through the use of surgically implanted deep brain electrodes. A growing number of reports suggest that electrical stimulation of PPN may produce promising results for patients with advanced stages of Parkinson’s disease. This technique appears to activate PPN and results in decreased gait freezing in patients with Parkinson’s disease. While this is a promising surgery, it does require brain surgery and all the associated risks.
If only there was a way to stimulate PNP in the brainstem non-invasively.
Some recent research suggests that non-surgical PPN stimulation is now possible. What’s even more encouraging is the ability to stimulate PNN and reduce freezing through the use of musical sounds played through special bone conduction headphones. Let’s see how it could work.
Research has shown that structures in the inner ear called otoliths can be stimulated by tones of very specific frequencies. These structures in the inner ear have direct connections with the PPN which, as we have seen, are important brainstem structures related to freezing symptoms in Parkinson’s disease. Stimulation of otoliths with sound played through special bone conduction headphones can activate PPN and has the potential to reduce gait freeze in patients with Parkinson’s disease. Other research suggests that neurological rehabilitation and spotting patients with auditory or visual cues may improve freezing symptoms in patients with PD. Thus, there is potential to improve gait freeze through the combination of rehabilitation with auditory cues using sound frequencies known to stimulate the PNP that is involved in gait freeze in PD.
This is very encouraging news for patients suffering from walking freeze associated with Parkinson’s disease.
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